Corrosion of Incoloy 800 and Nickel Base Alloy Weldments in Steam

Tests provide useful data from welded combinations of five base metals and four filler metals

BY J. P. HAMMOND, P. PATRIARCA, G. M. SLAUGHTER AND W. A. MAXWELL

ABSTRACT. The cor ros ion char­acteristics of similar and dissimilar meta| weldments in Incoloy 800 and various nickel base alloys for use in advanced gas-cooled nuclear steam generators were tested in isothermal exposures in dynamic steam at 1100 and.1200 F (595 and 650 C) at 900 psi pressure for periods to 16,000 h (2 years). Cursory examinations were made on some weldment spec­imens after exposure to 27,000 h. Twelve alloy combinations, in which base metals having good high tem­perature properties (Inconel 625, Has­telloy X, and IN 102) were joined to Incoloy 800 (a material having attrac­tive intermediate temperature prop­erties) and to themselves, were exam­ined in the surface ground condition. Three high temperature alloys and In­conel 82 were employed as filler met­als. To assess the effects of surface condition, the dissimilar metal weld­ments and non-welded specimens in the various base metals were also tested after being electropolished to eliminate worked surfaces.

General corrosion was determined by weight gain, weight loss, and scale t h i c k n e s s m e a s u r e m e n t s , a n d preferential attack in fusion line areas was assessed by meta l lographic means. Projected long t ime corro­sion amounts were very small (<11 mg/cm 2 in 20 years) for all the weld-

J. P. HAMMOND. P. PATRIARCA and G. M. SLAUGHTER are associated with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee. W. A. MAXWELL is with Southern Nuclear Engineering, Inc., Dunedin. Florida.

ments tested except those in Inconel 600, and for this weldment the pro­jected corrosion was only 43 mg/cm 2

after 20 years. No evidence of ag­gravated attack at fusion line areas was disclosed. These findings appear to be applicable to weldments in the same alloys exposed to steam at lower temperatures.

Introduction

In steam generators for advanced gas-cooled reaptors, certain ma­terials may be warranted for high tem­perature regions, others for inter­mediate temperatures, and still others for lower temperatures. In any case, many thousands of welds (both tube-to-tube and tube-to-tube-sheet) will be found in a typical steam generator system. Thus, dissimilar and similar metal welds jo in ing var ious base metals will be subjected to the steam c o o l a n t over a r ange of t e m ­peratures. This paper reports the

results of corros ion studies con­ducted on the weldments for the high and intermediate temperature re­gions. The alloys involved are all nickel base or highly alloyed with nickel. Test conditions consisted of i so the rma l exposu res to super ­heated steam at 1100 and 1200 F (595 and 650 C) at 900 psi pressure for periods to 16,000 h (about 2 years) and longer. Similar studies have been made on stPam generator materials in the wrought form,1 5 but the present work marks the first investigation of weldments in these materials with their compositional variations across weld regions. Of special concern was the prospect of aggravated attack at fusion line areas, especially in the dis­similar metal welds.

Since the test procedures em­ployed constitute an aggravated test for systems operating at lower tem­peratures, the findings appear to have application to a wide variety of other steam generation systems.

Table 1 1200 F

Code

A9 A13 A12 A18 A19 A20 A5 A6 A8 A7 A2 A3

— Alloy (595 and

Combinations Tested for C 650 C)

Base metal

Inconel 625 Inconel 625 Inconel 625 IN 102 IN 102 IN 102 Hastelloy X Hastelloy X Hastelloy X Hastelloy X Incoloy 800 Inconel 600

orrosion Resistance

Base metal

Inconel 625 Incoloy 800 Incoloy 800 IN 102 Incoloy 800 Incoloy 800 Hastelloy X Incoloy 800 Incoloy 800 Incoloy 800 Incoloy 800 Inconel 600

to Steam at 1100 and

Filler metal

Inconel 625 Inconel 625 Inconel 82 IN 102 IN 102 Inconel 82 Hastelloy X Hastelloy X Hastelloy W Inconel 82 Inconel 82 Inconel 82

268-s I J U N E 1 9 7 3

Table 2 — Chemical Analyses (a) of Base Metal and Filler Metal Alloys

Ele­ment

Ni Cr Fe Mo

Mb + Ta

W Al Ti

Cu Co

C Mn S P Si

Inconel 625

62.51 21.92

2.31 9.07 3.53

— 0.20 0.25 0.01

— 0.02 0.01 0.007

— 0.14

Base metals

Hast­elloy X

Bal 21.75 18.44 8.86

— 0.44

— — —

1.59

0.13 0.43 0.006 0.011 0.33

IN 1 0 2 (c )

68.01 15.05 6.62 3.04 3.15

3.03 0.47 0.60

— —

0.06 0.14 0.005 0.002 0.17

Incoloy 800

31.63 20.06 46.59

— — — — —

0.48

— 0.04 0.83 0.007

— 0.34

Content (wt%)

Inconel 600

76.48 15.43 7.35

— — — — —

0.18

— 0.06 0.21 0.007

— 0.26

Inconel 625

62.90 21.49

2.49 8.84 3.55

— 0.19 0.27 0.03

— 0.03 0.01 0.008

— 0.17

Filler

Hast­elloy X

Bal 22.10 17.84 9.20

— 0.48 — — —

0.95

0.07 0.74 0.004 0.018 0.74

metals <b>

Hast­elloy Wd>

Bal 5.64 5.00

24.32

—

— —

0.01

0.01 0.51 0.005 0.006 0.25

Inconel 82

73.13 20.37

0.35 — 2.50

0.03 0.40 0.03 —

0.02 2.96 0.007

— 0.16

(a) Vendor analyses. (b) Includes IN 102 filler metal, which was prepared from the same heat of the base i (c) Plus 0.024 Zr. 0.0066 B. and 0.02 Mg. (d) Plus 0.29 V.

letal alloy listed.

Materials

The dissimilar metal welds of this study join base metals having good high temperature properties (i.e., In­conel 625, Hastelloy X, and IN 102) to Incoloy 800, a material with attractive i n te rmed ia te t e m p e r a t u r e p r o p ­erties. Similar metal welds in each of these alloys are also included along with one in Inconel 600 for com­parison. Recommended welding filler metals were used for each of the ma­terials combinations. The weldments investigated are listed in Table 1. The chemical analyses of the base metal plates and filler metal alloys are given in Table 2.

Although the welds in steam gen­erators will consist of tube-to-tube and tube- to- tube-sheet jo ints, we used butt welds in plates for economy of fabrication and testing. However, the root passes of welds* were per­formed in such a way as to approxi­mate the conditions of alloying be­tween base metal and filler metal in the steam generator welds.

The weldments were fabricated from 12 X 6 X Vi in. plates by the gas tungsten-arc process, and Fig. 1 in­d i c a t e s the c o n f i g u r a t i o n s and welding parameters. The plates were furnished in the hot rolled, descaled, and annealed condit ion, and the filler

"In steam generators the root or bore side of welds is exposed to the steam.

