ferrite limitation for ss316l

Ferrite limitation for SS316L.doc Page 1/ 12

18.01.2008

Ferrite limitation for SS material SOURCE: http://www.welding-advisers.com/PRACTICAL_WELDING_LETTER-PracticalWeldingLetterNo53.html

Article - Ferrite in Austenitic Stainless Steels

Austenitic Stainless Steels are considered the most easily welded than all other types. The term Austenitic refers to the main face-centered cubic (fcc) phase in their microstructure, called austenite, that is maintained by alloying additions over a wide range of temperatures.

Their composition determines not only the microstructure but also important physical properties. Most important are (besides corrosion- and oxidation-resistance) Thermal Conductivity, about half that of other steels, and the Coefficient of Thermal Expansion (CTE) considerably greater. These characteristics influence their welding penetration, warping (deformation) and residual stresses, requiring adaptation of the techniques to obtain acceptable results.

The major concern while welding these stainless steels is their tendency to cause solidification cracking unless the weld metal contains more than 3% ferrite. This phase is body-centered cubic (bcc) like the main constituent of iron base alloys at normal temperature (alpha ferrite), except that it is present at elevated temperatures and is therefore designated as delta ferrite.

The primary phase appearing upon solidification may be either austenite or ferrite. The austenitic phase is more susceptible to weld solidification cracking.

The main precautions that can be exercised to minimize weld cracking involve alloy selection, process optimization and postweld heat treatment.

A useful concept that was developed with experience along the years is that of equivalence, whereby the elements active as ferrite forming (Cr, Mo, Nb) are normalized by multiplying their percentage with an empirical factor and then summed with the Chromium percentage to give a composite Chromium equivalent.

Similarly the percentage of austenite forming elements (Ni, C, N and Cu), each one multiplied by its factor, are summed up to give the Nickel equivalent.

While the exact proportions and influence of the single elements are still a matter of debate, in general the adoption of the concept has permitted the drawing of useful diagrams starting with that of Schaeffler (in the 1940s), modified by DeLong (1973) and further updated by the Welding Research Council (WRC) first in 1988 and then in 1992.

The use of these diagrams permits to predict the structure of the resulting weld metal by dilution of base with filler metal of different compositions. The diagrams delineate regions identified by the main or composite structures of the weld materials as pointed by composition (Austenitic, Austenitic-Ferritic, Ferritic-Austenitic, Ferritic) depending on the primary structure solidified.

Similar diagrams determining the same zones by slightly modified criteria were developed by other researchers. It is not uncommon to use all available diagrams to check the results obtained with any one of them.


Unfortunately the boundaries defining these structures may move by cause of other parameters like heat input and solidification speed or constraint conditions. Furthermore quite large uncertainties exist in compositional analysis determination, and the exact effect of impurities unaccounted for, as well as the influence of process and parameters.

One must remark that the amount of ferrite that is found at room temperature is only a fraction of that resulting immediately after solidification, because of transformations occurring in the solid state phase while cooling.

The use of commercially available instruments for determining the Ferrite Number, based on ferromagnetic characteristics of the ferrite phase, can help in giving an idea of the ferrite content. One must remember however that it is almost impossible to determine the absolute ferritic content of austenitic stainless steels specimens, and that significant differences may be found among specimens made under the same conditions.

Finally welds performed with high energy density processes may differ significantly from those welded by traditional means. The differences are attributed to rapid solidification speeds and also to microstructures not known from processes with slower cooling rates.

In conclusion the development of suitable welding procedures for austenitic stainless steels must take into account the composition of weld metal and the general guidelines briefly summarized here.

SOURCE: http://www.welding-advisers.com/PRACTICAL_WELDING_LETTER-PracticalWeldingLetterNo05_B.html 9.6 - Ferrite limitations in 316L are generally recommended to reduce the susceptibility to pitting corrosion in certain aggressive environments: a generally agreed upon maximum is as yet not available. However a minimum of delta-ferrite is usually prescribed to reduce the risks of hot cracking or microfissuring: this is established at about 3 to 5%. The solidification modes and the structure types present in the welds are determined mainly by chemical composition, as modified by filler metal and dilution. The phases are examined with reference to the Schaeffler's diagram, or more recently to a modified constitution diagram including also nitrogen effect. Other researchers study the resulting structures based on the ratio between Chromium equivalent and Nickel equivalent: one must remark however that calculations of equivalents by empiric formulas may be based on different assumptions. One such study describing weldability and corrosion research is listed in the section "In the press" in this publication.


