o I I I| R I | I I,. ... - •

USA-CERL TECHNICAL REPORT N-88/12

August 1988

Upgrading Army Water and Wastewater

US Army Cc" Treatment Plants

of EngIneers

ResearchLaborar A D -A 200 105

Development of the Pipe Loop System for

F etermining Effectiveness of Corrosion

*Control Chemicals in Potable Water Systems

by

Temkar M. Prakash

Richard J. Scholze

Chester H. Neff

Stephen W. Ma!oney

Mark Heath

Edgar D. Smith

In the Army's 12,000 miles of water lines, internal corrosion slowly destr,,s a large investment and creates significant problems for Army water treatment plant operators,

who try to maintain the water quality at acceptable levels.

Corrosion can be slowed using corrosion-inhibiting chemicals, but it is difficult to measure the extent of corrosion

and the effectiveness of inhibitors without excavating

actual pipes.

This study surveyed corrosion-inhibiting water quality

control chemicals and methods for monitoring corrosion. D T IC

With this knowledge, a pipe loop system was developed ELECTE and installed at Fo Bragg, NC and Fort Monroe, VA. It

was shown to be effective in gathering data on corrosion OCT 2 5 1988

rates. After a standard procedure has been established, this

loop will allow a water treatment plant operator to monitor with ease , the effectiveness of corrosion-inhibiting treatments.

Approved for public release; distribution is unlimited.

0O

. iil ... ... mmi illIii INI •Hi I I I.-
The contents of this report are not to be used for advertising, publication, or

promotional purposes. Citation of trade names does not constitute an

official indorsement or approval of the use of such commercial products.

The findings of this report are not to be construed as an official Department

of the Army position, unless so designated by other authorized documents.

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Fort Belvoir, VA 22060-5580 PROGRAM PROJECT TASK WORK UNIT

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4A62720 A896 B 048

11 TITLE (Include Security Classification)

Development of the Pipe Loop System for Determining Effectiveness of Corrosion

Control Chemicals in Potable Water Systems (U)

12 PERSONAL AUTHOR(S)

Prakash, Temkar M.; Scholze, Richard J.; Neff, Chester H.; Maloney, Stephen W.; (Cont)

13a TYPE OF REPORT 1lb TIME COVERED 14 DATE OF REPORT (Year. Month, Day) 15 PAGE COUNT

final FROM _ TO _ 1988, August 58

16 SUPPLEMENTARY NOTATION

Copies are available from the National Technical Information Service

Springfield, VA 22161

17 COSATI CODES 18 SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP -corrosion inhibition; Fort Monroe

13 11 water pipes. Fort Bragg

13 02 pipe loop system" & .... 19 AIATRCT (Continue on reverse of necessary and Identify by block number) 1

In the Army's 12,000 miles of water lines, internal corrosion slowly destroys a large

investment and creates significant problems for Army water treatment plant operators,

who try to maintain the water quality at acceptable levels. Corrosion can be slowed

using corrosion-inhibiting chemicals, but it is difficult to measure the extent of corrosion

and the effectiveness of inhibitors without excavating actual pipes.

This study surveyed corrosion-inhibiting water quality control chemicals and

methods for monitoring corrosion. With this knowledge, a pipe loop system was

developed and installed at Fort Bragg, NC and Fort Monroe, VA. It was shown to be

effective in gathering data on corrosion rates. After a standard procedure has been

established, this loop will allow a water treatment plant ope or to monitor with ease

the effectiveness of corrosion-inhibiting treatments. - ,'f" ., ,

20 DISTRIBUTIONIAVA'I aif r C €

C A7eTRACT 121 ABSTRACT SECURITY CLASSIFICATION

0UNCLASSIFIED/UNLIMITED & SAME AS RPr 0 DrIC USERS Unclassified

22a NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) 22c OFFICE SYMBOL

Jane Andrew 1(217) 352-6511, x388 CECER-IMT

DD FORM 1473. 84 MAR 83 APR edition may be used untI exhausted SECuRITY CLASSIFICATION OF THIS PAGE

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BLOCK 12. (Cont'd)

Heath, Mark; Smith, Edgar D.

UNCLASSIFIED
FOREWORD

This work was done for the Facilities Engineering Division (now part of the U.S.

Army Engineering and Housing Support Center), Office of the Assistant Chief of

Engineers (OACE) under Project No. 4A62720A896, "Environmental Quality Technology";

Technical Area B, "Environmental Design and Construction"; Work Unit 048, "Upgrading

Army Water and Wastewater Treatment Plants." The Technical Monitor was T. Wash,

The work was performed by the Environmental (EN) Division of the U.S. Army

Construction Engineering Research Laboratory (USA-CERL). Dr. Ravinder K. Jain is

Chief of USA-CERL-EN. The technical editor was Jane Andrew, Information Managereview of the report.

Thanks are expressed to Mike Schock of the Illinois State Water Survey for his

Shaffer is Technical Director.

COL Carl 0. Magnell is Commander and Director of USA-CERL, and Dr. L. R.

AOcssion For

NTIS GRA&I

DTIC TAB 0

Unannouneed 1

Justifioation

/4%, ~~Distributionl/ ____

Availability Codes

By ail 

and/or Dist Special

3 L

yva
CONTENTS

Page

DD FORM 1473 1

FOREWORD 3

LIST OF TABLES AND FIGURES 5

1 INTRODUCTION ...................................................... 7

Background

Objectives

Approach

Scope

Mode of Technology Transfer

2 CORROSION CHARACTERISTICS OF WATER AND

DISTRIBUTION SYSTEM MATERIALS .................................... 10

Water Quality

Water Distribution System Materials

3 CORROSION-INHIBITING CHEMICALS USED FOR

DRINKING WATER TREATMENT ....................................... 18

Types of Corrosion Inhibitors

Effects on Various Plumbing Materials

Use of Inhibitors

4 MONITORING TECHNIQUES FOR CORROSION CONTROL ................. 23

Indirect Methods

Direct Methods

Electrochemical Methods

5 DEVELOPMENT OF A PIPE LOOP SYSTEM FOR INHIBITOR

EVALUATION ................................................... 31

Pipe Loop System Design

Features

Possible Experimental Designs

6 EVALUATING THE PIPE LOOP SYSTEM AT FORT MONROE,

VA AND FORT BRAGG, NC ............................................ 37

Background on Fort Monroe Water Plant

Background on Fort Bragg Water Plant

Experimental Setup

Preliminary Results

7 CORROSION CONTROL REGULATIONS AND ECONOMICS ................ 49

Corrosion Control Regulations

Costs of Coirosion Control

8 CONCLUSIONS AND RECOMMENDATIONS ............................. 52

METRIC CONVERSION FACTORS 52

REFERENCES 53

DISTRIBUTION

4
TABLES

Number Page

1 Chemical Factors Influencing Corrosivity of Water 11

2 Types of Materials Used in the Water Industry 12

3 Effect of Corrosion of Materials Used in the Water Industry 13

4 Water Quality Characteristics That Minimize Corrosion of

Materials Used in the Water Industry 14

5 Estimated Duration (Months) Required for Corrosion Tests 25

6 Typical Water Quality at Fort Bragg, NC and Fort Monroe, VA 40

7 Preliminary Results of Pipe Loop Experiments at Fort Bragg

and Fort Monroe 44

8 Type and Extent of Pitting in Pipe Loop System Specimens 46

9 Comparative Costs of Corrosion Inhibitors (1984) 50

10 Typical Annual Chemical Costs for Corrosion Control (1982) 50

11 Total Costs of Corrosion Control Treatment (1979) 51

FIGURES

1 Schematic of ISWS Corrosion Tester 26

2 Cross-Section of Assembled ISWS Corrosion Tester 27

3 Schematic Diagram of Metal Uptake Test Loop Device 28

4 Scheme of the Test Pipe Rig 28

5 Schematic of USA-CERL Pipe Loop System 32

6 Assembled Pipe Loop System 33

7 Cross-Section of USA-CERL Corrosion Tester 34

8 Pipe Loop System Locations 39

9 New Pipe Specimen and Pipe Specimen Exposed to Water

in Pipe Loop System 42

10 Corrosion Byproducts on a Galvanized Iron Pipe Specimen

Exposed to Water in Pipe Loop System 42

5
FIGURES (Cont'd)

Number Page

11 Corrosion Byproducts on Mild Steel and Zinc Coupons

Exposed to Water in Pipe Loop System 43

12 Corrosion Rates of Mild Steel Specimens at Fort Bragg, NC 44

13 Corrosion Rates of Galvanized (Zinc) Iron Specimens at

Fort Bragg, NC 45

14 Effect of Various Corrosion Inhibitors on Mild Steel

Corrosion Rates at Fort Monroe, VA 47

15 Effect of Various Corrosion Inhibitors on Galvanized (Zinc)

Iron Corrosion Rates at Fort Monroe, VA 47

6
EVALUATING EFFECTS OF WATER QUALITY CONTROL

CHEMICALS IN WATER DISTRIBUTION SYSTEMS

I INTRODUCTION

Background

Ordinary drinking water can extensively damage water treatment plants by

corroding their metal components. Some of the effects of metal deterioration due to the

corrosive action of potable water are leakage, reduced carrying capacity, structural

failure associated with main breakage and street washout, and deteriorating water

quality as corrosion products enter the potable water system (e.g., "red water").

Nationwide, drastic economic losses have been reported due to Internal corrosion of

water distribution system materials. In 1979, the National Bureau of Standards (NBS)

reported that annual corrosion costs in the water supply field totaled about $700

million.' Actually, far greater costs are incurred through damage to interior piping and

plumbing systems in homes. 2 The Army also faces large costs due to corrosion in the

drinking water treatment plants it owns, operates, and maintains. These systems, which

include 12,000 miles of pipe at permanent installations, represent a major investment for

the Army, so cost effective corrosion control is important.

Aside from economic concerns, regulatory issues must be considered. Corrosion

products that enter the water distribution system lead to violations of the Safe Drinking

Water Act, which requires that water quality regulations be met at the consumer's tap.

The U.S. Environmental Protection Agency (USEPA) recognizes that corrosion problems

are unique to each water supply system and thus sets forth regulations (National Interim

Primary Drinking Water Regulations [NIPDWR]) 3 to identify potentially corrosive waters

and to determine what materials are present in distribution systems.

For both maintenance and regulatory purposes, it is necessary to carefuliv evaluate

and monitor the physical condition of the materials in the distribution system. There has

been no simple, standard procedure for doing this. The actual materials cannot be

examined unless they are excavated. It would be very difficult to define general rules

for the effect of a particular water on a particular material because water qualities and

distribution system materials vary worldwide, creating a huge matrix of parameters.

Many of these parameters are difficult and expensive to measure. Methods do exist, but

the regulations do not specify any standard procedures. Each plant tests differently and

reports the results differently, so it is extremely difficult to make meaningful comparisons of water characteristics from place to place.

1L. H. Bennett, et al., "Economic Effects of Metallic Corrosion in the United States,"

Corrosion '79 (National Association of Corrosion Engineers [NACE], Atlanta, GA, March

1979).

2R. A. Ryder, "The Costs of Internal Corrosion in Water Systems," Journal of the Amer3 ican Water Works Association, Vol 72, No. 5 (1980), p 267.

