Boiler Door

[Truckdriver2]

A contractor recently took it upon himself to do a weld repair to a boiler door. He decided he knew what he was doing and did the following:

1) Pre heat to 150 Deg C
2) Tig weld
3) Post heat to 300 Deg C and leave with thermal blanket over night.

The door was reportedly 30 Deg C in the morning.

Are there any opinions as to what this may have done to the parent metal?

 

[metengr]

Truckdriver2;
If this is a boiler door, it was probably manufactured from carbon steel plate. You did not mention the filler metal used, but other information you reported seems correct to me.

Why are you worried about the base metal? The heat from welding will alter the original properties, however, if the welding was done properly there should be little concern. If I were you, I would be much more concerned about what exactly was done for the weld repair.

 

[Truckdriver2]

Thanks for your response Metengr,

I am currently off site but am getting the steel details tomorrow.

Welding on pressure vessels of this size by "cowboys" is always of concern as the consequences of failure are extreme.

I do not think that the weld process used 'should' cause any concerns but would like to assure my self with a greater degree of confidence then 'should'.

The door is your typical oval door of low carbon steel. It had pitting on the seal face. 4 runs of weld were put over the seal face and the face machined flat.

My initial research leads me to believe that a post heat of somewhere around 900 Deg C for 12 hours or so should have been applied for stress relief?

My worry is that the heating/welding/post heat process may have affected the base material and indeed that the filler may not have been compatible.

My concern is that the material may have been affected such that the repair could de-laminate (for want of a better description) or basically crack on the parallel axis.

 

[metengr]

The door is your typical oval door of low carbon steel. It had pitting on the seal face. 4 runs of weld were put over the seal face and the face machined flat.

My initial research leads me to believe that a post heat of somewhere around 900 Deg C for 12 hours or so should have been applied for stress relief?

I have seen this type of weld build-up and I consider it routine if done by a qualified repair organization. In general, PWHT is not required for this type of build-up.

I would ask for a copy of the welding procedure used for the weld build-up by the contractor. Also, was there any post weld repair nondestructive testing?

 

[moseley]

Trucker2,
If I am not mistaken NBIC does limit the "routine" repair to limit on "thickness deposited" and area of "wasted area". Also, the other kicker would be was there PWHT/ NDE required per the original design code this was built to? The contractor definately should be very careful doing things in this manner due to protecting their liability.

 

[metengr]

moseley;
The boiler door may not be under the requirements of the NBIC for welding. If the door is water-cooled and part of the waterwall tube circuit, yes, it would be under the NBIC. If the door is simply a steel plate that is protected by refractory, it is not under the NBIC for weld repairs.

 

[Truckdriver2]

Thanks all for your replies
The door is being sent for mag particle or X-Ray testing and the purported procedure is being checked as appropriate for the material in question.
TD.

 

[rmw]

There seems to be some confusion among the members and that includes me. Is this "typical oval door" a boiler door, as in a furnace or ductwork access door, or is this "oval door" the boiler drum access door? If the latter it certainly does come under NBIC while if the former, unless water cooled as noted, it doesn't.

rmw

 

[Truckdriver2]

rmw,
The door is the drum door. It comes under the Classification Societies rules.

I am still having trouble determining what the correct pre-heat and post-heat treatments for carbon steel of this type should be.

The boiler was built under Design Code: BS2790-1982.

The material specification I have for the door is limited to BS1501-161-430B.

TD.

 

[metengr]

Truckdriver2;
The welding requirements for the lower drum door would fall under British Standards, since this is the original code of construction. You need to obtain a copy and review the weld requirements. General guidance for preheat is what you had in your OP. PWHT is typically based on nominal thickness, this is the thickness of the weld build-up, not the pressure part thickness.