SOURCE: http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=8811

By Martin Forster Date 03-22-2006 15:47

I am after information on allowable ferrite levels in the Heat Affected Zone after welding of 304L stainless pipe. Excessive levels may be caused by too much heat during welding. This can lead to long term corrosion problems.

By chall Date 03-22-2006 15:57

I'm sure you will get plenty of solid advice from some of the posters here. I am curious about your need for the info. If elevated ferrite, leading to reduced corrosion resistance is that much of a concern, why don't you change to a more corrosion resistant stainless? Charles (the stainless newb)

By - Date 03-22-2006 17:10

I'm not sure if I understand exactly what you're saying here. I don't see how you can get excessive ferrite in the HAZ when welding a 304L pipe. When welding the austenitic grades of SS, the ferrite tends to decrease in the HAZ, sometimes up to approximately 80%. Normally a 304L base metal has somewhere around 3-6 FN, and if you are using a 308L filler metal the FN is around 3-8FN. But, that would only affect the FN of the weld metal, not the HAZ. Even in the desposited weld metal the FN will tend to decrease due to dillution with the base metal and the possibility of chromium loss through the weld arc. I just cannot see how you can gain ferrite above the equilibrium of the potential for ferrite. Actually, to much heat during welding will have the propensity for lowering the FN, rather than increasing it. If you are using too much heat during welding I would more concerned with sensitization in the HAZ than excessive ferrite levels, which I don't see how that can happen. Long term corrosion problems will be related to sensitization in the HAZ, or if you did not restore the HAZ back to the steel's natural anti-corrosive state by removing the chromium depleted oxide layer in the HAZ. Chuck


Thanks for the good info here. We had 304L pipes welded in China (filler 308L in documentation) and the client is rejecting them on weld quality (RT and/or visual), although the quality documents are in order. Excessive penetration indicates too much heat during the process also. The client has cut the welds with a razor disk & will re-weld for good RT & visual without haing to purchse any pipe & fittings, to get job commissioned. However the client states that the pipe may have to be replaced long term due to corrosion concerns due to the possibility of "the ferrite level being too high due to excessive heat" - the HAZ will be the only part of the original pipe in existence. (These reports are coming secondhand from site). I agree about the sensitization due to too much heat. This has never been mentioned. Further comment would be welcome. Thanks.

By - Date 03-22-2006 20:09

First of all, excessive penetration can be a result of high heat input. I am not doubting that your client said the ferrite levels in the HAZ are attributed to excessive heat input during the weld process. I'm not doubting he is saying that, I


just don't agree with it. Actually, there are a couple of issues I'm not understanding. One, why is he attributing the ferrite levels in the HAZ to long term corrosion concerns? Secondly, ferrites in the HAZ will not exceed that of the equilibrium of the base metal and the filler metal. Metallurgically speaking, the FN in the HAZ will be less than the FN of the deposited weld metal. You said this is secondhand reports from the site. I would suggest you get the information firsthand because saying that excessive ferrites in the HAZ will cause long term corrosion concerns makes no sense to me. Seems there is some misinformation being relayed to you.


Comments on excessive ferrite were made by the lab we employed to test that the material was in fact 304L as the fabricator has been unreliable. The results of their ferrite tests (in the weld metal) were, in the China pipe butt weld 7.5-10FN with small areas of 10-12.5FN, china pipe to flange weld 5-7.5FN. The repaired weld outside china pipe butt 5-7.5FN, flange to pipe 7.5-10FN. we have struggled to find a maximum limit on this, but one weld society advise a maximum figure of 12FN. I agree with you that sensitization could lead to long term intergranular stress corrosion cracking, but this has never been raised. Could carbide solution heat treatment be a possibility if it became an issue? If there is a large enough furnace locally. This could save re-manufacture if it came to it.