WELDING PARAMETERS AD­JUSTED TO GIVE 50 ± 10 % DILUTION FACTOR

SUBSEQUENT PASSES CONDUCTED AT 30,000 joules per in

GAS-LENS-CONTAINING WELDING TORCH EQUIPPED WITH PROTECTIVE GAS TRAILER

BACKING PLATE PROVIDING BOTTOM-SIDE GAS SHIELDING FOR ROOT PASS

Fig. 1 — Procedure for preparing steam generator alloy weldments for steam corrosion testing. Specimens were welded by the gas tungsten-arc process, and protection at the root was obtained by the arrangement shown. After deposition of the root pass, the plate was welded to a 1 'A in. thick steel plate to provide high restraint for subsequent passes

W E L D I N G R E S E A R C H S U P P L E M E N T ! 269-s

Fig. 2 — Corrosion test specimens (weldment A12 of Table 1): (left) as ground, (middle) electropolished, and (right) electropolished and exposed 2000 h in steam at 1200 F. In­coloy 800 is the lower base metal in the photograph

appreciable attack at grain boun­daries. Figure 2 illustrates rep­resentative corrosion specimens in the as-ground, electropolished, and steam-corroded states.

Steam Corrosion Facility

The design of the overall steam corrosion loop is shown schematically in Fig. 3. The unit is fabricated of type 316 stainless steel and incorporates two test autoclaves. These have an in­side diameter of 1.9 in. and 4 linear feet of useful working space, con­trollable within ±35 F of operating temperature. The autoclaves were cooled to room temperature at 1000 h intervals, irrespective of whether any specimens were re­moved, to subject specimens inter­mittently to saturated steam. Dis­tinguishing features of this loop are economy of corrosion testing and the use of actual plant steam. The loop was operated in the Bartow Plant of the Florida Power Corporation on steam taken directly from a steam generator superheater. Southern Nu­clear Engineering operated the test loop under subcontract to Oak Ridge National Laboratory.

The steam was of high commercial quality. Figure 4 illustrates the water and steam control practice at Bar-tow, and Table 3 lists allowable ranges of impurities and results of random chemical analyses made on the boiler water and steam. The hyd raz ine added to the de-mineralizer (Table 4) is for removing oxygen, and the trisodium phosphate added to the boiler is for controlling the pH. Chemical analyses of the saturated steam consistently showed the chloride ion below the minimum chemically detectable amount, 0.5 ppm, and oxygen in the feed water never exceeded 1 ppm. Steam flowed through the loaded loop at a velocity of 5 fps and 900 psi (65 kg/cm2) pres­sure.

metals as 1/16 in. diam wire in the cold drawn, annealed, and cleaned condition. Weldments were dye pene­trant tested after deposition of the root passes and were examined by radiographic and fluorescent dye penetrant methods after completion.

Strips Vs in. thick were cut from the weldments to prepare the corrosion specimens. These were taken in a plane normal to the welding direc­tion, the long axis of the strip cor­responding to the plate rolling direc­tion. Corrosion specimens measuring 2% X Vz x 1/16 in. (with weld in cen­ter) were then machined from these strips, and 3/16 in. diam holes were drilled 7/32 in. from the ends for mounting.

Corrosion characteristics were ex­amined for two separate surface con­ditions: (1) ground on a 100 mesh grit belt and (2) ground and then electro­polished to remove 0.002 in. of metal from the surface. The electro­polishing removed material that had been heavily cold worked by the prior grinding operation and exposed the underlying weld or hot rolled metal structure of the plate.

We electropolished using a bath containing 10 parts acetic acid and 1 part perchloric acid at 50 to 60 V, maintaining the temperature below 40 C. A metallographic examination of the weld deposits and base metals revealed that electropol ishing produced mirror-type finishes with no

Experimental Procedure

We studied general corrosion of weldments in the as-ground condi­tion by determining weight gained during corrosion and by periodically examining scale thickness. Weight gains were measured on duplicate specimens after 1000, 2000, 3000, 4000, 6000, 8000, 12,000, and 16,000 h, at both 1100 and 1200 F. Metallographic observations were made after 2000, 4000, 8000, and 16,000 h of test, and, for a limited number of weldments, after 27,000 h. Scale thicknesses were recorded after 4000 and 8000 h. The amount and character of scaling was metal­lographically assessed in both the base metal and weld deposit, with

270-s I JUNE 197 3

particular emphasis being placed on fusion lines and the root pass.

To assess the effects of surface condition on corrosion, the dissimilar metal weldments in the electro­polished condition were exposed for periods of 4000 and 8000 h. Scaling characteristics and thicknesses of the base metals and weld deposits were compared metallographically with those of specimens in the ground condition. Further, a series of base metal specimens (nonwelded) in both the ground and electropolished con­ditions were examined by the weight-gain method in duplicate for periods of 1000, 2000, 4000, 6000, 8000, 10,-000, 12,000, and 14,000 h at 1200 F.

The propensity of scales to flaking was assessed for the .alloys rep­resented in the weldments, both for the ground and electropolished con­ditions. Base metal specimens were exposed for 14,000 h at 1200 F, and their corrosion was measured by both the weight-gain (oxygen) and metal-consumed (difference be­tween the original and descaled weights) techniques. These- base metal specimens were exposed alongside the weldment specimens and handled similarly at the same in­te rva ls d u r i n g ' t h e repea ted weighings. Appropriate analysis of the two kinds of weight change measurements determined whether scale was lost during corrosion testing and the extent of loss.

Specimens were descaled by im­mersing for 2 h in a boiling solution of 20 wt % NaOH and 3 w t 0 / KMn04 in water.1' 3 Specimens were taken from the solution at 15 min intervals to re­move digested oxide with a soft-rubber eraser. Control specimens of the uncorroded base metals showed practically no loss of metal for the same time in the solution. Relative ease of digestion of the oxide depends upon the reaction of the solution with chromium in the scale.1

SCHEMATIC PIPING DIAGRAM

mO'0°F AUTOCLAVE

ENLARGED CROSS SECTION

HEATERS

STEAM

AUTOCLAVES

Fig. 3 —- High-pressure steam corrosion loop for operation at 1100 and 1200 F

Results

The validity of corrosion findings based on weight-gain determinations depends upon the test specimens re­taining their corrosion products dur­ing test, a situation not always safely assumed until proven. Where the scale sporadically flakes off, the weight-gain method is invalid and the weight- loss or scale thickness methods are generally considered. The analysis involving the com­parison of total corrosion determined by weight gain with that assessed by weight loss indicated that corrosion products were well retained in the cases of all alloys examined except possibly Inconel 600. The findings on the tenacity of scales of the different alloys are given subsequently.

