Residual Stress Relief
Welding can introduce residual stresses in the material due to the localized heating and cooling cycles. These residual stresses may lead to distortion or cracking over time. PWHT helps alleviate these stresses, reducing the risk of post-weld cracking.
Microstructure Modification
The welding process can also cause changes in the microstructure of the material, particularly in the heat-affected zone (HAZ) adjacent to the weld. PWHT allows for the reformation of a more uniform and desirable microstructure, improving the material's mechanical properties.
Typical Temperatures
PWHT temperatures are typically chosen based on the material to be welded and the specific requirements of the application. Common temperature ranges for post-weld heat treatment include:
Carbon Steels: PWHT temperatures may range from 550°C to 650°C (1022°F to 1202°F).
Low-Alloy Steels: Temperatures for low-alloy steels might be in the range of 600°C to 700°C (1112°F to 1292°F).
Heating and Soaking
The PWHT process typically involves heating the welded component to the prescribed temperature and holding it at that temperature for a specific duration. This soaking period allows for the uniform distribution of temperature throughout the material and is usually related to the part thickness.
Cooling Phase
After the soaking period, the component is gradually cooled to room temperature.
Controlled cooling helps avoid the reintroduction of undesirable stresses.
It's essential to note that specific PWHT parameters (temperature, soaking time, and cooling rate) depend on factors such as the material to be welded, the welding process used, and the specific requirements of the project or industry standards. PWHT is a critical step in ensuring the long-term reliability and performance of welded structures in various engineering applications.
POST WELD HEAT TREATMENT
Post weld heat treatment (PWHT) is the process of reheating a material to below its lower critical transformation temperature and holding it at that temperature for a specific time. PWHT furnaces are used to maintain the integrity of a part after it has been welded, by reducing the residual stress in weld joints. PWHT helps reduce brittleness, strengthens the material, and reduces weld failures by improving the material’s ductility. Processes such as annealing, aging, normalizing, stress-relieving, tempering, and more, are often performed in conjunction with post-weld heat treatment, so PWHT furnaces can be dual-use machines. With PWHT, you can carefully control the hardness of the material to give it your desired properties by varying the heating time and temperature.
Wisconsin Oven’s post-weld heat treatment furnaces are durable, reliable, and built to last! They are designed with double-wall construction and a patented high-efficiency design to reduce heat loss and maximize energy efficiency. Reaching temperatures of 1000˚F to 1400˚F (538˚C to 760˚C), they are also excellent for applications such as annealing, aging, normalizing, stress-relieving, and tempering. PWHT furnaces help ensure the strength of welds and avoid cracking and fracturing. These furnaces provide stable parts after welding by reducing residual stresses and preventing brittle fractures within weld joints. Our PWHT furnaces are thoroughly factory tested, adjusted, and certified by an extensive quality inspection process before shipment, resulting in lower installation and start-up costs for you!
Benefits
Fully tested before shipment, to reduce installation & start-up costs.
Tight temperature uniformity to ensure consistent results and provide desired material properties.
Each furnace is designed to meet your specific requirements in regard to heating time, temperature, and loading requirements.
Standard Features
NFPA 86 compliant
Multiple interlocks such as high/low gas pressure switches, high temperature interlocks, air proving switches, door proximity switches, and more.
Maximum temperature ratings of 1000°F (538° C), 1250°F (677° C), or 1400°F (760° C).
Recirculation fans and air distribution ducting for fast heating and tight uniformity.
Gas or electrical heated.
Batch or conveyor style
Many models available with Wisconsin Oven’s exclusive 3-year or 5-year warranty
Available Options
Ramp/soak controllers or standard single set point control
Temperature recorder
Wide variety of conveying systems available, including belt conveyors, chain conveyors, and many others
AMS 2750 or CQI-9 compliance.
IoT system to remotely monitor the equipment. Allows predictive maintenance, and reduces downtime due to unexpected component failures