Normalizing (Heat Treatment)
Benefits of Post Weld Heat Treatment Services (PWHT):
Tremendous amount of heat generated during welding induces two types of stresses (elastic and residual stress) and increases the ductility of the metal. Post heated weldments have significantly less residual stress compared to untreated welds, therefore having better resistance to corrosion & caustic embrittlement. Residual stresses developed through machining affects dimensional stability of the components by continuous micro movements of plastically misfit and unstable atoms. PWHT helps reorient these atoms into a new equilibrium position.
Preheating Services
Preheating of weldment eliminates weld defects and improves weld quality by avoiding cracking in the heat affected zone (HAZ) or at the weldment, which is one of the priorities of welding. Cold cracking increases with the hardness in the weld. Preheating reduces the hardness of the weld. Electric arcs break down moisture into it elements –oxygen & hydrogen which easily dissolves in the weld at higher temperatures, causing porosity in the weld while solidifying. Preheating removes moisture, greases oil etc. Uncontrolled cooling of the weld joint induces hardness into the weld and heat affected zone (HAZ). Pre heating helps reduce the risk of cracking caused with hardening by reducing the hardening via controlled cooling.
Furnace Heat Treatment (Static / Temporary / Gas / Electrical)
High velocity gas fired burners creates a ‘scrubbing action’ of hot gases against the walls of the component eliminating any cold spots. This ensures convective heat treatment to achieve temperature uniformity and efficient distribution of heat throughout the furnace chamber. The combustion system inputs high volumes of turbulent hot gases, which maintain a positive pressure within the chamber. This purges the chamber of oxygen, minimizing oxidation after PWHT.
Electric Resistance Localized Post Weld Heat Treatment
Carefully controlled localized post weld heat treatment by electric resistance is a crucial step in maximizing the life of process equipment’s. PWHT tempers the metal and reduces tensile stresses, minimizing the risk of brittle fracture, stress and corrosion cracking and metal fatigue. This is especially important for equipment’s used in harsh service environments. The structural integrity of the vessel or unit is ensured during this treatment.
Advantages
The advantages and Normalizing (Heat Treatment) methods are as follows:
- Controls and documents welding preheat to reduce thermal stress.
- Improves the microstructure and durability of the heat-affected zone.
- Tempers the metal and reduces tensile stresses, minimizing the risk of brittle fracture, stress, corrosion cracking and metal fatigue.
- Ensures the structural integrity of the vessel or unit during treatment.
Refractory Dry Outs
This type of heat treatment is done using a variety of special burners. In consultation with the customer, an air-drying procedure will be drawn up. Various thermocouples are installed to accurately monitor how the drying process is proceeding. The entire process will be recorded on a temperature recorder. Upon completion, the air-drying time/temperature curve will be provided. During the drying process, continuous human monitoring can be arranged if necessary.
