×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Crack in the weld transverse to the direction of weld run
2

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.

RE: Crack in the weld transverse to the direction of weld run

More than likely hydrogen cracking, but there are several other possible causes listed in this article. Transverse cracks are toward the end of the article. Make sure the weld filler metal was correct if at all possible. Another factor for induced stresses is the rolling of the plate, but unlikely at that thickness.

http://www.lincolnelectric.com/en-us/support/proce...

RE: Crack in the weld transverse to the direction of weld run

(OP)
Thanks DVWE. Hydrogen cracking was my first thought too.. thanks for the Lincoln Electric article.

RE: Crack in the weld transverse to the direction of weld run

It would be interesting to look at the ID of the weld there. That is a high stress location and less than full penetration would make the stress much higher, though H is a likely cause weld quality could have aggravated it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Crack in the weld transverse to the direction of weld run

1)Excessive fillet weld
2)Check calculation of reinforcement required

Regards
r6155

RE: Crack in the weld transverse to the direction of weld run

(OP)
Thanks EdStainless and r6155.

RE: Crack in the weld transverse to the direction of weld run

I would not attribute the crack to hydrogen unless the crack occurred when the vessel was relative new. The most critical time period would be with in the first 48 hours or so. As time passes, the hydrogen effuses into the surrounding atmosphere, thus the probability of cracking is reduced over time. Granted, a small hydrogen crack may have initiated and grew over time, but I would expect it to manifest itself relatively quickly.

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

By the way, nice photograph of a transverse crack. I would love to have a copy of that for my presentation on welded defects!

Best regards - Al

RE: Crack in the weld transverse to the direction of weld run

(OP)
Thanks gtaw.

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

Perhaps someone just got the design wrong. If its a common fault that would tend to rule out manufacturing error as it would be difficult to get the same spot to fail.

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

"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 "

And people are still buying them ?

RE: Crack in the weld transverse to the direction of weld run

Hydrogen cracking based on the orientation and appearance.

RE: Crack in the weld transverse to the direction of weld run

(OP)
Thanks LittleInch. But that is all the data I have.

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

Is this oil water separator a pressure vessel and if it is what is the name of the manufacturer, and did you get a copy of the manufacturer's data sheet from the National Board for information on the tank and its tower material, allowable pressure and temperature.

RE: Crack in the weld transverse to the direction of weld run

Transverse cracking in steel weldments are most caused by hydrogen (vast majority of cases) or other local contaminant. It would be interesting to know the filler metal chemistry because one would not expect hydrogen cracking in .25-inch wall thickness welds even without preheat; however, they may have used a high strength filler like ER80S-D2.

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

(OP)
chicopee - yes, this is a pressure vessel. But I don't know the name of the manufacturer, nor do I have the data sheet.

Thanks, weldstan.

RE: Crack in the weld transverse to the direction of weld run

That crack has opened-up pretty wide and extends into the heat affected zone so there must be a lot of residual stress. I believe that preheat of the vessel before welding or post weld stress relief may have been lacking.

RE: Crack in the weld transverse to the direction of weld run

(OP)
Thanks Compositepro.

RE: Crack in the weld transverse to the direction of weld run

No information, no documents: Discard this pressure vessel

Regards
r6155

RE: Crack in the weld transverse to the direction of weld run

The vessel does have a name plate on it in the picture. It has been painted-over.

RE: Crack in the weld transverse to the direction of weld run

If it is a NB/ASME code pressure vessel, there should be a tack welded nameplate with a National Board number. Providing the NB number to the National Board, you can get a copy of the manufacturer's data sheet. I got a feeling that you have a Chinese clone which was cheaply purchased. If there are no nameplate get rid of it and get a NB code constructed unit.

RE: Crack in the weld transverse to the direction of weld run

Yeah, I now see it too Compositepro as it is tack welded on the tower section.

RE: Crack in the weld transverse to the direction of weld run

The nozzle diameter is almost the diameter of the vessel. Unfortunately there is no information about the pressure, temperature, materials and wall thicknesses. It seems to me that there is a lack of nozzle reinforcement, therefore the weld is highly stressed. The direction of crack and location are the clear proves of it.

RE: Crack in the weld transverse to the direction of weld run

Saplanti, that was my point, maybe it's just bad design rather than bad construction, especially if it's happened more than once in the same place.

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

2
How is the material of construction known to be is SA 455?

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

Probably the designer took into consideration the number of weld passes as reinforcement. I am estimating six weld passes including the root weld.

RE: Crack in the weld transverse to the direction of weld run

Gtaw:
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

I see that the crack is across the weld. It's stress on the tank guys. The huge opening for the dome must be reinforced regardless of calculations so this design qualify for more analisys period. It may even need pwht. I'm surprised deformation did not show during hydrostatic test. T
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

If it were reported to the National Board and investigated by it, there would be an article in one of their bulletins.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources