A11107

NBSIR 74-429

Corrosion of the Stainless Steel

Piping in the Kuwait Water

Supply System

G. M. Ugiansky and J. Kruger

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

January 1974

Prepared for Tho Ministry of Electricity and Water

ernment of Kuwait

iOO ait, Kuwait

NBSIR 74-429

CORROSION OF THE STAINLESS STEEL

PIPING IN THE KUWAIT WATER

SUPPLY SYSTEM

G. M. Ugiansky and J. Kruger

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

January 1974

Prepared for

The Ministry of Electricity and Water

Government of Kuwait

Kuwait, Kuwait

^—7^-—7

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

TABLE OF CONTENTS

Page No.

SUMMARY iii

I. INTRODUCTION 1

II. CHEMICAL ANALYSES 4

A. Stainless Steel Specimens Collected in Kuwait. ... 4

B. Water Samples Collected in Kuwait 5

C. Corrosion Products 6

III. FAILURE ANALYSIS 8

A. Examination of Damaged Pipes 8

B. Environmental Investigations 13 .

1. Electrochemical Measurements 13

2. Accelerated Short-Term Exposure Tests 16

IV. DISCUSSION 20

A. Causes of Failure 20

B. Measures to Make System Operative as Soon

as Possible 21

C. Measures to Minimize the Chances of Future

Failures 23

V. CONCLUSIONS 26

ACKNOWLEDGEMENTS 28

REFERENCES 29

APPENDIX A 30

APPENDIX B 32

APPENDIX C 34

TABLES 35

FIGURES 41

CORROSION OF THE STAINLESS STEEL PIPING IN THE

KUWAIT WATER SUPPLY SYSTEM

G. M. Ugiansky and J. Kruger

Institute for Materials Research

National Bureau of Standards

Washington, D.C.

SUMMARY

The Ministry of Electricity and Water (MEW), Kuwait, contacted the

U.S. Department of State, which requested the assistance of the National

Bureau of Standards (NBS), U.S.A., in the problem of the corrosion of

the stainless steel pipes in their water supply system. This request was

honored, and accordingly, Gilbert M. Ugiansky of the Corrosion and

Electrodeposi tion Section, NBS, visited Kuwait from April 8 to April 22,

1973, to carry out an examination and collect samples of material for

analysis and investigation.

This investigation shows that the stainless steel pipes in the Kuwait

water supply system are susceptible to localized attack under the conditions that were reported to have been used during the disinfecting procedure.

Thus, it is reasonable to conclude that the severe pitting found in the

pipes occurred during this operation.

The NBS data and observations show that both alloys type 304L and

316 cannot be used with confidence in their ability to resist localized

corrosion attack in the Kuwait water supply system unless new protective

measures are undertaken.

Recommendations to make the water system operative as soon as possible are as follows:

(1) Repair penetrated pipes by welding;

(2) Install cathodic protection system using sacrificial zinc

ribbon or cable anode. Reference electrode ports should be included in

this system. Special care should be taken to see that the anodes used

do not contain any toxic materials . All internal surfaces of the pipes

should be polarized (or protected) to a potential at least as negative

as -0.65 V vs SCE (Saturated Calomel Reference Electrode).

Measures to minimize the chances of future failures are:

(1) Test coupons of unprotected pipe steels should be installed

in the water system;

(2) Disinfection should take place after cathodic protection system

has been installed and should occur immediately before the system is put

into operation;

(3) If available, a non-Cl containing non-oxidizing disinfectant

should be used in low chloride water. The solution should be drained and

pipes rinsed and put into use without delay;

(4) Inspection should be made when the system is ready to be put

into operation;

(5) Periodic inspections of the pipes, cathodic protection system,

and coupons should be made at three-month intervals for the first year

of operation. Future inspection intervals should be decided on at the

end of the first year of operation;

(6) During the time the short-term solution is in use, possible

long-term solutions should be investigated. The possibilities to be

considered are: Replacement of the pipes with another material; cathodic

protection using sacrificial anodes; cathodic protection using an impressed

current system; protection by coating or lining the pipes; and the possibility that the pipes can be used as designed at some of the sites.

i V

CORROSION OF THE STAINLESS STEEL PIPING IN THE

KUWAIT WATER SUPPLY SYSTEM

G. M. Ugiansky and J. Kruger

Institute for Materials Research

National Bureau of Standards

Washington, D.C.

I. INTRODUCTION

The Ministry of Electricity and Water (MEW), Kuwait, contacted the

U.S. Department of State, which requested the assistance of the National

Bureau of Standards (NBS), U.S.A., in the problem of the corrosion of

the stainless steel pipes in their water supply system. This request

was honored, and accordingly, Gilbert M. Ugiansky of the Corrosion and

Electrodeposi tion Section, NBS, visited Kuwait from April 8 to April 22,

1973, to carry out an examination and collect samples of material for

analysis and investigation. The historical and background material in

this introduction was provided to Ugiansky by MEW.

Kuwait, with a population of approximately 900,000 and a limited

natural water supply consisting of virtually all brackish water, produces

its drinking water at several desalination plants. These plants, with

a daily capacity of approximately 50 million gallons, distill seawater from

the Arabian Gulf and blend this distilled water with brackish water from

ground wells or seawater to make it palatable. The distribution of this

potable water has in the past been accomplished primarily by tank truck

with reservoirs on location at residences and commercial facilities.

With the growth and modernization of the city of Kuwait, the design

and construction of a water distribution system was initiated. A schematic

diagram of the Kuwait water supply system is shown in Figure 1. It can

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be seen from this diagram that along with the potable water system there

is a parallel distribution system for brackish water primarily for

agricultural and industrial uses. Because potable and brackish waters

are to be distributed throughout Kuwait, the entire system is designed

to be compatible with both. The piping in the main part of the system is

cement-lined cast iron. Type 316 stainless steel (0.05%C) was specified

for piping at the water storage tower sites, blending plants, and pumping

stations. The specification for piping at most of the tower sites was

later changed to type 304L.

The Kuwait water distribution system includes six sites of water

storage towers. Five of these sites consist of clusters of mushroomshaped reinforced concrete towers which will store both potable and

brackish waters. A description of the number of towers, heights, etc.,

at each of these sites is given in Table 1. The piping at the above sites

is constructed of type 304L stainless steel. The sixth site (designated

D-6) is the Kuwait Tower, a combination of water storage towers and

visitors' center (Figure 2). It is at this site that the pressure required for the water distribution system is produced. Type 316 (0.05%C)

stainless steel was used for the pipes at the Kuwait Tower.

Type 316 (0.05%C) stainless steel is also used at the two blending

stations in the water distribution system. These sites are designated P

and P-5.

During the summer of 1972 several of the sites reportedly underwent

leak tests using brackish water with sodium hypochlorite (NaOCl) added for

disinfection. This water was never analyzed. However, the specifications

for disinfecting the reservoirs stated the following: "Water shall be

fed into the reservoirs with chlorine applied in amounts to produce at least

-3-

10 ppm after 24 hours' standing. The dosage must not exceed 50 ppm without

the approval of the Engineer. The disinfecting solution shall remain in

the reservoirs for such periods as the Engineer instructs, but in no case

for less than 24 hours." Although NBS has had some difficulty in reconstructing the exact details of what took place during the disinfection

operation, it appears that the disinfecting solution remained in at least

some of the pipes for from four to six weeks; in some of these pipes the

water was apparently drained, but some 10 cm of water remained in the bottom.