FEED WATER

DAILY CHEMICAL ANALYSES OF WATER

CHEMICAL ANALYSES OF SATURATED STEAM

1

DEMINERALIZER

ADD: 1 HYDRAZINE

2 MORPHOLINE

WATER —•-

)

BOILER

ADD: 1 SODIUM HYDRO

STEAM

IDE 2 SODIUM SULPHITE

3 TRISODIUM PHO SPHATE

T

1

1

SUPERHEATER

5 < UJ

U)

ORNL-SNE CORROSION LOOP

Fig. 4 — Water and steam control at Bartow Plant, Florida Power Corporation

WELDING RESEARCH S U P P L E M E N T ! 271-s

Weight-Gain Studies

The weight-gain data for the v a r i o u s a s - g r o u n d w e l d m e n t specimens showed an initially high rate of corros ion that decreased gradually to a lower and seemingly constant rate during the first 1000 or 2000 h. Such a rate law transition is common in steam corrosion of high temperature alloys and has been reported for most of the base metals represented here in wrought form.1 If weight-change data are obtained for periods sufficiently beyond the transi­tion, then the amount of total corro­sion in the linear range may be ex­pressed by the equation

AW AWn + K,T

where AW = total weight gained (ox­

ygen), mg/dm 2 , AWn = extrapolated intercept (T =

0), mg/dm 2 , K| = l i n e a r r a t e c o n s t a n t ,

m g / d m 2 - 1 0 0 0 h, T = exposure t ime, 1000 h. The corrosion results are shown in

Figs. 5 and 6 for the ground similar metal weldments at 1100 and 1200 F and in Figs. 7 and 8 for the ground dissimi lar metal weldments . The linear portion of the curves was es­tablished from corrosion data by the least squares method. Rather than fit curves of a parabolic form to the short-t ime data (below 3000 h), the straight lines were extrapolated to zero t ime to establish the intercepts.

Numerical values for the inter­cepts and slopes of the similar metal curves (Figs. 5 and 6) are given in Table 4. To better grasp the signifi­cance of these data, the corrosion that would occur in 20 years and dis­tance penetrated into the weldment are also presented in this table. These ca lcu la t i ons were based on the following simplifying assumptions: (1) the surface area of the welded specimen is 23% weld deposit; (2) the proportions of metallic elements in scales are the same as those in underlying metal alloys; and (3) the oxides formed are NiO, Fe203, and F304 at a 1-to-1 ratio, Cr203 , Mo203 , NbP0.„ and W?03 . The information on the oxides formed was taken from the work of Wozaldo and Pearl.1

Observe in Table 4 that the an­ticipated corrosion in 20 years is relatively low for all weldments. For all three of the high temperature weld­ments (A9. A5, and A18), penetration into the metal is only 0.5 mil or less. The highest penetration is for the In­conel 600 weldment, but even here the penetration is only about 2 mils (at 1200 F) after 20 years.

Noteworthy features of the plots for the similar metal weldments (Figs. 5 and 6) were the very low corrosion rates for the Inconel 625 (A9) and Hastelloy X (A5) weldments as con­trasted to higher rates for Inconel 600 welded with Inconel 82 (A3). The con­stant corrosion rates on all weld­ments were greater at 1200 F than at 1100 F except for the IN 102 weld-

Table 3 — Allowable Ranges of Impurities and Chemical Analyses of Boiler Water and Steam at Bartow Plant

PH Impurities, ppm:

Na2SO„ NaCI P04

Na?S04

Si02

NH3

Cl Conductance, micromhos Total dissolved solids, ppm

Boiler water

Allowable ranges of concentrations

10.1 — 10.7

0.6—1.0 3—10 1.0—5.0 5—25 0.12—0.20

30-50

Chemical analyses at random dates

pH 10.7 10.7 10.3 Impurities, ppm:

Na2SO, 1.0 0.6 0.7 NaCI 4 3 4 P04 5 2 3 Na2S04 8 13 14 Si02 0.14 0.13 0.15 NH3 — — —

Conductance, micromhos — — — Total dissolved solids, ppm — — —

Saturated steam

8.8—9.0

0.005 max 1.0 max 0.5 max 2.2—4.5 0.5-1.0

0 0.153 4.5 0.7

8.9

0 0.180 4.0 0.7

ment (A18), which was lower at the higher temperature. This reversal is consistent with metallographic results presented later, since the IN 102 specimens usually exhibited larger amounts of total scale after the 595 C exposures than after 650 C. Note also that the level and rate of corrosion of the Incoloy 800 weldment (A2) in­creased substantially from 1100 to 1200 F.

The foregoing trends for the similar metal weldments (Figs. 5 and 6) cor­relate with the results for the dissim­ilar metal weldments (Figs. 7 and 8) and can be used to explain the close bracketing of curves for the 1200 F exposure and their separation into two groups at 1100 F.

Metallographic Examinations of Scale Thickness and Localized Corrosion

The thickness of scales formed on the different alloys were measured two ways, similar to the method of Eberle.'The scales were observed to have two principal components: first, a continuous surface layer of gen­erally uniform thickness and, second, protrusions that extended into the substrate. These protrusions gen­erally consisted of in tergranular p e n e t r a t i o n s , t r a n s g r a n u l a r Widmanstatten-type formations, or sporadic pit-type (bulky) formations. Eberle3 indicates that the surface scales that form on many ferritic, austenitic, and high nickel alloys gen­erally consist of two distinct layers. In the present case, surface scales sometimes contained more than two phases, usually indistinguishable as layers, and consequently the surface scale was considered as an integral unit.

The integrated surface layer and the total depth penetrated (com­prising both surface layer and pro­trusions) were measured separately. Both measurements were generally made in concert, with care taken to make the latter measurement where the protrusion extended deepest for a part icular area. The scale th ick­nesses thus defined are given for the various base metal and filler metal materials as a function of temper­ature, time of exposure, and surface finish in Table 5.

Because the surface layer often was not very uniform in thickness, nine or more readings were made in establishing thickness values. Small mushrooming growths seemingly fed from superficial inclusions appeared in some of the scales, but these were considered nontypical and were el im­inated from measurements.

The characteristics of the individ­ual scales that formed on steam gen­erator alloy weldments are illustrated in typical photomicrographs in Figs. 9 through 13. These micrographs, as

272 -s I J U N E 1 9 7 3

^ -

— ? fo=? / /

3£1_

rfi/ f ( 0 /

,^AA jjiiS-^-

„ j INCONO-JS. BOOj l i ^—^~

1 y ^ I N C O N E L 625

WITH ITSELF

/ i3

^ ^ — • A18

_____

HASTELLOY X WITH ITSELF

A2

A9 A5

^ - ? /

/ /

r_~*̂ • = : = = :

7 «A /

( 1

N 102 WITH ITSELF

/ A 3

HASTELLOY X WITH ITSELF -

T T T T ^ l l ^

A2

A5

A18 —

A9

F/g. 5 — Corrosion of ground similar metal weldments in super­heated steam at 1100 F. The curves are a best fit to a linear rate law. Specimen surface area was 20 cm2

Fig. 6 — Corrosion of ground similar metal weldments in super­heated steam at 1200 F. The curves are a best fit to a linear rate law. Specimen surface area was 20 cm2

well as scale thickness measure­ments (Table 5), were taken with the field of view parallel to the grinding direction (longitudinal axis of spec­imen).

According to the metallographic in­formation, Incoloy 800 displayed vast­ly greater corrosion resistance in the ground condition than in the electro­polished, whereas Inconel 625, Hastelloy X, and IN 102 appeared to be somewhat better in the electro­polished condition. Inconel 600 ap­peared to have moderately superior corrosion resistance in the ground condition than in the electropolished.