By - Date 03-23-2006 14:33

Yes, a full annealing heat treatment is the only one recommended for this grade unless specifically specified otherwise. I know of nowhere where a "maximum" FN is specified for 304L pipe. That would be determined by the FN of the base metal and the filler metal. During the welding process, and due to dillution, the FN in the HAZ will virtually always reduce, as will the as-deposited-weld metall.

By swnorris Date 03-23-2006 14:48

As chuck said, the method of depositing weld metal can alter ferrite content. Ferrite content is modified by variations in weld metal cooling rates, arc length, and atmospheric contamination. Weld passes that have high dilution with the base metal can have altered ferrite content. Significant variations in ferrite content can exist from weld to weld, and within a weld from the root to the face. For example, production pipe welds have shown that nearly 50% of all welds examined differed by at least 2 FN from procedure qualification ranges. For applications where ferrite content of the weld metal is critical, welding procedures must be rigorously controlled. Nitrogen and chromium variations can significantly influence the ferrite content. Improper welding technique can result in nitrogen contamination because of excessive arc length, and the loss of chromium through oxidation. The result can be a weld with far less ferrite than specified.

If you're not moving forward, you're standing still

By - Date 03-23-2006 15:53

With all respect, I cannot imagine a reputable metallurgical lab stating that a 304L material has "excessive ferrite levels". Ferrite, in a base metal or a filler metal, is determined by the actual chemistry, with the filler metal normally being overalloyed compared to the base metal. I know of no way that one can "gain" ferrite levels when welding a 304L base metal and using a 308L filler metal above the equilibrium potential for the ferrite determined by the chemistry. It will, in virtually every case I've seen, reduce the FN in the HAZ and the deposited weld metal. I would question the lab that made that statement about excessive ferrite levels to present evidence that 12FN for the 304L is determined to be excessive. If the chemistry of the base metal and the filler metal adheres to AWS


specifications for chemical requirements and it is within the limits of the Code, the ferrite level will be what it is. If it is determined to be 12FN, who can say it is excessive? If this was a concern, your customer spec should have listed limitations for ferrite levels. What weld society are you referring to that listed the maximum 12FN for a 304L to be excessive? I've never seen that.

By MBSims Date 03-24-2006 00:54

I agree with Chuck. The base metal has some ferrite-forming ability that can be predicted using the WRC-1999 ferrite diagram, but usually is much lower due to solution annealing. The presence of ferrite in welds or base metal increases resistance to stress corrosion cracking (SCC), but can reduce resistance to microbial induced corrosion (MIC). It seems that MIC is attracted to ferrite. So it depends on the type of "corrosion" that is of concern for the service conditions. If the concern is SCC, then the results of a susceptibility test of ASTM A262 Practice A should be requested. Practice A is simply a screening test, if it passes then it is not susceptible, and if it fails the Practice E test (a much longer duration test) must be performed. If it passes Practice E, then the lab that raised concern with base metal ferrite increase in the HAZ is off base.

Marty Sims

By ssbn727 Date 03-25-2006 09:09

Hello Martin Forster, Chuck, MBSims, swnorris!!! I was looking through my favorites and I stumbled across this website. In it, is a NRC regulatory guide, #1.31- " Control of Ferrite in stainless steel weld metal". Revision 3, dated: April, 1978. http://www.nrc.gov/reading-rm/doc-collections/reg-guides/power-reactors/active/01-031/ If you look at the last paragraph in "B." heading: "Discussion", just above "C." heading: "Regulatory Position", also in the last paragraph in #4., in "C. Regulatory Position", heading: "Acceptability of Test Results", one will find some interesting comments regarding the initial query and your own opinions for which I believe are well founded... I know it does'nt cover ferrite #'s for the HAZ but, I thought this could cover acceptable F#'s in the welds... I'll look for the other(HAZ F#'s) info and get back to you! http://www.osti.gov/bridge/servlets/purl/14580-mGkMzM/webviewable/14580.pdf http://www.osti.gov/bridge/servlets/purl/11739-cfMpBF/webviewable/11739.pdf http://scholar.google.com/scholar?hl=en&lr=&q=cache:IuIpuSm6tkQJ:www.atc-ssm.com/PDF/TWR89.pdf+304+Stainless+Ferrite+numbers+in+Heat+Affected+Zone http://www.doeal.gov/nnsaota/SafetyGuides/SG100Revision2/SG-100_ch9_09-30-05_final.pdf What do you think Chuck, MBSims, swnorris? I hope this helps...http://sti.srs.gov/fulltext/tr2004456/tr2004456.pdf Respectfully, SSBN727 Run Silent... Run Deep!!!