Whatever the case, after this exposure, the stainless steel pipes at these

sites were found to be perforated by pitting corrosion attack. Table 2

lists the tower and blender sites and information on the state of the

stainless steel as of April 1973. As can be seen in Table 2 the pipes

at tower sites D-1 (Figure 3) and D-2 (Figure 4) were perforated as was

also the pipe at blender P. These were the sites that underwent leak tests.

A number of organizations studied the corrosion problem for the

Government of Kuwait, Ministry of Electricity and Water (MEW), and for

the contractors and consultants. Because a number of questions still

remained unanswered, MEW asked the U.S. Department of State to request

the assistance of NBS in accomplishing the following objectives:

(1) Resolve discrepancies in the analyses of the stainless steels;

(2) determine the cause of failure; (3) recommend a short-term solution

(to get the water supply system operational as quickly as possible); and

(4) recommend a long-term solution that would meet the design criteria of

2

reliability for 50 years at 50°C and 9 kg/cm . This report deals with

the first three objectives. The long-term solution should be studied after

the implementation of the short-term solution.

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II. CHEMICAL ANALYSES

A. Stainless Steel Specimens Collected in Kuwait

Stainless steel pieces for analysis at NBS were cut from the pipes

in Kuwait as directed by Ugiansky. A list of the pertinent information

on the specimens removed is given in Table 3. At NBS a 3.5 cm square was

cut from each of the specimens, turned down to a 3.18 cm diameter disk,

and polished to a 6 ym diamond finish. The specimens were analyzed by

NBS, along with appropriate standard reference materials, by X-ray

fluorescence analysis. Carbon was determined by a combustion chromatographic method. Qualitative X-ray fluorescence analysis was made for

each specimen; the range of elements considered included all those above

scandium (atomic number 21). The qualitative tests indicated no element

which would prevent the specimens from being classified as type 304L or

316 stainless steels was present above 0.1%. The results of the quantitative analyses are given in Table 4. (See appendix A for NBS certificate

of Analysis)

.

All specimens were found to conform to ASTM specifications A312 for

304L stainless steel and A409 for 316 stainless steel. There is an apparent

slightly high silicon content in two samples of the 316 stainless. However,

when the analysts' estimate of accuracy is taken into account, these values

are also within specifications.

As a check, duplicate analyses were performed by a coirmercial

laboratory. Within the levels of accuracy of the methods used, the results

of both analyses were identical. NBS analyzed quantitatively for only the

more important elements while the commercial laboratory's analysis also included phosphorus and sulfur. These two elements were also found to be

within specifications.

-5-

Cross section^ were made along the weld bead centerline of specimens

of both type 304L and 316 stainless steels. The composition of the weld

bead was then determined by the same techniques discussed above. The

results of this analysis are also given in Table 4. (See Appendices B

and C for NBS cert i fates of analysis.) All the specimens were within

specifications with respect to Mn, Ni, Cr, and C. A possible, but not

likely, exception is specimen SW whose C was not determined. Specimen

9 and SW (316) met specifications for Mo, but specimen 2 (304L) also

contained 1.92% Mo, indicating that a Mo containing welding rod was used

for this weld. Such a rod is not ordinarily specified for welding 304L

stainless steel. Differences in the composition of the weld nd base

metal could lead to galvanic corrosion, although this is not ikely in

this case. This is discussed later in this report.

B. Water Samples Collected in Kuwait

In Kuwait, Ugiansky collected water samples at both the Shaiba

Desalination Plant and at the (Old) Shuwaikh Pumping Station. For chemical

analyses, the samples were collected in polyethylene bottles. For biological studies, they were collected in sterile glass bottles. The

chemical analysis of the waters was performed at the U.S. Environmental

Protection Agency. The results are listed in Table 5 along with the

analyses of several "synthetic" waters; i.e., waters made up for performance

of laboratory tests to be discussed later in this report. The Kuwait

sample of brackish water was found to be similar in composition to the

typical brackish waters as stated in the water towers contract specifications.^^^ Two one-ml samples from each of the Shaiba seawater and Shuwaikh

brackish, potable, and distilled water samples (Table 5) were tested at

NBS in accordance with American Petroleum Institute Recommended Practice

38, Second Edition, 1965, "API Recommended Practice for Biological Analysis

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of Subsurface Injection Waters." One-ml samples were added to vials containing Bacto-Sulfate , API Broth, and incubated at 28±1°C for four and

a half months. At the end of that time no blackening was observed in any

of the bottles. The test, therefore, indicated an absence of sulfate

reducing organisms in the water samples.

A second method was also used to test duplicate samples of the

Shaiba seawater and Shuwaikh potable and distilled water samples for sulfate

(0)

reducing bacteria. This method was devised and performed by Iverson^ '

of NBS. After incubation for four and a half months, no evidence of blackening in the medium was present, again indicating the absence of sulfatereducing bacteria in the water samples.

If the brackish water that caused the failure were similar in bacterial content to the water analyzed at NBS, it is likely that the cause

of failure was not due to the presence of sulfate reducing bacteria, nor

would there be future problems from this source if the water's bacteria

content is the same as that determined above.

C . Corrosion Products

Several pitted specimens were examined to determine if any unexpected

corrosion products were present. A few particles from a pit on stainless

steel specimen 8 were examined using the X-ray Debye-Scherrer technique.

Lines were found that could be ascribed to the spinel structure, the FeO

structure, and the alpha iron structure.

Elemental analysis was also carried out on pit corrosion products

on specimens 2 and 5 by nondispersive X-ray analysis in conjunction with

the scanning electron microscope (SEM). Elements found in the corrosion

-7-

products were Ni , Fe, CI, Ca, and possibly S. Considering the composition

of the alloys and of the brackish water, all the above corrosion product

structures and elements are not at all unusual.

-8-

III. FAILURE ANALYSIS

A. Examination of Damaged Pipes

Substantial portions of the inside of the 800 rmi diameter pipe at

site D-1 and 1000 mm diameter pipe at site D-2 were examined by Ugiansky.

Pits, which in some cases penetrated the 6 mm wall thickness, were found

to be mostly at the bottom of the pipes where the water had reportedly

remained the longest; however, pits were also found at other positions

on the inside circumference of the pipes. There was some evidence that

pitting was associated with scratches, welds, weld splatter, and other

irregularities in the surface, but there were also numerous other examples

of pitting of otherwise regular surfaces. The overall surface condition

of the pipe interiors was good in terms of corrosion except for the scattered pitting. There was very little if any general surface attack -

merely severe pitting of otherwise uncorroded surfaces.

Specimens removed from pipes in Kuwait were examined for a determination of pit locations with respect to any gross irregularities in the

surface of the steel. Figures 6 through 14 show the nine stainless steel

pipe samples removed from Kuwait as described in Table 3. Before the

photographic record was made, pieces were taken from these samples for

chemical analysis as seen by the areas missing from the originally rectangular pieces.

Atmospheric pitting was evident on specimen 1 (Figure 15). The

pipe from which this specimen was removed was exposed to the seacoast

atmosphere of site D-5 on the Arabian Gulf. This pipe was not installed

in the system. It was being stored. at the site.

-9-

Examples of pitting caused by the exposure to brackish water with

sodium hypochlorite are seen in Figures 16 through 19. Figure 16 shows

pits adjacent to a weld and Figure 17 a pit associated with a scratch on

type 304L stainless steel. Pits on type 316 stainless are seen in Figures

18 and 19. These two latter pits were not associated with any observable

flaw in the surface.

