NBSIR 74-484

Progress Report on the Corrosion and Stress

Corrosion Behavior of Selected Stainless

Steels in Soil Environments

Part II. Stress Corrosion and Electrochemical

Behavior

W. F. Gerhold, E. Escalante, W. P. Iverson, and B. T. Sanderson

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

May 1974

Progress Report

Prepared for Committee of Stainless Steel Producers

American Iron and Steel Institute

150 East 42nd Street New York, New York 10017

NBSIR 74-484

PROGRESS REPORT ON THE CORROSION AND STRESS

CORROSION BEHAVIOR OF SELECTED STAINLESS

STEELS IN SOIL ENVIRONMENTS

PART II. STRESS CORROSION AND ELECTROCHEMICAL

BEHAVIOR

W. F. Gerhold, E. Escalante, W. P. Iverson, and B. T. Sanderson

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

May 1974

Progress Report

Prepared for Committee of Stainless Steel Producers

American Iron and Steel Institute 150 East 42nd Street New York, New York 10017

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

PROGRESS REPORT ON

THE CORROSION AND STRESS CORROSION BEHAVIOR OF SELECTED

STAINLESS STEELS IN SOIL ENVIRONMENTS

Part II. Stress Corrosion and Electrochemical Behavior

by

W. F. Gerhold, E. Escalante, W. P. Iverson, and B. T. Sanderson

A. INTRODUCTION

Stainless steels have been successfully used in limited

applications (such as for pipe clamps for cast-iron sewer lines) in soil

environments for many years. In recent years, other applications in use

or under test, include ground rods, transformer cases, submerged switches,

underground residential distribution equipment, gas lines, [1,2] water

lines, caskets, culverts, residential sewage disposal, etc. Corrosion

data for selected annealed, unstressed austenitic and ferritic stainless

steels, buried in various soils, have been reported in NBS Circular

579 [3]. Branch [1] and Steinmetz and Hoxie [2] have reported on the

suitability of stainless steel alloys for some underground uses.

NBS tests conducted for 14 years in various soils in the United

States showed that austenitic Type 304 (containing Ni ) and the Type

316 (containing Ni and Mo) stainless steels were highly resistant

to both pitting and general attack. Type 304 was susceptible to pitting

corrosion in certain highly aggressive soils, while Type 316 was relatively

unaffected by corrosion. The ferritic stainless steels. Type 410 (12%

Cr) and Type 430 (17% Cr) were found to be fully resistant to corrosion

in only one-third of those NBS soil test sites where exposed.

Stress corrosion cracking had not been reported to be a problem

with Types 304 or 316 in actual underground applications. [1]

In order to evaluate more fully the corrosion and stress corrosion behavior of some of the alloys proposed for use in soil environments,

NBS in cooperation with the American Iron and Steel Institute initiated

in 1970 a soil burial program in representative corrosive soils utilizing

9 stainless steels, in both the annealed and cold-worked conditions,

with various treatments. Test specimens incorporated welds, crevices,

galvanic couples, and specimens which had been sensitized to induce carbide precipitation. In 1971 afid in 1972, this program was expanded to

include additional stainless steels.

The results obtained from field tests conducted to determine the

general corrosion behavior of materials buried up to 2 years were given

in Part I [4] of this report. This report (Part II) contains the results

obtained from tests conducted to determine the stress corrosion and

electrochemical behavior of the stainless steels.

B. EXPERIMENTAL PROCEDURE

1. Soils at NBS Test Sites. The soils at the 6 NBS Soil Corrosion
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Test Sites have been fully described in Part I [4] of this report. Some

of the properties of these soils are given in Table I.

2. Materials, Treatment, and Preparation . In order to simulate some

of the conditions which may exist with components fabricated from stainless

steels, materials for these soil studies included stressed and unstressed

galvanically coupled specimens and stressed non-welded and welded specimens.

A description of all of the various stainless steel systems buried

at each test site is given in Table II, This report contains the results

obtained from the evaluation of specimens from Systems Nos. 20 through 42

and 67 through 92 after exposure for up to 2 years. The evaluation of

specimens from the remaining systems was covered in Part I. [4]

Upon receipt of the materials from the stainless steel companies,

the 1" X 12" sheet specimens were first stamped with identification

numbers at one end using chromium plated steel dies. All of the specimens were supplied with sheared edges which had been deburred. In some instances, further deburring was necessary.

All of the sheet materials to be stressed as either single or double U-bends had oblong holes 1/4" x 1/2" punched near each end so as

to be self-aligning after bending. Specimens to be connected to a dissimilar metal (galvanic couples) had an additional hole (0.093") drilled

1/4" from the end and side for wire connections.

The specimens to be stressed were initially bent in a die (shown

in Figure 1) to about 20° (internal angle). The only portions of the

die in contact with the specimens were fabricated from Type 304 stainless steel . .

•

All of the stainless steel alloy specimens, both stressed and un- stressed, were then degreased in trichlorethylene vapor and passivated

in accordance with the treatments given in Table II. Following the passivation procedure, the specimens were scrubbed with a bristle brush,

thoroughly rinsed with water, and air dried.

Single U-bend specimens were formed by bending the two ends in a wooden jig so that they were parallel (the inside diameter at the bend

was approximately 1") and clamping them in this position with a Type 316

stainless steel nut and bolt. Double U-bend specimens for the crevice

corrosion studies were formed in the same manner except that the two

strips were bolted together prior to the bending operation. The welded

double U-bend specimens were spot welded at an area centrally located

from the edges and ends (Figure 2). They were then bent together to

form the U and clamped at the ends with Type 316 stainless steel fasteners.

