Welding over porosity

[gwelch123]

We are building a API 650 tank and the production guys are welding over porosity saying it's ok and it will burn out. What does the code say about this or if not what can happen by doing this?

They are also gouging the backside and then with all the nonfusion present after gouging they are welding over that as well..

 

[Metalmeister]

There should be no porosity in plate steel, so I assume it is in the weld metal. When you back gouge you should remove all the nonfused areas. Sounds to me like the welding process is putting in the porosity, and they will just add more unless the process is corrected. Visual porosity is pretty darn big.
Worst case is failed NDE and/or leaks.

 

[unclesyd]

Personally I think your concern is warranted.

Take a few radiographs and compare them to what's allowable in API 650. Normally you would tell the inspection company to what code or standard you want weld graded to and let them give you a starting point.

Can you come back with some dimensions of the tank.

Weld details, electrode and thickness and especially what code are the welders qualified to.

In my 40+ years around welders the most common refrain is "I'll float it out".

 

[stanweld]

I general the existing porosity will not burn out when welding over it.

 

[Mr168]

I would immediately reject the welds and revoke the welders' qualifications for whatever procedure they're running. Why an inspector hasn't done this already is beyond me.

Porosity does not just magically disappear or "burn out" with carbon steel. If NDE is performed, they WILL end up cutting the entire thing out and rewelding it anyways. In addition to porosity, gouging and welding over unfused material is just begging for that seam to crack. If a full penetration weld is require, the inspector can reject the entire seam based on that criteria alone.

 

[metengr]

They are also gouging the backside and then with all the nonfusion present after gouging they are welding over that as well..

This is a violation using either API or NBIC codes and standards. Nowhere in recognized codes and standards is it permitted to weld over defects.

 

[Mr168]

API 650 Section 5.1.5 will outline the need for full penetration joints. 7.4.1 indicates that all defects must be called to the attention of the purchaser's inspector, and 7.4.2 indicates that the only porosity that may be welded over is pinhole porosity on tank bottom joints, and that is only if the porosity is less than the visual criteria established in section 8.5.

 

[JStephen]

I'm not sure I understand the question here. Are they getting porosity on one pass and then welding over it in a subsequent pass? Or is this a completed weld and they are repairing it by welding over porosity?

The items in 7.4.1 and 7.4.2 would apply to finished welds, but I don't believe they would be applied to intermediate passes of a weld. Not to say it would be acceptable, but the determinant would be the testing of the finished weld, not the appearance of intermediate passes.

"with all the nonfusion present after gouging"- what nonfusion is present after gouging? Is this the porosity again, or a different issue?