On the basis of the above observations and laboratory(studies to

be described later)of the samples brought back to NBS, and on the inspection of the pipes by NBS in Kuwait, it is concluded that the presence of

gross surface flaws is not a necessary condition for the initiation of

pitting corrosion under these conditions.

Pits were examined using both the optical microscope and the scanning

electron microscope (SEM) to characterize the exact nature of the pitting

attack. Figure 20 shows a pit at the end of a scratch on specimen 5.

Observation at higher magnification shows the crystal lographic nature (i.e.,

faceting and etch pitting) of the attack (Figures 21 and 22) and combined

crystal lographic etching within grains and grain boundary delineation

(Figure 23). All these characteristics of attack were found to be common

to most of the pits examined.

Figures 24 and 25 show the cross section of one of the large pits

which penetrated the wall of the 1000 mm pipe at site D-2. These two

micrographs show another feature that was typical of many of the pits

examined, namely, the stepwise process of the pitting. Figure 25 also

shows the immunity of the molybdenum containing weld metal as compared

to the base 304L. Because the attack occurred near the Mo rich weld, it

is possible that in this particular case galvanic action was instrumental

in producing the attack. However, in numerous other cases, pits were found

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where galvanic action was not to be expected, and hence it is concluded

that in the system as a whole galvanic action is not necessary to e;(plain

the attack.

Another example of pitting near a weld is shown in Figures 26-28.

In this case the type 316 base metal is nearly the same composition as

the weld metal and the probability for galvanic corrosion effects is very

low. Figure 27 shows two types of corrosion attack within the pit, both

a honeycomb surface in what is probably the heat affected zone of the weld

and the faceted surface farther away from the weld. This faceted surface

is seen (Figure 28) also to have the same grain boundary delineation as

described earlier for the type 304L stainless (Figure 23).

In general the pits on both the type 304L and 316 stainless steels

showed the same characteristics in surface structure. Both steels appeared

(3)

to have pitted in a manner described by Frankenthal and Pickering.^ ' In the

work of these authors a typical pit initiated at an inclusion and grew radially

under the metal surface away from the inclusion; further surface penetration

came from underneath, giving rise to the lace-like structure covering

the pit (Figures 29-31). As the pit grew the cover eventually was completely dissolved, leaving a large open pit, the bottom of which was normally rough with occasional evidence of faceting (Figure 32). Similar

(4) (5) observations were also made by Streicher^ ' and by Rosenfeld and Danilow^ '

,

but they did not associate the initiation of these pits with inclusions.

The type of pitting described above was the most common type observed on

(3) stainless steels by Frankenthal and Pickering ^ ' in solutions containing

chloride and sulfate ions (both of which are present in the brackish water).

The observation of this type of pitting is indicative of corrosion occurring

at highly anodic potentials (positive) and is discussed further in the

-nsection entitled Environmental Investigations.

Numerous examples of faceting at the bottom of pits as described

above were found. Examples for both the type 304L and 316 alloys are

shown in Figures 21 through 23 and 28.

Microscopic examination of the localized atmospheric attack of

specimen 1 (Figures 6 and 15) was also made. As seen in Figure 33 this

attack typically resulted in a corrosion product (rust colored) on the

surface of the pipe.

When this corrosion product was cleaned from the surface, some

evidence of attack of the metal surface was seen (Figure 34). Apparently

in the seacoast atmosphere at site D-6, both chloride and moisture could

easily contact the surface of the pipe. Through alternate dissolution

and drying, the chloride could have then become concentrated on the

surface of the pipe and caused the initiation of pitting attack. This

attack is obviously in its early stages here and is manifested mostly

by corrosion products. An example of a more advanced case of atmospheric

pitting is shown in Figure 35. In this case, the corrosion product has

been removed and an attacked area where the surface grains are completely

missing is seen. This attacked area (Figure 36) has all the topographical characteristics of the pits caused by the brackish water exposure and

appears to have occurred by a similar mechanism.

The final examination made of the specimens removed from Kuwait was

of the surface condition of the stainless steels. Observations of the

surfaces of the pipe steels in the SEM showed all surfaces to have been

attacked in an intergranular mode. Figures 37 through 42 show both inner

and outer surfaces of pipes from sites D-2, D-6, and P. Steels from each

site were examined because of the different origin of steels at each as

listed in Table 2. Also examined was a piece of hot rolled, annealed, and

pickled 304 stock from the NBS Storeroom (Figures 43 and 44). The

surface structure of the Storeroom stock 304 is seen to have a very rough,

etched surface but no intergroinular attack as seen in the steels from the

Kuwait water system. Because of the intergranular attack exhibited by the

Kuwait pipe steels, the specimens were subjected to tests for sensitization

according to the American Society for Testing and Materials Recommended

Practices for Detecting Susceptibility to Intergranular Attack on Stainless

Steels, ASTM Designation A262-70. Specimens from each of the three sites

mentioned above passed these tests; i.e., they were not sensitized. Further

studies were carried out to determine the possible causes of the intergranular attack seen. Since both inner and outer surfaces of the pipes

exhibited this same type of attack, it was felt that the attack could

have originated from the pickling operation during manufacture. Attempts

were made with polished specimens of the steels from Kuwait and from the

NBS Storeroom to reproduce the intergranular attack by pickling in several

of the standard pickling solutions. In the limited number of attempts

made, the intergranular attack could not be exactly duplicated. However,

a close approximation to the surfaces of the Kuwait samples was reached

on the NBS Storeroom stock 304 with a pickling treatment in 25% H2SO4 for

30 minutes at 90°C (Figure 45).

It is concluded from the above that the rough, intergranularly

attacked surfaces of the pipe steels could have resulted from the pickling

treatment of these steels. For a material that is subject to pitting and/or

crevice corrosion attack, a smooth surface is to be preferred over a rough

one. As will be seen later, both these steels are susceptible to these

forms of attack in normal Kuwait waters.

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B. Environmental Investigations*

1. Electrochemical Measurements . Various electrochemical methods

are now commonly used to determine the susceptibility of a metal to pitting

corrosion. The most common consists of comparing the open circuit or

corrosion potential E^ of the metal under investigation with the so-called

critical (or breakdown) potential for pitting E^, both measurements

being made in the same environment. The critical potential is defined

as the potential above which pits will nucleate. There is, however, some

controversy over whether it is possible to observe pitting when a metal

is at a potential below E^. Such a question may arise as a result of the

technique used to determine E . This may be so because the value of E

c c determined depends on the time allowed at a given potential to observe

the initiation of pitting. The time for pit nucleation can be rather short

when the potential of the metal surface is significantly above E^. However,

as the potential of the surface decreases and approaches E^, the time for

pit nucleation becomes increasingly longer. A technique described by

Pessall and Liu^^^ makes it possible to determine a value of E^ which

is not dependent on time. This technique consists of polarizing the

specimen to the desired potential and then lightly scratching the surface. While the potential is held constant, the polarizing current

is recorded as a function of time after scratching until the electrode

*All laboratory tests were conducted at the most severe operating conditions

of 50°C and stagnant solutions unless otherwise stated.
?
either repassivates (the current decreases to the value before scratching)

or stable pit growth sets in (the current increases to some high level).