In those systems connected to steel (iron), zinc, or magnesium

anodes or to copper for galvanic couple studies, 14 gauge stranded copper

wire was used to make the connections to the specimens. The connections

were soldered with 50-50 acid core solder. These areas, including portions

of the exposed copper wire, were then covered with a bituminous coating

(coal-tar epoxy)

.
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The iron anode consisted of a 12" length of cold finished steel

(AISI 1017-1018) 3/4" hexagonal shaped rod with a hole drilled in the

rod mid-way between each end for the electrical connection.

The magnesium anode (48" long, bent in the form of a horseshoe)

was of the commerical flexible extruded type with a cross-sectional

area 3/4" x 3/8" and a continuous centrally located 1/8" diameter iron

wire core. The copper stranded wire was soldered to a 1" extension of

the iron wire core using a 50-50 acid core solder. A bituminous coating

was applied to the exposed copper and iron surfaces at the connection

and to both 3/4" faces of the anode to extend its effective life.

The zinc anode (12" long) was also of the commercial flexible

extruded type with a diamond shaped cross-section (5/8" x 7/8") and a continuous centrally located 0.1" diameter zinc coated (galvanized) wire

core. The stranded copper wire was soldered to an extension of the

galvanized wire core and coated as in the case of the magnesium anode.

Copper strips which were electrically coupled to the stainless

steel specimens were cut from cold-rolled copper sheet, 0.065" thick

and of the same dimensions as the stainless steel specimens (1" x 12").

3. Exposure . Specimens were buried at each test site about

1 foot apart in trenches approximately 2 feet wide x 2-1/2 feet deep.

The U-bend specimens were connected with nylon cord looped around the

bolts at one foot intervals to facilitate recovery. The specimens electrically connected to the steel and zinc anodes and to the copper strips were placed with the dissimilar metal parallel to the specimens and

separated by approximately 1 foot. Specimens electrically connected to

the horseshoe shaped magnesium anodes were placed at the center of the

horseshoe. Upon backfilling the trenches, the insulated wires soldered

to those specimens to be used in potential and corrosion current (couple

corrosion) determinations were connected above ground to terminal strips

mounted on 4" x 4" x 6' wooden posts. Leads from the anodes and copper

strips were connected to leads from the specimens at the terminal strips

(potential and current measurements).

Sufficient specimens were buried at each of the 6 test sites to

permit recovery of a complete set at specified intervals (1, 2, 4, and

8 years) and a final set to be removed at a date to be determined. Each

set for each removal consisted of two specimens.

4. Electrochemical Measurements . All electrochemical measurements

(potential, couple current, and corrosion current) were made initially

and 3 times a year when possible with the exception of Site A where

measurements were usually made once a year.

Electrochemical potentials of the specimens and couples vs_. a Cu-CuS0i+ half cell were measured using a high precision portable pH

meter as a millivoltmeter. The half cell was placed in a remote area (usually at the edge of the test area) and shielded from the light to

prevent photochemical effects.
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The couple currents of the anode systems and the stainless steelcopper systems were measured using a zero impedance circuit employing

an operational amplifier (Figure 3) for small currents and a commercially

available zero resistance ammeter for larger currents.

Corrosion currents were measured using a modification of the linear

polarization technique based on the following relationship derived by

Stern and Geary [5]:

1 B B aE _ 1 a c Al 2.31 I B +B corr a c

where aE is the overvoltage of the corroding specimen produced by a polarizing current, Al. B and B are the slopes of the anodic and

cathodic polarization curves, respectively, in the Tafel region and

I is the corrosion current. Assuming B and B equal to 0.1 V in

tH?E'^investigation (the error will usually Be abou^ 20% or less, as established by Stern and Weisert [6]), the following equation was derived:

T /mA^ - 2.7Al(mA)

. ^corr ^"^^ - AE(mV )

The electrical circuit described previously, [7] but minus the

bridge circuit was employed. A soil auger was utilized as the auxiliary

electrode. The change in potential was measured directly, using the pH

meter or an electrometer (0-10 mV scale) plus a battery and variable

resistor (to null the initial potential) and a Cu-CuSOi+ reference electrode. Electrodes (auxiliary and reference) were placed so that the specimen was between them or at approximately right angles to them. In making

these measurements, an increment of current was applied to the specimen

until a stable over potential of usually 2 to 10 mV occurred. The potential

and current readings were then recorded. Occasionally the open circuit

potential of the stainless steel alloy was found to fluctuate and the

corrosion current measurements could not be made. At other times, ex- tremely humid or rainy conditions prevented these measurements.

C. RESULTS

1. Visual Examination . Upon removal from the test site, each of

the stressed specimens was examined for indications of failure by cracking

or fracture. All specimens were then returned to the laboratory for

cleaning and a more thorough examination.

In the laboratory, the specimens were rinsed in tap water to remove adhering soil particles. They were then examined visually prior

to further cleaning. The stressed U-bend specimens were then disassembled

by removing the Type 316 stainless steel fasteners. The copper wires

were unsoldered from those specimens that had been coupled to the magnesium,

zinc, steel, and copper materials. All of the specimens were then cleaned

ul trasonical ly using a lOX nitric acid solution, heated to 120 to 130°F

for 20 to 30 minutes and then rinsed in distilled water and air dried.
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2. General Corrosion Behavior . The results obtained from visual

examination of the 300 series, the 400 series, and several proprietary

stainless steel specimens, buried up to 2 years in the various soil

environments, are given in Table III.

AISI 300 Series . With a few exceptions, there was little or no apparent visible corrosion noted on the stressed or unstressed stainless

steel alloy specimens buried for up to 2 years in the soils at Sites A,

B, and D.

Of the single U-bend specimens exposed for 2 years at Site C, the

only systems on which little or no corrosion was observed were the Type

301 (full-hard). Type 304 (full-hard), and the Type 316 (annealed).

Similarly, except for crevice areas, there was little or no degradation

from corrosion on the Type 301 (full-hard) or the annealed Type 304 and

Type 316 spot-welded double U-bend stainless steel specimens. The un- stressed Type 304 (annealed) specimens that were coupled to copper were

also unaffected by corrosion after exposure for 2 years at this site.