3USEPA, "National Interim Primary Drinking Water Regulations," Code of Federal

Regulations, Title 40, Part 141 (1981), pp 309-354.

7
This lack of standard methodology impairs the evaluation of the various corrosioninhibiting chemicals. These chemicals can reduce a water's corrosive effects, but their

effectiveness depends largely on characteristics of the water in which they are used.

There is a bewildering array of treatment options, but water treatment plant operators

presently have no systematic means of determining which plan is best for their plants.

Thus, a need exists for a standard, simple, easily implemented apparatus and

procedure that will allow a water plant operator to monitor the effect of various treatments, helping him or her evaluate the effectiveness of water quality control chemicals.

If this helps the operator choose the most appropriate treatment for corrosion control,

future maintenance costs may be reduced.

Objectives

The objectives of this study were:

1. To develop, primarily for the water treatment plant operator, a standard

apparatus and procedure for selecting and determining the effectiveness of corrosion

control chemicals in drinking water systems, which would enable the operator to maintain water quality.

2. To test this apparatus in the field.

Approach

Various corrosion control strategies were reviewed, along with their effects on

distribution system materials. Also, methods for analyzing and evaluating the internal

corrosion potential of water systems were compiled from the literature. These methods

include evaluation of the characteristics of water supply, laboratory analysis, and field

investigation techniques. Based on the information gathered, a standard apparatus to

evaluate and monitor internal corrosion was designed, developed, and fabricated. This

pipe loop system was installed at the water plants at Fort Monroe, VA and Fort Bragg,

NC and operated under field conditions. The data ot ained were interpreted to determine the existence and extent of corrosion, the possible influencing factors, and the

effectivenes: of alternative water treatment chemicals.

Scope

This report discusses chemicals and techniques in general terms only; details of

procedures and equipment can be found in the references. Some preliminary data from

both installations are discussed, but the purpose of this analysis is not to provide a final

evaluation of the chemicals tested. Rather, it illustrates the type of data which can be

obtained from the pipe loop systems. More comprehensive analyses will be performed in

the future in the effort to establish a standard evaluation procedure.

Mode of Technology Transfer

It is recommended that the pipe loop system technology described in this report be

universally adopted at all permanent Army installations as a standard apparatus for

monitoring internal corrosion in water distribution systems. In the interim, all treatment

8
plant offices will be informed of this development through an Engineer Technical Note

(ETN) and an Engineer Technical Letter (ETL). The U.S. Army Engineering and Housing

Support Center (USAEHSC) will be the primary technology transfer agency: they will

include the pipe loop system in their operator assistance program. The information in

this report should be used to update Technical Manual (TM) 5-813-3, Water Supply, Water

Treatment.

9
2 CORROSION CHARACTERISTICS OF WATER

AND DISTRIBUTION SYSTEM MATERIALS

Corrosion may be defined as the deterioration of a material or its properties due to

reaction with its surroundings. In the waterworks industry, the "material" which

deteriorates may be a metal pipe or its fixtures, the cement in a pipe lining, or an

asbestos-cement (A-C) pipe. For internal corrosion, the material reacts with water. 4

Almost all waters can be corrosive to some degree. The corrosive tendency of a

water depends on its physical, chemical, and biological properties and on the nature of

the material with which the water comes in contact. For example, water which may be

corrosive to galvanized pipe may be relatively noncorrosive to copper pipe in the same

system.

Water Quality

In most iases, the corrosion phenomenon involves a complex interaction of several

factors. The following presents the common water properties that are known to have an

influence on the corrosion of a material.

Flow velocity and temperature are the two main physical characteristics of water

that affect corrosion. Very high velocity water can cause physical erosion of the pipe

material, but usually the velocity has a greater influence on the corrosion mechanisms

which depend on the pH, dissolved oxygen, galvanic couplings, etc. Extremely low flows

or stagnant waters have been shown to promote tuberculation and pitting in water mains.

An increase in water temperature, in general, increases the corrosivity. Water

which shows no corrosive tendency in the distribution system may cause severe damage

in hot water heaters and plumbing systems. However, in waters with high hardness, an

increase in temperature increases the potential for calcium carbonate scale to form,

which protects the metal from corrosion. On the other hand, excessive scale formation

may lead to clogged pipes and heat exchangers.

The chemical water quality plays an important role in the corrosion reactions with

metal. Table 1 presents the major chemical characteristics of water and their general

effects on corrosion. Several of these factors are closely related and an understanding of

their relationship will aid in understanding corrosion.

Dissolved oxygen in water has long been recognized as one of the most potent

corrosive agents to ferrous metals. Oxygen accepts the electron given up by the

corroding metal and allows the cc-rosion reaction to continue. The reaction products

then enter the water system and create a "red water" problem.

The pH is a measure of the hydrogen ion, H+, concentration in water. Hydrogen

ions also accept the electrons given up by a metal, allowing the corrosion to continue.

The pH affects the formation or solubility of protective films. At pH values below 5 the

corrosion of metals such as iron and copper occurs rapidly.

4J. E. Singley, et al., Corrosion Prevention and Control in Water Treatment and Supply

Systems, Pollution Technology Review No. 122 (Noyes Publications, Park Ridge, NJ,

1985).

10
Table 1

Chemical Factors Influencing Corrosivity of Water*

Factor Effect

pH Low pH may increase corrosion rate; high pH may protect pipes

and dcreme corrsion rates

Alkalinity May help form protective CaCO) coating, helps control pH

ml rduces corrosion

DO lm, ra of many corrosion reactions

Cblorine residual lcream metallic comma.

TDS High TDS iama conductivity and corrosion rate

Hardmss (Ca and Mg) Ca may precipitate as CaCO) and thus provide protection and

reduce corrosio rates

Cbloride. sulfate High levels increase corrosion of iron, copper, and galvanized steel

Hydrogen sulfide Increases corrosion rates

Silicate posphates May form protective films

Natural color, organic matter May dase coea

ino. zauc or mangane. May react with compounds on interior of A-C pipe to form protective cting

*Source: J. E. Singley, et al., Corrosion Prevention and Control in Water

Treatment cud Supply Systems, Pollution Technology Review No. 122 (Noyes

Publications, Park Ridge, NJ, 1985), p 15. Information originally obtained

from Environmental Science and Engineering, Inc. Used with permission.

The alkalinity of water is its ability to neutralize acids. Alkalinity depends mostly

on the concentrations of carbonates and bicarbonates, which in turn depend on pH.

Carbonates and bicarbonates Influence the water's ability to lay down a protective

metallic carbonate coating. Alkalinity also controls the concentration of calcium ions

that may be present in water at a specific pH.

Hardness, predominantly caused by the presence of calcium and magnesium, can

help form a protective calcium carbonate lining on the pipe walls, under proper conditions.

Chlorides and sulfates, if present in high concentrations, have been shown to cause

pitting of metallic pipes. The reaction products of chlorides and sulfates prevent the

formation of protective metallic oxide films. The ratio of chloride plus sulfate to bicarbonate (Cl- + SO4- / HCO3 -) has been used as an indicator of the corrosivity of water.

Many other substances in water, including hydrogen sulfide, natural color, organic

matter, and microbial factors can influence corrosion reactions. A detailed discussion of

these factors Is beyond the scope of this report, but can be found in the literature listed

In the reference section.

11
Water Distribution System Materials

The chemical properties of materials present in a water distribution system greatly

dictate the extent of corrosion-related problems. The corrosion behavior of each

material also is the basis for considering specific corrosion control alternatives.

A variety of materials are used by the water works industry for the construction of

treatment plant, storage, distribution pipes, and internal plumbing. The majority of the

materials are used in construction of pipes and storage.

Detailed information regarding the nature and magnitude of corrosion and corrosion

control in the water works industry is presented by Singley et al. The following tables

were selected from that document. Table 2 presents the common materials and their

specific uses. Identifying what construction materials were used in a water utility

requires researching records, archives, and surveys. Samples of old pipes which are being

replaced also provide an opportunity to identify the type of material used. The significance of corrosion of various materials is presented in Table 3. This table presents a

discussion of the known extent of use of each material as well as the contaminants that

have been found associated with the use of each material. Table 4 presents an overview

of the factors influencing or affecting corrosion of each material. Water quality

parameters included are pH, hardness, alkalinity, dissolved oxygen, carbon dioxide, total

dissolved solids, metal ion, and organic acids. The effect of velocity and temperature

are also discussed.

Table 2

Types of Materials Used in the Water ndustry"

IN1 PLANT SYSTIS:

MATERIAL PIPING APPURITE- TRANSIIISSION STORAGE DISTRIBUTION StE ICE IOUSEHOLO

NANCES LINES RAINS LIIES

IROUGT IRN / /

CASTIDUCIIl1 1/ /1 // 1// 1 1 (cant Iron)

STEEL / 1/ / /

GAtWANIIZEO / / / /

IRON

STAINLESS 1/ /

ST EEL

COPPER / (brass) V//

LIAO / / 1 (gaskets)

AI q~U~lql /

ASSISIOS- / / / (I(INT

(()NCR[IT / /1 // /

PLAiTI( I I 1.' '1

Fly V/.' Uted ISO% for the partlcular ervire. . Urpluently, used D.r tlw ,larilcular %ervte

• ' aee. or Is us ed nr tP, parlrlIrIr ,prdle

*Source: J. E. Singley, et &I., Corrosion Prevention and Control in Water Treatment and

Supply Systems, Pollution Technology Review No. 122 (Noyes Publications, Park Ridge,

NJ, 1985), p 299. Used with permission.

12
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17
3 CORROSION-INHIBITING CHEMICALS USED

FOR DRINKING WATER TREATMENT

A corrosion inhibitor as defined by the National Association of Corrosion Engineers

(NACE), is "a substance which retards corrosion when added to an environment in small

concentrations." 5 This definition is rather broad and includes materials that would be

inappropriate and unacceptable for use in drinking water treatment. This chapter

outlines the major types of water quality control chemicals used as corrosion inhibitors in

drinking water. It describes these chemicals' characteristics, advantages, and disadvantages, and how their effectiveness depends on water characteristics, inhibitor dosage,

and the distribution system. (More details can be found in the sources listed in the

reference section.)

Much research has been conducted in the area of corrosion inhibition in drinking

water systems. However, due to the complex nature of the mechanisms involved, results

of studies often contradict each other or accepted theory and often pertain only to highly

specific test cases.

The underlying theory behind corrosion control by addition of inhibitory substances

is quite simple. An inhibitor reacts with the water or ions in the water to form a

protective coating that shields the pipe material from the corrosive action of the

water. There are three general classes of inhibitors commonly used for drinking water

treatment. They include pH control for calcium carbonate precipitation, inorganic

phosphates, and sodium silicates. The extent to which these inhibitors provide corrosion

protection depends on a number of factors, including water characteristics, plumbing

materials, inhibitor dosage, and flow characteristics of the water system.