Figure 46 shows actual results both above and below the pitting potential

(E^), This process is repeated until the minimum potential is found at

which the electrode does not repassivate after scratching. This value

was reported^'^^ to be reproducible and independent of the surface preparation and prior history of the electrode. Scratching provides the initiation step in pitting, so that most of the factors that have caused the

lack of agreement among pitting potential measurements are minimized.

In the present investigation, this technique was one of the methods used

to determine the susceptibility to pitting of the pipe stainless steels.

The breakdown or critical potential is referred to as E . The "s" is

added for "with scratching."

Tests were made on both the 304L and the 316 steels in various

environments. The environments used were made up to duplicate as nearly

as possible the waters to be used in the Kuwait water distribution system.

The analyses of these "synthetic" waters are given in Table 5 along

with the analyses of the water samples collected in Kuwait. Although the

composition of the synthetic potable water does not correspond well with

the Kuwait Shuwaikh potable water analyzed by NBS, it is close to the

composition of some of the potable Kuwait water as given in Table 5. The

chlori nation of the Kuwait waters was simulated by adding NaOCl to produce

the 0C1~ equivalent to 2 ppm CI2.* The solutions used were also air

saturated before the NaOCl addition and kept sealed afterward to minimize

*Although values are given in this report as ppm Clp, additions of NaOCl

were made to the solutions to give the equivalent free CI2 as that indicated in this report.

-15-

loss of the hypochlorite.

The critical potential for pitting, E , and the open circuit or

c , s corrosion potential, Ej^, were determined for the 304L and 316 in both

potable and brackish waters with 2 ppm CI 2- These results, as well as the

difference E ^-E^, are given in Table 6. It should be pointed out that

C , S K

these results were obtained on polished surfaces, since, as will be shown

later, the susceptibility to pitting changes greatly when a crevice is

introduced (simulating a much more realistic engineering condition). As

can be seen in Table 6, the 304L is the most susceptible alloy to use and

the 316 is the least susceptible, especially in the potable water.

Another electrochemical measurement was made in the analysis of

the failure itself. This measurement consisted of recording Ej^ as a function of time for both alloys in the brackish water of composition that could

have been present during the failure. In this case the brackish water

contained 50 ppm CI2 (the specified maximum value) and 100 ppm CI2 (a

possible overdose of CI2). As can be seen from the results, also given

in Table 6, for both alloys in brackish water with either 50 or 100

ppm Cl^ reached values above the E determined previously with the 2

ppm CI2. This shows two important facts: That CI2 is a strong oxidizing

agent that raises the potential, E^, significantly; and, that since the

final Ep reached was qreater than E^ ^, pitting would be expected and

K ~ C ,S

was, in fact, observed on polished surfaces of both alloys when exposed

to the brackish waters with 50 and 100 ppm 012- An example of the early

stages of pitting on 316 in brackish water + 50 ppm CI2 is shown in Figure

47. (Further examples of pitting on a specimen with a crevice are shown

later.) The potential -time curve for the above specimen is shown in

Figure 48. As can be seen graphically the potential rose above E and

breakdown did take place.

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2. Accelerated Short-Term Exposure Tests . A test recently developed

for determining the susceptibility of an alloy to localized corrosion by

Smith and Peterson of the U.S. Naval Research Laboratory involves the

use of an artificial crevice to accelerate the rate of attack. This test

is a particularly useful one in evaluating the susceptibility to localized

attack (which would include pitting attack) of materials when they are

ultimately to be used in a real plant or equipment. In this test an

artificial crevice was produced on the surface of a polished coupon of

the alloy under consideration by tying a piece of 3.4 mm diameter latex

tubing around the coupon. This approximates closely the conditions that

could easily exist in the stainless steel pipes in Kuwait where there are

almost certainly small crevices associated with the usually observed

defects in the steel itself. However, crevices need not be due only to

defects in the steel. The production of crevices by stones or debris

resting on the steel surface is also highly possible. Likewise, crevices

can exist at welds and at flange joints.

This "rubber band" test was first used to evaluate the alloys under

the reported conditions of the failure; i.e., both alloys were tested in

brackish water + 50 ppm CI 2- The results of all "rubber band" tests are

listed in Table 6. Both the 304L and 316 pitted very rapidly. (These

tests were terminated after corrosion product was evident near the rubber

band, usually in a time of from a few hours to a few days). Scanning electron micrographs of the attack on the 304L and 316 specimens are shown

in Figures 49-52. The same characteristic of surface topography is seen

within the pits in these examples as was seen earlier in the actual pipe

failures (compare to Figures 21-23, 28, and 32).

-17-

To determine the feasibility of disinfecting the pipes with Kuwait

distilled water with NaOCl added, the crevice test was carried out on both

stainless steel alloy types in the synthetic distilled water + 50 ppm CI2.

Attack was again observed as can be seen in Table 6 and in Figures 53 and

54. A potentially dangerous situation would exist if the pipes were disinfected even in distilled water if 50 ppm CI2 were present.

The next evaluation made with the "rubber band" test was to determine

the susceptibility of the alloys to attack in the waters to be carried by

the Kuwait distribution system. That is, tests were made in both the

brackish water and the potable water with 2 ppm CI 2 added to simulate the

chlorination of the Kuwait waters. In this test, it was seen that the 304L

is likely to be attacked in either water (Table 6 and Figures 55-56). The

test of the 304L in the potable water was not run long enough to see visible

attack; only corrosion product was evident. In these tests, the 316 did

not show that it was positively susceptible to attack. However, this does

not mean that this alloy is imnune to attack in these waters. It should

be remembered that these are short-term tests and that the reported design

criteria calls for actual specifications of reliability for 50 years at

50°C, and it is very likely, as previously mentioned, that the system v/ould

contain crevices.

Since the amount of hypochlorite (or chlorination) of the waters

seemed to be an important factor in the susceptibility of the steels to

attack, and since the concentration of chlorine in the Kuwait waters is

likely to vary at least locally, another series of "rubber band"

tests v/ere carried out in the waters with an addition of 4 ppm CI 2 (to

provide for the possibility of too high an oxidizer concentration). Both

304L and 316 were severely attacked in both the brackish and potable waters

-18-

with 4 ppm (Table 6 and Figures 57-60). As in previous cases shown,

the features of the attack are also very similar to those seen in the pits

of the failed pipes, indicating the same type of attack.

Because of the known effect of acceleration of pitting attack (or

lowering of E^) with increasing temperature, all previous tests were

carried out at the maximum design temperature of 50°C. As a check on the

performance of 304L and 316 in the Kuwait waters at lower temperatures,

both of the above alloys were subjected to the crevice test in both

potable and brackish waters with 4 ppm CI 2 added. After several days,

there was evidence of corrosion product on all but the 316 in potable water.

In fact, the attack of the 316 in the brackish + 4 ppm CI 2 occurred away

from the rubber band crevice. Both samples of 304L were severely pitted.

These results are also listed in Table 6.

The type of attack seen in both the actual failures and in the

laboratory attack is characteristic of attack on stainless steels occurring

at highly anodic (positive) potentials. The surface of the steel can be

raised to a highly anodic potential in either of the following ways:

By introducing an oxidizing agent (such as hypochlorite or chlorine) into

the solution in which the steel is exposed; or by applying a polarizing

current between the steel and an auxiliary electrode. In the actual

failures and in the laboratory tests explained above, the hypochlorite

was the oxidizing agent responsible for raising the potential of the

stainless steels. A final test was carried out to produce the highly

anodic potential with a polarizing current. In this case, a polished

specimen of 316 was polarized potentiostatical ly to +600 mV vs SCE

(saturated calomel reference electrode) in brackish water without hypochlorite. After a 30-minute exposure, the specimen was severely attacked.