Of the stressed single U-bend specimens exposed at Site E for 2 years, the only systems which appeared to be relatively unaffected by

corrosion were the non-coupled annealed Type 316 and those annealed

Type 304 alloy specimens coupled to zinc, magnesium, or carbon steel.

There was also no apparent corrosion noted on the annealed Type 316 spotwelded double U-bend specimens exposed at this site.

With the exception of the non-coupled annealed Type 316 and the

full-hard Type 301 single U-bend specimens, all of the specimens exposed

at Site G were affected in varying degrees by corrosion.

400 Series . Materials in this series included in this investigation were the lype 434 and the Type 409 stainless steels. Of these, the

Type 434 was exposed in the stressed condition (single U-bend and spotwelded double U-bend specimens), while the Type 409 ms galvanically

coupled to copper and exposed in the unstressed condition.

The Type 434 was relatively unaffected by corrosion at Sites A,

B, and D. However, pitting and tunneling corrosion was noted at crevice

areas on one of the spot-welded double U-bend specimens that had been

buried for 2 years at Site A. Pitting corrosion was noted on stressed

specimens exposed at Sites C and G for 2 years, while pitting and tunneling

corrosion was noted on the specimens exposed at Site E.

Corrosion in the form of pitting, etching, or general attack was observed on unstressed Type 409 specimens coupled to copper and exposed

at Sites A, C, D, E, and G. Similar specimens at Site B were relatively

unaffected by corrosion after exposure for 2 years.

Proprietary Alloys . Materials included in this portion of the

investigation may be grouped as follows according to major alloying

constituents

1. Cr-Ni Stainless Steels

18 Cr-8Ni(N)

26Cr-6.5Ni

20Cr-24Ni-6.5Mo
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2. Cr Stainless Steels

26Cr-lMo

18Cr-2Mo

In general, these alloys were relatively unaffected by corrosion in any

of the soil environments. Corrosion, where noted, (See Table III) was generally very localized and superficial.

3. Stress Corrosion Behavior . The results of visual and micro

examinations, made to determine failure of the various systems due to

stress corrosion cracking, are given in Table IV for non-gal vanical ly

coupled specimens and in Table V for stressed galvanically coupled specimens. It may be noted that many of the specimens contained microcracks.

While cracking of these specimens could not be ascertained without optical

means, these specimens were considered to have failed.

Non-Galvanically Coupled Stressed Specimens

300 Series . Examination of Type 301 in the half-hard condition,

after exposure for 2 years in the various soils, indicated that the alloy

was susceptible to stress corrosion cracking in the acid clay at Site C.

Microcracki ng was observed on 1 specimen exposed for 2 years at this

site. Sensitization of the half-hard alloy increased the susceptibility

to stress corrosion cracking in all of the soil environments, particularly

at Sites C, D, and E, where all of the specimens had failed. The same alloy exposed in the full-hard condition had not failed after 2 years in

5 of the 5 soil environments. Microcracks were noted at the edge on 1 of the spot welded double U-bend specimens exposed in tidal marsh (Site G).

No failures were noted for the Type 304 specimens exposed in the half-hard

condition. Sensitized Type 304 specimens buried in the acid clay at Site

C were found to be susceptible to stress corrosion cracking. Similar

specimens exposed in the other soil environments did not fail. Type 316

stainless steel did not fail in any of the soils in which it was exposed

and sensitization of this alloy did not appear to affect its stress

corrosion behavior.

AISI 400 Series . Type 434 stainless steel was the only alloy in

this series exposed in the soils. There were no apparent failures of

this alloy in any of the soil environments.

Proprietary Stainless Steels . Alloys in this category included

26Cr-lMo, 18Cr-2Mo, 20Cr-24Ni-6.5Mo, 18Cr-8Ni(N), and 26Cr-6.5IMi.

There were no apparent failures of stressed specimens of these alloys

after exposure for 2 years in any of the soil environments.

Galvanically Coupled Stressed Specimens

There were no apparent failures of the Type 304 (full -hard), 26CrIMo (annealed), or 26Cr-6.5I\li (annealed) stainless steels that were coupled

to zinc, magnesium, or carbon steel after exposure up to 2 years in the

6 soil environments.
Type 301 (half -hard) specimens that were coupled to carbon steel

and exposed for two years at Site C had failed. Type 301 (full -hard)

specimens coupled to carbon steel failed in one year at Site C and 2 years at Site G. No failures were observed for Type 301 (half-hard or

full -hard) specimens exposed at the other sites.

Failures were noted on all of the Type 301 (half-hard and full -hard)

specimens coupled to magnesium and exposed for one and two years at Sites

B, C, D, E, and G. At Site A one specimen exposed for one year and one

I specimen exposed for two years had not failed while other specimens exj. posed at this site for one and two years did fail.

No failures were noted on Type 301 (half-hard) specimens coupled

to zinc and exposed at Site A for one and two years or at Site B for one

year. One of the two specimens exposed at Site B for two years had failed.

Of the specimens at Site D, failures were noted on one each after exposure

for one and two years. All of the specimens galvanically coupled to zinc

and exposed for one and two years at Sites C, E, and G had failed.

There were no failures of Type 301 (full -hard) specimens coupled

to zinc and exposed at Site A for one year, but after exposure for two

years one specimen had failed. Failures were noted on all of the Type

301 (full-hard) specimens galvanically coupled to zinc and exposed for

one and two years at Sites B, C, D, E, and G.

4. Electrochemical Behavior . All of the results given in this

section pertaining to the electrochemical behavior of the stainless steels

galvanically coupled to dissimilar metals refer to materials still buried

in the soils at the 6 test sites. Further, the results are based solely

on data gathered in situ through electrochemical means (i.e., couple

currents, and potentials). This should be considered when comparing

these results with visual observations previously given for materials

removed from the soils after exposure for 2 years.