Types of Corrosion Inhibitors

pH Control for Calcium Carbonate Precipitation

It has long been recognized that precipitation of calcium carbonate is an effective

form of corrosion control. The reactions of calcium ions with carbonate ions form a solid

protective coating of calcium carbonate. In addition, other metal ions present in water,

whether present naturally or as products of corrosion, are capable of forming complexes

and precipitates with carbonate ions when their solubility products are exceeded. Metal

ions such as iron, copper, zinc, and lead will form protective coatings when precipitation

of a metal-carbonate complex occurs. Calcium carbonate forms a rather solid coating

that has good adhering characteristics, enabling it to stick to the interior of metal

pipes. Of the other carbonates formed, zinc carbonate forms the most dense coating,

providing good protection against corrosive water. The most effective protective

coatings form very slowly, providing a hard, impenetrable coating.

The amount of calcium carbonate formed and the rate at which the coating is

deposited are determined by the water characteristics. The water characteristics most

affecting the precipitation of calcium carbonate are pH, alkalinity, calcium concentration, chloride concentration, and sulfate concentration. For precipitation to occur at all,

51NACE Glossary of Corrosion Terms," Materials Protection, Vol 4, No. 1 (1965), pp

79-80. 18!
the water must be oversaturated with respect to calcium carbonate. Empirical results

have shown that the optimum degree of oversaturation is in the range of 4 to 10 mg/l* as

calcium carbonate.6 This range allows for a slow rate of precipitation and the formation

of a hard coating. Calcium and alkalinity concentrations should be greater than 40 mg/I

as calcium carbonate, pH in the range of 6.8 to 7.3, and the ratio of bicarbonate alkalinity to chloride + sulfate concentration should be at least 5:1 to insure the formation of a

good protective coating.

Because corrosive waters are generally low in alkalinity and pH and often high in

carbon dioxide, additions must be made to the water to alter its characteristics to

promote the formation of protective coatings. Chemicals can be added that increase

alkalinity, pH, and calcium concentration, and reduce the carbon dioxide concentration.

(All these factors are interrelated.) The choice of the method depends on economic

factors and on the characteristics of the water to be treated. For waters low in

alkalinity and calcium, lime can be added to increase alkalinity and calcium concentration simultaneously. When carbon dioxide is inexpensive, it can be made to react with

lime or limestone to produce a concentrated solution of calcium bicarbonate, which can

then be mixed with the water to be treated. If this method is used, additional lime may be required to increase the pH to the optimal range. Other methods have been employed

that entail passing the water through a porous bed of crushed limestone; however, this

method often involves prohibitively long contact time, and pH values above 6.5 are

seldom achieved. For low alkalinity waters, lime appears to be the most effective and

least expensive method to increase alkalinity, calcium, and pH.

Many other factors affect the degree to which calcium carbonate precipitation is

an effective corrosion control method. These include water temperature, plumbing

materials, flow velocity, dissolved oxygen content, and concentration of dissolved

solids. Temperature affects the solubility of calcium carbonate and the rate at which

chemical reactions occur. As the water temperature increases, calcium carbonate

becomes less soluble. For example, water that Is just saturated with respect to calcium

carbonate at 25 0C will tend to precipitate calcium carbonate as the temperature rises.

Reactions of water constituents with plumbing materials can result in unwanted or

harmful products. For example, in lead pipes, toxic lead corrosion products may form if

pH adjustment is used without sufficient carbonate and alkalinity. Waters in the eastern

and northwestern portions of the United States are generally too soft to allow for pH

adjustment alone and require additions to increase alkalinity and hardness. The flow

velocity in the water system can affect the precipitation of protective coatings. Water

velocities should be greater than 1 ft/s to ensure an even distribution of calcium carbonate. Dissolved oxygen indirectly affects the strength of the protective coatings as

well. Because the strength of the coating is increased by the presence of ferric oxides, it

is suggested that a minimum of 5 mg/I of oxygen be present. The dissolved oxygen

content of a water must be carefully controlled because as oxygen content increases the

rate of corrosion also increases due to stimulation of the cathodic reaction. Other

dissolved materials In the water affect the solubility of calcium carbonate by increasing

the ionic strength of the water and thus increasing the solubility of calcium carbonate.

*Metrlc conversion factors are given on p 52.

6 R. L. Sanks, Water Treatment Plant Design for the Practicing Engineer (Ann Arbor

Science, Ann Arbor, Ml, 1978).

19
Inorganic Phosphates

Three basic types of phosphates are used as corrosion inhibitors for drinking water

systems. (1) Orthophosphates ("crystalline phosphates"), specifically sodiuni orthophos- phate, are often used In Germany, either alone or with zinc. 7 (2) Polyphosphates ("glassy phosphates") are formed from the combination of a caustic soda or soda ash with

phosphoric acid. They can exist in many forms depending on how they are manufactured. (3) Bimetallic phosphates are usually a combination of 10 percent zinc with 90

percent polyphosphate. Other types of phosphates are used, including zinc orthophosphates and other phosphate blends.

Phosphates, when added to water, form negatively charged particles. 8 To form a

protective coating, the negatively charged particles form complexes with divalent

cations, creating colloidal particles, which then migrate toward the cathode (the pipe) and form a protective coating on the pipe's interior. Phosphates can form complexes with many divalent cations. Ferric pyrophosphate and iron-calcium metaphosphate compounds have been observed as components of protective coatings. However, calcium

appears to form the most effective corrosion-inhibiting complex.

The effectiveness of phosphates for corrosion control depends on the phosphate concentration, flow velocity, pH, temperature, calcium concentration, iron concentration, and carbonate concentration. The various types of phosphates respond differently to different water characteristics. As with any of the protective-coat-forming corrosion

inhibitors, flow velocity affects the quality of the coating. The general rule is that a

flow velocity greater than 1 or 2 ft/s should be maintained to form an even coating: as

the velocity increases the quality of the coating increases as well. More turbulent flow

through a water pipe will more evenly precipitate a protective coating and will promote the formation of a harder, more adherent coating by shearing off the less adherent

precipitation products. In water systems with intermittent flow patterns, this type of

inhibitor is ineffective. As with calcium carbonate precipitation, temperature affects

both the solubility of phosphate precipitates and the rate at which complexes form. The

remaining factors mentioned above have different effects depending on the type of

phosphate used. The polyphosphates appear to perform better at pH values of 7 or less

and are affected by the calcium concentration. A calcium to phosphate ratio of at least

0.2 should be maintained and a ratio of 0.5 or more is preferred. In contrast, the

orthophosphates appear to be more effective in more alkaline waters than the polyphos- phates. Bimetallic phosphates seem to be most effective in more mineralized and harder

waters, are more effective at lower dosages than the polyphosphates, and can extend the

pH range in which polyphosphates are most effective up to around 8.0. The presence of

iron in the water seems to promote the formation of calcium-iron phosphate complexes which can also precipitate to form protective coatings.

Sodium Silicates

Sodium silicates have been used in water systems as corrosion inhibitors for over 50

years. They exist in dry form ("water glass") or in liquid solutions. In solution they exist

in varying proportions of sodium oxide and silica. The availability of various ratios of

sodium oxide to silica makes silicates suitable for use with various water conditions and

piping material.

7Internal Corrosion of Water Distribution Systems (American Water Works Association

[AWWA] Research Foundation, Denver, CO, 1985). 8Internal Corrosion of Water Distribution Systems.

20
In the proposed silicate inhibition mechanism, a silica gel forms when the silicate is

added to the water, 9 then corrosion products such as iron, zinc, magnesium, calcium, and

other metals present in the water adhere to the gel, forming a protective film. The

silica gel will not form a protective coat alone, because some corrosion is required

before a protective coat is formed to provide the corrosion products that adhere to the

gel.

The factors most affecting silicate inhibition are flow velocity, temperature, pH,

hardness, presence of corrosion products, dissolved solids concentration, bicarbonate

concentration, and chloride concentrations. Temperature and velocity effects are

similar to those on phosphate and calcium carbonate inhibition. The effects of bicarbonate and pH are closely related to each other. When silicates are used, the presence of

bicarbonate has been shown to increase the rate of corrosion; therefore, because

bicarbonate and pH are related, waters with low pH values are best suited for silicate

treatment. Water hardness, chloride concentrations, and dissolved solids concentration

affect the dosages required for effective inhibition. The dosage aspects of corrosion

inhibitors will be discussed later in the chapter.

Effects on Various Plumbing Materials

Lead

With lead pipe, the major concern is the presence of lead in drinking water, but not

the corrosion of pipes. 10 Calcium carbonate can prevent the uptake of lead into the

water by forming a protective coating that prevents the water from contacting the lead

pipe. Recent studies have shown that polyphosphates and silicates do not reduce the

solubility of lead in water and thus are ineffective for controlling lead concentration.

Orthophosphates have been shown to form insoluble compounds with lead that can form a

layer on the pipe surface, reducing soluble lead concentrations.

Copper

Copper pipes are affected by both general corrosion and by pitting or localized

corrosion. The formation of protective calcium carbonate coatings will prevent both

types. Of the silicate and phosphate inhibitors, the most effective seems to be an

orthophosphate-polyphosphate mixture. Orthophosphates have exhibited some degree of

corrosion control when used alone but are much more effective in combination with

polyphosphates. Silicates seem to have little effect on corrosion of copper. This small

effect seems to be associated only with the increase in pH when silicates are added.

Pitting corrosion has not been shown to be affected by the use of phosphates or silicates.

Galvanized Steel

Orthophosphates are the most effective for reducing the corrosion rate of the

protective zinc coating in galvanized steel. Polyphosphates have been shown not to

affect the corrosion rate of the zinc coating. Silicates will only prevent general corrosion of the zinc coating in very high concentrations.

9 lnternal Corrosion of Water Distribution Systems.

I nternal Corrosion of Water Distribution Systems.

21
Use Of Inhibitors

A corrosion control program using inhibitors usually consists of a period of

pretreatment in which concentrations are high enough for protective coatings to form,

then a period of gradual decrease in concentration over time, and then a steady state

concentration sufficient to maintain the protective coating. I

1 Dosage requirements for

both the pretreatment stage and maintenance stage depend on water characteristics such

as chloride concentration, dissolved solids concentration, and water temperature. The

type of inhibitor used depends on the water characteristics and the plumbing material, as

described in this chapter. In general, as water temperature, chloride concentration, and

dissolved solids concentration increase the amount of inhibitor required also increases.

One example of a treatment schedule used for a polyphosphate inhibitor consisted

of one day feeding at concentrations of 20 to 40 mg/l, reduction over one week to 10

mg/l, followed by reduction over one month to 5 mg/l, and subsequent reduction over one

additional month to 1 to 2 mg/l. Bimetallic phosphates require dosages of about half of

that required for the above hexametaphosphate treatment. A manufacturer of zinc

orthophosphate recommends feeding at 3 mg/I for three days followed directly by reduction to a maintenance dosage of 0.3 mg/l. Silicates require pretreatment with

between 8 and 20 mg/l for 3 to 4 weeks followed by maintenance dosage of 5 to 10

mg/l. During the pretreatment stage it is very important to keep the water velocity above 0.5 ft/s and preferably at 2 ft/s. For systems with dead ends, this means water

lines must be flushed regularly or continuously to maintain sufficient flow velocity during

the pretreatment stage.

I J. E. Singley, et al.

