8/2/2019 Welding SAF2205 Tubes to CS Tubesheet

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Texgrande(Petroleum) 30 Jun 09

15:02

We are having problems welding duplex 2205 tubes to a carbon steel tube sheet using inconel 625 rodswith the GTAW process. We keep getting small indications after PT testing and after grinding out the1ndications and repair welding the PT test shows no indications. Upon making the 2nd pass of the

strength welds the PT tests are revealing more indications some of which go down to the 1st pass and(1) had what appeared to be a crack across the face of the weld. We are at a loss to determine theproblem. Has anyone had this problem before or any suggestions.

boilerone(Mechanical) 30 Jun 0917:13

I am not a welding guy at all but Inconel 625 (58% Nickel Min.) seems not a good candidate forwelding 2205 (6.5% Nickel max.) to carbon. Both of the two electrode selecting guides that I found

point to use AWS E309MoL (13% Nickel) for 2205 to carbon GTAW welding. Here is the link to a verydetailed 2205 welding guide:

http://www.outokumpu.com/35058.epibrw

metengr(Materials) 30 Jun 09

17:27You need to use a 309Mo filler metal as mentioned above for dissimilar metal welds with duplex tocarbon steel. The problem with using a Ni-base filler is that the duplex structure in the weld deposit iscritical. In this case, you have so much Ni that the primary weld solidification mode is austenitic and

results in hot cracks.

MikeMet(Chemical) 30 Jun 09

18:37

Inconel 625 is not the best choice for dissimilar metal welds due to the Nb additions. The Nb in thefiller metal can form intermetallic compounds, such has hard nitrides, that can cause cracking in theweld as it cools and degrade the corrosion resistance Better choices would be ERNiCrMo-10 (Inco 622,Hast C22), ERNiCrMo-14 (Inco 686) or ER309LMo. Tube to tube sheet welds are subject to very highcooling rates due to the heat sink of the thick tube sheet. You should also consider adding 1-3%

nitrogen to the shielding gas. Nitrogen is an austenite former and help ensure you get a properaustenite/ferrite balance in the weld nugget.

Texgrande(Petroleum) 2 Jul 0913:21

Just wanted to thank you guys for the quick response and valuable information. It appears that thechoice of filler metal is a bad selection, however that is what the customer is requesting so we areattemting to make the best of a bad situation.

jmiles(Mechanical) 2 Jul 09

15:52

Its been my experience that alot of customers can toss around terms like inconel and duplex cause they

ahve ehard somethign or other about it, not always because they know alot about it, in this case id

suggest its worth challenging the customer ina polite way about why they are insisting on using inconelfor the filler material as you would prefer to use another amterial for better welding properties.

You would be surprised how often someone telsl you they want one specific thing because they cant

think of other options but they are really happy with whatever work.

fegenbush(Mechanical) 6 Jul 09 9:40

If the customer is insisting on Inconel 625 filler material, it may be for corrosion resistance reasons. Ifyou have an appropriate welding procedure, it may be most economical to overlay the 625 onto the

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8/2/2019 Welding SAF2205 Tubes to CS Tubesheet

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309Mo. This, of course, depends greatly on the diameter of the tubes and thickness both of the tube

and tubesheet.

Fegenbush

stanweld(Materials) 6 Jul 09

17:44

Texgrande,How are you cleaning? Are you welding after pressure rolling the tubes? Cleanliness is mandatory whenwelding making the weld described.

I'm not sure why your customer is requiring 625 alloy for the involved weld. If the tube sheet/channelside only requires carbon steel, the shell side should be the corrosive side requiring the 2205 alloy,assuming U-Tube design. If that is the case ER309Mo would be recommended. Mikemet's

recommendationas would be superior to 625 if a nickel base, up-alloyed, weld filler metal isrequired.

Texgrande(Petroleum) 9 Jul 0915:10

Just wanted to thank all you guys for the quick and concise responses. I will be passing this info on tothe powers that be in hopes that they will take a better look at the situation next time. Oh, they didmanage to get the tube ends all welded and PT tests revealed no rejectable indications but I agree withyou guys that 309 would be the answer to problems with these welds. They did do a light roll prior tothe first pass on the welding so it is possible that the tube ends were not cleaned as well as they shouldhave been. However I am in agreement with you guys that due to the dissimilar metals that 309 wouldbe the choice for filler material in this application.Lets hope the hydro test goes ok. Thanks again, TexGrande

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