-19-

This attack produced all the characteristics of attack seen previously.

In Figure 61 and 62, the same type of undercutting of the surface as seen

in the actual failures (Figure 29-31) can be seen. Also, the same etch

pitting, grain boundary delineation, and faceting as seen in actual

failure pieces is seen in Figure 63 (compare to Figures 21-23 and 28, and

32 from failed pieces).

-20-

IV. DISCUSSION

A, Causes of Failure

The data presented in this report clearly show that both the stainless steel types 304L and 316 used in the Kuwait water supply system are

susceptible to pitting attack when exposed to brackish water containing

50 ppm Cl^ at 50°C. The results in synthetic distilled water containing

50 ppm Cl^ also indicate that even if this were the disinfecting solution,

attack would be likely to occur rapidly at 50°C. Thus, the rapid pitting

of the stainless steel pipes appears to have been due to the long exposure

(reported to be four to six weeks for the leak test) to water containing

approximately 50 ppm CI2. Whether such rapid pitting would occur at normal

operating conditions is a question that cannot be answered with confidence.

However, the NBS data also show both alloys to be positively susceptible

to attack at crevices in both brackish and potable waters under stagnant

conditions containing as little as 4 ppm CI 2 (simulating possible local

fluctuations in Cl^ concentration or over-chlorination) at 50°C,in brackish

water + 2 ppm CI 2 at 50°C and in brackish water + 4 ppm CI 2 at 23°C.

Positive susceptibility to attack in crevices was also found for the 304L

in potable water containing 4 ppm CI 2 at 23°C.

The only tests not showing positive susceptibility to attack vyere

for 304L and 316 in potable water + 2 ppm CI 2 and for 316 in potable water

+ 4 ppm CI 2 at 23°C. Perhaps these too would be attacked if sufficient

exposure time were allowed. Reliability under even these latter conditions

in which the alloys did not show positive susceptibility to attack is thus

by no means assured for the design period of 50 years at 50°C.

-21-

Based on the above data and observations made by NBS, both the

materials used (types 304L and 316 stainless steels) appear to have a

great deal of uncertainty associated with their use in the Kuwait water

supply system.

Admittedly, the literature shows that these two alloys can be used

safely in waters with even higher concentrations of chloride than the

(9) Kuwait waters; e.g., seawaterr but only when there is a substantially

higher flow rate. In fact, 316L is used to carry seawater for desalination

in Kuwait. But the literature also points out that under low flow rate

or stagnant conditions (flow rate < 1 m/s), these materials are very sus-

(9) ceptible to pitting corrosion.^ ' The stainless steels used in the

Kuwait water supply system will be exposed to essentially stagnant conditions.

Because our tests under stagnant conditions do show tendencies to

pitting attack, it is worthwhile to note the statement by Fontana and

Green ^^^^ in their book Corrosion Engineering with regard to prevention

of pitting corrosion: "Materials that show pitting, or tendencies to pit,

during corrosion tests should not be used to build plant or equipment

under consideration."

B. Measures to Make System Operative As Soon As Possible

Because of the possible instability of the present pipes even

under operating conditions, it cannot be recommended that the present

pipes be used without some kind of protection. Since we are concerned

here mainly with a short-term solution that will allow the system to

be made operative as quickly as possible, replacement of the pipes also

would not be recommended. This leaves protection of the present pipes as

the only reasonable solution.

-22-

Various methods of protection were considered. Coating or lining

of the pipe interiors was considered too costly and time consuming. Impressed current cathodic protection was also ruled out due to the difficulty of reliably operating such a system and to its high installation costs

for a short-term solution. The method recommended for short-term protection

of the Kuwait water system is that of cathodic protection using sacrificial

zinc ribbon anodes. This type of cathodic protection has the advantages

of being easy and inexpensive to install and maintain.

Before a cathodic protection system can be installed at sites D-1

,

D-2, and P, the holes in the pipes must be repaired. In any pipes large

enough to be welded from the inside, all pits and holes should be patched

with the same alloy and/or welded using the proper filler metal for that

alloy. The welds should be ground smooth and passivated as per the original

contract specifications. With the smaller diameter pipes, all penetrating

holes should be welded from the outside with care taken to avoid unnecessary

crevices. Any additional holes which are discovered after the system is

operative (where shutdown would be difficult) could be drilled and riveted.

After completion of the sealing of holes in the pipes, the sacrificial anode cathodic protection system should be installed by a competent

cathodic protection company. The type of anode most desirable for the

Kuwait system is the zinc ribbon or cable anode. Note: Care should be

taken that the zinc is a high purity zinc especially made for potable vyater

systems; i.e., it should not contain cadmium or any other harmful material .

This anode is easy and inexpensive to install because it can lie on the

bottom of horizontal pipes (or against the side in vertical pipes) and needs

only to be connected to the pipe at the ends of the cable, which can be

installed in relatively long lengths. The zinc anodes should be installed

-23-

in sufficient number and size to maintain the surface of the stainless

steels at a potential at least as negative as -0.65V vs SCE at all points.

That is, the anodes should be installed along the entire lengths of the

stainless steel pipes and no point on the surface of the pipe should be

at a potential greater than (not more positive than) -0.65 V vs SCE.

Much service experience exists to show that the stainless steel

alloys type 304L and 316 can be satisfactorily protected for long times

in chloride containing waters at about 25°C when cathodically protected

to -0.65 V vs SCE. However, there is little experience in the cathodic

protection of stainless steels in brackish and potable waters identical

to those in Kuwait and at the high temperatures experienced in Kuwait

(50°C). Thus, it would be highly risky to predict reliable service for

50 years under the above conditions. However, considering the urgency

to make the Kuwait water supply system operational as soon as possible,

cathodic protection at a potential of -0.65 V vs SCE using high purity

zinc ribbon or cable anodes seems to be the best choice for the shortterm solution. It is felt that the cathodic protection system described

above is the best possible solution for making the water system operative

as soon as possible with the minimum expenditure in time and money.

C. Measures to Minimize the Chances of Future Failures . Since the pipe

stainless steels appear to be extremely unstable in the disinfecting solution, safeguards must be taken to avoid this type of exposure. The zinc

anodes will impart some protection even in the disinfecting solution used

previously. Therefore, disinfecting should take place only after the

cathodic protection system is completely installed. It is highly recommended that health experts be consulted to find, if possible, a non-Cl

-24-

containing non-oxidizing disinfectant (i.e., one not containing hypochlorite

or chlorine, etc.). Any disinfectant used should be applied in preferably

distilled (low Cl~) water and should be exposed to the pipes for as little

time as possible and then drained and rinsed with potable or preferably

distilled water. After disinfection, the pipes should be put into use

without delay.

As mentioned previously, there is little data for cathodic protection

of a system identical to that in Kuwait. Therefore, although pitting

should be minimized by the steps spelled out above, various precautions

must be taken and contingency plans considered. The first of these precautions involves the installation by a reliable cathodic protection company

of reference electrode ports for the monitoring of the potential of the

stainless steel pipes. These ports should preferably be of the porous

plug type that would allow potential measurements without keeping reference

electrodes installed at each measurement site. These ports should be installed at various points on the circumference of each different diameter

pipe for both types of water at each site. The cathodic protection company

can advise on the exact locations of these reference electrode ports in

order to monitor the potential of the pipes.