22
4 MONITORING TECHNIQUES FOR CORROSION CONTROL

A number of techniques for monitoring the effects of corrosion exist, ranging

from very inexpensive methods such as customer complaint logs to relatively expensive and more technical methods of electrochemical rate measurement. 2

The choice of which technique to use depends on the objectives of the corrosion

study being undertaken. For instance, one might be interested in determining the

corrosiveness of one water compared to another water, the rate of corrosion in a

water distribution system, the concentration of corrosion byproducts in a water

supply, or the effectiveness of various corrosion control methods. Each of these

objectives might be best handled with different monitoring methods or combinations

of different methods. The purpose of this chapter is to outline the various monitoring

methods and to describe their advantages and disadvantages in relation to the

objectives of the corrosion study being undertaken.

There are two general classes of corrosion monitoring methods--direct and indirect. The indirect methods include customer complaint logs, corrosion indices, and

water sampling and chemical analysis. These methods do not measure corrosion rates;

however, the data obtained can be interpreted and compared to show trends or

changes in the system. The direct methods include examining scale or pipe surface

and measuring rates.

Indirect Methods

Customer Complaint Logs

Complaints by customers are typically the first indication of a corrosion

problem. Customer complaints can arise for a number of reasons, not all of which are

caused by symptoms of corrosion. If good records of complaints are kept, however,

trends can be seen that may indicate a corrosion problem. A complaint map shows the

water distribution system with codes to indicate the location, frequency, and type of

complaints received. Such a map can be useful in determining if a problem exists and

where it may be located. Customer surveys may also be used to get the same

information more quickly than compiling records of customer complaints. These

methods are quite inexpensive and, depending on how the data is used, can be very

effective as a first step in a corrosion control program.

Corrosion Indices

Many corrosion indices have been developed to determine and predict whether a

water is corrosive, but they have had only limited success. These indices include, the

Langelier Index, the Calcium Carbonate Precipitation Potential, the Aggressiveness

Index, the Ryznar Stability Index, Riddick's Corrosion Index, and McCauley's Driving

Force Index. Perhaps the most widely used of the corrosion indices is the Langelier

Index (LI). It is based on the effect of pH on the solubility of calcium carbonate.

12J. E. Singley, et al.; Internal Corrosion of Water Distribution Systems.

23
Water parameters needed to calculate the LI are total alkalinity, calcium concentration, total dissolved solids (or, more precisely, ionic strength), pH, and temperature.

With these parameters it is possible to calculate the pH at which a water is in

equilibrium with solid calcium carbonate, which is known as pHs . The LI is simply

calculated as the difference between the actual pH of the water and the value of

pHs . A positive value means the water will tend to precipitate calcium carbonate. A

negative value indicates that the water will tend to dissolve calcium carbonate. A

value of zero, by definition, indicates that the water is in equilibrium with calcium

carbonate. This index is useful for estimation purposes, but its use is limited by

temperature and ionic strength considerations. The other indices mentioned are

similar in theory and have similar limitations; however, they can be used as quick estimates of the corrosive tendencies of a particular water and require only simple

calculations.

Sampling and Chemical Analysis

Chemical analysis of water samples can be a very useful method of determining

whether a corrosion problem exists. Because corrosion is affected by the chemical

composition of the water, it may be useful to know what constituents in the water

may be accelerating or inhibiting the rate of corrosion. A chemical analysis can show

where there are higher than normal concentrations of corrosion products, and by

sampling at various points throughout a water system, locations of corrosion problems

can be determined. Chemical analyses are also useful in showing whether or not a

corrosion control program is working as predicted. A sampling program must be

carried out on a regular basis to insure reliable data collection. Proper sampling techniques are crucial. Water samples should be taken without adding any gas which

may react with or remove any of the water constituents. Analyses should be made as

quickly as possible to insure that the sample being analyzed is an accurate representation of the water in the system.

Direct Methods

These methods monitor corrosion by measuring corrosion rates directly. They

include experimentation, examination of metal samples, and electrochemical analysis. The procedures are quite simple, with fairly straightforward calculations, but

sometimes the experimental apparatus is expensive. Great care must be taken,

however, in preparing metal samples and the apparatus to insure accurate measurements of corrosion rates. The following sections discuss various direct methods.

Inserts In Pipe Loops And Plumbing Systems

To insure accurate data collection, four criteria must be met: (1) the metal

samples must be representative of the material in the plumbing system, (2) the water

used must be of the same quality as that of the system being studied, (3) the flow

velocity, flow pattern, and stagnation time should be similar to those of the full scale

system, and (4) the duration of the test must be long enough to insure formation of any

scale that may affect the rate of corrosion. (Table 5 shows rough estimates for times

required (in months] for accurate data collection).

24
Table 5

Estimated Duration (Months) Required for Corrosion Tests*

Comparison of Uniform

Corrosion Rates Comparison of Inhibitors

Material or Metal Leaching New Pipe Old Pipe Pitting

Iron 12-24 3-6 12-24 12-24

Copper 3-6 1-3 3-6 12-36

Galvanized Iron 3-6 1-3 6-12 12-36

(Zinc)

Lead 6-12 2-6 6-12

Asbestos 18-24 6-12 12-18

Cement

Mortar Lining 24-36 12-24 24-36

*Reprinted from Internal Corrosion of Water Distribution Systems, by permission. Copyright 0 1985, American Water Works Association.

It is necessary to use metal samples of the same material used in the full scale

system in such a way that the flow pattern around the sample is similar to that of the

full scale system. Therefore, insertion of flat metal samples (coupons), for example,

will not give flow patterns similar to those in a circular pipe section. Circular

samples of actual pipe material inserted into a loop system or plumbing system will

insure more accurate representation of the flow patterns in the full scale system.

Illinois State Water Survey (ISWS) Machined Nipple Test

This method is described in detail in ASTM Standard D-2688-83, Method C. 13 A

short length of the actual pipe material, encased in a polyvinyl chloride sleeve, is

inserted into the pipe system using pipe unions, so the sample can be removed for

analysis. A bypass line must also be inserted to allow for water flow around the

sampling area when the specimen is not in place. The specimen holder must be

designed to insure smooth flow through the pipe sample. Figures 1 and 2 show the

details of the specimen and PVC sleeve used in this method.

It is recommended that the sample be a I m length of straight pipe. If more

than one sample is used in series and one is removed for analysis, a plastic insert

should be put in place to insure that the flow is not disturbed for the samples farther

down stream. The analysis consists of removing any scale that has formed on the

interior of the sample and weighing the sample to determine the amount of pipe

material lost to corrosion. Once weighed, the sample can be cut open so the interior

13ASTM Standard D-2688-83, "Standard Test for Corrosivity of Water in the Absence of

Heat Transfer (Weight Loss Methods)," ASTM Annual Book of Standards (American

Society for Testing and Materials [ASTM]).

25
1.125 in (28.58 mm) O.0.

t I

INSERT 1 in I.D.

k4 in (0 1.6 mm) -. ]

B

_ _ _ 1__ 2 in (292 mm) al

Pv V C f - =I

S L E E V E 1.140 in (28.96 mm) I.D. 1 in I.D." 1.140 in (28.96 mm) I.D.

F*- 4 in (101.6 mm)i -- a- 4 in (101.6 mm)-- 4

A % 1.5/8 Bn a

1(41.3 mmn--

S P A C E R i n . .

1.05 in or 26.7 mm STEEL. TAPERTOFIT

GALVANIZED, & PVC

1.025 in or 26.0 mm COPPER

Figure 1. Schematic of 1SWS corrosion tester. (Reprinted from

Internal Corrosion of Water Distribution Systems, by permission. Copyright 0 1985, American Water Works

Association.)

surface can be examined for irregular corrosion patterns and pitting. Corrosion rates are

usually expressed in units of mass per area per time; thus the calculation of corrosion

rate would be

corrosion rate = (g/m 2/day) = W/A/T [Eq 1]

where W is the mass removed by corrosion, A is the internal surface area from which the

material was removed, and T is the duration of the test. Other units are used for

corrosion rates as well, the most common being corrosion velocity, which is usually

expressed in v m/yr.

The Metal Uptake Test

This method is used when corrosion rates are to be determined by measuring the

corrosion products concentration. Since the machined nipple test involves analysis of a

pipe sample, It cannot be used to determine the concentrations of corrosion products in

the water because of Insufficient contact time between the water and the pipe sample.

Instead, this method uses a recirculating loop system constructed entirely from the pipe

material being studied. This Insures adequate contact time between the water and the

26 

1
B A

1-1/4 in "UNION

PVC INSERT PVC SPACER I in SERVICE LINE

SLEEVE

1.1/4 in " PIPE NIPPLE

10 in 1254 mm) LENGTH I i *-. BUSSING

I 1.66 in or 42.16 mn 0.0.

E1.315 in or 33.40 mn O.D.

- ISWS CORROSION TESTERFigure 2. Cross-section of assembled ISWS corrosion tester. (Reprinted

from Internal Corrosion of Water Distribution Systems, by

permission. Copyright 0 1985, American Water Works

Association.)

pipe material and allows high enough concentrations of corrosion products to develop so

they can be accurately measured by analytical methods. The apparatus is pictured in

Figures 3 and 4.

Before the test begins, the system is flushed with fresh water for 30 minutes. Once

the flushing is completed, the system is changed to the recirculating mode, samples are

taken, and water is added equal to the amount removed in the sample. The water

samples are then analyzed for metal concentration. The test is usually run for 30

minutes, and the results obtained represent the instantaneous status of the corroding

metal. A plot of metal concentration versus time is made, from which the rate of metal

uptake in the water is determined. To determine the rate of metal uptake it is necessary

to know the internal surface area of the pipe used in the test and the total volume of the

closed loop system. The slope of the concentration versus time plot, in units of mass per

volume per time, is multiplied by the system volume and divided by the surface area of

the system to give the metal uptake rate in units of mass per area per time.

27
ret pe 4-

effluentfrhwte

from Intrna CorosconoftaterDirouinSytm, ypr

oxygen coefntrueio

watermpraur ~ i 24rsue 

conirso

Figure 3. Schemetcdia thalupae of pipe rigic. testfo (Reprinted nenlCro

frmIta of orsion Water Distribution Systems, by permiso.Coyih

miso.Coyih* 1985, American Water Works Association.)

28lun
Corrosion Coupon Testing

In this method, an accurately weighed pipe specimen, a "coupon," of the same

material as the pipe system being studied is inserted into a section of the actual pipe

system for a period of between 90 to 180 days. The coupon, usually a flat bar, is

attached to a plug, which is then screwed into the pipe system and left for the duration

of the test. At the end of the test period, the coupon is removed and weighed to

determine the amount of material lost to corrosion. This method is somewhat less

involved than the two previously described methods and requires much less analysis time

and money (although the test duration is quite a bit longer in this method ). The results

obtained from this method, however, may not be as accurate because the metal coupon is

not a circular pipe section and the flow patterns around the coupon are not at all similar

to those around the actual pipe system.

Electrochemical Methods

The methods of coupon testing previously described are rather costly and timeconsuming. This fact has lead to the development of electrical instruments that can

quickly measure corrosion rates using electric resistance, linear polarization, and

galvanic current techniques. These instruments are particularly attractive because they

can be made as portable instruments for use in field operations for instantaneous rate

measurement.

