Cracks in Fillet, 316L to 316L?? 2

[Capntom]

hello All: We are welding Ø 1.25 sch 40 pipe to a slip-on flange mfg'd to ASME B16.5, SA 182 alloy. Both are 316L with 316L filler made to MIL-E-19933. We are experiencing circumferential cracks. No toe cracks though. Ø 1/16 filler putting a 1/16 fillet on using manual GTAW. Argon purge. No preheat or PWHT used. Cracks appear upon solidification. We are using 2 different suppliers of flanges also. Could a gas contamination cause these??? What should I look for??? HELP........

 

[stanweld]

It appears that you have a hot cracking problem and because the fillet size is so small high welding residual stress caused by improper joint fit up, or low ferrite content filler metal are likely suspects. Is this a true slip-on or a socket welded joint? If a socket weld, make sure you leave an approximate 1/16" space between bottom of socket and end of pipe. If true slip-on, make sure that there is a 1/32" minimum gap all the way around between the flange and pipe surface. If joint design is acceptable, check ferrite content of deposited weld metal. If zero or very low ferrite is obtained, change filler metal to provide higher ferrite (> 2%). Also advise checking sulfur and phosphorous content of filler metal.

 

[Capntom]

Thank you for your quick response. Ferrite number is 10FN on the Delong diagram. 7 percent by by the "AFN WRC" ?? Don't know whath that is. Gotta do some reading today. The joint is a true slip-on, no socket. Sulfer content of filler is 0.01, Phosphorous is 0.02.

 

[GRoberts]

Sounds like the main thing you need to do is increase your fillet weld size. A 1/16" weld is very small. If there is any root gap, it could make it exceptionally thin. Gas would not generally be the problem for cracking. It would more likely cause porosity or lack of fusion.

 

[unclesyd]

It sounds like you don't have enough metal to hold the stresses. If the fit is too wide this could be the problem and can only be corrected by carrying more metal while welding or closing the gap. If you have as mentioned 1/32" gap and it slips to one side then there is a 1/16' gap on the opposite side and a 1/16" fillet will not work very well.
I don’ ever remember have a problem welding 316 S/S pipe and slip-ons that involved the materials.

Exactly where is the weld cracking?
Are you welding on both sides of the flange?
Is this a true slip-on or is it possibly a lap-joint flange?

 

[stanweld]

I concur with unclesyd and GRoberts. Assuming that your filler metal has the ferrite stated, the initial fillet weld pass size should be increased.

Please note that when I asked for the ferrite content, I meant the actual weld deposit ferrite, which is measured with a magnetic ferrite gage - not as calculated from the chemistry provided with the wire by the wire supplier. The deposited weld metal chemistry is a combination of the base metal chemistry and the filler metal chemistry. More than once, I have found that supporting MTR was in no way representative of the material received.

 

[corvin]

In addition to the very good points above, please keep in mind that the cleanliness of the base and filler material is also critical. Make sure you degrease both with alcohol, acetone etc.
You also need to be aware that in a small fillet weld like that there is a lot of dilution with the base material, consequently you will end up with a FN a lot closer of that of the base material not of the filler. Usually the base material has less ferrite than the filler. So, you may want to look into the base material, too. It's always more difficult to weld 300SS autogenously than with filler wire addition which brings the extra ferrite that makes the weld deposit more resistant to cracking. However, don't forget that 310SS welded with 310 filler is also possible even it's fully austenitic, but with precautions.
In addition to the above you can either try to increase the size of the weld (which will take care of the solidification stresses better and increase the participation of the filler)and/or use a low heat input and technique which will minimize the dilution with the base material and keep the heat input low. Also try to produce a convex weld not a concave one that is too shallow and cannot accommodate the stresses. You can also break the weld into shorter beads which will solidify one at a time, reducing the cracking risk but increasing the potential of start/stops defects.

 

[JP0506]

Corvin has good points but one thing that may help in all this is do small tacks using minimal heat but enough tacks to hold the job in position before fully welding, and I have found once you start to run your full weld, pretty much don't stop until it is completed. The bigest downfall with stainless as a material is the inflexability and sufferance of heat stress so as you weld it is trying to pull and reshape itself.

 

[SWang]

I am familiar with ASTM materials. Now someone asked me about 316L material. Can you point out for me what this material is?

Thanks!

 

[Capntom]

Do a search for "UNS 31603". Unified Numbering System. This is a Austenitic Stainless Steel. Similar to 304 SS except the addition of Molybdenum for corrosion resistance. The "L" is for the Low carbon (<.3%) grade which is used for welding applications where you want to minimize chrome carbides that will decrease your corrosion protection.