Figure 9 illustrates the scales form­ed on weldment A8 (Hastelloy X weld­ed to Incoloy 800 with Hastelloy W filler metal) after 4000 h exposure at 1200 F for the ground, and electro­polished conditions. Figure 10 sim­ilarly shows the scales on weldment A13 (Inconel 625 welded to Incoloy 800 with Inconel 625 filler metal) after 8000 h at the same temperature. Con­siderably more scale formed on In­coloy 800 in 8000 h than in 4000 h.

-Not only was the amount of scale formed on this alloy vastly greater when it had been electropolished rather than ground, but the character of the scale was different. The pro­trusions into the base metal were bulky and more fully developed for the electropolished condition, and four separate oxide phases were readily noted.

The scales on the Hastelloy W filler metal of weldment A8 as ground has a protrusion component of thin Wid-

o 4

x • - « M - rr—

A 20 AI9

A8 A12

-7;A6 XA7

A13

8 10

TIME (hr) 12 14 16 (x10 5 )

Fig. 7 — Corrosion of ground dissimilar metal weldments in superheated steam at 1100 F. The curves are a best fit to a linear rate law. Specimens were 20 cm2 in surface area and are identified in Table 1

manstatten platelets extending to considerable depths into the sub­strate. This scale on the electropol­ished specimen was considerably greater in amount, and its compo­nent within the substrate appeared to have filled out. (See Table 5 and Fig. 9-)

Inconel 625, Hastelloy X, and IN 102 were used both as base metals and as filler metals. Very little difference was noted between the scales formed on these alloys in either use. (See appearance of Inconel 625 as filler metal and plate in Fig. 10; also com­pare scale thicknesses given in Table 5.) Figure 11 compares the scales formed on Hastelloy X as base metal

and filler metal after 800 h at 1200 F. Again, little difference was noted be­tween the scale on base metal and on weld deposit.

Figure 12 illustrates the scales that formed on weldment A20 (IN 102 welded to Incoloy 800 with Inconel 82) after exposure to steam for 8000 h at 1200 F. The IN 102 base metal show­ed more scale (as surface layer plus pit-type substrate attack) formed at 1100 F than at 1200 F, agreeing with the weight-gain corrosion results (weldment A18 of Table 4 and Figs. 5 and 6). The scales formed on IN 102 as filler metal were thin and reason­ably uniform.

The character of the scale formed

WELDING RESEARCH S U P PLE M E NT | 273-s

12

10

<

x a

S 4

1%^' s?^ 5 * *

A12 A13 A6 A19

^ A 8 , A2 XA7

8 10

TIME (hr)

12 14 16 (xlO5)

Fig. 8 — Corrosion of ground, dissimilar metal weldments in superheated steam at 1200 F. The curves are a best fit to a linear rate law. Specimens were 20 cm2 in surface area and are identified in Table 1

ponent of this scale was clearly inter­granular, extending inward to a sub­stantial depth.

We thoroughly examined fusion lines and adjacent regions on the var­ious weldments and noted no evi­dence of aggravated corrosive attack. The scale that formed on the root pass of the weld deposits usually was similar to that associated with the re­mainder of the weld metal. The transi­tion in scale microstructure from base metal to filler metal after 2000 h at 1100 F was hardly discernible in some, instances. With longer exposures, scale microstructures became dis­tinctly different, but the transition from one scale structure to the next generally was gradual.

Specimens of weldments A2, A3 (Incoloy 800 and Inconel 600, respec­tively, welded with Inconel 82), and A12 (Inconel 625 welded to Incoloy 800 with Inconel 82) were examined after a total exposure of 27,000 h at 1100 and 1200 F. No evidence of serious aggravated attack at fusion line areas was revealed.

on Inconel 82 filler metal at 1100 and 1200 F was similar, although the amounts formed at these two tem­peratures appeared to be somewhat less when the finish was electropol­ished than when ground (Table 5). The scale formed on Incoloy 800 at 1100 and 1200 F was somewhat dif­ferent. The layer and protrusion com­ponents of the scale formed at the higher temperature were more fully developed (Fig. 12).

The scale formed on Inconel 600 base metal, as ground and electro­polished, after 8000 h at 1200 F is shown in Fig. 13. The scale shown is characteristic of the scales formed on this alloy at both temperatures. Mea­suring the integrated surface scale on this alloy was difficult since it con­tained three separate and highly irregular layers, one and sometimes two of which were missing at some loca t ions . The p r o t r u s i o n s co rn -

Influence of Surface Finish on Corrosion of Base Metals

Since the foregoing tests on dis­similar metal weldments showed that surface finish can have a profound effect on extent of corrosion, further tests were conducted on the individ­ual base metals, using the weight-gain and weight-loss methods of anal­ysis combined to better assess the effects of finish. Specimens in the base metals were examined in dupl i ­cate both in the ground and electro-

Table 4 — Corrosion and Metal Penetration of Similar Metal Weldments Calculated from Weight-Gain Data

Code Weldments

Exposed at 1100 F (595 C) A9 Inconel 625 with itself A5 Hastelloy X with itself A18 IN 102 with itself A2 Incoloy 800 with Inconel 82 A3 Inconel 600 with Inconel 82 Exposed at 1200 F (650 C)

A9 Inconel 625 with itself A5 Hastelloy X with itself A18 IN 102 with itself A2 Incoloy 800 with Inconel 82 A3 Inconel 600 with Inconel 82

Intercepts and slopes of weight-gain curves, (b> with standard errors

K„ mg/dm2—1000 h

0.42 ± 0.03 0.31 ± 0.04 1.41 ±0.10 0.68 ±0.05 5.93 ±0.19

0.80 ± 0.07 1.08 ± 0.11 0.84 ± 0.06 2.02 ±0 .14 7.57 ± 0.52

-ivv0 , mg/dm2

11.0 ±0.23 12.1 ±0.29 20.8 ±0.90 12.4 ±0.37 2.2 ± 1.42

14.4 ±0.51 14.5 ±0.81 17.7 ±0.45 31.1 ± 1.02 16.5 ±3.82

Calculated metal consumed

in 20 years, mg/cm2

2.7 1.9 8.8 3.7

33.4

4.9 5.8 5.4

10.7 43.0

Calculated penetration in 20 years, Am mils

3.1 2.3

10.3 4 6

39.6

5.8 7.0 6.3

13.2 52.1

0.12 0.09 0.41 0.18 1.56

0.23 0.28 0.25 0.52 2.05

(a) Amounts 01 corrosion do not allow for oxide flaking during test and are based on the following calculated concen­trations of metal in the scales of the respective weldments: A9 — 76.1%, A5 — 74.1%. A18 — 76.7%. A2 — 73.5%, and A3 — 76.2%. (b) AW(mg/dm2) = AW0(mg/dnV) + K| (mg/dm' — 1000 h)T(1000 hi. where AW is weight gain and T is time. (c) The standard error of the intercept is for an individual specimen.

274-s I J U N E 1 9 7 3

polished conditions for exposures to 14,000 h at 1200 F. Because the effect of finish was so pronounced for In­coloy 800, this material was exam­ined at both 1200 and 1100 F.