In order to determine the feasibility of using cathodic protection

as a long-term solution or, in fact, whether or not this protection is

actually needed under real operating conditions, several other steps are

advisable. The installation of test coupons of actual pipe pieces (with

original surfaces intact) would be advisable. These coupons should be

installed without cathodic protection at sites to be determined later.

Periodic inspections of both the cathodically protected pipes and the

unprotected coupons is also necessary in order to determine the best longterm solution. The first of these inspections should be made just before

-25-

the system is put into operation. Later inspections would preferably be

at three-month intervals for the first year (due to the uncertainties

inherent in the system). Befcre the first year is past, a decision can

be made on future inspections.

During the time that the above short-term sol jtion is in use, a

replacement material for the pipes or protection by :oating or lining the

pipes can be investigated in the event that cathodic protection is deemed

Inadvisable for the long-term solution. Also, during this time if cathodic

protection seems to be the likely long-term solution, it can be evaluated

whether this protection should be accomplished via the sacrificial anode

(which would require a quick, simple replacement periodically) or via

an impressed current system. Also, the possibility that cathodic protection

will not be necessary at all sites can be investigated through the examination of the test coupons.

-26-

V. CONCLUSIONS

The stainless steel pipes in the Kuwait water supply system are

susceptible to localized attack under the conditions that were reported

to have been used during the disinfecting procedure. Thus, it is reasonable

to conclude that the severe pitting found in the pipes occurred during

this operation.

The NBS data and observations show that both alloys type 304L and

316 cannot be used with confidence in their ability to resist localized

corrosion attack in the Kuwait water supply system unless new protective

measures are undertaken.

Recommendations to make the water system operative as soon as

possible are as follows:

(1) Repair penetrated pipes by welding;

(2) Install cathodic protection system using sacrificial zinc

ribbon or cable anode. Reference electrode ports should be included in

this system. Special care should be taken to see that the anodes used

do not contain any toxic materials . All internal surfaces of the pipes

should be polarized (or protected) to a potential at least as negative

as -0.65 V vs SCE.

Measures to minimize the chances of future failures are:

(1) Test coupons of unprotected pipe steels should be installed

in the water system;

(2) Disinfection should take place after cathodic protection

system has been installed and should occur immediately before the system

is put into operation;

-27-

(3) If available, a non-Cl containing non-o;(idizing disinfectant

should be used in low chloride water. The solution should be drained and

pipes rinsed and put into use without delay;

(4) Inspection should be made when the system is ready to be put

into operation;

(5) Periodic inspections of the pipes, cathodic protection system,

and coupons should be made at three-month intervals for the first year of

operation. Future inspection intervals should be decided on at the end

of the first year of operation;

(6) During the time the short-term solution is in use, possible

long-term solutions should be investigated. The possibilities to be considered are: Replacement of the pipes with another material; cathodic

protection using sacrificial anodes; cathodic protection using an impressed

current system; protection by coating or lining the pipes; and the possibility that the pipes can be used as designed at some of the sites.

-28-

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the following persons for their

invaluable contributions to this study: E. Passaglia, J. R. Ambrose, C.

H. Brady, C. J. Bechtoldt, U, Bertocci , D. E. Harne, K. F. J. Heinrich,

W. P. Iverson, M. L. Picklesimer , S. D. Rasberry, T. R. Shives, J. I.

Shultz, J. L. Weber, Jr., and S. A. Wicks of the National Bureau of

Standards; T. J. Lennox, Jr., and M. H. Peterson of the U.S. Naval

Research Laboratory; E. McFarren of the U.S. Environmental Protection

Agency; and L. P. Sudrabin of the of the Wallace and Tiernan Division of

the Pennwalt Corporation.

-29-

REFERENCES

(1) Kuwait Water Towers Contract Specifications.

(2) Applied Microbiology H, 529 (1966).

(3) J. Electrochem. Soc. 1304 (1972).

(4) J. Electrochem. Soc. 103^, 375 (1956).

(5) Z. Physik. Chem. 226^, 257 (1964).

(6) Metals Handbook, 8th Edition , Vol. 2, American Society for Metals,

Metals Park, Ohio, p. 346.

(7) Electrochimica Acta 16, 1987 (1971).

(8) Proceedings 1972 Tri -Service Conference on Corrosion, 357, National

Technical Information Service, U.S. Department of Commerce, Springfield, Virginia.

(9) Corrosion Engineering , McGraw-Hill Book Company, N.Y., N.Y., 1967, p. 268.

(10) Corrosion Engineering , McGraw-Hill Book Company, N.Y., N.Y., 1967, p. 57.

(11) Materials Protection 8, 41 (1969).

-30-

FORM NBS-34S

<U-«S) APPENDIX A

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D.C. 20234

REPORT OF ANALYSIS 310.02-11/73

on

X-ray Fluorescence Analysis

of

Nine Samples of Stainless Steel Plate

Submitted by 310. OU

Attention: G, Ugiansky

Date Received

Laboratory Nos

.

References

Analysts

5-10-73

310.02-38750 thru 38758

Book 2U5, pp. 113-219; Carbometric Book 1, p. 6I

J. L, Weber and S. D. Rasberry

Frob lem : Determine if specimens 1, 7, 8, 9, and S. W, are type 3l6 with 0.05^

carbon maximiam, and if specimens 2, 3, 5, and 6 are type 30hL stainless steels

according!!: to ASTM specifications Al+09 and A312,

Procedure : A 1 3/8-inch square was cut from each of the specimens, turned down

to a 1 1/U-inch diameter disk and polished to a 6-micron diamond finish. The

specimens were analyzed, along with appropriate standard reference materials,

by x-ray fluorescence analysis. Carbon was determined by a combustion chromatop;raphic method.

Results : Qualitative x-ray fluorescence analysis was made for each specimen;

the range of elements considered was all those above scandium (atomic number

21). The qualitative tests indicated that no element which would prevent the

unknowns from being type 3l6 or 30U stainless steels were present above 0,1%,

The results of the quantitative x-ray fluorescence spectrcanetric analysis are

given in Table 1.

Joseph L, Weber, Jr., Physicist

Coordination Chemistry Section

( James I. Shultz ^

73-l^i* Service Analysis Coordinator

May 22, 1973 Analytical Chemistry Division

-31-

APPENDIX A (Con't)

310.02-11/73 p. 2

Table 1.

Percent Concentration*

Specimen

No. C Mn Si Ni Cr Mo Ti

1 0.050 1.97 0.9 13.8 16.9 2.38 <0.02

7 O.OU2 1.90 0.5 11.4 17. U 2.06 <0.02

8 0.035 1. 78 0.6 12.1 17. ^+ 2.23 <0.02

9 0.035 1.80 0.6 12.1 11 ,h 2.23 <0.02

s.w. 0.050 1.97 0.9 lU.l 17.1 2.38 <0.02

AGTM Gpecification

A)»09, type 3l6

0.08

max.

2.00

majc.

0.75

max.

11.0-

lU.O

16.0-

20.0

2.0-

3.0

Not

Specified

2 0.019 1.59 o.u 9.2 18. J4 o.oU <0.02

3 0.025 1.68 0.5 9.U 18.3 0.05 <0.02

5 0.023 1.70 0.5 9.U 18.3 0.05 <0.02

6 0.026 1.77 0.6 9.2 17.9 0.07 <0.02

ASTM Specification

A312, type 30i4L

0.035

max

.

