Stress Relieving
Pre-Weld Heat Treatment (PWHT)
IXAR specializes in local Pre-Weld Heat Treatment of carbon steel and alloy steel piping welds by means of the electrical resistance method, in the form of ceramic heater pads and by using a source of electricity as a source of heating for stress-relieving of weld joints.
All Heat Treatment services are designed to minimize downtime, improve structural integrity and enhance effective plant life. Additionally, depending on the mobility of the required equipment many of our heating processes can be applied on-site or at your facility.
Preheating involves rising the temperature of the parent material locally, on both sides of the joint to a value above ambient. The need for preheating is usually determined by the pertinent fabrication code and verified by the weld procedure qualification test.
Preheat may be required as an aid to welding for one of the four basic reasons;
1) To control the rate of cooling.
2) To control the diffusion rate of hydrogen in a welded joint.
3) To reduce thermal stresses.
4) Compensation for heat loss.
Post Weld Heat Treatment (PWHT)
Post Weld Heat Treatment (PWHT) reduces the residual stresses formed during welding. It also restores the macrostructure of the steel. Mandatory in high-pressure applications, constructors have to strictly follow PWHT requirements to avoid component failures. These residual stresses and macrostructure changes, combined with operating stresses, can lead to catastrophic failure of the pressure vessel.
PWHT eliminates these effects by heating, soaking, and cooling the weld area in a controlled manner to temperatures below the first transformation point, giving the macro structure sufficient time to readjust to its original state and removing the residual stress.
Induction Heating
Induction heating services is a non-contact type method. It works on the principle of electromagnetic induction in which heat is directly produced in the workpiece. Induction heating coils are placed around the electrically conductive part. The position of the metal body or workpiece in an alternating current induces eddy currents inside the part. These currents are concentrated in the outer layer of the metal body due to the skin effect.
These eddy currents excite the material’s molecules and generate internal heat. As a result, the workpiece itself becomes the source of the heat, not the heating element. The depth of heating is influenced by the amplitude of AC frequency, the concentration of flux capacity, the material of the workpiece and the property of materials.
Induction heating for preheating, post-heating and stress relieving has been used in manufacturing and construction welding applications in industries such as mining, oil and gas refineries and pipelines, structural welding, shipbuilding, transportation, precision casting and injection moulding.
Induction heating is mainly used for
1) Melting of steel, stainless steel, and other non-ferrous materials
2) Heating of ferrous and non-ferrous billets for forging extrusion and piercing.
3) Through heating of the wire, tube, pipe, rods, flats etc.
4) Induction Hardening, tempering, annealing, stress relieving & softening.
The benefits of Induction heating are,
1) Uniformity and Quality- Provides the highest degree of temperature control across the heat-affected zone (HAZ).
2) Reduced Cycle Times- Significantly faster time-to-temperature than resistant methods.
3) Cost Reduction- No fuel cost and minimum insulation costs; reusable insulation reduces disposal.
4) Power Efficiency- Operates at maximum efficiency transferring more energy to the part, and decreasing heating times.
5) Ease of Use- Simple set-up using preheat blankets or flexible heating cables. In some cases, how to use the induction equipment can be taught in one day.
6) Reliability- Induction heating system components make the cycle uninterrupted. The cabling for induction is simple, making it less likely to fail. Also, no contactors are used to control the heat input to the part.
7) Versatility- Pipe preheat and stress relief; weldolets, elbows, valves, I-beams, complex shape. Induction coils have the ability to adjust during the heating process to accommodate unique parts and heat sinks.
8) Safety- Fewer fumes, eliminate fuel gases; no exposure to flame, gases or hot elements.
9) Environment- Less airborne particulate; improved work environment results in higher work productivity.
