Experience Welding T92,P92 prevent lack of fusion

[Nhan NguyenHong]

Could you share experiences to prevent welding defect type Lack of fusion on material Pipe SA335-P92 (OD 219 x T61) with Stub SA213-T92 (OD 43.2 x T9.2) ?
Now we use welding rod GTAW ER90S-G(Bohle Thermanit MTS 616) , Preheating by electric Pad keep the temperature min 205°C and interpass max 300°C

 

[kingnero]

9 mm wall thickness is a lot for such thin pipes, probably hindering proper torch positioning if you're using gas cups that are too big.
I'd firstly look at welder error(s) instead of process parameters. Probably the bevel angle needs to be wider (with a "nose" instead of a feather edge, allowing higher amps) or even the entire weld prep needs rethinking.

 

[weldstan]

I assume that LOF is on the pipe (thick side) rather than on the tube side. If so the welder must concentrate the arc on the pipe side of the weld to a greater degree. Also assure that the pipe side surface is fully cleaned and all mill scale removed prr to welding. Also take a look at the gas cup size and tungstun electrode point configuration and filler wire diameter.

 

[Nhan NguyenHong]

Your Idea suggests design remove the Red color area same as a the picture to make a wider edge for easy work.

 

[Dhurjati Sen]

Champhering of the stub is required. It is already provided in the drawing.

Match the stubs with the drawing to ensure dimensional integrity. Many times, the machine shop / workshop does not do their work properly.

Of course, welder experience and skill is another issue.

But this sort of welding is very common in boilers and HRSGs, lack of fusion should not be an issue.

DHURJATI SEN
Kolkata, India

 

[weldstan]

The primary fab shop we used for these weldments and the shop the company purchased required welders to perform and qualify (additional compamy standard) on mock ups of these welds prior to being permitted to do production welding of same header to tube welds.