Removal of boiler water wall tube pannels

[weldor]

We had a contractor remove a water wall tube pannel from our boiler.
The process that they used was to sever the membrane with an arc air torch.
In doing so they struck the ajoning tubes leaving gobs of molten material to be ground off.
Our concern is that in the process I an sure that a large quanity of carbon was intermixed in to the ajoning tube, which would alter the chemical composition thus when welding the membrane back to the ajoning tube I fear that this will create a sub standard weld and possible future tube failure.
I remember reading that the use of an arc air torch for this purpose was not allowed by the NBIC if one could not leave adequate material enabling the carbom to be ground out, In our case the tubes are near tangent with only a 1/4" membrane between them.
I would like to know what the governing bodies have to say about this.

 

[pipewelder1999]

I'm not familar with the current codes but I am not aware of any restriction for carbon arc gouging.

I don't think grinding of slag from gouging can cause carbon to mix with the base metal. If a tube is gouged or nicked with an air carbon arc then it should be evaluated and repaired in accordance with the requirements of ASME Sec I and the current NBIC. I have seen cases in which the slag was ground smooth but not removed and showed up during welding.

I have worked for boiler contractors that specifically prohibit arc gouging in a boiler, yet its OK in a new prssure vessel?

1/4" Membrane would be difficult to gouge or abrasive saw so I could see the slag problem. Maybe a Magnetic Particle test or Liquid penetrant test would be in order. If a large amount of carbon were present, the membrane welds might show some cracking.

In my opinion a lack of skill on the part of craft people in conjunction with a lack of knowledge in supervision has caused restrictions that are above and beyond good engineering practice and the applicable codes and standards.

There are cases in which I recommend arc gouging not be performed when I QC on ASME/NBIC work. I have never backed yjis up with a code requirement. If one exists, I too would like to know about it.

 

A little late in the game......

a 1/4" membrane is quite narrow, it is more common to have a 1/2" membrane between the waterwall tubes. It would be far more common to use a ZIP disk to cut the membrane when it is so thin. Nowadays, they would use a cutting disk to make the cut through the tubes as well so the equipment would be on hand. If the actually "struck" the tube then it will be most likely that some grinding a a weld repair will be required. If it is just spatter then it can usually be chipped away.

In short, use a cutting disk, it can be almost as fast with a lot less chance of mistakes.

 

[metaltrade]

we've just replaced the superheater in one of our boilers. Boilers are ASME code stamp and manufactured in Japan. We've got both the AI and the boiler mfr rep (as our consultant) plus the contractor own asnt inspector.

some bank tubes,screen tubes and baffles tube (from and to the steam drum and mudrums) has to be cut and remove. method we use is torch. during reinstatement, wled prep using disk grinder then visual check prior to fitup. Works OK and passed by all concerns.