Arc Burn and Temporary welds on pipelines

[engresague]

Hi. I need your help again,
The cuestion is as follow:

First:
In accordance to API-1104, the welding procedure can be qualified by "Welding of Test Joints-Butt Welds" or "Welding of Test Joints-Fillet Welds".
Moreover, a major change in joint design constitute an essential variable.

The cuestion: Can we weld T or Lapped fillet joints with a WPS qulified by "Welding of Test Joints-Butt Welds" ??

Second:
For ASME B31.4, the ARC BURN on the pipes surface shall be repaired because this is a stress concentrator.

The cuestion: Should be considered a temporary T or Lapped fillet weld on the pipe surface, as much or more harmful than the arc burn ??
(temporary weld made with the above described procedure qulified by "Welding of Test Joints-Butt welds")

Thanks in advance for your comments or help about.

 

[weldstan]

Arc burns may form a thin, hard, martensitic layer on the surface due to the rapid quench effect of the heat conductive base metal. This layer is crack sensitive and a crack may be present due to the rapid cooling effect.
Properly made fillet welds can be made such that cracking is not an issue (greater heat input + slower cooling). A very small tack weld to attach a temporary part to the base pipe can act the same as an arc burn and I have seen cold cracks in the base metal that led to fracture when this type of tack was used.

 

[dhengr]

Engresague:
An arch strike is often worse than a real weld, because it leaves a small crater and very much hardened steel. There is enough heat input to cause the crater and harden the steel in the immediate area of the stress raiser (crater), but not enough heat input, for a long enough period of time, for the typical welding metallurgy to take place, or for some of the tempering/annealing/ mixing which comes with a regular welding process. Tack welds (or temporary welds) are usually o.k. if the are welded over as the weld joint is completed, or if they are ground down/out and cleaned up, so as not to leave a stress raiser.

 

[BigInch]

We always required arc welds to be cut out and replaced with new pipe.

ASME B31.4 & 8 Generally you should NOT be welding anything directly to pipe, except more pipe.
Use full encirclement sleeves, no weld attachments.

 

[engresague]

OK, Thanks you very much for your help.
I have an other question about.

How can we avoid the possible detrimental efects from welds as the cathodic protection (exothermic), on the body pipe..?
I do not know which one standard or way to use as reference for qualify a welding procedure for this application.

 

[BigInch]

Not enough heat to do any damage, if you follow the directions.

 

[DekDee]

Quite some time ago I read about a little experiment conducted to demonstrate the problems of arc strikes to the welders (actually think it was one of our members but on another forum).
Cut 8 x straps from plate and prepared them for bend testing.
Took 4 of them and laid side by side.
Dragged an electrode across the centre so the arc strikes basically formed a line across the 4 straps.
Bent the first 4 - no problem.
Bent the next 4 and all 4 straps snapped.

We can tell the welders over and over how dangerous arc strikes can be but they cannot seem to appreciate the metallurgical changes that happen with instant heat / instant cooling.
Picture is worth a thousand words ?

Cheers,
DD

 

[zengx]

As an answer to your first question, the following is a copy-paste from an API 1104 commmittee reply to an interpretation:

"PROCEDURE QUALIFICATION One of the essential variables listed in Paragraph 2.4 is 2.4.2.3 "Joint Design." Here it states that a major change in joint design constitutes an essential variable. A change from a butt to a fillet weld is a major change in joint design, thus requiring that a new procedure be qualified."

Mohammed Diab.
Inspection Supervisor - Saudi Aramco.