Post weld heat treatment is a controlled process which consists in heat the welded joint without reach the critical temperature of transformation (AC1). The post weld heat treatment is often usually after the union by welding of two material base such us carbon steels or alloy steels.

Post weld heat treatment (PWHT) can be apply to one complete piece or locally, by applying only the heat treatment to the welded joint area.

The post weld heat treatment (PWHT) will help to:

-remove the hydrogen that could be retained in the base material after welding

-reduce tensions created in the HAZ (Heat-affected zone)

-reduce and control hardness

As a consequence, it will be reduced the possibility of appearance of cracks. The cracks could contribute to have problems of corrosion.

Generally, the post weld heat treatment (PWHT) must be done following the rules established by international standards or codes, or sometimes, more restrictive procedures issued by the client. Some of this codes are, for example, ASME code (American Society of Mechanical Engineers) or normative EN 13480 (European Normative).

In this codes or procedures will be detailed the requirements to follow when we have to apply post weld heat treatment (PWHT) to one welded joint. It will be detailed the heat treatment temperature and the holding time, which will be different depending on material composition (carbon steel-carbon steel, alloy steel-alloy steel, alloy steel-carbon steel…), and depending on material thickness too. Moreover, it is necessary to check the heating rate from ambient temperature to treatment temperature and the cooling rate from heat treatment to ambient temperature. The code will detail too the necessary surface to preheat in both sides of the joint. Sometimes. The client could have more restrictive procedures to follow.

The post weld heat treatment can be performance in fixed or portables ovens, or by using electrical resistances. The machine, connected to the power supply, sends the energy to the resistances, fixed around the joint, and heating the base material. By the colocation of thermocouples, the temperature is constantly checked and one signal is sent to the machine, which will be precalibrated with the heat treatment temperatures values, holding time of the temperature and heating and cooling rates.

During the post weld heat treatment, the thermocouples send the signal to one register, which prints and saves one chart of the treatment. This chart could be attached to the quality dossier of the client.

We have electrical machines for heating of 70 KVA-6 channels and 9 KVA-3 channels, suitable for preheating and calibrated. We can performance the post weld heat treatment in the installation of the client or others. It is possible to performance the preheat with our machines and our staff and it is possible too to hire the machines.

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