Galvanic Couples

Unstressed Stainless Steel Alloys vs. Copper . The direction of

current flow between two dissimilar metals, such as stainless steel

coupled to copper, indicates which of the materials is corroding (or

|j which of the two is anodic), while the magnitude of the current gives

' an indication of the degree of corrosion.

Measurements obtained for a particular stainless steel coupled to

copper indicates that the couple current may fluctuate through zero from

time to time or remain consistently positive or negative. An illustration

of these conditions is given in Figure 4, which shows the magnitude of

the couple current and its direction as a function of time for one of

the systems buried at the six test sites.

, Table VI gives the couple current data obtained for the unstressed

I stainless steel specimens coupled to copper at each of the six test sites.

For purposes of brevity, only the maximum current at either condition of

polarity is given. Where only one value is given, there was no observed

current reversal. Thus, Type 304 stainless steel specimen 91-10 was
-8-

cathodic to copper at Site A throughout the 2-year period with a maximum

current of 193 yA. The current for a similar specimen exposed at Site E fluctuated from anodic to cathodic with maximum current of 46 and 56 yA

respectively. These fluctuations can be seen in Figure 4.

From the data given in Table VI it can be seen that Type 304 is

predominantly cathodic to copper at Sites A, B, and C with Site C being

somewhat on the border line. At Sites D and E, the direction of the

current varies from specimen to specimen. For specimens exposed at

Site G, Type 304 was found to be anodic to copper.

Type 409 stainless steel appeared to be predominantly anodic

at Site A and at Site B (to a lesser degree than at Site A). At Sites

C, E, and G, Type 409 tended to be anodic with relatively high currents.

Type 409 coupled to copper was variable in the soil at Site D and could

be either anodic or cathodic.

Alloy 26Cr-6.5Ni connected to copper produced very low couple

currents. At Site B, initial couple current measurements indicated that

this alloy was anodic to copper. Within 4 months, the situation was reversed with the result that the alloy was protected by the copper.

This effect is not evident from the data given in Table VI. At Site

C Alloy 26Cr-6.5Ni was cathodic initially but then became anodic to

the copper and generally remained that way. At Site D, the couple

currents were low and uncharacterized. The behavior of Alloy 26Cr6.5Ni was similar at Sites E and G in that the alloy was in general

cathodic to copper. One exception was noted for one specimen exposed

at Site G which switched from a cathode to an anode without further

change.

Stressed Stainless Steel Alloys vs. Magnesium, Zinc, or Carbon

Steel . While the connection of some stainless steels to copper may

possibly result in general corrosion or pitting corrosion of the stainless steel, other stainless steel galvanic couples may fail by different

mechanisms. Hydrogen embri ttlement as a result of cathodic protection

of the stainless steel is one example. To evaluate the susceptibility

of various stainless steels to this form of failure, stressed specimens were connected to 3 types of anodes (magnesium, zinc, and steel)

which produced 3 ranges of potentials (1.5 V, 1.1 V, and 0.7 V vs. CuCuSOt^ respectively). In addition, similar specimens, not coupled, were

also included in this study as controls which may or may not give an indication of other modes of failure such as stress corrosion cracking.

Table VII gives the average couple currents for specimens still buried

and the number of failures of similar specimens observed after exposure

for 2 years in the 6 soil environments.

Type 301 in the half-hard or full -hard condition was found to be

susceptible to cracking at the higher current densities. All of the Type

301 specimens coupled to magnesium had failed after exposure for 2 years

regardless of the soil environment in which they were buried. With a few exceptions, most of the Type 301 specimens coupled to zinc had also

failed while most of the specimens coupled to the carbon steel had not

failed. Similar uncoupled specimens were nearly completely resistant
-9-

to cracking in all of the soil environments (Table VI). There appears

to be a clear correlation between current density and susceptibility to

cracking of this alloy.

Alloys 18Cr-8Ni(N), 26Cr-lMo and 26Cr-6.5Ni appeared to be com- pletely resistant to cracking whether coupled to a dissimilar metal or not.

Stressed Stainless Steel Alloys (Non-Coupled) . The corrosion current for each of 10 different stainless steels was measured at approximately 4-month intervals over a period of 2 years. Four stressed specimens

of each material were evaluated at each site. The resulting average

current obtained for these stainless steels is shown in Table VIII.

Throughout the two years, fluctuations in corrosion occurred and are reflected in the table as a maximum and minimum corrosion current for

each type of material. The measured corrosion current gives an indication

of the degree of electrochemical dissolution occurring at the specimen.

This corrosion current will be correlated with the actual observed

corrosion when these specimens are recovered and evaluated.

D. SUMMARY

In order to evaluate more fully the corrosion and stress corrosion

behavior of stainless steels in soil environments, stressed and unstressed

stainless steels were buried in 6 different soils. Test specimens incorporated welds, crevices, galvanic couples, and specimens which had

been sensitized by heat treatment. The general corrosion behavior of

unstressed and non-gal vanically coupled specimens has been reported in

Part I [4] of this paper. This report (Part II) gives the results obtained

for non-galvanic coupled stressed specimens and galvanically coupled stressed

and unstressed specimens buried up to 2 years in the soils.

1. Non-Galvanic Coupled Stressed Materials . In general, the

corrosion behavior in the various soil environments was similar to that

observed in Part I of this paper.

The austenitic (300 series) alloys, with a few exceptions, ex- hibited good resistance to stress corrosion cracking in all of the soil

environments. One of the single U-bend Type 301 (half-hard) specimens

buried in the acid clay (Site C) had failed after exposure for 2 years.