Electric Resistance Measurement

This method (which is really electrical rather than electrochemical) is rather

straightforward and easy to use. It consists of a low resistance Kelvin bridge circuit

constructed entirely from the same material as the pipe being monitored, except for the

slide wire. As the probe corrodes, its cross-sectional area is reduced and its resistance is

increased. The instrument measures the change in resistance of the probe with time,

which can be recorded manually or automatically, yielding a plot of resistance versus

time. From this data, with the proper conversion factors supplied by the manufacturer,

the corrosion rate is determined from Equation 2:

CR = ([D2 - D1] x PF x 0.365)/T [Eq 21

where CR is the corrosion rate in mils per year, D1 and D2 are the initial and final

(respectively) dial readings from the instrument in microinches, PF is the probe factor

supplied by the manufacturer, and T is the time in days of the test. These instruments

are easy to use, reliable, and fairly economical; however, they give no indication of

pitting corrosion, and data from scale-covered specimens may be hard to interpret.

Linear Polarization

These instruments are based on the principle that a linear relationship exists

between small shifts in electrochemical potential or polarization and the corrosion rate

of a metal. They consist of either two or three probes through which a small direct

current is passed, creating a 20 millivolt electrochemical polarization of the probes.

They provide a direct readout of corrosion rate and indicate whether pitting is occurring. The theory behind these Instruments is rather involved and beyond the scope of this

29
report. The details of the theory can be found in most corrosion science texts (e.g.,

Fontana and Greene [19781). 1

Galvanic Current Method

These Instruments use a zero-resistance ammeter to measure corrosion of dissimilar metals. They are useful in measuring galvanic and ground currents, which in some

cases are related to internal corrosion.

The electrochemical instruments provide for quick, convenient, and often portable

means by which corrosion rates can be measured. They are fairly economical and require

no experimental apparatus. They are also very well suited for permanent monitoring of

pipe corrosion in situations where corrosion can lead to expensive or catastrophic failure.

14M. G. Fontana and N. D. Greene, Corrosion Engineering (McGraw Hill, New York,

1978).

30
5 DEVELOPMENT OF A PIPE LOOP SYSTEM

FOR INHIBITOR EVALUATION

It is evident, from literature available on the corrosion phenomenon in water utilities, that the nature of corrosion and possible corrosion control alternatives are

extremely complex. Defining the corrosiveness of a water using a universal corrosion

index or parameter is not feasible at this time. Instead, it appears that corrosion control

can only be accomplished through a comprehensively applied program on a case by case basis. 15

The commonly used techniques and apparatus for corrosion detection, control, and

monitoring have been presented in Chapters 3 and 4. A number of corrosion measurement techniques are less applicable because they are short-term and do not properly take

into account the effects of slowly accumulating scales.

Although a large data base is available in the literature, often the data may not be

useful for comparing the corrosivity of various waters and the effectiveness of control

measures for these waters. Many times it is reported that a particular corrosion control

treatment works in a specific water utility but did not work in another water system with

similar water characteristics. A part of the problem may be inconsistencies in monitoring procedures. For example, both coupons and pipe inserts have been used as specimens

for determining effectiveness of measures. However, the results obtained using coupons

may not be comparable to results obtained using pipe inserts. This is due to the difference in the shape of the specimens and the resulting differences in water flow characteristics during exposure. Further, other influences may not have been taken into account.

Factors such as temperature and velocity of water are seldom considered in evaluating

and reporting the corrosion characteristics of a specific water utility. The effect of a

particular chemical varies with the water characteristics. These in turn vary with the

seasons. Many times, measurements assume the water quality is constant, which is not

necessarily the case.

Pipe Loop System Design

To determine the effect of various chemical inhibitors, inhibitor dosage rates, or

water quality on the corrosion of piping materials occurring in public water supplies, a

standard testing procedure is needed to minimize extraneous influences. To insure that

the data gathered by such a procedure can be used for meaningful comparisons, the water

quality must be closely controlled and experiments must be carefully designed. The

design of the USA-CERL pipe loop system (Figures 5 and 6) makes both those efforts

easier; at the same time it simulates conditions in an actual distribution system, as

closely as possible. The design's standard pipe configuration will be usable at most

installations. The design was a compromise among several objectives: maintaining the

water velocity within a range found in distribution systems, restricting the physical

dimensions of the loop to a practical size, and limiting water usage at test locations

where water reuse was impractical.

'Singley, et al.

31
SECTION

aA" c c LOOP E E

R R

L L

SECTION FR SECTION V28ct

METERek SAMPLE

MIXI

SUPPLY v R

==vWASTE

MATERIAL LISTING

MIXER -STATIC METEINGL

VS - MAIN WATER SUPPLY SHUT-OFF VALVE PUMP

PRV - PRESSURE REGULATING YLVE

V1 - TEST LOOP ISOLATION VALVES CHEMICAL

FC - FLOW RATE CONTROLLER, PVC, 3GPM CONTAINER

FR - ROTAMETER, 0-5 GPM

M - WATER METER, TOTALIZING

C - CORROSION COUPONS

CERL - PIPE SPECIMENS

V2 - SAMPLE VALVE, 1/4*

PIPE S FITTINGS- 3/4-, SCH. 40, PVC

Figure 5. Schematic of USA-CERL pipe loop system.

32
Figure 6. Assembled pipe loop system.

Features

The test loop was constructed of polyvinyl chloride (PVC) and chlorinated polyvinyl

chloride (CPVC) pipe and fittings with schedule 40 pipe, and 3/4-in, nominal pipe size.

These materials were readily available and had suitable characteristics. This design

eliminates all metallic components, except for the corrosion specimens, and electrically

isolates the corrosion specimens from one another. The test loop was oriented vertically

to minimize the amount of suspended matter deposited on the exposed surfaces of the

corrosion specimens. A flow controller (FC), flow rate meter (FR), and regulating valves

(Vi) were provided to maintain the flow rate through the loop at desired values during

normal test conditions. If fluctuating water pressures occurred, a pressure regulating

valve (PRV) was used on the inlet piping of the test loop. A totalizing water meter (M)

was also included in the design to verify water usage information during monitoring

intervals. A chemical container, chemical metering pump, and static mixer were added

to the loop to study the effects of selected corrosion inhibitors on the corrosivity of a

particular water supply. The continuous flow of both water and inhibitor insured that

constant inhibitor concentrations were in contact with the corrosion specimens at all

times. A sampling valve (Vi) was installed in the loop to collect water samples periodically for chemical analysis and to verify inhibitor concentrations.

33
This design allows two measurement methods: weight loss of a pipe insert and

weight loss of a metal coupon. Both are discussed in Chapter 4 and specified in detail in

ASTM Standard D-2688-83. With the pipe loop system, these methods can be used

simultaneously on multiple specimens. Four coupon and four pipe insert specimens can

be accommodated by the test loop, so that different materials can be studied during the

same exposure period, duplicate specimens can be used for statistical evaluation, or the

planned interval exposure procedures described by Wachter and Treseder' 6 can be

carried out. Both coupon and pipe specimens were included so any differences in

corrosion occurring on pipe walls could be compared to the corrosivity of the bulk water.

The USA-CERL corrosion tester (Figure 7) was developed because the ASTM

Standard D-2688-83 Method C corrosion tester could not be incorporated into the USACERL's standard test loop due to incompatible size and construction materials. The new

USA-CERL design (constructed entirely of PVC) eliminates the sleeve used in the ASTM

design, reduces fabrication time, and, with its uniform dimensions, allows corrosion

testers to be interchanged. Streamline flow is maintained through the tester to simulate

/2

O 3/4" PVC service line

1" union, PVC, socket type

1 x 10" pipe nipple, PVC, Sch. 40

0 1 x 3/4" reducing bushing, PVC, socket

3/4" PVC spacer, Sch. 40, O.D. reduced 0.015"

® Union gasket

(D Corrosion specimens, 3/4", O.0. reduced 0.030",

machined from Sch. 40 galvanized steel or steel pipe

3/4 x a 2" specimen separator,

PVC, Sch. 40, O.D. reduced 0.015"

Figure 7. Cross-section of USA-CERL corrosion tester.

16A. Wachter and R. S. Treseder, "Corrosion Testing Evaluation of Metals for Process

Equipment," Chemical Engineering Progress, Vol 43, No. 61 (1947), p 315.

34

Ir " -9 • " 
deposition or corrosion processes occurring on the walls of piping in distribution systems. Corrosion specimens for this tester may be constructed from any material

available in 3/4-in., schedule 40 pipe. Specimens are prepared in accordance with ASTM

procedures. Each pipe specimen exposes 10.25 sq in. of pipe wall to the water.

Four standard metal coupons can be installed in the test loop, all oriented in the

same direction in relation to the flow of water through the loop. The 1/2 in. by 3 in. by

1/16 in. coupons are mounted on a PVC pipe plug by means of a nylon stem (attached to

the plug) which protrudes into the middle of the pipe. Each coupon exposes 3.38 sq in. of

surface area to the bulk water. The coupons and mounting hardware are commercially

available in a variety of materials and the coupons can be readily evaluated by most

laboratories according to ASTM procedures.

All of the components of the test loop are assembled with pipe hanger supports on a

4 ft by 4 ft plywood sheet. The completed assembly requires minimal wall space when

installed and is easily transported as a complete unit. Ten identical units were assembled

for installation at Fort Monroe (five) and Fort Bragg (five).

Possible Experimental Designs

Because of the pipe loop system's segmented, multisample, standardized design, a

great variety of experimental designs are possible. Care must be taken so that data can

be compared meaningfully and so that the many complicating factors are controlled as

much as possible. The system's design is especially useful for side-by-side comparison

tests. For example, pipe loops could be used to:

" Evaluate effect on materials of water that has not been treated with corrosion

inhibiting chemicals

" Evaluate the effect of water that has been treated with the corrosion inhibiting

chemical normally used by the plant in question

" Using multiple loops, compare (side-by-side, simultaneously) the effects of

several corrosion inhibitors

" Compare the effects of varying dosages of one inhibitor

" Evaluate the effect of changing the inhibitor used

" Evaluate the effect of changing other aspects of the treatment process (filtration, chlorination, etc.)

* Investigate changes in water corrosivity characteristics over time

* Investigate the variability in the weight loss method of measuring corrosion

rates (significant differences in weight loss can occur when active corrosion

sites develop on one specimen more easily than on another specimen)

" Determine when the corrosion rate stabilizes, under various conditions.

The design also permits variations in exposure time. For example, four coupons

could be placed in a loop at one time, and then removed at staggered intervals: one

coupon could be removed after 3 months, one after 6 months, etc.; the last would be

35
exposed for a whole year. New ones could replace the ones removed so the loop would

remain in continuous use. This data could be manipulated in numerous ways. Two

factors must be considered in the choice of intervals: seasonal variation and nonlinear

change in the corrosion rate. The seasons affect the corrosion rate, partly because of

changing temperatures. Second, the corrosion rate of a newly prepared specimen

decreases exponentially (roughly) over time. In the more aggressive waters, galvanized

steel specimens have been shown to require 12 to 18 months of exposure to approach a

minimum stable corrosion rate. 7 A less aggressive water and another material may

reach a stable value in much less time. A 1-year interval would include all the seasonal

changes and allow the corrosion rate to stabilize. However, the optimum interval has not

been determined with certainty.

