Questions about HAZ and NDT for piping 3

[fatdogs81]

My customer has asked me to increase a distance between two welds on a pipe at least 50mm(welded toe to toe), which is now 45mm from each welding center as shown in the attached picture.
Unfortunately, the distance cannot be increased anymore due to several reasons. I therefore am trying to find a way to persuade the customer to keep the current condition.

It would very helpful to me if you could let me have answers to the followings:

* Pipe info.
- Pipe size: 250A(Thickness: 9.3)
- Pipe mat'l: Carbon steel (JIS CODE: STPG370-ERW)
- Medium: Lub. Oil (Working pressure: under 3 bar)
- Welding: Butt welding

* What I need to know
1) Is there any possibility to overlap HAZ of each welds? How can I calculate width of HAZ?
2) If HAZ is overlapped, What problem occur?
3) What should I do to verify integrity of the pipe? Welds penetrant test alone is enough to verify? or is any other examination necessary?

Hyunik Cho

HYUNDAI Engineering & Technology
Ulsan, South Korea

 

[gtaw]

Who cares whether the HAZ overlaps? The material is low carbon steel pipe that is manufactured using hot roll plate or pierced at temperatures above the lower critical transformation temperature and utilizes uncontrolled cooling rates. Welding is unlikely to change the mechanical properties. Having said that, if notch toughness requirements apply or if the base metal was not low carbon steel, it would be a different conversation.

The HAZ of two adjacent welds is no different or detrimental than two adjacent weld beads in a groove weld that requires several passes to complete.

Unfortunately, there are many old wives tales that people believe.

That isn't to say there are not materials that could be affected by multiple thermal cycles, but carbon steel; not so much. If this was austenitic stainless steel subject to sensitization, yes, it could be a problem. If the base metal was heat treatable aluminum that is sensitive to time at temperature; yes, it could be a problem. More than likely the problem is the person involved probably saw the limitation on another project, but didn't appreciate why the restriction was in place.

Best regards - Al

 

Al - you have answered well.

(1) A little knowledge is a dangerous thing.
(2) There are legions of amateur welding engineers (refer to (1) above).

 

[gtaw]

Thanks for the vote of confidence.

Best regards - Al

 

[fatdogs81]

Al, many thanks for your answer. I learned much more from you than what I got from google for half a day.
I'm now trying to persuade the customer with an explanation based on your answer.

Ironic metallurgist, I will keep your first words in mind.

Hyunik Cho

HYUNDAI Engineering & Technology
Ulsan, South Korea

 

[gtaw]

Happy to help.

Best regards - Al

 

[mk3223]

See thread378-242240 for the length discussion of the subject.
IMO, without any Code or Standard, the design may be based on the project specification and/or the owner requirements.

 

[DekDee]

That is the touchy one - " Owners requirements"
If it is not listed in the applicable codes, project specs or any other contract documents the client has no right to require anything.
Basically, they get what they paid for !
Cheers,
Shane

 

[weldstan]

Owners always have the right to specify additional requirements to the Codes within the Contract. If done after the signed Contract, a Change Order is required to be agreed upon by both parties to the Contract.

In the OPs case, gtaw is absolutely correct. In any event there will be no overlapping of HAZs and the thickness and distance involved will not induce any unreasonable weld residual stress on the miter like narrow component.