Hi anyone:
U know if the length of welding shoe is longer than 300mm,it need intermittent welding for the plate of the shoe which is welded to pipe normally,but why not applying continuous welding,is there any code supported this point.I am urgently looking forward to anyone can give me a reply.
Tks a lot in advance.
Song,

My opinion is that continuous welding is more expensive in that it takes more material, time, and increased risk of warping.

Having too good of an attachment could also mean that you need to treat it as a SIF - e.g. a trunion.

Hi Michael,
Tks a lot for your reply, is there any code to support the point it is necessary to use intermittent welding to avoiding risk of warping.
Thank you.

I am not cognizant of any, though I'm no welding expert. I know some people require PWHT for shoes on thick piping due to HAZs. The answer may lie in there.

Ultimately, what's the benefit to a continuous weld? Improved shear strength? I'd want my shoe to shear off before I'd want this connection to create a rupture.

Avoidance of crevice and crevice corrosion? Cut a slot out of the shoe and have two continuous welds per shoe.

Hi Michael,

I think it is depend on how long is the shoe,for long length shoe it is need to weld intermittently, to avoid risk of warping, maybe this is just comment knowledge but not indicated in any code.
Tks a lot.

Michael is correct in case the installation temperature, content temperature and the shoe temperature are the same all the time. Most of the cases this is not true, and the pipe will have higher temperature than the shoe.

The stiffness of the shoe and the pipe, if continuously welded in the long length, will will be different, and the temperature differential will introduce additional secondary stresses on the pipe in the longitudinal direction. The connection, and so the pipe will fail either in the first cycle or at an unknown cycle. Therefore there is a need for reducing the weld length in the longitudinal direction of the combined section to be able to reduce the bending action under thermal differential. I hope this is clear.

Second paragraph first sentence should be the following:

"The stiffness of the shoe and the pipe, if continuously welded in the long length, will will be different, and the temperature differential will introduce additional stresses on the pipe in the longitudinal direction."

Just to add to what Ibrahim said, the temperature at the junction of shoe and pipe is same for all insulated pipe & therefore, the differential expansion doesn't come in picture for welding at junction. However, as you move away from junction, the differential temperature rises and this may create an issue for welding and put it in shear!! Outside insulation, everything more or less is less significant due to heat transfer to structure through conduction and surroundings through radiation..

Regards,

SJ

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