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Preheat & Interpass Temperatures

Preheat & Interpass Temperatures

Postby Sanjay N Variya » Sun Sep 28, 2014 7:26 am

Could anyone tell me how to choose preheat and interpass temperatures as per ASME sections for carbon steel, low alloy steel and stainless steel for the thicknesses of 25 mm, 25-50 mm, 50-75 mm, 75-100 mm and above 100 mm?
Sanjay N Variya
 
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Re: Preheat & Interpass Temperatures

Postby mawsamit » Thu Oct 02, 2014 6:14 pm

Dear Sanjay N Variya,

Please let us know which is the applicable ASME code.

thanks,
mawsamit
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Re: Preheat & Interpass Temperatures

Postby Sanjay N Variya » Fri Oct 03, 2014 6:16 am

Dear mawsamit,

As per ASME Sec VIII Div 1 or AWS. If you don't know the requirements for preheat & interpass temperatures of those codes, please give me the requirements (for materials/thicknesses of my previous post) of the codes for which you are aware about.
Sanjay N Variya
 
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Re: Preheat & Interpass Temperatures

Postby techupon » Fri Oct 03, 2014 5:57 pm

Dear Sanjay N Variya,

Regarding preheat temperature as per ASME VIII-1 please have a look at Appendix R and for AWS D1.1 please have a look at Table 3.2. Interpass temperature shall not be lower than preheat temperature.

regards,
techupon
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Re: Preheat & Interpass Temperatures

Postby Sanjay N Variya » Mon Oct 13, 2014 4:09 pm

Dear techupon,
As per non-mandatory appendix R of ASME VIII-1, preheat for P4 material is 121 deg C for thickness exceeding 13 mm. If you are to prepare WPS for joining P4 material to P4 material with thickness 128 mm, will you choose preheat 121 deg C or more? If more, what's the concept for that?
Sanjay N Variya
 
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Re: Preheat & Interpass Temperatures

Postby alvaro » Mon Oct 13, 2014 8:12 pm

In most cases the main issue is: what's the minimum preheat temperature that is required and even some welding codes specify minimum preheat temperature, there are cases where that temperature is not sufficient for that specific case.

When no welding codes are specified, and the need for preheat has been established, how does one determine an appropriate preheat temperature? As a basis for discussion, consider AWS D1.1-96, Annex XI: "Guideline on Alternative Methods for Determining Preheat'' which presents two procedures for establishing a preheat temperature developed primarily from laboratory cracking tests. These techniques are beneficial when the risk of cracking is increased due to composition, restraint, hydrogen level or lower welding heat input.

The two methods outlined in Annex XI of AWS D1.1-96 are: (1) heat affected zone (HAZ) hardness control and (2) hydrogen control. The HAZ hardness control method, which is restricted to fillet welds, is based on the assumption that cracking will not occur if the hardness of the HAZ is kept below some critical value. This is achieved by controlling the cooling rate. The critical cooling rate for a given hardness can be related to the carbon equivalent of the steel, which is defined as:

CE = C + ((Mn + Si)/6) + ((Cr + Mo + V)/5) + ((Ni + Cu)/15)

From the critical cooling rate, a minimum preheat temperature can then be calculated. (Blodgett's paper entitled "Calculating Cooling Rates by Computer Programming'' outlines a calculation procedure based on cooling rate, heat input, plate thickness, temperature at which cooling rate is critical, preheat temperature, thermal conductivity and specific heat.) It should be pointed out, however, that "although the method can be used to determine a preheat level, its main value is in determining the minimum heat input (and hence minimum weld size) that prevents excessive hardening'' (Annex XI, paragraph 3.4,AWS D1.1-96.)

The hydrogen control method is based on the assumption that cracking will not occur if the amount of hydrogen remaining in the joint after it has cooled down to about 120°F (50°C) does not exceed a critical value dependent on the composition of the steel and the restraint. This procedure is extremely useful for high strength, low-alloy steels that have high hardenability. However, the calculated preheat may be too conservative for carbon steels.

The three basic steps of the hydrogen control method are: (1) Calculate a composition parameter similar to the carbon equivalent; (2) Calculate a susceptibility index as a function of the composition parameter and the filler metal diffusible hydrogen content; and (3) Determine the minimum preheat temperature from the restraint level, material thickness, and susceptibility index.
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Re: Preheat & Interpass Temperatures

Postby Sanjay N Variya » Wed Nov 26, 2014 5:08 am

Thanks alvaro

For your best clarification...
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