How to perform heat treatment after on-site pipeline welding
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This post was last edited by jacques0920 on 2015-8-3 16:37. Hello everyone, how is post-weld heat treatment for pipes carried out in practice? Mainly, how is heating and heat retention achieved? Thank you.
An electric heating element is wrapped around the pipe, and then rock wool insulation is used to cover the electric heating element as well.
Multiple rows of electric heating wires are wrapped around ceramic insulating blocks, similar to those used in mahjong sets, to cover the welded areas, thereby providing insulation. Some small, marginal welds require an electric heating wire, which is a wire coated with a series of ceramic blocks.
In the image above, it’s actually explained in some detail
What is the purpose of ceramic insulating blocks?
So, is the post-weld heat treatment for carbon steel and stainless steel done using the same method?
I don’t know that. However, stainless steel should be more than carbon steel.
First is the insulation between the heating wire and the pipe fitting being treated, and second is the insulation between the heating wires.
One requirement for heat treatment is that if it is interrupted due to an unexpected situation, the weld should be kept insulated to cool down slowly before undergoing heat treatment again. However, after the power outage interrupted the heat treatment process, the construction team resumed the heat treatment once power was restored. It is unknown whether this had a significant impact on the quality of the heat treatment
1. First, preheating can be done using a track heater (i.e., an electric heating element), and the material can also be kept warm after welding with an electric heating element. 2. For the heat treatment of carbon steel and stainless steel joints, it should be determined by the heat treatment technicians and welding technicians based on the on-site welding procedure qualification. Generally speaking, stainless steel is not heat-treated because it has a sensitization temperature around 450–850 degrees. If it must be done, it should be carried out quickly during the sensitization temperature period; generally, solution treatment can be performed at over 1,000 degrees. 3. If heat treatment is interrupted, there is generally no problem due to the insulation provided by the insulation cotton. Due to insufficient heating time, it is equivalent to a dehydrogenation treatment (around 400 degrees); once the appropriate conditions are met, heat treatment can be carried out again. However, since the heat treatment curve looks very poor, it is best to have a welding expert confirm it. Otherwise, it’s pointless to do it.
There are specialized manufacturers that handle pipeline heat treatment. There’s no need to bother figuring out how to do it. But it's even better to know the principle.