Figure 14 compares the weight-gain corrosion results of the individ­ual alloys in the two finishes for expo­sures at 1200 F, while Fig. 15 gives the same results on an expanded scale and includes curves for Incoloy 800 at 1100 F as well. The curves are drawn through averaged values for the duplicate specimens. The corrosion resistance of Inconel 625, Hastelloy X, and IN 102 was somewhat improved after electropolishing, whereas that of Incoloy 800 was substantially reduced and Inconel 600 moderately so.

Table 6 gives the amounts of corro­sion that the alloys incurred in 14,000 h exposure at 1200 F as determined both by the weight-gain and weight-loss methods. The use of the weight-loss method of analysis was limited in that electropolished Incoloy 800 and Inconel 600 proved very difficult to descale. Notwithstanding, the two categories of information qualitative­ly agreed. Both revealed corrosion resistance of ground alloys in the same order displayed in other series of tests (Figs. 6 and 14), except for IN 102, which was slightly improved. Both showed Inconel 625, Hastelloy X, and IN 102 to possess very high resis­tances to scaling, with resistances in the electropolished condition being superior to that in the ground.

Additional information that can be inferred from these data concerns the tenacity of the scales that form on the alloys. Moreover, the acceptability of the weight-gain method of analyzing corrosion depends on corrosion product retention. Comparing the amount of scale theoretically asso­ciated with the weight gained during test (as oxygen) with that associated with metal consumed (weight differ­ence between specimen before test and after testing and descaling) gives a good indication as to whether flak­ing occurred.

The data of Table 6 suggest that the scales formed on Inconel 625, Has­telloy X, and IN 102 did not flake off during test. To the contrary, a small "hold-over" of oxide after descaling (possibly oxide more deeply im­bedded in the substrate) is sug­gested.

For Incoloy 800 in the ground con­dition, an indication of very slight flak­ing was ob ta ined . However , the degree is probably within the accu­racy of this method of determining flaking. Flaking to a more significant degree is indicated for ground In­conel 600. On the other hand, de­scaling ground Inconel 600 for longer periods indicated greater and greater flaking, suggesting that metal par-

Table 5 — Scale Thicknesses'3' of Base and Filler Metals as a Function of Surface Condi tion and Exposure

Alloys, expo­sure, and surface condit ion

Inconel 625 4000 G W

E(h) 8000 G

E Hastelloy X

4000 G E

8000 G E

IN 102 4000 G

E 8000 G

E Incoloy 800

4000 G E

8000 G E

Inconel 600 4000 G

E 8000 G

E Inconel 82

4000 G E

8000 G E

Hastelloy' W 4000 G

E 8000 G

E

Base 1100F(595C) WOP(b)

0.7 0.3 0.7 0.5

0.7 0.6 0.8. 1.3

0.5 1.1 0.4 1.4

0.6 12.8

0.7 17.2

1.2(n)

1.8,n)

—

—

—

WPici

1.4 i e l

1.0 |e)

1.5 (e)

1.5 (e)

1.3(8)

1 4 0 )

1.6'-Q1

2.1< 9 )

3 2 (e ) 3.2(k> 4.9(e)

2.7 | k )

1.5'" 28.0 (e |

1.7<" 24.8(e)

9.7(0)

1 3 > '

— —

—

—

metal at 1200F(650C) WOP

1.0 0.4 1.3 0.4

1.0 0.6 0.9 0.5

0.4 1.2 0.8 1.3

2.1 16.9 2.5

18.9

2,3 (n)

2.0(n)

—

—

—

WP

1.9 «> 0.7 (e)

2.3 « 0.6 «>

2,0 (i) 0.8 (9)

2.1 " 0.8 «>

(i) 3.2 (e)

2 2 (9)

2 ; 4 (e)

4.1 l m )

3.08 (e)

4.4 26.4 (e>

11.6 (0)

14.4 ' 0 |

— — — —

—

—

Filler 1100F(595C) WOP

0.8 0.5 0.9 0.3

0.6 0.6 0.6 0.8

0.6 1.2 0.6 1.4

— — — —

—

—

0.8 0.5 0.5 0.3

0.3 2.1 0.6 4.4

WP

1.4 ,g l

1.4<e)

1.4 (9)

0.8 (e)

1.4 ,9)

2.2 ( 9 )

1.4 l9)

1.7(9)

1.4<9)

3.2<e)

1.6 , g l

4.0 (k)

— — — —

—

—

i g ( s ) 1.9 (9)

2 2 O)

2^0 <e)

2.5 (p)

4.1 k

4'1 £ 6.3 <k)

metal at 1200F(65CC) WOP

0.9 0.4 1.1 0.4

0.6 0.6 0.6 0.6

0.4 0.6 0.7 0.9

— — — —

—

—

0.9 0.7 1.1 0.6

0.6 6.6 0.3 6.7

WP

(f) 1 - 7 . °-9 2 ' 7 . 0.7

(i) 1.6 ' 1-°

2.3 (e)

— — — —

—

—

2.6<9) ' 1.5(91

2. 7 (g) 1.4 (9)

3.5 ( q )

7.7(k> 2.7(P)

8.6 (k>

(a) Determinations are in microns and are averages of at least nine readings made to the nearest 0.1 »tm. (b) WOP — Without protrusions into base metal (thickness of surface layer only). (c) WP — With protrusions (thickness of surface layer and protrusions into the base metal combined). (d) Specimen finished by grinding with 100 mesh grit belt. (e) Moderate frequency of protrusions, bulky and generally integral with surface layer. (f) High frequency of protrusions, bulky and generally Integral with surface layer. (g) Low frequency of protrusions, bulky and generally integral with surface layer. (h) Specimen electropolished to remove 0.002 in. of metal from surfaces after the grinding operation. (i) Low frequency of protrusions, bulky and both integral and disconnected with surface layer. (j) Very low frequency of protrusions — not measured. (k) Very high frequency of protrusions, both Intergranular and transgranular, and continuous with surface layer. (I) Moderate frequency of protrusions, both transgranular and intergranular, and continuous with surface layer. (m) High frequency of protrustions, both transgranular and Intergranular, and continuous with surface layer. (n) Highly irregular in thickness. (o) Very high frequency of protrusions, deep, intergranular, and continuous with surface layer. (p) Low frequency of protrusions, both Widmanstatten platelets and bulky oxides integral with surface (copious very faint Widmanstatten platelets protruded deeper into base metal but were not measured). (q) Very high frequency of protrusions, transgranular Widmanstatten platelets continuous with surface layer.

t ides were being removed along with the oxide as the descaling operation was prolonged. The fact that the microstructure adjacent to the scale showed oxide penetrating intergran-ularly into the metal substrate to some substantial depth (see Fig. 13, left, and Table 5) explains why this might be the case for this particular mate­rial.

As mentioned earlier, the descaling solution attacked the scaled electro­polished Inconel 600 very little, (see large amount of scale remaining after descaling in Table 6) and the scaled electropolished Incoloy 800 spec­

imens practically none at all. Attempts at descaling electropolished Incoloy 800 in other solutions also were un­successful . To further study the tenacity of the scale formed on elec­tropolished Incoloy 800, specimens exposed to steam for 8000 h at 1100 and 1200 F were quenched in room-temperature tap water from the expo­sure temperature. An examination of the quenching water for traces of ox­ide and weighing the specimens before and after quenching showed no perceptible oxide loss.