Similarly one of the spot-welded double U-bend specimens buried in the

tidal marsh (Site G) for 2 years had also failed. Sensitization of

Type 301 (half-hard) induced failures in all of the soils, while

sensitization of Type 304 resulted in failures of specimens exposed at

Sites C and E (Coastal sand) only. No failures were observed on the Type

316 specimens buried in any of the soils for 2 years. Failure of the

materials noted above is attributed to stress corrosion cracking.

Of the 2 stressed Type 434 ferritic systems included in this

investigation, none had failed after exposure in the 6 soils for 2 years.

Similarly, there were no failures noted for any of the proprietary

(Alloys 18Cr-8Ni(N), 26Cr-6.5Ni, 26Cr-lMo, 18Cr-2Mo, and 20Cr-24Ni-6.5Mo)

stainless steels.
-10-

2. Galvanican.y Coupled Stressed and Unstressed Materials . There

was little or no apparent corrosion observed on the Type 304 alloy specimens coupled to copper after exposure for 2 years in 4 of the 6 soils.

Unstressed Type 409 coupled to copper was completely unaffected by

corrosion at Site B onlyo There was no apparent corrosion on any of

the unstressed Alloy 26Cr-6.5Ni specimens galvanically coupled to copper

and buried for 2 years in the various soil environments.

Of the stressed systems galvanically coupled to zinc, magnesium

or steel, there were no apparent failures of Type 304 or of Alloys

26Cr-lMo and 26Cr-6.5Ni in any of the soils. Type 301 in the half-hard

condition when coupled to zinc was immune to cracking at Site A. No

failures were observed on the Type 301 half-hard or full -hard specimens

coupled to steel and buried at Sites A, B, D, and E. Specimens of this

alloy in the half-hard condition had not failed after exposure for 2

years at Site G, but specimens in the full-hard condition exposed at

this site for 2 years had failed.

In general, although some failures apparently due to hydrogen

embri ttlement were noted on stressed specimens, there appeared to be

little or no appreciable degradation of the systems buried for 2 years

in the soils at Sites A, B, and D. Pitting and/or general corrosion was noted on many of the systems exposed at Sites C, E, and G.

3. Electrochemical Measurements . Based on electrochemical measurements obtained from specimens still buried in the various soils, the Type

304 alloy appeared to be cathodic to copper at Sites A, B, and C and anodic

to copper at Site G. At Sites D and E, it varied from specimen to specimen (being anodic on one and cathodic on another). Type 409 stainless

steel appeared to be predominantly anodic to copper at Sites A and B and anodic with relatively high corrosion currents at Sites C, E, and G.

At Site D it was variable and could be either anodic or cathodic to the

copper. Alloy 26Cr-6.5Ni was initially anodic to copper at Site B,

but had reversed in less than 4 months to being cathodic to copper.

At Site C the alloy was cathodic initially but became anodic to the

copper and remained that way. In general, at Sites E and G, the alloy

was cathodic to copper.
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REFERENCES

[1] Branch, H.C., Corrosion Resistant Materials for URD Equipment,

Materials Protection and Performance , 12 , 9-14 (March, 1973).

[2] Steinmetz, G.F. and Hoxie, E.G., A Field Test of Type 304 Stainless

Steel for Gas Service, Materials Protection and Performance , 12,

41-44 (September, 1973).

[3] Romanoff, M., Underground Corrosion (NBS Circular 579) U.S. Dept.

of Commerce Clearinghouse, PB 168 350 (1957) April.

[4] Gerhold, W.F., Iverson, W.P., Escalante, E., and Sanderson, B.T.;

The Corrosion and Stress Corrosion Behavior of Stainless Steel

Alloys in Soil Environments, Part I, General Corrosion (unpublished).

[5] Stern, M., and Geary, A.L., Electrochemical Polarization, I. A

Theoretical Analysis of the Shape of Polarization Curves, Journal

Electrochemical Society , 104, (1) 56-63 (1957).

[6] Stern, M., and Weisert, E.D., Experimental Observations on the

Relation between Polarization Resistance and Corrosion Rates,

Proceedings ASTM , 59, 1280-1291 (1959).

[7] Iverson, W.P., Tests in Soils, p. 588, Handbook on Corrosion Testing

and Evaluation , (W.H. Ailor, Ed.), Wiley, New York (1971).

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Table II. Stainless Steel Systems in Underground Corrosion Tests^^'

Bur i a

1

Stainless Spec

,

Passi vation° Spec.

oyi LcUl I CO 1 Steel rnirfin V^UIII A0( ^i7P* -J 1 L.XZ Trpatmpnt"^ 1 1 CO blllt- 1 1 1. Procedure Stressed * Coupled To

1 1 071 tO vi 1 riu OIICCL Shppt fft"xl?'M Al^ J T

II 10 L r ^ 11 y 3'

' „ II II XBW __

. 4

1, 20 Cr-24 Ni-6.5 Mo M II C

9

II II II s

' i

fiu

1' Ifi Tr-? Mn II II 7 I J / c 18 Cr-2 Mo (Nb) II II QO 1 Q71 II II g

II II XBW __

1 0' 26 Cr-6.5 Ni

II II IT1 1 1972 1ft 1 O fr-? \f\ ^ Mn\ \\i fNb) \ liU f H II XBW 1?1 £ Tube (2" 00x12") HW

14 1971 Composite A Sheet (8"xl2") __ __ 15 II

ifi II II II 17IV

II Of. pr-l Mn Tiihp (2" 00)(1?'M HW

T 18 ^ 1 o /I 1 y o II nn., t o ii \ ^1 1 /o UDX

1

d } HU

T

1 7

„ C-U 70 Cr-9d ^I~£.t Ni-fi 111 \J * -JR MnI t\J 1 1 /on Ariwi oii\ (7/8 00x12 ) OilCC L \ 1 A 1 ^ I HW J CM CO y^V" \ riu 21