SSBN727 Run Silent... Run Deep!!! "There are two kinds of ships... Submarines and Targets!!!" Even though we who either worked on Submarines or served in them or both, call them "Boats!!!" Btw, You can call me "Hank!"

By MBSims Date 03-25-2006 16:50

These are some good links on the benefits of ferrite in welds to prevent hot cracking. But, I didn't notice any specific reference to the effect of ferrite in the HAZ on corrosion resistance. Here is a link (I hope it works) that provides some good guidance on IGSCC prevention: http://us.share.geocities.com/welder4956/nureg0313rev2.pdf

Marty Sims

By ssbn727 Date 03-26-2006 06:45

Hey Marty Chuck! I was hoping that your link worked but, apparently it does'nt... I'm not disagreeing with you Marty or Chuck!!! Personally, the only thing that would remotely make sense here is the very low probability that the chemical composition of the filler metal was such that, 1.an unusually high percentage of ferrite needs to be present, 2. interpass temperature was at least 2-1/2 to 3 times the recommended amount or even higher which as a result, transformed most of the greater than normal amount of ferrite originating from the fller metal, into "delta ferrite" otherwise known as "gamma iron" compared to "alpha iron", resulting in enbrittlement of the welds due to the formation of sigma phase. 3. As a result of excessive dilution, enough of the ferrite that originated from the filler metal, precipitated into the HAZ... Check these 2 .pdf's... I found them interesting enough... http://www.arpansa.gov.au/pubs/rrrp/csiro1-10.pdf http://www.arpansa.gov.au/pubs/rrrp/csiro11-14.pdf I know it sounds like mush but, under certain conditions it could happen - does cheap, counterfeit filler metal originating from the "far east" ring any alarm bells??? However, if the filler metal came from reputable sources such as Avesta/Outokumpu, the previous hypothesis would not hold any water... Marty, this one might help shed some light towards your query: http://www.bbs-systems.com/Pages/PagesGerman/ BegriffeUnDefinitionen/Fachbegriffserkl%E4rungen.html#FachbegriffeInfluenceAnker I apologize for not keeping the link active in this thread... I wanted you fellas to be able to read my 2 cents worth regarding the so-called excessive ferrite content in the HAZ or whatever this lab was trying to explain!! ! Respectfully,


SSBN727 Run Silent... Run Deep!!!


By MBSims Date 03-26-2006 17:38

The last link is interesting. It suggests that the presence of ferrite contributes to pitting corrosion in concentrated sulfuric acid/sodium chloride solutions. We would not normally select a 304L material for this type of service. A 316L or 317L would be the minimum depending on chloride levels, increasing to a 2205 duplex, AL6XN, C-276 or 254SMO for the higher chloride levels. It would seem either a very low heat input during welding or a solution anneal after welding would be required to reduce the ferrite levels in a 304L to as low as possible.