Because the we igh t -ga in data points for electropolished Incoloy 800

W E L D I N G R E S E A R C H S U P P L E M E N T ! 275 -s

Fig. 9 — Typical scales on weldment A8, tested 4000 h at 1200 F. Top to bottom are plate (Hastelloy X), tiller metal (Hastelloy W), and plate (Incoloy 800)

— 10*.. -10,

lOu 1

r4¥;'£i|f*

•

iiSAAAJL. . % ^Wjp*W~' ;

i 1 0 M — i

Elecfropolished

Fig. 10 — Typical scales on weldment AI3, tested 8000 h at 1200 F. Top to bottom are plate (Inconel 625), filler metal (Inconel 625) and plate (Incoloy 800)

AW = AW0 + T/(B + CT)

where AW = the weight gained,

T = time, and AW0, B, C = constants.6

Figures 16 and 17 show plots of the weight-gain data for electropolished Incoloy 800 exposed at 1100 and 1200 F, respectively, with superimposed corrosion models for the duplicate specimens.6 Table 7 lists estimates of the equation constants with standard errors for the individual specimens, together with the amounts of corro­sion in 20 years calculated from these constants.

Features characteristic of the cor­rosion of electropolished Incoloy 800 thus are constantly diminishing rates of corrosion throughout exposure and comparatively large amounts during earlier stages (Figs. 16 and 17). Al­though the amounts of corrosion oc­curring on Incoloy 800 at 1100 and 1200 F were vastly different in the ground and electropolished condi­tions after 3000 h (about 39 and 15 times higher for electropolished at 1100 and 1200 F, respectively), the amounts after 20 years estimated in Table 7 for electropolished Incoloy 800 are comparable with those listed for ground Incoloy 800 weldments in Table 4.

Discussion of Results

As indicated earlier, localized cor­rosion at fusion lines of welds does not appear to be a problem with the s imulated steam generator we ld­ments. Changes in scale microstruc­ture across fusion line areas general­ly were gradual in both ground and e l ec t ropo l i shed s p e c i m e n s , and careful scrutiny failed to uncover signs of aggravated attack in these regions. The extent of corrosion in root passes did not appear to be much different from that of the bulk weld deposits. This was true in spite of the fact that root passes were deposited with a dilution factor of (5Q ± 8)%, whereas that in subsequent passes ostensibly was much less.

Equally encouraging, the amounts of general corrosion observed for the various alloys studied were relatively low. Also, the calculated amounts of corrosion in 20 years were quite small by practical standards. For expo­sures of the order of one year or shorter, surface f inish somet imes proved to be a more impor tant var iable than temperature of ex­posure.

showed essentially no scatter from smooth curves and clearly exhibited nonlinear corrosion rates throughout exposure, a detailed analysis of the data seemed justified. Instead of dis­

playing a constant rate second stage of corrosion generally depicted for in­termediate and high nickel alloys,' the data throughout (to 14.000 h) con­formed to an equation of the form

Correlation of Data

In general, the weight-gain, weight-loss, and scale thickness data corre­lated with each other reasonably well.

276-s I J U N E 1 9 7 3

The weight-gain method of examining general corrosion proved to be just i­fiable and the most valuable method of analysis. The weight-loss method had only limited use because of the difficult problem of removing all oxide corrosion products without including some of the metal substrate. The metallographic method was indis­pensable for assessing the general characteristics of scales — e.g., their adherence, soundness, and uni­formity of thickness — but it, too, did not appear to be entirely effective for quantitatively determining the amount of scale.

The scales formed on Inconel 625 and Hastelloy X, both ground and electropolished, were relatively uni­form in structure and thickness and s e e m i n g l y ve ry t e n a c i o u s . For ground, similar metal weldments in these alloys, small amounts of initial corrosion and very low subsequent linear rates indicated predicted 20 year metal penetration depths less than 0.15 mil at 1100 F and less than 0.30 mil at 1200 F (Table 4).

Ground, similar metal weldments in IN 102 showed somewhat higher ini­tial corrosion and linear corrosion rate at 1100 F, to give about 0.4 mil penetration in 20 years. Paradox­ically, a significantly lower linear cor­rosion rate at 1200 F than at 1100 F was responsible for a very low pre­dicted 20 year penetration value of 0.25 mil at the higher temperature (Table 4). This unexpected influence of temperature on cor ros ion was reproduced with nonwelded spec­imens, but its cause is unknown. The scale formed on this alloy at 1200 F was very uniform and tenacious, while that formed at 1100 F displayed spo­radic "pi t t ing" attack into the metal substrate.

Col lect ively, the cor ros ion data indicated that the scale formed on ground weldments in Incoloy 800 had good cha rac te r i s t i c s . Ca lcu la ted metal penetration in 20 years was about 0.5 mil at 650 C and substan­tially lower at 595 C (Table 4). As indi­cated earlier, the amount of corro­sion incurred by this alloy for short periods was substantially greater for the electropolished condit ion than for the ground. However, as a result of a decreasing rate for the electropol­ished material, comparable and at­tractively low amounts of corrosion were displayed in both conditions after 20 years. This coupled with the observed extreme tenacity of the scale formed on the electropolished material reflects encouragingly on In­coloy 800 for high-temperature steam applications.

Weldments of ground Inconel 600 displayed the highest corrosion rates of all the materials examined. We cal­culated 20 year metal penetration

Ground Electropolished

Fig. 11 — Typical scales on weldment A5, tested 8000 h at 1200 F. Top represents the plates (Hastelloy X) and bottom the filler metal (Hastelloy X)

H—IOU H

Eiectropolished

Fig. 12 — Typical scales on weldment A20, tested 8000 h at 1200 F. Top to bottom are plate (IN 102), filler metal (Inconel 82) and plate (Incoloy 800)

Ground l lecfropoi ! lined

Fig. 13 — Typical scales on base metal of weldment A3 (Inconel 600), tested 8000 h at 1200 F

W E L D I N G R E S E A R C H S U P P L E M E N T ! 277-s

130

120 h

110

100

90

80

70

INCOLOY 800, 65Q2;J

—

K INCOLOY 800, 595°C

A 1 GROUND ELECTROPOLISHED '

© IN 102. HASTELLOY X, AND INCONEL 625 GROUND. 650°C

(2) INCOLOY 800, 595°C

12 ( x ! 0 ° )

TIME (hr)

TIME (hr)

Fig. 14 — Total weight gain of base metal alloys at 1200 F, as ground and electro­polished. Curves are drawn through aver­aged values for duplicate determinations. Specimen surface area was 20 cm2

values of 1.56 and 2.05 mils for 1100 and 1200 F, respectively. These results correlated with the undesir­able scale microstructure (Fig. 13) and flaking characteristics of this material (Table 6).

Fig. 15 — Total weight gain of Incoloy 800 as ground and electropolished in com­parison with other base metals. Curves are drawn through averaged values for dupli­cate determinations. Specimen surface area was 20 cm2

Weld deposits of Inconel 82, as well as deposits in Inconel 625, Hastelloy X, and IN 102 formed uniform and well anchored, thin scales.