2.00

max.

0.75

max

.

8.00-

13.0

18.0-

20.0

Not

Specified

Not

Specified

*The analysts' estimate of accuracy for the following elements is: Mn, ±0.05;

Si. ±0.2; Ni, ±0.2; Cr , ±0.2; Mo, ±0.0U.

-32-

FORM NBS-34t

APPENDIX B

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D.C. 20234

REPORT OF ANALYSIS 310.02-18/73

by

X-ray Fluorescence Analysis

of

Three Weld Specimens

Submitted by 312. OU

Attention: G. Ugiansky

Date Received

Laboratory Nos.

References

Analyst

9/6/73

310.02-38778 thru 38780

Book 2I+5, PP 156-166

S, D. Rasberry

Problem : We were requested to determine manganese, silicon, nickel, chromium,

molybdenum and titanium in each of three small weld surfaces. The surfaces

are approximately 2.0 by O.U cm and are too small for determination of

titanium and silicon (present only in minor amounts) at a level of accxiracy

useful to Ugiansky. We decided to go ahead with the determination of the

other four elements.

Procedure and results : Results of quantitative determination of manganese,

nickel, chromium and molybdenum are presented in Table I,

The molybdenum in all three specimens is consistent with type 3l6 specifications and not like type 30U stainless which is nearly zero in raolybdeniim

concentration. The other three elements are at appropriate concentrations

for the three welds to be of type 3l6 stainless.

Kurt F. J. Heinrich, Chief

Surface Microanalysis Section

Analytical Chemistry Division

7U-29

September 21, 1973

-33-

APPENDIX B (Con't)

Table I. Results of X-ray /'jrialysis of Three Weld Samples

Klement

30Ul 316 2^ 9 Sv

Concentration (in weight percent)*

Mn 2.00 max. 2.00 max. O.65 l.Uo O.6I

Ni 8.00-13.0 ll.O-lU.O 11.0 12.1 12.7

Cr 18.0-20.0 16.0-18.0 18.2 17.2 17.6

Mo 2.0-3.0 1.92 2.30 2.50

*The ajialyst's estimate of accuracy for the following elements is;

Mn, _+0.08; Ni , +^0.3; Cr, +_0.3; Mo, +_0.06.

FORM NBS-S48

(12-6S)

-34-

APPENDIX C

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D.C. 20234

REPORT OF ANALYSIS

Steel Specimen

Weld Metal

Carbon Determination

Project No: 3120575

Requested By: Mr. Ugiansky

Work Order IJo : 4 412

Analysed

Sample No

2

9

Combus tion- thermoconductivi ty Method

%C

0.024

0.029

S. A. VJicks, Chemist

^Jamep I. Shultz

\Seryices Analysis Coordinator

ilytical Chemistry Division

October 11, 1973

74-29

-35-

Table 1. Kuwait Water Storage Towers

^^.^g No. of Towers Height, m High Water Level, m

Designation

potable Brackish Potable Brackish Potable Brackish

D-1 6 . 3 40 40 +60.0 +60.0

D-2 6 3 37 37 +62.0 +62.0

D-4 3 3 30 25 +83.0 +78.0

D-5 3 3 30 25 +85.0 +80.0

D-7 1 - 42 - +125.0
V
-36-

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-l-> -»-> CO $-

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E (O O

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•I— to 0

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rO

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s- +J CU o fO Q. u toE 1—1 1—1

-37-

Table 3. Stainless Steel Specimens Collected

in Kuwait in April, 1973

Specimen Removal Stainless Steel

No.n) Location Alloy Type

1 D-6 (Kuv^ait Towers) from 316

pipe stored at site.

2^^^ D-2 1000 mm diameter pipe 304L

.(2) II M M II II II

^

II II II II 11 II

5(2) I, gQQ ,1 U „

7 P (Shuwaikh Blending Plant) 316

Q II II II II II

II II II II II

S.W.^^^ D-6 "Special weld" section made

especially for NBS

Specimen 4 was not removed from site D-2 due to difficulties in cutting the pipe specimen from a support member.

These specimens contained welds.

-38-

Table

Specimen C

No.

ASTM 0.08'''

Specification max. A409, type 136

1 0.050

7 0.042

8 0.035

9 0.035

9 weld 0.029

S.W. 0.050

S.W. weld

ASTM 0.035

Specification max. A312, Type 304L

2 0.019

2 weld 0.024

3 0.025

5 0.023

6 0.026

4. Analysis of Stainless Steel

Collected in Kuwait.

Percent Concentration*

Mn Si Ni

2.00 0.75 11.0-

max. max. 14.0

1.97 0.9 13.8

1.90 0.5 11.4

1.78 0.6 12.1

1.80 0.6 12.1

1.40 - 12.1

1.97 0.9 14.1

0.61 , - 12.7

2.00 0.75 8.00-

max. max. 13.0

1.59 0.4 9.2

0.65 - 11.0

1.68 0.5 9.4

1.70 0.5 9.4

1.77 0.6 9.2

Specimens

Cr Mo Ti

16.0- 2.0- Not

20.0 3.0 Specified

16.9 2.38 <0.02

17.4 2.06 <0.02

17.4 2.23 <0.02

17.4 2.23 <0.02

17.2 2.30

17.1 2.38 <0.02

17.6 2.50

18.0- Not Not

20.0 Specified Specified

18.4 0.04 <0.02

18.2 1.92

18.3 0.05 <0.02

18.3 0.05 <0.02

17.9 0.07 <0.02

*The analysts' estimate of accuracy for the following elements is: Mn, ±0.05; Si, ±0.2;

Ni, ±0.2; Mo, ±0.04; Cr, ±0.2.

tSpecial specification for 316 in question, C = 0.05 max.

-39-

I/) +->

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in>>

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cucn <Cco

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OJ -MO

c:

cuEdo>

LU

on

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Figure 3. Towers site D-1 . Stainless steel type 304L pipes

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atmospKeric pitting (dark spots). (304L) X2

Figure 16. Enlarged view of area of specimen 2 containing

penetrating pits adjacent to weld. (304L) X2
[rcccccrrr[rrrrr
Figure 17. Enlarged view of area of specimen 5 showing pit

at end of scratch. (304L) X2

Figure 18. Enlarged view of area of outer surface of specimen 7 showing penetrating pit and oxide stain. (316) X2
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Figure 19. Enlarged view of area of inner surface of specimen 8 showing pit and oxide stain, (316) X2

Figure 20. Scanning electron micrograph (SEM) of pit on

specimen 5 shown in Fig. 17. (304L) X20
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Figure 21. Surface within pit shown on Fig. 20 (specimen

5) showing etch pitting and faceting of surface.

(304L) SEM XIOOO

Figure 22. Surface within pit shown in Fig. 20 (specimen

5 showing faceting. (304L) SEM XIOOO
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Figure 23. Surface within pit shown in Fig. 20 (specimen

5) showing faceting and grain boundary delineation.