17C. Neff, M. Schock, and J. Marden, "Relationship Between Water Quality and

Corrosion of Olumbing Materials in Buildings, Volume I: Galvanized Steel and Copper

Plumbing," State Water Survey Contract Report 416-I (University of Illinois, 1987).

36
6 EVALUATING THE PIPE LOOP SYSTEM AT

FORT MONROE, VA AND FORT BRAGG, NC

Background on Fort Monroe Water Plant

Fort Monroe receives its potable water supply from its own Big Bethel Water

Treatment Plant, Hampton, VA. The water plant also supplies water to Langley Air

Force Base and NASA. The plant maintains two reservoirs, with raw water being drawn

off the lower reservoir. The water treatment process consists of prechlorination, alum

flocculation, settling, sand filtration, fluoridation, and postchlorination. Corrosion control is achieved by adjusting the pH by adding lime; zinc metaphosphate (Virginia Chemical Co. [Virchem] No. 937) is used as a corrosion inhibitor. The finished water is

maintained at a pH of 7.3 to 7.5, and phosphate is maintained at 2.5 mg/L as P0 4 .

Chemical testing is performed daily at the plant on the treated water in the plant and at

several points in the distribution system.

In 1968-69, the Big Bethel Treatment Plant changed the chemical treatment for

corrosion inhibition from sodium silicate at a pH of 8.5 to Calgon TG10 (sodium hexametaphosphate). Calgon advised the plant that by feeding TG10, a lower pH could be

used to remove iron and manganese. With this treatment scheme no red water problems

occurred. For economic reasons, the plant switched to Virchem corrosion inhibitor 937

(zinc metaphosphate). A corrosion coupon study conducted by Virginia Chemical Co.

showed corrosion rates of 6.80 to 7.85 mils/year with this treatment. Another coupon

testing in December 1982 showed that Virchem 931 (orthophosphate) decreased corrosion

rates to 2.81 to 3.79 mils/year. However, red and black water problems appeared when

Virchem 931 was used; hence the plant went back to using Virchem 937.

A water quality survey conducted by the Facilities Engineering Support Agency 8

in July 1983, using chemical analyses and Langelier Index calculations, concluded that

the water was extremely corrosive and non-scale-forming at ambient temperatures.

Approximately 42 mi of supply and distribution mains provide potable water to Fort

Monroe. These mains have cast-iron piping with leaded bell and spigot type joints. The

service lines are galvanized steel and copper. None of the supply or distribution lines at

the installation have cathodic protection or cement linings. All of the on-post distribution mains, except 4 in. lines, were "pigged" in 1983, but the lines were not lined with

cement after the pigging. Fort Monroe is currently experiencing red water problems with the water supply due to the pigging of lines without subsequent cement lining. However, efforts are underway to replace the old distribution mains.

Background on Fort Bragg Water Plant

Fort Bragg's drinking water source is a reservoir which collects water from the onpost watershed. The water treatment process consists of powdered activated carbon,

alum coagulation, settling, sand-anthracite dual-media filtration, fluoridation, and chlorination. Treated water pH is adjusted by adding lime. For corrosion control, Dabco 22

(bimetallic polyphosphate) corrosion inhibitor is added at the end of the treatment

process. (However, until January 1987, Virchem 937 was used, as at Fort Monroe.)

| 8 "Water Treatment Survey Report - Fort Monroe, VA" (Facilities Engineering Support

Agency, 1984).

37
Routine finished water analysis is conducted daily at the well-equipped water plant

laboratory.

A recent survey of domestic-water-side corrosion found that the water should be

corrosive to steel and galvanized steel because it has an unusually low alkalinity (5 mg/)

and is nearly saturated with dissolved oxygen (8 mg/l).' 9 The water has no tendency to

deposit any protective calcium carbonate scale based on the Langelier saturation index

(LSI = -2.3).

The principal corrosion problem associated with conveying domestic water at Fort

Bragg involved galvanized-steel pipes and fittings. No significant corrosion problems

were associated with copper tubes and fittings. Although no known corrosion-induced

leaks were reported in the cast-iron mains, these pipes and fittings were heavily tuberculated. The cast-iron mains (6 to 12 in. in diameter) are being pigged and lined with

cement to prevent further corrosion. The water plant personnel reported no current "red

water" problems in the distribution system. Such problems had been frequent in the past,

before a corrosion inhibitor was used.

Experimental Setup

Equipment

The equipment was identical at both installations: five pipe loops located at

various places in the water treatment system. These locations were distributed as shown

in Figure 8.

Each loop is operated independently, that is, in parallel with the others. The

effluent from loops inside the plant is recycled to the head of the plant, to avoid wasting

water. For the loop at the booster station, the effluent flows into a drain. Of the five

loops, the control loop, which receives treated water just before any corrosion inhibitor

is added, is of vital importance because all others will be compared to it.

Samples

This report discusses data for samples of mild steel (C1010), zinc, and galvanized

steel (zinc coated). In the future, results will be available for tests on samples of copper,

lead, and cast iron.

There is space for eight samples in each loop: four coupons and four pipe inserts.

For the data reported here, each loop had two of each type of specimen: two mild steel

coupons, two mild steel pipe inserts, two zinc coupons, and two galvanized steel pipe

inserts. Thus all the sample slots were filled.

Exposure Times

The exposure time was 3 months for all samples reported. Tests began in July

1986. The data for Fort Bragg is for the period 22 July 1986 to 23 October 1986; for Fort

Monroe, the period is 22 January 1987 to 23 April 1987. The staggered removal concept

was not used for these samples.

1

9 J. R. Myers, "Data Summary Related to the Relative Corrosivity of Soils and Domestic

Water at Fort Bragg, NC" (Prepared for USA-CERL by JRM Associates, Franklin, OH,

1986).

38
Distribution

WFter System

Rapid/

MixL i Alum

SFlocculatior Settlingt- "Flerhli C le a r Wel

Cor Inhibitor

Flouride

Control 4 _

Test Chem !

F--L= Pipe Loop

Figure 8. Pipe loop system locations.

Chemicals

At Fort Monroe the general water supply was treated with the corrosion inhibitor

Virchem 937, zinc metaphosphate. This chemical reached two loops, the one receiving "finished" water and the loop at the booster pumping station. At Fort Bragg the general

corrosion inhibition treatment was Virchem 937 until January 87; after Jan 87 the plant

switched to Dabco 22 (bimetallic phosphate). (This change does not affect comparison of

the data presented here because during the interval reported for Fort Bragg [July to

October 1986] they were still using Virchem 937.)

At Fort Monroe two "extra" chemicals were pumped through the "test" loops, which

received fully treated water just before the corrosion inhibitor was to be added. The two

chemicals were Nalco 937 and Nalco 7393. The rate at which these test corrosion inhibitors were injected was adjusted so the concentration of inhibitor was maintained at

about 1 ppm (1 mg/I). During the interval reported, no "extra" corrosion inhibitors were

tested at Fort Bragg. All of the same equipment is in place, however. So, the only

comparisons shown for Fort Bragg are among "no inhibitor," "finished," and "distribution

system" water.

Typical water quality data from Forts Bragg and Monroe are shown in Table 6.

39
Table 6

Typical Water Quality at Fort Bragg, NC and Fort Monroe, VA

Fort Bragg Fort Monroe

Parameter Units Water Plant Water Plant

pH pH units 7.4 7.7

C02 dissolved mg/L <5

02, dissolved mg/L 8

Total alkalinity mg/L CaCO3 5 40

Total dissolved solids mg/L 77 182

Total hardness mg/L CaCO3 36 126

Calcium mg/L as Ca 12

Magnesium mg/L as Mg 0.78

Zinc mg/L as Zn 0.07 0.332

Iron mg/I as Fe 0.09 0.04

Copper mg/L as Cu <0.01

Manganese mg/L as Mn 0.03 0.025

Sodium mg/L as Na 2.2 8.3

Silica mg/L as SiO 2 8

Chloride mg/L as Cl 14 16

Sulfide mg/L 0

Sulfate mg/L as SO4 13 144

Measurement

After 3 months, the samples were removed and taken to the laboratory for

analysis. The composition of the deposits was analyzed using x-ray diffraction. The

corrosion rate was determined using the ASTM weight loss method (ASTM Standard

D-2688-83). In the overall procedure, the samples are:

* Precleaned (ASTM)

* Weighed

* Exposed

* Removed and weighed (to determine weight gained in corrosion byproducts)

9 Loose scale removed (ASTM)

9 Thoroughly cleaned (ASTM)

* Weighed (to determine material lost overall).

40
Precautions for Controlling Variability

The following measures were taken to eliminate as much variability as possible and

to simulate as closely as possible the actual conditions found outside a treatment plant, in the distribution system.

e Each loop was identical.

* Specimens were put in the same place in each loop.

* A constant water flow of about 3 gpm or about 2 ft/s was maintained (water

meters were monitored daily and the flow rate was adjusted as appropriate).

* This constant flow insured that all loops experienced the same ambient water

temperature.

* The water quality did change, but all loops in the system experienced the same

changes. (As part of normal treatment procedures, the water is routinely

sampled to monitor its chemical composition.)

Preliminary Results

The first set of samples was removed from the pipe loop systems for observation

and analysis after 3 months of operation. Virtually no maintenance was required, except for occasional flow meter check, during the experimental period. The water meters

recorded flows between 2.5 to 3 gpm (corresponding to a water velocity of 1.8 to 2.2

ft/s). The water quality parameters during the experimental period were analyzed and

recorded by the water plant laboratory as a part of routine water plant operations.

At Fort Bragg, a visual observation of the flow meter in the pipe loop systems showed that the pipe loop receiving finished water with the corrosion inhibitor was not

stained. In contrast, the flow meters of the pipe loop systems which received water just

before the addition of corrosion inhibitor were stained dark brown, apparently by the

corrosion byproducts. This indicated that the corrosion inhibitor was able to react with

and remove the corrosion byproducts which can cause "red water" complaints.

The specimens from the pipe loop systems at Fort Bragg were removed for visual

comparison. Figure 9 shows the condition of the interior surface of the mild steel before

and after exposure in the oipe loop system which received finished water with corrosion

inhibitor. As shown, a layer of deposits accumulated on the interior surface of the pipe. These deposits can be corrosion byproducts or precipitates from the water. Similar

effects were observed (Figures 10 and 11) in the galvanized pipe specimen as well as on

the mild steel and zinc coupon specimens. The deposits on steel specimens were visually different from deposits on zinc and galvanized specimens. Similar visual inspections

indicated very little deposition in any of the pipe or coupon specimens in the pipe loop

system which received treated water just before addition of corrosion inhibitor. Perhaps in this system the corrosion byproducts were released into the water, staining the flow

meters rather than the coupons or pipes. Hence, from this visual observation, it appears

that the presence of corrosion inhibitor in the water had a definite effect on the

interaction with the metal specimens in the pipe loop system.

41
Figure 9. New pipe specimen and pipe specimen exposed to water in

pipe loop system.

Figure 10. Corrosion byproducts on a galvanized Iron pipe specimen

exposed to water in pipe loop system.

42
Figure 11. Corrosion byproducts on mild steel and zinc coupons exposed

to water in pipe loop system. (From left, coupons are [1 mild

steel, [2] zinc, [3] mild steel, and [4] zinc.)