Marty Sims

By ssbn727 Date 03-27-2006 00:18

Hi Marty! I agree wholeheartedly!!! Here's a link that hopefully will add on to your previous post with regards to weld decay testing... Although it covers ASTM A249 supplmental requirement 7 ( S7 weld decay testing testing ), it does mention that ASTM262 is the wider application choice of the two tests and S7 testing only accounts for a small percentage of conditions where the use of Hydorchloric acid is required for cleaning out tubes that are "Coked" or lined with organic matter. In this situation, Nickel & high nickel alloys are some of the few metallic materials that possess useful long-term resistance to Hydrochloric acid solution...The Austenitic stainless alloys are not suitable for long term exposure to any significant level of Hydrochloric acid. http://www.rathmfg.com/welddecay.pdf ASTM262 practices A & E, which test for sensitization or susceptibility to intergranular attack, have good general applicability in a wide range of environments & alloys including 304L, 316L and 317L in both oxidizing and reducing acids. The article also explains the difference in the ferrite patterns found in both the base metal (isolated & discontinuous) and the weld metal (skeletal, offering a near continuous path for preferential chemical attack)... It also explains what heat treatments actually do to the ferrite in the weld metal (slightly reducing ferrite content but, mostly spheroidizing the the weld ferrite and break up the continuous/skeletal nature)... It also explains why Laser beam welding of 304L, 316L and 317L has definite advantages over GTA welding of the same material... virtually eliminating the need for heat treatment in order to suppress the weld ferrite through vert fast non-equilibrium solidification ( three times faster than conventional arc processes), high energy density and low total heat input which should result in a very small, almost "invisible" HAZ and very little residual stresses in and and adjacent to the joint. LBW is becoming more and more applicable to joining a wide variety of metals as


the technology improves and will hopefully become one of the most popular welding/joining processes of choice in the very near future because of its clear advantages over conventional arc processes. Here's another good link about different forms of corrosion types in Stainless Steels. Delta ferrite formation, etc. http://www.al6xn.com/SSSguide.pdf Last ones: http://www.mbaa.com/TechQuarterly/Articles/2001/38_2_67.pdf http://www.outokumpu.com/files/Group/HR/Documents/STAINLESS20.pdf Respectfully, SSBN727 Run Silent... Run Deep!!!


By - Date 03-25-2006 18:59

I agree with Marty. The post confused me becausee someone was confusing "excessive ferrites" will directly cause "long term corrosion problems" in a 304L. I disagree with that.


Source: http://www.nrc.gov/reading-rm/doc-collections/reg-guides/power-reactors/active/01-031/

Regulatory Guide 1.31 - Control of Ferrite Content in Stainless Steel Weld Metal

Revision 3 April 1978

Availability Notice

A. Introduction

General Design Criterion 1, "Quality Standards and Records," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50 requires that components important to safety be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety function to be performed. Criterion 14, "Reactor Coolant Pressure Boundary," of Appendix A requires that the reactor coolant pressure boundary be designed, fabricated, erected, and tested so as to have an extremely low probability of abnormal leakage, of rapidly propagating failure, and of gross rupture. Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Processing Plants," to 10 CFR Part 50 requires that a qua1ity assurance program be applied to the design, construction, and operation of structures, systems, and components. Appendix B also requires that measures be established to ensure that special processes, including welding, are controlled and accomplished by qualified personnel using qualified procedures and that proper process monitoring be performed.

This guide describes a method acceptable to the NRC staff for implementing these requirements with regard to the control of welding in fabricating and joining safety-related austenitic stainless steel components and systems in light-water-cooled nuclear power plants. The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.

B. Discussion

Inspection of some welds in austenitic stainless steel components of nuclear reactors has revealed the presence of microfissures. Further investigations related the presence of the microfissures to the low delta ferrite content of the deposited weld metal. Since microfissures in austenitic welds may have an adverse effect on the integrity of components, the control of weld deposits to ensure the presence of delta ferrite in these welds is advisable.

As part of achieving this control, recommendations to test production welds were made in the original version of this guide (Safety Guide 31, "Control of Stainless Steel Welding"), and these recommendations were retained in Revision 1. Because licensees and other representatives of the nuclear industry believed that adequate control of filler metal ferrite content would consistently provide sound weld deposits with an absence of microfissures, a cooperative study group was formed by ASME, ANSI, and NRC to investigate the problem and the alternatives that would ensure adequate control of ferrite content. The study group analyzed data from welds prepared by eight different procedures. About 1500 test results were analyzed, and recommendations were made to both ASME and NRC on how testing of production welds could be reduced without sacrifice of ferrite content control. Revision 2 and this Revision 3 are

based on those recommendations. At present, the ASME Code1 provisions incorporated by reference into

the NRC regulations require compliance with one of two alternative methods for control of delta ferrite in weld metal filler materials; either a chemical analysis method or a magnetic measurement method. The NRC staff does not consider either method adequate by itself to ensure controlled delta ferrite in production welds. The recommendations of this guide are intended to supplement the ASME Code requirements to ensure control of delta ferrite in welds in austenitic stainless steel core support structures and Class 1 and 2 components.


