Weld issue 304H flange to 304L pipe

[Danbury]

Appreciate it if anybody could comment on this below:
300# SO 304H flange welded to 304L pipe by filler material of 308H, cracks observed ai weld joint after temperature cycles 1250F. Can 304H be welded to 304L? is 308H a right filler material?
Thanks,

 

[metengr]

Danbury;
Yes, 308 is the correct filler metal for this weld joint. What kind of cracks are you seeing visually? Orientation of the cracks relative to the weld? Are the cracks in the weld deposit itself or other location near the weld? Are there one or more cracks?

 

[Danbury]

See attached pic. for crack. Thanks,

 

[metengr]

Danbury;
This is a classical hot crack from welding based on your attached photo. Back grind till sound metal and re-weld using 308 filler metal. I would perform a Liquid Penetrant examination after weld repair.

 

[arunmrao]

Can't help ,but agreeing with metengr,. Did you try 310 welding rod ? Also did you use manual metal arc welding or TIG?


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[metengr]

Not sure of the camera angle, but it appears to me that the welder was fighting a wider than normal gap based on the wider than normal face of the fillet weld. If this is correct, hot cracking is typical because of the large width to depth aspect ratio of the weld joint.

Weld repair as I mentioned above should work.

 

[EdStainless]

Do you have a FN for the weld? It could be very low, making this more likely.
It makes wonder about the heat input, it may be too high.

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Plymouth Tube

 

[GRoberts]

After looking at the photo, I'm not sure that it would be hot cracks. Also, hot cracks form before the weld cools. Danbury mentioned that the cracks formed after service at 1250F. In the lower right corner of the photo (near the seam in the pipe), the weld is also cracked at the toe of the weld instead of the throat. Almost all hot cracks are either crater cracks or centerline cracks. As Metengr mentions, it looks like it was possible the root gap was excessively large. In this case, it could just result in an undersized weld throat. The pipe doesn't look that thick (based on the narrow pipe seam weld), but the flange is. After a few heating cycles, it is easily possible that the weld was just overstressed. Can you take a cross section of the weld to see what the weld geometry is like?

That being said, there isn't anything inherently wrong with welding 304L to 304H with 308H. There is probably some other problem at work here.

 

[metengr]

GRoberts;
Good advice regarding sample removal. I think your statement regarding cracking from an undersized fillet has merit if a post weld NDT was indeed performed to ensure there were no cracks prior to service. There was no mention of any NDT that was performed prior to service.

I have seen hot cracking that actually opened first time in service as a result of subsurface hot tears breaking through to the fillet weld face due to poor weld joint geometry and shortly after solidification of weld metal due to lower than normal ferrite content in the weld metal.

 

[Danbury]

Thanks to all for your reply. Just wonder if any one has yield and tensile stress for 308 at 1250 F? We have done FEA analysis and noticed that transient stress from cold to hot could reach 36k psi.
Thanks again.

 

[metengr]

Danbury;
Go to the web site below and download this paper. It is an excellent source for high temperature properties. You can ballpark UTS and YS at temperature from the list of austenitic stainless steel grades.

http://www.nickelinstitute.org/inde...acteristics of Stainless Steels/method/1.html