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Up Topic Welding Industry / Technical Discussions / Star cracks in 304L radiograph
- - By kseven Date 03-31-2006 01:04
Pipe is 6" .280 wall 304L (non-domestic). Actually leaks about 1" from weld edge at 700lb salt water service. Welded GTAW all the way out. Saw the film this am. and there were some discontinuities but nothing that should be causing the cracks that look like they propagate from the root area. Technician said he had never seen these in stainless welds before. This pipe and fittings come from some countries I've never heard of before. The man that fabricated this stuff CAN WELD.ok? Client, shop, and suppliers are all pointing fingers. We need some advice. Thank you in advance for any reply.
Parent - - By jwright650 (*****) Date 03-31-2006 01:10
Is it a crater crack?
John Wright
Parent - By kseven Date 03-31-2006 02:42
John,Thank you for replying. I have not seen this piece since it went out to go in service. Only heard about leak and viewed film this morning.Maybe using the "star crack" term was inappropriate because it looked as though the "stars" were larger than what I've seen in carbon [not to sound like I know anything about RT]. Anyway the crack supposedly starts from a small (less than 1/8") area of IF in the root and makes it's way about an inch from the weld at the surface allowing the leak.
Parent - - By thirdeye (***) Date 03-31-2006 04:18
kseven,

I have seen many weld failures (which leaked over time) that started from a flaw in the root and eventually worked their way to the weld toe on the cap, but propagation into the base material is not as common. Have you ruled out lamination? Although lamination is more common in plate, I have seen it in pipe and fittings.

I ran into a similar oddity recently but it does NOT involve a weld. The first picture is of an area on the OD of a 16" X .375 section of wall carbon steel pipe. It failed during hydrostatic testing around 850 psi.

http://img.photobucket.com/albums/v377/thirdeye2/welding01/d3fa4eb2.jpg

I performed a UT examination which disclosed a longer area on the ID of the pipe so a section was removed. The ID indication is shown in the photograph below.

http://img.photobucket.com/albums/v377/thirdeye2/welding01/0bc0f866.jpg

It appears to be a manufacturing flaw and the piece has been returned for evaluation. Keep us posted on the results of your investigation.

~thirdeye~
Parent - - By kseven Date 04-04-2006 23:47
thirdeye,parts of the process piping were brought in today. We dye-penned the areas where X-ray marked "cracks" and came up with no perceptible flaws. Cut the pipe adjacent to the welds to perform a "test" weld using the same procedure. After pipe prep performed a dye pen on the weld face of the pipe. A series of wormholes? and a definite lamination jumped right out. Have not checked the fittings yet. Supplier will still probably fault welding but I don't have any idea on what criterion. Thank you for your post. Just another dumb welder trying to make sense of it all. Klay
Parent - By thirdeye (***) Date 04-05-2006 13:36
Klay,

Bear in mind lamination itself will not show up on a radiograph (but can be detected with UT), however other manufacturing discontinuities may and you may have a combination of both to some degree. Linear indications between gas pockets (or tails on single pockets) is quite common. It is possible that orientation of indications gave the "star like" appearance on the radiographs.

The supplier should replace the material and they usually will pay for some inspection on the remainder of the material. Reimbursing you for welding labor or downtime is another issue, I've seen it go both ways.

~thirdeye~
Parent - - By jwright650 (*****) Date 04-05-2006 14:10
Hi Klay,
Here are a couple links regarding a problem another member here had with a supplier's bad pipe.
http://www.aws.org/cgi-bin/mwf/topic_show.pl?id=8803#42130


http://www.aws.org/cgi-bin/mwf/topic_show.pl?id=8834#42366

John Wright
Parent - - By kseven Date 04-06-2006 03:08
John & thirdeye, I think you have both hit the proverbial nail. We're not in as deep as Deb yet, but are getting close. Some of this pipe had literally split at "seams" in between welds with a stress of less than 1/4 of yield(figured by stress= PR/T). Looks like we will get new pipe,hopefully not from the same source,and start over. Thank you both very much for sharing insight and knowledge with us. I stand in awe at the level of wisdom that abounds in this forum. Makes me think of those two dumb kids on their knees with hands up reciting "we're not worthy'! Thanks again, Klay
Parent - By Jim Hughes (***) Date 04-06-2006 12:03
KSeven,

I would look into microbial assisted corrosion (MAC). Also chloride stress corrosion cracking (CSCC). I would check the chloride levels in the water your using to Hydro or even in the service. You can put some of the most wicked chemicals in 300 series SS, but water with a high level of chlorides can kill SS fast. If your cutting some of this pipe appart look for what looks like a dirt dobber nest on the surface. It looks brown with a brown tint to it that forms on or ajacent to the weld. We had MAC form in a 10" SS line in a matter of 3 months.

Just a thought

Thanks
Jim Hughes
Up Topic Welding Industry / Technical Discussions / Star cracks in 304L radiograph

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