The extremely beneficial influence of the grinding on Incoloy 800 was ob-

Table6 — Calculated Amount of Corrosion on Base Metal Alloys After 14,000 hat 1200 F and Indications of Scale Tenacity During Test (a l

Al loys ' " '

Inconel 625 Ground Electropol.

Hastelloy X Ground Electropol.

IN 102 Ground

Incoloy 800 Ground Electropol.

Inconel 600 Ground Electropol.

Weight loss,

metal, mg

14.4 7.1

18.9 7.5

11.6

28.1

—

79.1 20.9

Weight gain,

oxygen, mg

5.2 2.1

6.8 2.9

4.0

13.1 126.1

27.2 37.1

Calculated scale f rom

Weight loss, A,

mg

18.2 9.0

25.5 10.1

15.1

41.3

—

109.5 29.0

Weight gain, B,

mg

25.0 10.1

26.3 11.2

16.9

41.1

—

98.2 13.4

Scale flaked

off<c)

%

— —

— —

—

0.5

—

10.3

—

Scale re­maining after de­scaling (d)

%

27.2 10.9

3.0 9.8

10.7

— —

— 78.5

(a) Calculations were based on the following computed concentrations of metal in scales for the respective alloys: In­conel 625 — 79.2%, Hastelloy X — 74.1%, IN 102 — 76.7%, Incoloy 800 — 68.1%, Inconel 600 — 72.3%. (b) Specimen had a surface area of 20 cm2. (c) Percent scale flaked off = 100(A - B)/A, where A is the calculated scale from weight loss (metal) and B is the calculated scale from weight gain (oxygen). (d) Percent scale remaining after descaling = 100(8 - A)/B.

served to an equal degree in experi­ments in our laboratory7 on weld­ments in type 304 stainless steel jo in­ed with type 308. To a lesser degree this beneficial grinding influence was observed in Inconel 600. (See Figs. 14 and 15.) On the other hand, Inconel 625 and Hastelloy X displayed a slightly better scaling resistance in the electropolished than in the ground condition. An almost identical effect of surface condition on steam corro­sion of these alloys was recently ob­served by S. Leist ikow and co-workers.5

French investigators, working with austenitic stainless steels,8 also have shown that work hardening the sur­face improved resistance to steam corros ion. Accompany ing the en­hanced corrosion resistance was a decided improvement in the tenacity of the scale. For type 304 stainless steel, this improved corrosion resis­tance resulted from an enrichment of the inner layer of the scale in chro­mium and, to a smaller extent, man­ganese. Cold working the metal sur­face had promoted the formation of the alloyed subscale by aiding the dif­fusion of the beneficial elements from the metal substrate into the scale. Leistikow5 confirmed the French f ind­ings with austenitic stainless steel and also showed a similar mechanism of improving corrosion resistance in In­coloy 800. He found metalworking by cold reduction and also grain refine­ment to have beneficial effects.

Comparisons With Other Work

Wozaldo and Pearl1 investigated the isothermal corrosion of the base metals included in this study (except for IN 102) as wrought materials in superheated steam at 1050 and 1150 F. Their corrosive environment sim­ulated a boiling water reactor and consisted of steam containing 20 ppm 0 2 and 2.5 ppm H2 at a pressure of 1000 psi and 20 fps velocity. A com­parison of our 1200 F exposure results on 100 mesh ground, similar metal weldments with Wozaldo's 1150 F data shows our corrosion rates to be only one-third to two-thirds as high as theirs except in the case of Inconel 600, for which our rates were higher.

Leistikow et al5 investigated the same wrought alloys in steam con­taining 6 ± 2 ppm 0 2 under isother­mal conditions at 1150 F, 1 atm, and about 2 fps velocity. A comparison of our results on ground similar metal weldments with their materials abrad­ed with a 400 mesh cloth again show­ed our rates to be somewhat lower, except for Inconel 600.

We suggest that the rather small discrepancy in corrosion rates be­tween our work and the above-cited investigations may have arisen from differences in oxygen concentrates in

278 -s I J U N E 1 9 7 3

6.5

6.0

5.5

5.0

4.5

5 4.0

3.5

3.0

2.5

i

i / 1

r iA L

800 -

• -3E , .—-•—

L — * — ,k—

2 4 6 8 10 12 14 (X10s)

TIME (hr)

6.5

z Z

5.0

2 4.5

<

4.0

3.5

3.0

2.5

/

1/ /

^ ^ — • < <

^ - — ,

X -

8 0 0 - 2 - 2 E 1

800 -2 -3F ,

* — i —

•— •—

4 6 8 10 12 14 (xl0°)

TIME (hr)

Fig. 16 — Corrosion of electropolished Incoloy 800 in steam at Fig. 17 — Corrosion of electropolished Incoloy 800 in steam at 1100 F 1200 F

Table 7 — Equation Parameters and Calculated 20-Year Corrosion for Electropolished Incoloy 800

Specimen

800-1-2E 800-1-3 E 800-2-2E 800-2-3E

Temper­ature, degC

595 595 650 650

Least squares estimates of parameters (a)

AW0, mg/cm2

2.22 ±0.215 2.56 ±0.166 4.95 ± 0.070 4.73 ± 0.042

B, h cm7mg

330 ± 55.6 405 ± 57.1

1080 ± 163 1710 ±196

C, cmVmg

0.256 ± 0.0125 0.266 ±0.0100 0.661 ± 0.0256 0.755 ± 0.0178

Calculated 20-year corrosion Weight Metal Penetra-

gain consumed*' tion (b)

mg/cm2 mg/cm1 mils

6.1 6.3 6.4 3.0

13 13 14 13

0.63 0.65 0.67 0.63

(a) To fit the weight-gain equation W = W„ + T/(S + CT). (b) Based on the assumption that the concentration of metal in the scale is 68.1% and the density of Incoloy 800 is 8.01 g/cm\

the respective steam environments. Whereas their oxygen concent ra­t ions were pu rpose l y h igh , our makeup water was scavenged of ox­ygen, and its concentrations in the steam was extremely low.

In short-t ime steam corrosion tests, Ruther and Greenberg9 found that the corrosion of Incoloy 800 doubled when the oxygen content of the steam was raised from 0.03 to 30 ppm. Leistikow,5 in citing work conducted by Maffel, states that increases from below 0.05 to 3-4 ppm 0 2 enhanced corrosion at 1020 F in a number of superheater materials. Leistikow has shown oxygen in steam to have a par­ticularly pronounced effect on abrad­ed or cold worked materials whose corrosion resistance is improved sig­nificantly by concentrating chromium in the scale. An outer Cr203 layer was said to react with oxygen to form Cr0 3 , which is volatile in steam.5

The comparatively poor corrosion resistance experienced with the In­conel 600 in our study possibly results from our particular material being of a slightly inferior quality. Its

carbon content was 0.02% higher than the limit generally placed on it.

Conclusions

1. Isothermal corrosion testing in superheated steam at 5 fps (1.5 m/s) velocity and 900 psi pressure at 1100 and 1200 F for 16,000 h yielded the ratings (Table 8) of similar metal weldments based on their general corrosion as f inish-ground speci­mens. Except for weldments in In­conel 600, the expected depths of metal penetrated in 20 years ranged from about 0.1 to 0.5 mil . The corro­sion resistance of the dissimilar metal weldments at 1100 and 1 200 F were explainable on the basis of the corrosion properties found for the in­dividual base metals making up the weldments.