(304L) SEM X800

Figure 24. Cross section of one of the large pits near

the weld in specimen 2 (see Fig. 16). White areas are

corrosion product. (304L) SEM XI

6
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Figure 25. Cross section of the other half of pit shown

in Fig. 24. Note relative resistance of weld metal to

attack. (304L) Etched in 10% oxalic acid. X6

Figure 26. Pit adjacent to weld bead of specimen 9

seen in Fig. 13. (316) SEM X40
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Figure 27. Surface within pit of Fig. 26. Note honeycomb structure of what is probably the heat affected

zone and faceting further away from weld. (316) SEM X400

Figure 28. Area within pit of Fig. 26 showing both faceting

and grain boundary delineation. (316) SEM XI 600
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Figure 29. Area of specimen 6 showing lace-like structure

covering pit. (304L) SEM X16

Figure 30. Area of specimen 6 showing lace-like structure

covering pit near weld splatter metal. (304L) SEM X14
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r

Figure 31. Cross section of pit shown in Fig. 29. White

area is cut surface. Lace-like metal is seen folded over

at right of pit. (304L) SEM X40

Figure 32. Area within pit shown in Fig. 31 showing

faceting. (304L) SEM X400
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Figure 33. Microscopic view of one of the pits seen on

specimen 1 in Figs. 6 and 15. Corrosion product is in form

of barnacle-like incrustation. (316) SEM X500

Figure 34. Identical area as shown in Fig. 33 with most of

corrosion product removed. Some attack other than intergranular effect is present. (316) SEM X500
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Figure 35. Area of specimen 1 in which grains of metal are

missing from surface. (316) SEM X240

Figure 36. Area within attacked region shown in Fig. 35.

Note faceting, etch pitting, and grain boundary delineation.

(316) SEM X600

Figure 37. Typical area of inner surface of specimen 5 from

site D-2. (304L) SEM X650

Figure 38. Typical area of outer surface of specimen 5 from

site D-2. (304L) SEM X600
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Figure 39. Typical area of inner surface of specimen 1 from

site D-6. (316) SEM X600

Figure 40. Typical area of outer surface of specimen 1 from

site D-6. (316) SEM X600

Figure 42. Typical area of outer surface of specimen 8 from

site P. (316) SEM X600
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Figure 44. Typical area of surface on other side of 304 piece

shown in Fig. 43. SEM X600
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Figure 45, Area of NBS storeroom stock 304 after polishing and

pickling in 25% H2SO4 for 30 minutes at 90°C. SEM 600X
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o 0)

to O ^ O) •4->

a

-t->

s-o

C/1

E O

to

C\J 1

+ 03

U3

CD

Si4->

lO

=3 O

CJ> 03

•1- $_

Li_ JZl

+J

C

OJ

+-> o

a.

+j

03

toE

<D

V

* 4U9jjno peiiddv
r

r

I

L

r*

II
Figure 47. Pit in early stages of propagation on polished surface of specimen 1 exposed to brackish water +2 ppm Clo at 50°C.

(316) SEM X2000
L
o

o

oo

o

o

o

o

o

o

o

in 5^- rO CNJ

—

30S SA AiJU *|D!4U»40d

Figure 49. Localized attack on surface of specimen 2 after

20-hour "rubber band" test in brackish water +50 ppm CI 2 at

50°C. (304L) SEM XI 00

Figure 50. Area of pit shown in Fig. 49 showing etch pitting,

faceting, and grain boundary delineation. (304L) SEM XIOOO
LL1rL

,[ ' . rL ' L • LL

4

L[ U \, lb
Figure 51. Area on specimen 1 of pit produced by 20-hour

"rubber band" test in brackish water +50 ppm CI? at 50°C.

Note grain boundary delineation and faceting. (316) SEN! X950

Figure 52. Another area of specimen shown in Fig. 51. This

area shows examples of etch pitting and faceting. (316) SEM XI 000
[rr[rrCcL
Figure 53. A small pit on specimen 2 after 20-hour "rubber

band" test in synthetic distilled water +50 ppm CI 2 at 50°C.

Examples of faceting and grain boundary delineation are evident. (304L) SEM XIOOO

Figure 54. Attacked area on specimen 1 after 20-hour "rubber

band" test in synthetic distilled water +50 ppm CI 2 at 50°C.

Etch pitting, faceting, and grain boundary delineation can be

seen. (316) SEM X540

Figure 55. Area on specimen 2 of pit produced by 7-day "rubber

band" test in brackish water +2 ppm CI 2 at 50°C. Note etch

pitting. (304L) SEM X900

Figure 56. Another area on same specimen shown in Fig. 55.

This area shows examples of faceting. (304L) SEM XI 800
[[[[[[[[[[[[[[[[
Figure 57. Area on specimen 2 after 5-day "rubber band" test

in brackish water +4 ppm CI 2 at 50°C. Note grain boundary delineation and some faceting. (304L) SEM XIOOO

Figure 58. Area on specimen 2 after 5-day "rubber band" test

in potable water +4 ppm Clp at 50°C. Note etch pitting and

faceting. (304L) SEM XIOOO
I

L

r

[

r

r

I.

rm 9

[

I

\ t

\L
Figure 59. Area on specimen 1 after 5-day "rubber band" test

in brackish water +4 ppm Cl2 at 50°C. Examples of etch pitting,

faceting, and grain boundary delineation can be seen. (316)

SEM XI 000

Figure 60. Area on specimen 1 after 5-day "rubber band" test

in potable water +4 ppm Clo at 50°C. Note faceting and grain

boundary delineation. (31b) SEM XI 000
L

[

[

[

L

[

r

[

[

I,

r"

1

1
Figure 61 . Surface of specimen 1 after 30-minute exposure to

brackish water. Specimen was polarized to +600 mV vs SCE.

Attack has undercut surface as in actual failure (see Fig. 29

and 30). (316) SEM X210

Figure 62. Cross section of pit shown in Fig. 61, Undercutting

nature of pitting is shown. (316) SEM X200
rrr
Figure 63. Area of surface within pit shown in Fig. 62.

Examples of etch pitting, faceting, and grain boundary delineation are seen. (316) SEM X2800
[[
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 74-429

2. Gov't Accession

No.

4. TITLE AND SUBTITLE

Corrosion o£ the Stainless Steel Piping in the

Kuwait Water Supply System

5. I^ublication Date

1974

6. Performing; Organization ( ode

7. AUTHOR(S)

G. M. Ugianskv and J. Kruper

8. Performing Ori>mi. Report No.

NBSIR 74-429

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiett/Ta.sk/Work Unit No.

3120575

1 1 . ( '.oniract /(iranl Nt).

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Ministry of Electricity and Water

Government of Kuwait

Kuwait. Kuwait

13. 1 ype of Report & Period

Covered

14. Sponsoring Agency ( ode

15. SUPPLEMENtARY NOTES

Through: The Department of State (U.S.)

16. ABSTRACT (^4 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

This investigation shows that the stainless steel pipes in the Kuwait water

supply system are susceptible to localized attack under the conditions that

were reported to have been used during the disinfecting procedure. Thus, it

is reasonable to conclude that the severe pitting found in the pipes occurred

during this operation.

The NBS data and observations show that both alloys type 304L and 316 cannot be

used with confidence in their ability to resist localized corrosion attack in

the Kuwait water supply system unless new protective measures are taken.

Recommendations to make the water system operative as soon as possible are

made and measures to minimize the chances of future failures are given.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Brackish water; disinfecting solution; pitting corrosion; potable water; sodium

hypochlorite; stainless steel; 304L; 316.

18. AVAILABILITY |

' Unlimited

L2Qi|[For Official Distribution. Do Not Release to NTIS

I

I Order From Sup. of Doc, U.S. Government Printing Office

Washington, D.C. 20402, SD Cat. No. C13

I ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGi:s

81

22. Price

USCOMN/I-DC 29042-P74