Crack in the weld transverse to the direction of weld run
Crack in the weld transverse to the direction of weld run
(OP)
Hi Al,
Can anyone take a look at the two pictures below and advise the cause for the fracture shown here.


It is an oil separator tank made from SA 455 material. To my knowledge there are no temperature extremes and vibrations in service. Material is 0.25" thick; it is code vessel. Thanks in advance.
Can anyone take a look at the two pictures below and advise the cause for the fracture shown here.


It is an oil separator tank made from SA 455 material. To my knowledge there are no temperature extremes and vibrations in service. Material is 0.25" thick; it is code vessel. Thanks in advance.





RE: Crack in the weld transverse to the direction of weld run
http://www.lincolnelectric.com/en-us/support/proce...
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
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P.E. Metallurgy, Plymouth Tube
RE: Crack in the weld transverse to the direction of weld run
2)Check calculation of reinforcement required
Regards
r6155
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
I suspect there is a discontinuity in one of the initial weld beads. Perhaps there is incomplete fusion at the start of the weld bead where two beads overlap, possibly incomplete joint penetration in the root of the root bead, who knows unless the weld is sectioned an examined.
Transverse cracks can also occur if the weld filler metal overmatches the base metal. This can happen if a highly deoxidized filler metal is used on multiple pass welds on "clean" steel. The deoxidizers become alloying constituents if the deoxidizers are not utilized. As alloying constituents, the silicon or manganese increase the hardness and strength of the weld, i.e. the weld overmatches the strength of the base metal. The resulting residual stress in the longitudinal direction can exceed the tensile strength of the base metal and cause a transverse crack.
Having thrown that possibility out there, my money is a defect in the root bead.
Best regards - Al
RE: Crack in the weld transverse to the direction of weld run
Best regards - Al
RE: Crack in the weld transverse to the direction of weld run
I have been told that most oil separation tanks (identical to the one shown in the picture and built by same fabricator) show the same defect. Don't know if the defects manifested soon after being put in the service.
The picture is not mine; however I will find out if I can get permission for use in presentation.
Regards, RKT
RE: Crack in the weld transverse to the direction of weld run
This looks like the highest stress point. Pressure in service and number and size of pressure cycles would be good to know. when you have a hole that big that close to a dished end, the stress calcs can get a bit indistinct.
The issue might well be the weld if its much stronger than the base metal, but there look like other things at play here and maybe the weld is only one part of the story. - More data please!
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Crack in the weld transverse to the direction of weld run
And people are still buying them ?
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
DekDee - perhaps these separation tanks were all delivered at the same time for a project. Seems very unlikely that people will keep buying them knowing fully well of this problem.
Thanks metengr.
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
The location of the crack in the weld and apparent extent of the crack into the base metal may also indicate fit-up problems during welding causing a localized high stress in the location. I would also check the root for a major discontinuity per EdStainless.
RE: Crack in the weld transverse to the direction of weld run
Thanks, weldstan.
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
Regards
r6155
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Crack in the weld transverse to the direction of weld run
If that information is known, the operating temperature and pressure should be known or the information should be located on the attached nameplate. My point being, there should be a bit more information available or obtainable from the source that knew the material of construction.
There have been several hypothesis tossed out, but without sufficient information they are no more than speculations as to the cause. There is a couple that I find interesting and worth looking into:
1) Proper design: It seems likely that the opening should have been reinforced considering both major components are nearly the same diameter.
2) Stress: The hoop stress usually exceeds the axial stress and the crack is oriented transverse to the hoop stress.
3) Welding: The carbon content is typically below 0.3% and the wall thickness is ¼ inch, so it doubtful preheat is necessary and less likely to have been provided. The likelihood of hydrogen cracking seems low with the thickness and carbon equivalency involved.
4) Weld defects: The presence of a weld discontinuity is relatively high regardless of whether a complete joint penetration groove weld was employed or if for some reason the fabricator used fillet welds to join the two major components. If this is an ASME designed and fabricated vessel one would expect a CJP groove weld was used. That isn’t necessarily the case if it was constructed to a different design standard. The probability of incomplete joint penetration is high if the complete joint penetration groove was welded from one side. If the joint was back gouged, it is not uncommon for the welder to skimp on the depth and width of the back gouge especially considering it has been stated the thickness is only ¼ inch. Welders often leave remnants of the unfused root with the assumption they will “melt it out” with the next bead. Incomplete joint penetration is a common problem. If the width of the back gouge is insufficient, incomplete fusion can often result as the weld flows into the BG cavity but doesn’t fuse to the groove face of the excavation.
If the joint was designed as a fillet weld, the root acts as a crack initiation point. If the initiation point of a weld bead is not properly fused, it acts as a stress riser and a possible location for crack initiation. While the weld profile in the photograph is uniform, unless this is a standard product that employs mechanized or automatic welding equipment, the welds are most likely deposited using a semi-automatic welding process. The welder cannot weld the entire perimeter of the joint without starting and stopping several times. Each time the weld is initiated, a “cold start” is a potential crack initiation point. Good practice would include a grinding operation to remove the “cold start”, but good practice is not always the common practice.
Best regards - Al
RE: Crack in the weld transverse to the direction of weld run
RE: Crack in the weld transverse to the direction of weld run
Nicely done. Your comments on this thread have been right on the money. That’s about all that could possible be said, without guessing, and with so little of the important design info being kept secret. It never ceases to amaze me that people who claim to be engineering or tech professionals don’t seem to have any idea what info. is needed to be provided, if they want to start a meaningful discussion about their problem.
RE: Crack in the weld transverse to the direction of weld run
As the poster says it's common n on this product, then also qualifies to be reported to the National al Board. That is if the Code is the ASME. Or the jurisdiction if in the US or Canada. GenBlr.
RE: Crack in the weld transverse to the direction of weld run