,1 U

it 11 II 23 „ II II T u 94 II II II II s J UU

9'; II II II i 9R "l( II II II 97 II

1 <5 l^r-o IN 1 \ Vi}

11 II :

: 90 II II II (J

II CQ Li~U*9 I'll

II II IIu 33 II ?fi Tr-l Mn 11 II Zn 34 II II II 11 11u Mq1 ly 35 II II II M IIu Fe 36 II 26 Cr-6 Wl l^fa^J5 Ni111

II II II Zn

II II n

IIu Ma JO II II M n

IIu Fe 42 II ^ 11 II n Cu

50 1Q70 9(11

' JilCCL \0 Ate J 3 1

II 9h9 II II : 52 II ; 301

II M 53 II .11 II II s

0*T

" n II II ADn

EC. II II 11

' 90 II II. '- II II c

II II Tiihe 1 UUC I?" nnxi?"l V

1- UfA 1 C J

Lil.l / k \ 58 II 316 JIICCL Alt. J : 59 II II II II s 60 II 409 II II III

61 II II II II r

1^ 62 II II Tiihp 1 UUC (^\ 1 -1I/O/fi" nnyl \JUA 1 ?"l c. J HW ITT ill 63 II ill Tiihp 1 UDc diu." \ nnvi9"l i / o UUX

1

C } nrw III T T I 64 II ; 410 ' Sheet (8"xl2") III 65 II 430 11 11 II 66 II 11 M 67 II 301 Shppt M "k1 ?'M HH

:

II uo

II II II II tin 69 II r II II II nn • 0

i

UNUU 70 II M 11 II r n y

71 " II 11 II II FHr n 72 II 304 II : II I u 73 -

II II II II : hlll^ luu; 74 II li II II HH

75 ji II' II II . nn nun

76 II II II II co

^l n\ UU

77 II 316 II II IIu 78 II ii II 11 : vuu; 79 II II II, II c0

111! UU 80 II II II 1

1

u

81 II 11 , II II vuu; 82 II OU'l>

II _ii nn

:

IIu 83 II II II II nn

:

1

1

u Mnrig 84 It li II II MMnn

:

1

1

u re 85 II II II II rn J u Zn

86 II ' II II II FHr n

IIu MnPig 87 II ir II II r n

1

1

u re

88 II 304 II II u Zn 89 II II M II U Mg

90 II II M II U Fe

91 II II II II Cu

92 II 409 II II III Cu

* All sheet and tube specimens 0.064" thick.

+ All specimens 1n the annealed condition unless noted otherwise.

(a) Systems 1-19, 50-66, covered in this report.

(b) Welded with a full finish per ASTM Specification A249.
Table II. (Cont'd)

Key: S - Sensitized (by heating at 1200°F for 2 hours, followed by air cooling and descaling in sodium hydroxide);

XBW - Cross bead weld (specified to be done in accordance with Welding Research Council recommendations. On half

of these specimens, the welds were cleaned prior to exposure. The other half of the specimens were to be exposed "as welded.

HW - Heliarc weld, HFW - HFW High frequency weld;

C - Coated;

HH - Half hard;

FH - Full hard.

Key: — = Unstressed;

U = Single U-bend specimen;

UU = Double U-bend specimen, no spot weld;

(UU) = Double U-bend specimen joined by spot weld.

Passivation procedure:

I. 20 to 40% by volume of 67% nitric acid at 120-160°F for 20-30 minutes.

II. 20% by volume of 67% nitric acid plus 2-6% sodium dichromate at 110-140°F for 20-30 minutes.

III. 20 to 40% by volume of 67% nitric acid at 110-1 40°F for 20-30 minutes,

(g) Minimum specified concentration of acid, temperature and time for sensitized materials.

Table III. Sunmary of results obtained from visual examination of 1" x 12" stressed and unstressed specimens exposed for up to two years in various soil environments.

System Stainless

Steel Treatment Type of Specimen

Coupled Test Exposed 1 yr (a) Exposed 2 yrs (a) to Site Exposed surfaces Crevice areas Exposed surfaces Crevice areas

Exposed in 1970

67 Type 301

68 Type 301

69 Type 301

70 Type 301

71 Type 301

72 Type 304

73 Type 304

74 Type 304

Half -hard U

Half-hard (UU)

Half -hard UU

Full-hard U

Full-hard (UU)

75 Type 304

76 Type 304

77 Type 316

78 Type 316

(UU)

Half-hard U

Half-hard (UU)

UU

(UU)

N

N

N

N

N Et (sli)

N

N

N

N RS

N

N Et (sli)

Et (sev), P Et, P

N Et (sev)

N

N

N

N

N

N

N

N A (E)

N

N Et (sli), P

N

N

P (E)

N AT

P

NNEt

N

N

P

N

N

N

N

NEt

N

NN

NN

N

(E, W)

NIP A (E.mod), P

NIF

IP

N

N P,IP

N Et (sli). IP

P (E)

RS, IP Et (sli)

A (sev), P RS, P P, A, IP, RS

P, IP, RS

N

N

NNT

N

N N

N N

N N

N N

P (W) T, P (W, AW) A (sev), P (AW) A (E), P, IP

N

IP A (sev), P, IP

N

P, T, IP

P, IP

N

N

N

NT

P (F, E), A (E), IP

N

IF IP, A (E)

N

N

. . IE

N

N Et (sli)

M Et (sli)

Et (sli)

Et

Et (sli) Et (sli), P (E) Et (sli)

Et (sli)

N

N

NN

N

N

N

N

N

N

NN

N

Et (sli Et (sli Et (sli Et (sli

Et (sli A, P

N

N

N

N

N

IP

NNN

N

P, T, IP

Pf, A (^<;pvl, IP

N

M Et (sli)

NT

P, IP

Et (sli)

Et (sli) Et (sev) , P, IP

N H, A <E), P Et (sli), P, IP

NN

IF

N

N

N

N

N

N

NN P, IP

NN T (E), P NT

Et (sev)

RS

IF

P (E), Et (sli)

RS, B], IP RS, P, IP A (sev), P, IP

NIR

P (AW)

N P, Et, RS., T P, IP, A (mod)

N

N P. T

N RS,

P, IP,

>i IP

P, Et, T

N

P P, IP, A

Et (sli)

Et (sli), IP A (sev), P, IP

N Et (mod) Et (sli), P, IP

NN

IF

N

N

N
Table III. (cont'd.)