The recommendations for testing of production welds in Revision 1 of this guide have been replaced by recommendations for process control by testing of weld test pads. These changes will considerably reduce the testing effort needed to control delta ferrite in welds.

The staff recommends that ferrite content in the weld filler metal as depicted by a ferrite number (FN) be between 5 and 20. This lower limit provides sufficient ferrite to avoid microfissuring in welds, whereas the upper limit provides a ferrite content adequate to offset dilution.

C. Regulatory Position

1. Verification of Delta Ferrite Content of Filler Materials

Prior to production usage, the delta ferrite content of test weld deposits from each lot and each heat of weld filler metal procured for the welding of austenitic stainless steel core support structures and Class 1 and 2 components should be verified for each process to be used in production.

It is not necessary to make delta ferrite determinations for SFA-5.4 type 16-8-2 weld metal or for filler metal used for weld metal cladding. Delta ferrite determinations for consumable inserts, electrodes, rod or wire filler metal used with the gas tungsten arc welding process, and deposits made with the plasma arc welding process may be predicted from their chemical composition using an applicable constitutional diagram to demonstrate compliance. Delta ferrite verification should be made for all other processes by tests using magnetic measuring devices on undiluted weld deposits. For submerged arc welding processes, the verification tests for each wire and flux combination may be made on a production weld or simulated production weld. All other delta ferrite weld filler verification tests should be made on weld pads that contain undiluted layers of weld metal.

2. Ferrite Measurement

Appendix A to this guide contains extracts from a future edition of the American Welding Society's AWS A5.4, "Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel Covered Welding

Electrodes,"2 which describes a procedure for pad preparation and ferrite measurement. The NRC staff

considers this procedure acceptable for use with covered electrodes.

3. Instrumentation

The weld pad should be examined for ferrite content by a magnetic measuring instrument which has been calibrated against a Magnegage in accordance with American Welding Society Specification AWS A4.2-74, "Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic

Stainless Steel Weld Metal. "3 The Magnegage should have been previously calibrated in accordance with

AWS A4.2-74 using primary standards as defined therein.

4. Acceptability of Test Results

Weld pad test results showing an average Ferrite Number from 5 to 20 indicate that the filler metal is acceptable for production welding of Class 1 and 2 austenitic stainless steel components and core support structures.

The upper limit of 20 may be waived for (a) welds that do not receive postweld stress relief heat treatment or welds for which such postweld stress relief treatment is conducted at temperatures less than 900F, (b) welds that are given a solution annealing heat treatment, and (c) welds that employ consumable inserts.

5. Quality. Assurance

The applicable provisions of 10 CFR Part 50, Appendix B, should be used in verifying compliance with requirements for delta ferrite as described herein.

D. Implementation

The purpose of this section is to provide information to applicants regarding the NRC staff's plans for


using this regulatory guide.

Except in those cases in which the applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method described herein will be used in the evaluation of submittals in connection with construction permit applications docketed after October 1, 1978.

If an applicant wishes to use this regulatory guide in developing submittals for applications docketed on or before October 1, 1978, the pertinent portions of the application will be evaluated on the basis of this guide.

Appendix A

The following is mainly extracted from a future edition of the American Welding Society's (AWS) "Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel Covered Welding Electrodes,"

which the AWS plans to publish as AWS A5.4-78.4 This material describes a procedure for weld pad

preparation and ferrite measurement of covered electrode5 deposits.

EXTRACT:

A4.10 When it is desired to measure ferrite content, the following procedure is recommended:

A4.10.1 Weld pads as detailed in Figure 4 are prepared as prescribed in paragraphs A4. 10.2 through A4.l0.4.