At Fort Monroe, the flow meters in all pipe loop systems were uniformly stained

dark brown, indicating that the corrosion inhibitor had no effect which could be visually

observed. A visual comparison of the pipe loop system specimens indicated thick

deposits on the mild steel specimen surface and a very thin layer of deposits on the zinc

and galvanized steel surfaces. Similar deposits were seen regardless of whether the

specimen received water with or without corrosion inhibitor.

Further analyses were conducted in the laboratory to characterize the deposits and

determine the corrosion rates of the specimens from both installations. Table 7 presents

the corrosion rate data for all the specimens removed from Forts Bragg and Monroe

during the first three months of operation. In general, corrosion rates of pipe specimens

were different from those of coupon specimens of the same material. This may have

been because the different shapes of the specimens affected water flow characteristics.

Also coupon specimens may have accumulated stresses in their edges during preparation, which may have led to preferential corrosion of the edges. This preferential corrosion of the coupon edges was evident visually after the surface deposits were removed.

Figures 12 and 13 compare the corrosion rates of the specimens in Fort Bragg

water without corrosion inhibitor treatment, in the finished water at the plant, and in the

distribution system. In general corrosion rates of galvanized (zinc) specimens were lower

compared to mild steel specimens. However, as seen in the figures, the corrosion rates

of both mild steel and galvanized (zinc) steel were higher in the water which was treated

with the corrosion Inhibitor. Although an increase in corrosion rate in presence of a

corrosion Inhibitor was unexpected, it is not an unusual occurrence. Several cases have

been reported in the literature where, under certain conditions, the corrosion inhibitors

actually increased the corrosion rates of metals. However, this observation could not be

confirmed without side-by-side comparison and monitoring.

43
Table 7

Preliminary Results of Pipe Loop Experiments at

Fort Bragg and Fort Monroe

(Data for 22 July 1986 to 23 October 1986)

Location Water Source Average Corrosion Rate (mils/year)

Steel Steel GaIv. Zinc

Pipe Coupon Pipe Coupon

Fort Bragg Water w/o

Corrosion Inhib. 5.87 3.16 3.25 1.22

Fort Bragg Finished Water

(Virchem 937) 17.82 12.74 4.70 3.14

Fort Bragg Distribution

System Water

(Virchem 937) 16.77 13.23 4.54 2.97

Fort Monroe Water w/o

Corrosion Inhib. 29.19 12.79 7.10 7.42

Finished Water

Fort Monroe (Virchem 937) 21.87 12.38 5.05 5.82

Note: Both Forts Bragg and Monroe treated their water with Virchem 937 as

corrosion Inhibitor.

20

19 22 Jul '86 - 23 Oct '86

19

17 Steel Pipe

16

15 - Steel Coupon

213

S12 o 'i

10

2 9

7 - U 6

5

4

3

2

1

0%

No Corr. Inhi. Finished Water Dist. System

Water Source

Figure 12. Corrosion rates of mild steel specimens at Fort Bragg, NC.

44
to

22 Jul '86 - 23 Oct '86

8 M GoIv. Pipe Zinc Coupon

-

6-

0 4-

0

03

2

L

0 1

No Corr. Inhi. Finished Water Dist. System

Water Source

Figure 13. Corrosion rates of galvanized (zinc) iron specimens at Fort

Bragg, NC.

Table 8 presents the type and extent of pitting of specimens during the same

experimental period as above. It is clear from the table that pitting was the predominant

type of corrosion in mild steel specimens, whereas the galvanized specimens experienced

a general (uniform) type of corrosion.

Figures 14 and 15 compare the corrosion rates of mild steel and galvanized (zinc)

steel specimens in presence of various corrosion inhibitors at Fort Monroe. This data was

collected during the period of January through April 1987. The Nalco corrosion inhibitors

were injected into the pipe loop system using a pump, whereas the water plant added the

Virchem corrosion inhibitor in their finished water supply. As seen from the figures,

there were no significant differences in corrosion rates of pipe specimens with or without

corrosion inhibitor. However, the coupon specimens did show some reduction in corrosion

rates due to the presence of a corrosion inhibitor. Because of the limited experimental

time, the data did not show any conclusive evidence regarding the effectiveness of the

corrosion inhibitor.

At both Fort Monroe and Fort Bragg, it was clearly evident that the corrosion rates

of the specimens during the July to October 1986 period were significantly higher than

the corrosion rates during the January to April, 1987 period. This seasonal change in

corrosion rates is due to the changes in influent water quality parameters, especially

temperature, which plays an important role In the corrosion phenomenon.

These preliminary results are short term (3 months) and hence may not truly reflect

the corrosion status. Subsequent long-term studies with the pipe loop system have

revealed that the corrosion inhibitors do eventually reduce the corrosion rates of mild

45
Table 8

Type and Extent of Pitting in Pipe Loop System Specimens

Surface max. Range

Water Type of Area Depth of Depth Width

Location Source Metal Corrosion Affected (in.) (in.) (in.) Comments

Ft. Bragg Treated Mild

Water w/o Steel Pitting 30-40 S 0.001 <0.001 0.001 Numerous very small

Corrosion pits, fine streaks

Inhibitor on surface

Galv.

Steel General <10 % --- none --- No penetration of Zn

Ft. Bragg Finished Mild

Water at Steel Pitting 60-70 5 0.007 0.002-0.006 <0.003 Numerous pits

Water Plant

Galv.

Steel General <10 % --- none --- No penetration of

Zn, grain of metal

visible

Ft. Bragg Finished Mild

Water In Steel Pitting 70-80 % 0.015 0.010-0.015 0.010- Numerous pits

Distrib. 0.025

System

Galv.

Steel General 20 % -- none <0.002

Ft. Monroe Treated Mild

Water w/o Steel Pitting 90. % 0.016 0.000-0.015 0.05- Several large areas

Corrosion 0.13 attacked, many large

Inhibitor pits

Galv.

Steel General 90+ % --- none <0.002 No surface gloss, no

penetration of zinc

Ft. Monroe Finished Mild

Water at Steel Pitting 80-90 9 0.015 0.002-0.008 0.002- Numerous pits,

Water Plant 0.010 flow effects

Galv.

Steel General 30-40 S --- none <0.002 Uneven surface, no

penetration of zinc

46
15

22 Jon '87 - 23 Apr '87

1Steel Pipe Steel Coupon

13

12

11

10

9

a

C 7

0

0 5

3

2

0 - None Virchem-937 Nalco-937 Nalco-7393

(finished water)

Corrosion Inhibitor

Figure 14. Effect of various corrosion Inhibitors on mild steel corrosion

rates at Fort Monroe, VA.

10

22 Jon '87 - 23 Apr '87

1 Galv. Pipe Zinc Coupon

7-

6

0

0:: 5 " /,i / /-

i 4

0

2

I 11

None Vrchem-937 Nolco-937 Nolco-7393

(finished water)

Corrosion Inhibitor

Figure 15. Effect of various corrosion Inhibitors on galvanized (zinc)

iron corrosion rates at Fort Monroe, VA.

47
steel. This reduced rate was due to the formation of a thick layer of corrosion products

mixed with the corrosion inhibitor, which completely covered the pipe surface. The

corrosion rates of the pipes in the loop that received water prior to addition of corrosion inhibitor continued to be high, since no protective coating formed on the pipe

surface. The results of this study will be reported in full in a future technical report.

The observations and practical experiences reported in the literature illustrate

how difficult It is to fully understand the different effects of corrosion on a complete

system. This difficulty arises due to different materials, different water qualities, and

incomplete knowledge of corrosion phenomena. The pipe loop system concept is one

way of addressing these issues. The preliminary results of its field evaluation have

clearly demonstrated, both visually and by corrosion rate determinations, the effect of

corrosion control chemicals used in water treatment plants on pipe materials. However, much needs to be done on inhibitor mechanisms, monitoring methods, and costeffectiveness of analysis.,

48
7 CORROSION CONTROL REGULATIONS AND ECONOMICS

Corrosion Control Regulations

The Safe Drinking Water Act (SDWA) of 1974 (Public Law 93-523) was passed by

Congress to ensure that public drinking water supplies are safe for consumption. As a

result, the USEPA established the National Interim Primary Drinking Water Regulations (NIPDWR) 20 which define maximum allowable concentrations for various contaminants

(maximum contaminant levels [MCLI) in drinking water. These regulations will be

reviewed at least once every 3 years and can be amended at any time.

One target of these regulations is concentrations of specific trace metals. The

USEPA has recognized that corrosion products in a water supply can pose serious health

threats to the public. Since corrosion byproducts are the principal source of lead, zinc,

copper, and iron concentrations in drinking water, the importance of monitoring the

corrosivity of water has increased. The USEPA established secondary drinking water

regulations which specifically outline monitoring for corrosion-related parameters. 2

These secondary regulations state that potable waters should be "noncorrosive," a

term that has yet to be defined by any regulatory agency, making compliance with this

regulation impossible. Further complications in the regulation of corrosion in the water

treatment industry stem from the lack of generally accepted corrosivity measures and

the lack of corrosion control methods that are effective throughout the distribution

system. Complicating the regulation of corrosion still further is the requirement that

corrosion be regulated at "the free flowing outlet of the ultimate consumer of a public

water system," which requires a water utility to know about the plumbing materials used

not only in the distribution mains but also in the individual consumer dwellings, so it can

supply a water that is noncorrosive in both.

Costs of Corrosion Control

It has been estimated that the cost of corrosion to the water works industry is

between $700 million to $1 billion dollars per year. Although corrosion control cannot

completely eliminate the cost of corrosion damages to water distribution systems, substantial savings are possible by implementing some sort of corrosion control program. 22

Tables 9 and 10 give some typical dollar values for various chemicals used in

control of corrosion in drinking water systems. It should be stressed that these figures

are only representative values for comparison purposes and that actual values will depend

on many factors. The cost of installation of corrosion control systems is minimal

compared to the cost of repairing and replacing the plumbing damaged by corrosion.

Installation costs range from $5,000 to $40,000 depending on the size of the system and

the type of system (liquid or solid feed). 23 Capital costs are also small when compared

to the cost of corrosion damages.

2

2 °USEPA, 1 "National Interim Primary Drinking Water Regulations." USEPA, "National Secondary Drinking Water Regulations," Federal Register, Vol 44,

No. 140 (1979), p 42195. 2 2Singley, et al.

2 3Internal Corrosion of Water Distribution Systems.

49
Table 9

Comparative Costs of Corrosion Inhibitors (1984)*

Dosage Rate Inhibitor Cost Treatment Cost

Type (mg/L) (S/pound) ($/mil gal

Lime 10-30 0.30 2.50 - 7.50

Caustic Soda 10-30 0.12 10.00 - 15.00

Soda Ash 10-30 0.20 16.70 - 50.00

Sodium Hexameta- 1-4 0.90 7.50 - 30.00

phosphate

Bimetallic Phos- 0.5-2 1.50 6.25 - 25.00

phate

Zinc Orthophos- 0.12-0.5(Zn) 2.25(Zn) 3.75 - 9.37

phate

Sodium Silicate 4-10 0.65 22.00 - 58.00

*Reprinted from Internal Corrosion of Water Distribution Systems, by permission. Copyright 0 1985, American Water Works Association.