2. Removal of the ground finish by electropolishing (0.002 in. removed) greatly reduced the short-t ime corro­sion resistance on the Incoloy 800 weldment and moderately lowered that of the Inconel 600 weldment. On the other hand, the corrosion resis­tance of weldments in Inconel 625,

Hastelloy X, and IN 102 was slightly improved by electropolishing. As a result of a long term reduction in cor­rosion rate with time for electropol­ished Incoloy 800, as compared to a constant rate for it ground, 20 year metal penetration figures for this

Table 8 — Ratings of Weldments Ex­posed 16,000 h in High-Purity Steam at 1100 and 1200 F

Base metal

At 1100 F

Hastelloy X Inconel 625 Incoloy 800 IN 102 Inconel 600

At 1200 F

Inconel 625 IN 102 Hastelloy X Incoloy 800 Inconel 600

Filler metal

Hastelloy X / Inconel 6 2 5 / Inconel 82 ) IN 102 Inconel 82

Inconel 625 | IN 102 > Hastelloy X ) Inconel 82 Inconel 82

Rating

1

2 3

1

2 3

W E L D I N G R E S E A R C H S U P P L E M E N T ! 279-s

weldment at 1200 F were about the same (0.65 vs 0.5 mil, respectively) irrespective of the finish.

3. The corrosion resistance of In­conel 82 filler metal and Inconel 625, Hastelloy X, and IN 102 as filler metals were remarkably good. Hastelloy W filler metal was inferior, especially when cold worked.

4. All of the similar and dissimilar metal weldments tested in super­heated steam were free of any prefer­ential corrosion at fusion line areas after 16,000 h at 1100 and 1200 F.

5. From the viewpoint of general and preferential corrosion, all of the similar and dissimilar metal weld­ments investigated appear to be usable for steam applications up to 1200 F.

Acknowledgments

The authors wish to acknowledge the cooperation of the Florida Power Corpora­tion, in whose plant corrosion tests were conducted. Thanks are extended to C. T. Sawyer, L. E. Lohkamp, and R. P. Han­cock, of Southern Nuclear Engineering for assistance in conducting experiments. Also, acknowledgments are due several persons of the Oak Ridge National Labora­tory: D. R. Frizzell for preparing weld­ments, R. G. Shooster and J. J. Wood-

house for specimen preparation, B. C. Leslie and C. P. Haltom for metallograph­ic studies, and Sigfred Peterson for edi­torial assistance. Finally, the authors thank T. L. Hebble for assistance in analyzing the experimental data; he was responsible for the empirical equation describing corro­sion of electropolished Incoloy 800, includ­ing results in Figs. 16 and 17 and Table 7.

The research work was sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corpora­tion.

References

1. Wozaldo, G. P. and Pearl, W. L, "General Corrosion of Stainless Steels and Nickel Base Alloys Exposed Isothermally in Superheated Steam," Corrosion, 21, 1965. 355 to 369.

2. Ruther, W. E.. Schlueter, R. R., Lee, R. H.. and Hart, R. K., "Corrosion Behavior of Steels and Nickel Alloys in Super­heated Steam," Corrosion, 22, May 1966, 147 to 155.

3. Eberle. F. and Kitterman, J. H., "Scale Formations On Superheater Alloys Exposed to High Temperature Steam. Behavior of Superheater Alloys in High Temperature, High Pressure Steam," Sponsored by American Society of Mechanical Engineers Research Commit­tee on High Temperature Generation, Library of Congress No. 68-19905 (Copy­

righted. 1968) 67 to 113. 4. Tilborg, P. J. van and Linde, A. van

der. Corrosion of lnconel-625 Hastelloy-X280 and lncoloy-800 in 550-750 C Super­heated Steam, Report RCN-109, Reactor Centrum Nederland, Petten, The Nether­lands, Oct. 1969.

5. Leistikow, S., Berg, H. V., and Pott, E.. Long-Time Corrosion Studies on Austenitic Cr-Ni Steel and Nickel-Base Alloys in Superheated Steam (620 C, 1 atm), with Special Attention to the Be­havior of Cold-Formed Material Surfaces, Report KFK-1301, Karlsruhe Nuclear Re­search Center, Feb. 1971.

6. Hebble, T. L, ORNL Mathematics Division, private communication to J. P. Hammond.

7. Hammond, J. P., Patriarca, P., Slaughter. G. M., and Maxwell, W. A., "Corrosion of Advanced Steam Generator Alloy Weldments in 1100 and 1200 F (595 and 650 C) Steam," Paper presented at the National Association of Corrosion Engi­neers 26th National Conference, March 2-6, 1970, Philadelphia, Pa.

8. Societe d'Etudes, de Recherches et d Applications pour I'lndustrie, Brussels, Studies of Steel Corrosion in High Temperature Water and Steam, Final Report No. 1, June 16, 1962-Oct. 31, 1965, Report EURAEC-1581, 1965.

9. Ruther, W. E. and Greenberg, U.S., J: Electrochem. Soc. 111, 1964, 1116 to 1121.

Applications of Welding, Section 5 of the WELDING HANDBOOK, Sixth Edition. Pub l i shed by the A m e r i c a n We ld ing Soc ie ty

This final volume of the Sixth Edition of the WELDING HANDBOOK completes the following series begun in 1968:

Section 1 — Fundamentals of Welding Section 2 — Gas, Arc and Resistance Welding Sections 3A and 3B — Welding, Cutting, and Related Processes Section 4 — Metals and Their Weldability Section 5 — Applications of Welding

Section 5 provides extensive coverage of the entire field of welding applications, encompassing such key areas as buildings and bridges, nuclear power, automotive products, and railroads.

Each chapter describes both major and minor components which are welded for each application area. Details of joint designs, welding processes, filler metals, heat treatment, and inspection and testing are presented to give the reader a broad picture.

In many instances, actual production conditions are referred to, generally in tabular form. A bibl iog­raphy is included in each chapter, and an alphabetical index covers the contents of the entire volume.

The beginner in welding — including the engineer from another discipline just getting into welding — will find this volume a necessary part of his reference library. And the expert with long experience will find useful information concerning those fields with which he has had little direct contact. 608 pp. Cloth-bound, 6 in. X 9 in,

Chapter 81: Chapter 82: Chapter 83: Chapter 84: Chapter 85: Chapter 86: Chapter 87:

CONTENTS

Buildings Bridges Field-Welded Storage Tanks Pressure Vessels and Boilers Industrial Piping Transmission Pipelines Nuclear Power

Chapter 88: Chapter 89: Chapter 90: Chapter 91: Chapter 92: Chapter 93: Chapter 94:

Ships Railroads Automotive Products Aircraft Launch Vehicles Clad Steel and Applied Liners Filler Metals

The price of Section 5 is $14.00 for all AWS members, $21.00 for non-members, and $23.00 abroad. Send your orders for copies to the American Welding Society, 2501 NW 7th Street, Miami, Florida 33125.

280 -s I J U N E 1 9 7 3