Stainless Treatment Type of Coupled Test Exposed 1 yr (a) Exoosed 2 vrs (a) Steel c_..._.- ^- ^ _ , , - . _

>- J V /

Type 316 S UU — A N N Et (sli) N

N N . N

Type 434 — u a N — n

N

P (F, E), IP

N P, T, IP

P

Type 434 -- (UU) —AN N N P, T

N N N N P (E) P i£)

N N IF A P, T P, Et (sli) A P (F, E), A (E), IP P, IP Type 301 Half-hard U Zn A N — N

N Et (sli), P, IP

RS Et (sli)

P (E), IP

Type 301 Half-hard U Mg A N — N

N

Trea tment Type of Coupl Gd Test Ex pos ed Sp6C i rn6n to Si te Exposed surface

s UU N g Et (sli)

C Et (sli), A (E)

D Et (sli)

A \t) TP Ft ^ cl -i 1

u /\ N B N

- - C A (E)

D N

E P, A (E)

G IP

/ 1 II 1 \ (UU) "" A N

B N

C N D IF

E IF G P. A (E)

nd 1 T — Md 1

U

y Zn N

g N

C N

D N

E A (E)

G Et (sli), IP

Hal f-hard y Mg /\ N

B N

C N D N

N Q IP

Half-hard u Steel A NIL

' "c IV

D H

g N

r u 1 1 rid I u Zn N

g n C N

D N

t N G P , E

Full r U 1 1 -rid harriiQ y Mg nM N

B N c N

D N

E' N G E

Fill r U 1 1

1 -hariH -iidru 1

1

U btee 1 A N B N C N

D N

Nn G P

M

u £.n A N

B N

c N D N

E N

G N

u Mnrng

AM n

B N

C IF

D N

E N G Et (sli), IP

U steel A N

B N C IP, Et (sli)

D N

Crevice areas Exposed surfaces Crevice areas

N A (E) N

N N RS

^ A (E, sev), P A (E), Et (sli)

N IP

P, IP, Et (sli)

Et (sli)

Et (sli), IP

P, IP Type 301 Hal f-hard U Steel AN— N

IP, P, Et (mod)

N IF, IP

P

Type 301 Full -hard U Zn A N — Et (sli)

IP (E)

P (F, E), TP, Et (sli)

Et (sli) Et (mod)

P (F,E), IP

Type 301 Full -hard U Mg A n

' — N

N Et (sli), P (F, E), IP

N IF

P (F, E), IP (F, E)

Type 301 Full -hard U Steel A N — Et (sli), P

N Et (sli), P, IP

N Et (sli)

P, IP

Type 304 - U Zn A N - N

N

P (E), IP, RS

NN Et (mod), P, IP Type 304 ~ U Mg A N ~ N

N P, IP

N

N P, IP, Et (sli) Type 304 -- U Steel AN — N

N

P (F, E), IP

N
Table III. (cont'd.)

System Stainless Treatment Type of Coupled Test Exposed 1 yr (a) Exposed 2 yrs (a) Steel Specimen to Site Exposed surfaces Crevice areas Exposed surfaces Crevice areas

91 Type 304 — Unstressed Cu

92 Type 409 — Unstressed Cu

Exposed in 1971

2U 26 Cr- 1 Mo — (UU)

26 Cr- 1 Mo

A N N

B N N

C IP -- N

D Et (sli), IP

E N Et, A

G Et (sev), P P (E)

A Et, P - Et (sli). A, P (sev

B Et — IF

C H (E) , Et P Ft (<ifiv) TP

D IP — P, IP

E A (E) -- A (sev), H G A (sev) -- P (E), Et (sli), IP

A N P fi B N N H C IP IP N n N P, IP N

E P N N G N N N

A N N

B N N C N RS, IF

D N N

E N N G N N

IF, RS, IP

N

IP

22 20 Cr-24 Ni-6.5 Mo — (UU) — A

BC

D

EG

23 20 Cr-24 Ni-6.5 Mo — U — A

BC

D

EG

24 20 Cr-24 Ni-6.5 Mo S UU — A

BC

D

EG

25 18 Cr-2 Ho — (UU) — A

BC

D

EG

26 18 Cr-2 Mo — U — A

B

CD

E .G

27 18Cr-8Ni(N) — (UU) — A

B

C

D

EG

28 l8Cr-8N1(N) — U ~ A

6C

D

EG

N N N N

N IP IF N

N N N RS IF

N N N 'n N N N N

N N RS RS

N N

N N

N N

N N

N N

N N

N N N RS, IF

N N N N Et (sli) Et (sli) IP, RS Et (sli)

N N N N

IP IP N N IP, Et (sli) P, IP, Et Et (sli), IP N

N N IF IF

N RS (AW) N N

N N N IF, RS

P, T T N IF, RS (AW)

IF IF IF, IP N P, IP P, IP, A (AW) RS N

N N N RS, IP (E) N N

IP RS N

N N N

N N N P, IP N N

N N N N

N N N N P, IP RS RS IP

N N N H

IF IF IF RS

N N N RS (AW)

N N

N N IP IF

N N

N N P, IP P (E)
Table III. (cont'd.)