A4.10.2 The weld pad shall be built up between two copper bars laid parallel on the base plate by depositing single weld bead layers, one on top of the other, to a minimum height of 13 mm (1/2 in.). The spacing between the copper bars for the size of the electrode being tested shall be as specified in Figure 4. An optional welding fixture is shown in Figure 5. If carbon steel is used as the base plate, the weld pad shall be built up to a minimum height of 16 mm (5/8 in.).

A4.10.3 The welding current useel for the size of the electrode being tested may be as specified in Figure 4 and the arc length shall be as short as practicable. The weld bead layers may be deposited with a weave, if necessary, to fill the space between the copper bars. The arc shall not be allowed to impinge on the copper bars. The welding direction for each pass shall be alternated and the weld stops and starts shall be located at the ends of the weld buildup. Each pass shall be cleaned prior to depositing the next

weld bead. The maximum interpass temperature shall be 95C (200F).5 Between passes, the weld pad

may be cooled by quenching in water not sooner than 20 seconds after the completion of each pass. The last pass shall be air-cooled to below 430C (800F) prior to quenching in water.

A4.10.4 The completed weld pad shall be draw filed, machined, or surface ground to provide sufficient finished surface to make the required ferrite readings. Draw filing or its equivalent filing method shall be

performed with a 360 mm (14 in.)5 mill bastard file held on both sides of the weld with the long axis of

the file perpendicular to the long axis of the weld. The file should preferably not have been previously used on ferritic material and should be free from loosely adhering materials if previously used. Draw filing shall be accomplished by smooth forward and backward strokes along the length of the weld while applying a firm downward pressure. Crossfiling shall not be permitted. The finished machined, ground, or filed surface shall be smooth with all traces of weld ripple removed and shall be continuous in the length where measurements are to be taken. The width of the prepared surface shall not be less than 3 mm (1/8

in.).5

A4.10.5 A total of six ferrite readings shall be taken on the prepared surface along the longitudinal axis of the weld pad with an instrument calibrated in accordance with the procedures specified in AWS A4.2, "Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic Stainless Steel Weld Metal "(latest edition).

A4.10.6 The six readings obtained shall be averaged to a single value for conversion to Ferrite Number.

Figure 4 - Details of Weld Pad for Ferrite Test


Figure 5 - Optional Welding Fixture for Welding Ferrite Test Pads

Footnotes

1. Winter 1976 Addenda, Section III, ''Nuclear Power Plant Components," ASME Boiler and Pressure Vessel Code. Copies may be obtained from the American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York, New York 10017.

2. This specification has been recommended by the Subcommittee on Welding of Stainless Steels of the High Alloys Committee of the Welding Research Council and has been approved by the American Welding Society (AWS) It is expected to be published as AWS A5.4-78.

3. Copies may be obtained from the American Welding Society, 2501 N.W. 7th Street, Miami, Florida 33125

4. When published, copies of AWS A5.4-78 may be purchased from the American Welding Society, 2501 N.W. 7th Street, Miami, Florida 33125.

5. Note: The U.S. customary units in this specification are given as equivalent values to the SI units. The standard sizes and dimensions used in the two systems are not identical and for this reason conversion from a standard size of dimension in one system will not always coincide with the standard size of dimension in the other. Suitable conversions encompassing standard sizes of both can be made if appropriate tolerances are applied in each case. The SI values (including tolerances) given here for filler metal diameter, length, and package size were selected to fit the product sizes which presently are U.S. standards. Tolerances are used in some cases in this specification but not in others In those cases where no tolerances are given, the values are those that would be obtained if the measurements were taken in SI units. In this specification, a covered electrode is defined as follows: Covered Electrode--A composite filler-metal electrode consisting of a core of a bare electrode or metal cored electrode to which a covering sufficient to provide a slag layer on the weld metal has been applied. The covering may contain materials providing such functions as shielding from the atmosphere, deoxidation, and arc stabilization and can serve as a source of metallic additions to the weld.

Privacy Policy | Site Disclaimer Thursday, February 15, 2007