Services
Pre Heat Treatment
- Reduces the levels of thermal stress
- Compensates for high heat losses
- Minimizes the rate of weld hardening
- Reduces the porosity of the weld
- Reduces hydrogen cracking
- Improves microstructure of heat affected zone
Post Heat Treatment Services
Advantages of Post Weld Heat Treatment
- Relaxes residual stresses
- Relaxes thermal stresses
- Tempers (softens)
- Removes diffusible hydrogen
PWHT Services
Advantage Post weld heat treatment
Post Weld Heat Treatment Services ( PWHT ) is defined as one of heat treatments done after welding/machining to improve the Chemical mechanical properties of weldment / machined surfaces. In concept, PWHT covers many different potential treatments. However, in steel fabrication, most common procedure used is Stress Relieving.
Advantage Post weld heat treatment
Post Weld Heat Treatment Services ( PWHT ) is defined as one of heat treatments done after welding/machining to improve the Chemical mechanical properties of weldment / machined surfaces. In concept, PWHT covers many different potential treatments. However, in steel fabrication, most common procedure used is Stress Relieving.
i. Stress induced by welding
As a result of welding process used to join metals together. The base material near the weld metal and the heat-affected zones transform through various metallurgical phases. Depending upon the chemistry of the metals in their areas. Hardening occurs in various degrees, depending mainly upon the carbon content. This is particularly very true in the heat – affected zone adjacent to the weld metal deposit. The resultant stresses are highest due to melting and solidification. Stress, due to welding is of magnitude roughly equal to the yield strength of the base material.
ii. Stress induced by machining
Machining induces stresses in parts. The bigger and more complex the part, the more stresses. These stresses can cause distortions in the part in long term. Cracking could occur and location changes causing parts to go out of tolerances. Stress Relieving heat treatment is used to reduce the stress that remain locked in a structure as a consequence of the various manufacturing processes. Stress Relieving, as the name implies, is designed to relieve these imposed stresses by reducing the hardness and increasing the ductility, and by these, reducing the danger of cracking in the weldment.
How is Stress Relieving Done?
Stress Relieving is done by uniformly heating- fabricated equipment or the vessel or vessel part to a sufficiently high temperature, but below the lower transformation temperature range, then subjecting it to a thermal retardation for a sufficient time depending upon the material thickness and then finally uniformly cooling it which is also of utmost importance.
Advantages of Post Weld Heat Treatment – Stress Relieving
- A much greater dimensional stability is obtained and maintained
- The potential of stress induce cracking is reduced.
- Metallurgical structure is improved.
- Strength of the Material and Life of the equipment is Enhanced.
Advantage of Refractory dry outs
- Improves refractory strength
- Eliminates refractory separation
- Removes water content
- Avoids thermal stress
Industrial Annealing Services
Full industrial annealing solutions, annealing services is the process of slowly raising the temperature about 50 °C (90 °F) above the Austenitic temperature line A3 or line ACM in the case of Hypo eutectoid steels (steels with 0.77% Carbon) and 50 °C (90 °F) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon).
Aneealing is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 °C/hr (36 °F/hr) in a furnace to about 50 °C (90 °F) into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.
The grain structure has coarse Pearlite with ferrite or Cementite (depending on whether hypo or hyper eutectoid). The steel becomes soft and ductile.
Normalizing
Normalizing is the process of raising the temperature to over 60 ° C (108 °F), above line A3 or line ACM fully into the Austenite range. It is held at this temperature to fully convert the structure into Austenite, and then removed form the heating zone and cooled at room temperature under natural convection. This results in a grain structure of fine Pearlite with excess of Ferrite or Cementite. The resulting material is soft; the degree of softness depends on the actual ambient conditions of cooling. This process is considerably cheaper than full annealing since there is not the added cost of controlled cooling.
The main difference between full annealing and normalizing is that fully annealed parts are uniform in softness (and machine ability) throughout the entire part; since the entire part is exposed to the controlled furnace cooling. In the case of the normalized part, depending on the part geometry, the cooling is non-uniform resulting in non-uniform material properties across the part. This may not be desirable if further machining is desired, since it makes the machining job somewhat unpredictable. In such a case it is better to do full annealing.
Hardness Testing
Simply stated, hardness is the resistance of a material to permanent indentation. It is important to recognize that hardness is an empirical test and therefore hardness is not a material property. This is because there are several different hardness tests that will each determine a different hardness value for the same piece of material. Therefore, hardness is test method dependent and every test result has to have a label identifying the test method used.
Hardness is, however, used extensively to characterize materials and to determine if they are suitable for their intended use. All of the hardness tests described in this section involve the use of a specifically shaped indenter, significantly harder than the test sample, that is pressed into the surface of the sample using a specific force. Either the depth or size of the indent is measured to determine a hardness value.