Traitement thermique post-soudure

Post weld heat treatment (also referred to as stress relief) serves to mitigate and redistribute any residual stresses introduced during welding, while simultaneously improving toughness and ductility of both the weld itself as well as any heat affected zones surrounding it.

Specifications such as BS 4514-1 and ASME IX require welds to undergo post-weld heat treating (PWHT) at specific temperatures and times in order to avoid distortion, temper embrittlement or reheat cracking, which require careful monitoring with thermocouples and computer software.

Holding Temperature

Post Weld Heat Treatment (PWHT) specifications set the temperature and duration requirements, making this an important element of welding procedures. Any change outside these parameters requires recertification, while factors like material type, composition, soaking temperature of welds as well as stress relaxation during PWHT can have an impactful impact.

Food holding temperatures depend on whether or not the meal has been pre-prepared and placed in hot-holding equipment like chafing dishes and steam tables, or made according to customer orders (made-to-order). Either way, proper monitoring and documentation are crucial in both cases.

Temperature logs from restaurants could reveal that hot food dishes were kept at an unsafe temperature, potentially leading to foodborne illness outbreaks. To combat this risk, businesses can utilize FoodDocs’ digital platform for documenting all food safety tasks including inspections and temperature-controlled foods logs; this allows teams to work more efficiently while keeping food safety top of mind.

Soaking Temperature

Soaking temperature is essential to the PWHT process as it has a profound effect on microstructure. Soaking promotes recrystallization, grain growth and phase transformations depending on temperature regime; and redistributes alloying elements that have segregated during welding or casting processes.

Time at Soak Temperature directly affects stress relief and weld quality. In an ideal world, an even temperature should be applied throughout the weldment with minimum distortion, temper embrittlement or oversoftening.

To achieve this goal, the heating cycle should be carefully managed to ensure an even soaking temperature across the weldment and minimal time spent at that temperature. To achieve this, computerized systems that monitor and control each zone within the furnace automatically are essential; especially when dealing with complex geometry with differing section thicknesses. Such an approach helps minimize cycle times and energy consumption while guaranteeing optimal mechanical properties are obtained.

Loading Temperature

At the point of post weld heat treatment, the temperature of the load being applied will have an impactful impact on its structural and mechanical properties. Yield strength decreases with temperature increase and may become unfit to support its own weight; accordingly it must be adequately supported during pwht using trestles shaped specifically to fit around it at regular intervals for support during treatment.

Temperature changes can also cause gradual shifts in a load cell’s zero balance, making it inaccurately measure weight of an object. To overcome this effect, use of temperature-compensated load cells is recommended and they must be calibrated correctly prior to every use. Maintaining environmental stability, recalibrating frequently and filtering can all help minimize its impacts on accuracy.

Cooling Temperature

PWHT requires controlled cooling rates after each pass for maximum metallurgical integrity and to prevent brittle fractures of base metals. Furthermore, PWHT can result in tempering, precipitation or ageing effects on welded steel that reduce hardness while increasing ductility; however this only works on certain types of steel in certain temperature ranges.

Libratherm’s 6-Zone Ramp/Soak PWHT Temperature Controller features an inbuilt computer equipped with software for real-time temperature data logging and reporting of ramping, soak and hold temperatures. Individual heating zones can be independently set and thermocouples used for monitoring. Furthermore, this controller can also be programmed to control temperature gradient control zones (both axial and through thickness gradient). Typically this is accomplished by placing components shaped trestles at either end of heated zone to direct its heat source.