Equipment for local and volumetric PWHT (heat treatment of welded joints)
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Welding with preheating

01.11.2019 10:46:00
In manufacturing of heat exchangers with pipes and sheets made of heat-resistant chrome-molybdenum or chrome-molybdenum-vanadium steels, for example 12XM, 15XM, etc., preheating before and during welding of pipes into tube sheets may be required by a technological document.

Gas heaters often are used to solve such problems. It can be either an open flame or infrared heaters. Many technological documents prohibit the use of an open flame for heating. This is due to the fact that this heating method provides significant non-uniformity of heating. In addition, in the zone of direct contact of an open flame with a metal surface, accelerated oxidation of the metal occurs.

The use of infrared heating significantly reduces the influence of these factors. However, from the view point of safe work, this option is not much better. Because all the same, gas is supplied to the work area, which means that long and complex approvals are necessary. In addition, the welder is still exposed to open sources of heat and still has to breathe the combustion products of gas fuel.

All the above disadvantages are absented in method of heating before welding, such as heating during welding using resistance electric heaters, also known as heating mats, LEG heaters, thermobelt.Local PWHT during welding

In this case, the entire surface of the tube sheet is heated uniformly without thermal distortions. To do this, multi-post heat treatment plants are used, which allow for multi-zone automatic control of the process.

Heaters are installed evenly throughout the tube sheet and are divided into several control zones.

Preheating before welding

As in any job, training is an important step in ensuring quality work. Therefore, when our specialists go out to teach new customers safe and high-quality methods of performing heat treatment, it is often necessary to practice on mock-ups, and only then proceed to heating the products under working conditions.

PWHT training



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