Table 10

Typical Annual Chemical Costs for Corrosion Control (1982)*

Costs d o iclude freight

Cogt per year

Chemical Us. Feed rate Cost per unit 3-MGD plant 50-MGD plant

(S) () (S)

Quicklime, CaO pH adjustment 1-20 mg/L 63/tao butk 277-5,865 4.500-97,700

9-170 lb/MG

Hydrated lime. Ca(OH) 2 pH adjustment 1-20 ml/L 78/toe bag 342-7,254 5,700-121,000

6-170 lb/MG 65/ton bulk 2,-4,045 4.750-101,000

Caustic soda. NaOH pH adjustment 1-20 mg/L 200/too bulk 1,310-21.900 27,400-456,000

(M0% soluteon) 12-150 lb/MG

Soda ash. Na 2 CO 3 pH adjustment 1-40 mg/L 16/cwt bag 1,402-61,320 23.400->1.000.000

8-350 lb/MG 152/toe bulk 666-30,375 I 1,100-506.000

Inorganic pboaphata Inhibitor 3 mg/L 65/cwt bag 17.800 297.000

25 lb/MG

Sodium sdicate Inhibitor 2-8 ml/L 5.00/cwt tank 930-3,670 15,500-61,200

17-67 lb/MO

*Soure: J. E. Singley, et &1., Corrosion Prevention and Control in Water

Treatment and Supply Systems, Pollution Technology Review No. 122 (Noyes Publications, Park Ridge, NJ, 1985), p 89. Information originally obtained

from various chemical suppliers. Used with permission.

50
The estimated cost of a lime, soda ash, and sodium silicate storage and feeding

system for Seattle's 200-mgd Cedar supply in 1980 was $900,000.24 Table 11 gives some

figures for the Seattle Water Department's corrosion control program, which show that

the main cost in such systems is the chemicals. The use of corrosion inhibitors can

reduce the cost of corrosion damage bY 15 to 50 percent, corresponding to a reduction of

$150 million to $500 million annually. 5 The great variability in these figures suggests

that savings are possible; however, general projections of actual savings are not possible

and economic analyses must be done on a case by case basis.

Table 11

Total Costs of Corrosion Control Treatment (1979)

Cedar River Tolt River Total Percentage

Cost Item S/mil gal $1mil gal $/mil gal of Total

Capital Facilities 1.55 3.10 2.07 22.3

Chemical Cost 2.71 13.12 6.18 66.5

Labor 0.33 0.66 0.44 4.7

Maintenance 0.16 0.32 0.22 2.4

Power 0.04 0.08 0.06 0.6

Additional Chlorine 0.33 0.33 0.33 3.5

TOTAL. $5.12 $17.61 $9.30 100.

*Reprinted from Internal Corrosion of Water Distribution Systems, by permission. 01985, American Water Works Association.

24lnternal Corrosion of Water Distribution Systems.

2 s/nternal Corrosion of Water Distribution Systems.

51
8 CONCLUSIONS AND RECOMMENDATIONS

USA-CERL designed and developed an apparatus known as the "pipe loop system"

(Chapters 5 and 6) to objectively evaluate the effectiveness of water quality control

chemicals for protecting the water infrastructure. Thf- pipe loop system consists of

common, commercially available components, installed compactly on a 4 ft by 4 ft

plywood sheet. Using it, several metal coupons and lengths of pipe can be exposed to

water at a particular stage in the treatment process. The system's standard, multispecimen design lends itself to a multitude of experimental designs, but it is especiaily suited

for side-by-side, simultaneous testing. Corrosion rates are measured using the weight

loss methods specified in ASTM Standard D-2688-83.

The pipe loop system was installed and tested at Fort Bragg, NC, and Fort Monroe,

VA. It was used at these sites to perform side-by-side comparisons for evaluating water

quality control chemicals. Preliminary results are reported here only to illustrate the

use of data from this system:

Corrosion rates. At both installations, pipe inserts corroded faster than coupons

which were exposed to the same water. At Fort Monroe, the coupons corroded

less in the water treated with corrosion inhibitor, but no difference could be

determined for the pipes. At Fort Bragg, the corrosion rate appeared to be

greater for specimens in treated water.

" Type of corrosion. Mild steel specimens exhibited significant pitting. The corrosion of the galvanized steel specimens was more general.

" "Red water" problems. At Fort Bragg the normal corrosion inhibiting treatment

seemed to prevent "red water," while at Fort Monroe it did not.

The data presented in this report should not be taken as a comprehensive evaluation

of the treatment chemicals used. Further study is needed to demonstrate the full

capability of the pipe loop system and to establish standard operating procedures (SOP)

for specific uses.

METRIC CONVERSION FACTORS

I mil = 0.001 in. = 0.00254 cm

I in. = 2.54 cm

1 sq in. = 6.45 cm2

I ft = 0.3048 m

1 sq ft = 0.093 m2

I gal = 3.785 I

I oz = 2835 mg

*F = (C x 1.8) + 32

52
REFERENCES

ASTM Standard D-2688-83, "Standard Test for Corrosivity of Water in the Absence of

Heat Transfer (Weight Loss Methods)," ASTM Annual Book of Standards (American

Society for Testing and Materials [ASTM]).

Bennett, L. H., et al., "Economic Effects of Metallic Corrosion in the United States,"

Corrosion '79, National Association of Corrosion Engineers (NACE), Atlanta, GA

(March 1979).

Fontana, M. G., and N. D. Green, Corrosion Engineering (McGraw Hill, New York, 1978).

Internal Corrosion of Water Distribution Systems (American Water Works Association

[AWWA] Research Foundation, Denver, Co, 1985).

Myers, J. R., "Data Summary Related to the Relative Corrosivity of Soils and Domestic

Water at Fort Bragg, NC," Report submitted to USA-CERL, Champaign, IL, 1986.

"NACE Glossary of Corrosion Terms," Materials Protection, Vol 4, No. 1 (1965), pp 79-80.

Neff, C., M. Schock, and J. Marden, "Relationship Between Water Quality and Corrosion

of Plumbing Materials in Buildings, Volume I: Galvanized Steel and Copper Plumbing," State Water Survey Contract Report 416-I (University of Illinois, 1987).

Ryder, R. A., "The Cost of Internal Corrosion in Water Systems," Journal of the American Water Works Association (JAWWA), Vol 72, No. 5 (1980), p 267.

Sanks, R. L., Water Treatment Plant Design for the Practicing Engineer (Ann Arbor

Science, Ann Arbor, MI, 1978).

Singley, J. E., D. W. DeBerry, B. A. Beaudet, J. R. Kidewell, P. H. Markey, and D. A.

Malish, Corrosion Prevention and Control in Water Treatment and Supply Systems,

Pollution Technology Review No. 122 (Noyes Publications, Park Ridge, NJ, 1985).

USEPA, "National Interim Primary Drinking Water Regulation," Code of Federal

Regulations, Title 40, Part 141 (1981), pp 309-354.

USEPA, "National Secondary Drinking Water Regulations," Federal Register, Vol 44, No.

140 (1979), p 42195.

Wachter, A., and R. S. Treseder, "Corrosion Testing Evaluation of Metals for Process

Equipment," Chemical Engineering Progress, Vol 43, No. 61 (1947), p 315.

"Water Treatment Survey Report--Fort Monroe, VA" (Facilities Engineering Support

Agency, 1984).

53
REFERENCES FOR TABLES 3 AND 4

1. Anderson, E. A., C. E. Reinhard, and W. D. Hammel, "The Corrosion of Zinc in

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2. Bell, Winifred, "Effect of Calcium Carbonate on Corrosion of Aluminum in Waters

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3. Buelow, R. W., J. R. Millette, E. F. McFarren, and J. M. Symons, "The Behavior of

Asbestos-Cement Pipe Under Various Water Quality Conditions," Presentation-1979

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4. Burgmann, G., W. Frieke, and W. S. Schwenk, "Chemical Corrosion and Hygienic

Aspects of the Use of Hot-Galvanized Threaded Pipes in Domestic Plumbing for

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5. Campbell, Hector S., "A Natural Inhibition of Pitting Corrosion of Copper in TapWaters," J. Appl. Chem., Vol 4 (1954), pp 633-647.

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(August 1960), pp 1033-1040.

7. Davies, D. H., and G. T. Burstein, "The Effects of Bicarbonate on the Corrosion and

Passivation of Iron," Corrosion-NACE, Vol 36, No. 8 (August 1980), pp 416-422.

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24-45.

14. Geld, Isodore, and Colin McCaul, "Corrosion in Potable Water," JAWWA, Vol 67,

No. 10 (October 1975), pp 549-552.

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Canadian Journal of Chemical Engineering, Vol 38, No. 5 (October 1960), pp 167-173.

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J. Am. Ceramic Society, Vol 25 (1942), pp 164-168.

54
17. Goldfarb, A. S., J. Konz, and P. Walker, Interior Coatings in Potable Water Tanks

and Pipelines, MITRE Corporation, Technical Report MTR-7803, USEPA Contract

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18. Hale, F. E., "Relation of Copper and Brass Pipe to Health," Water Works Eng., Vol 95

(1942).

19. Hatch, G. B., "Unused Cases of Copper Corrosion," JAWWA, Vol 53 (1961), pp

1417-1429.

20. Karalekas, P. C., G. F. Craun, A. F. Hammonds, C. R. Ryan, and D. J. Worth, "Lead

and Other Trace Metals in Drinking Water in the Boston Metropolitan Area," J. New

England Water Works Association, Vol 90, No. 2 (1976), pp 150-172.

21. Lane, R. W., and C. H. Neff, "Materials Selection for Piping in Chemically Treated

Water Systems," Materials Protection, Vol 8, No. 2 (February 1969), pp 27-30.

22. Larson, C. D., Chief Technical Support Section, EPA Region I, letter to John Hagopian, Rhode Island Dept. of Health, November 14, 1979.

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Water to Corrosion of Steel and Cast Iron," Corrosion, Vol 14 (June 1958), pp 43-46.

24. McCauley, R. F, and M. 0. Abdullah, "Carbonate Deposits for Pipe Protection,"

JAWWA, Vol 50 (1958), pp 1419-1428.

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Part 1, A Practiced Approach for Plant Operators," JAWWA, Vol 69 (November

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222-223.

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30. Rudek, R., Blankenhorn, R., and H. Sontheimer, "Verzoegerung der Elsenoxidation

Durch Natuerliche Organische Wasserinhaltsstoffe und Duren Auswirkung auf die

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31. Schafer, G. T., "Corrosion of Copper and Copper Alloys in New Zealand Potable

Waters," New Zealand Journal of Science, Vol 5 (December 1962), pp 475-484.

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ILZRO, Battelle Memorial Institute, Columbus, Ohio.

55
33. Strelcher, Lee, "Effects of Water Quality on Various Metals," JA WWA, Vol 48, No. 3,

(March 1956), pp 219-238.

34. Stumm, W., "Investigation on the Corrosive Behavior of Waters," Proceedings of the

American Society of Civil Engineers, Vol 86, No. 5A-6 (November 1960), pp 27-45.

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Water Eng., Vol 42 (May 1940), pp 189-191.

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Water Eng., Vol 42 (June, 1940), pp 225-228.

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56
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