System Stainless Treatment Type of Coupled Test Exposed 1 yr (a) Exposed 2 yrs (a) Steel Specimen to Site Exposed surfaces Crevice areas Exposed surfaces Crevice areas

30 26 Cr-6.5 Ni — U

33 26 Cr-1 Ho — U Zn

34 26 Cr-1 Mo — U Mg

35 26 Cr-1 Mo -- U Steel

AN „ N

B IP (E) — N

C IP -- P, IP D N „ N E - N - - IF G V, IP — N AN ~ N

B N — N

C P (F, E). IP — P 0ENRS, IP ~ RS — N G P (E) ~ P (E), RS AN — N

B N — N C IP -- Bl, RS

D N ~ RS

E Bl — Bl G P. IP — RS, IP AN — Et (sli)

B N — N

C ET (sli), IP - Et, P, IP

DENN — N — N G IF — IP, RS

36 26 Cr-6.5 Ni — U Zn

37 26 Cr-6.5 Ni — U Mg

38 26)Cr-6.5 Ni — U Steel

42 26 Cr-6.5 Ni — Unstressed Cu

AN N B N — N C IP — Et, P, IP

DENN — N - Et (sli)

G P (F, E), IP - p (E), IP, Et (sli)

A Et (sli) ~ N

B N — N

C P (F, E), IP — Bl, P, IP

D N — N

E IP — N G P (F, E), IP — P, IP

ABPP N -. N C P (F, E), IP — P, IP

DENN — N — P G P (F, E), IP — P, IP, RS

A Et (sli), A (E) - N

B IP — N*

C P, IP — N

DENN — N — N G P, IP — N

* One specimen not recovered

(a) Abbreviations used:

A- general corrosion attack F- face

AW- adjacent to weld IF- irridescent film

E- edge IP- incipient pitting

Et- etch N- no apparent corrosion

P- pitting corrosion sli- slight

RS- rust stain T- tunneling corrosion

m- moderate W- weld

sev- severe
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Figure 1. Die for forming U-bend specimens.
Figure 2. Double or crevice U-bend specimen for underground

exposure.

-I -ijL- I i_ I i —J I 100 200 300 400 500 600 70

TIME, DAYS

Figure 4. Type 304 stainless steel (91-10)-copper couple vs. time.
|nD)-ll4A IHcIV. 7-7JI

U.S. DEPT. CF CCM'.'. BIBLIOGRAPHIC 0A7A

SHFRT

1. IH :il.U .\ 1 10.\ (ti< Kl :'C)K1 NO. NBSIR 74-4342. Cmv't Ac CIS.Mini No.

3. Kcc ipicni *s Accession \'o.

4. Tl 1 l.i; .\.M) M hill 1.1. The Corrosion and Stress Corrosion Behavior of Selected

Stainless Steels in Soil Environments. Part II. Stress

Corrosion and Electrochemical Behavior.

J. ruol iL at iL^n U-Ul* May, 1974

6. Ptrlorming Organization Co^c

r

7. At riic>K..-;> W. F. Gerhold, E. Escalante, Vi. P. Iverson, and B. T. Sandersor8. I'orforminj; (.>r^an. Report No.

1

:

li

i. PKKKOK.Ml.Ni; OKt...\.\l/..A I'iON N.^MH AMI .M)nKl-:SS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON. D.C. 20234

10. Project/ Ta.sk 'Aork L'nit No. 3120362

11, Contracc Cirant .\o.

1

2. Spon.-iormi l~>r^.'.:ii/..uu':i N.ini- .uui ( orrrUtt- .AJJres.-; (Street. City, Slate, ZIP)

Committee of Stainless Steel Producers

American Iron and Steel Institute

150 East 42nd Street

New York, New York 10017

13« Type of Report ^'^i PcTiod Covered jwQ-Year

j Progress Rsoort | 14. Sponsoriiii; Ai;(.ni.> (..o-li..

15. SUPPLi;.Mi:N l AK't NOI LS

16. .\nSl R.ACl (A 200-iVord or /ess tactual iL-.-n/rary ot west sigriificant mlonnation. If documerjt includes a signiticont

bibliography or literature survey, mention it here.)

Corrosion data is presented for uncoupled stressed and galvanlcally coupled

stressed and unstressed stainless steels exposed for up to two years in various

soil environments . Systems studied were austenitic (300 series) alloys,

ferritic and martensitic (400 series) alloys, and proprietary (major alloying

constituents Cr or Cr-Mi) alloys. Test materials included specimens in the

annealed, half-hard, full-hard, or sensitized condition. Some test specimens

incorporated welds and crevices. Galvanically coupled stressed specimens were coupled to steel, zinc, or magnesium wnile unstressed specimens v/ere couplea

to copper. Corrosion rate data ootained by electrochemical means is pre.senLed

for comparison with results obtained by visual and weight loss determinations.

17. KhY 'iORDS (six to f.velve t-nfries; alphabetical order; capitalize only the first letter of the first key word unless a proper name: separored b\' semicolons

)

Stainless steels; stress corrosion behavior; electrochemical behavior; soil

environments; field tests; galvanic corrosion.

18. AVAlLAniLITY | Unlimited

For Otficijl Disctibucion. Do .Not Release to NTIS

Q_ Otvler From Sup. of Doc, U.S. Government Printing Olfice

ttashincton. D.C. 20 lOJ. SO T.u. N... ("M

1 Order From N.itional Technical Inlormation Service (NTIS)

Sprinj;licld. Vir^-inia JJl'l

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UNCL.\SSIFIED

21. NO. OF PAGES

47

20. SLCURITY C LASS

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UNCLASSiriLO

22. Price

USCOMV-OC .>.Jv.4i.P-4
i
a stress

corrosioi ^ on the corrosion ana

^jerson.

progress J^^^^nte,

E.lverson, W. P-S

Gertiold-W^F-^Esc^g^ ^^^^ Sesearc. f-;;porto7 4«^^^

nbsir74-484

lun 17, 2015
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