POST WELD HEAT TREATMENT
It is defined as any heat treatment after welding is often used to improve the properties of a weldment.In concept,PWHT can encompass many different potential treatments ,However in steel fabrication the two most common procedures used are post heating and stress relieving.
Post Weld Heat Treatment, often simply referred to as PWHT, uses the application of heat to reduce and redistribute residual stresses in weldments. PWHT is one of the most common methods of stress relief and is used in a wide-range of industries and high-pressure applications where brittle fracture is likely to occur.
The requirements specified within various pressure vessels and piping codes are mostly due to the chemical makeup and thickness of the material. Codes such as ASME Section VIII and ASME B31.3 will require that a specified material be post weld heat treated if it is over a given thickness. Codes also require PWHT based solely on the micro-structural make-up of the material.A final consideration in deciding the need for PWHT is based on the components’ intended service, such as one with a susceptibility to stress corrosion cracking. In such cases, PWHT is mandatory regardless of thickness.
Ultrasonic Impact Technology:
tensile stress in critical zones and introduce beneficial compressive stress where it is most needed. The Ultrasonic Impact Technology, or UIT for short, uses ultrasonic energy to improve metal, reduce residual technology was developed and first brought to market by Progress Rail’s Ultrasonic Technology (UIT) Division and is specifically designed to be applied to welds. The Ultrasonic Impact Technology is portable and can be applied by a single technician using a handheld tool. Unlike heat treatment, UIT can be applied in hard-to-reach places and even robotically. This flexibility makes it the perfect solution for field, shop, manual or automated applications. As a result, UIT has proven to be an extremely safe, efficient and effective method of stress relief and is currently utilized in oil and gas, defense, shipbuilding, mining, infrastructure maintenance (weld treatment on bridges) and a host of other industries.