Post-Weld Heat Treatment (PWHT)

PWHT (Post-Weld Heat Treatment) is essential in ensuring pressure equipment can withstand high temperatures and harsh environments, and ensures welded joints adhere to stringent safety standards.

PWHT can be costly due to the long heating and cooling cycles required and special equipment necessary for its implementation.

Advantages

Welding is an indispensable process in the petroleum (upstream, midstream and downstream) and chemical processing industries. However, welding can inadvertently weaken equipment through creating residual stresses; to mitigate this potential issue a postweld heat treatment (PWHT) should be regularly undertaken in order to relieve these residual stresses and strengthen equipment further.

PWHT can significantly decrease weld hardness, redistribute weld-induced stresses and alter microstructure to enhance ductility and fracture resistance. PWHT may be required by standards for certain grades or thicknesses, or it can be decided upon based on cost, safety and efficiency considerations.

Although the benefits of PWHT can be many, its use requires considerable amounts of energy consumption and increases emissions, potentially leading to environmental concerns when used on pressure vessels or pipes. Luckily, alternatives exist which can eliminate such costly thermal processes altogether.

Libratherm offers single and multi-zone PID ramp soaking controllers to precisely control PWHT heating rates to achieve desired results. They accept grounded or ungrounded thermocouples directly and output analogue or SSR output with PID control action for PWM outputs. A MODBUS over RS-485 interface also facilitates easy integration into SCADA, PLC or data logging systems.

Our PWHT equipment features induction coils to quickly heat the workpiece with an insulation blanket to retain heat. Safe operation of this machine is assured through an emergency stop button, while temperature readings are displayed clearly on an intuitive touch screen display.