Welcome to the Forum kannan!
ASTM A516 or ASME SA516 is commonly used for pressure vessels yes?
ASTM A516 Gr 55, 60, 65, and Gr 70 preheat and interpass temps may be found in AWS D1.1 2015 Table 3.3 But this would apply only to structural steel applications governed by that code.
Others may be more able to assist if your project is governed by another specification.
Welcome Kannan!
What is the applicable code and what thicknesses are you welding on?
By 803056 
Date 08-12-2016 12:55
Edited 08-12-2016 13:04
Points to remember:
AWS welding standards for the most part are cookbook approaches to making acceptable welds. The cook book approach essentially means one does not have to be an expert to follow it. However, the user is expected to be literate and must have a basic understanding of the technology. If you follow the recipe, starting with design, selection of materials, fabrication, and inspection, the resulting welding documentation and the welds produced should function as intended. If all the conditions of prequalification are met (where prequalification is recognized) a sample weld need not be welded and tested. The industry has a history of success to justify our position on prequalification. However, if all the conditions for prequalification are not met, or if the standard does not recognize prequalification [aluminum structural code for welding aluminum (almost a metal)], a test sample must be constructed, welded , and tested to demonstrate the required mechanical properties can be produced. The permitted ranges for welding parameters are rather limited to ensure consistent predictable results. The bottom line is one need not be a welding expert to develop a welding documentation package that meets AWS requirements and will produce predictable results.
ASME does not tell one how to do anything. The user is expected to "know" the technology. ASME expects the individual designing the weld joint to know what root openings work, what groove angles are needed to provide adequate access, etc. Likewise, ASME expects the person writing the WPS to "know" what voltage range is reasonable, what current and wire feed speed is needed for the electrode diameter used, what technique will provide the required results, etc. However, to verify the WPS will work, a test weld has to be constructed and welded to "prove" the required mechanical properties will be met. ASME expects the person charged with developing the necessary welding documentation is a "welding expert" that understands the technology and has sufficient knowledge to include and provide direction to the welder.
I routinely consult other welding standards when developing welding documentation for applications that require compliance with ASME or NAVSEA standards. Many of AWS and MIL-STD-22 joint details work for pressure vessels, preheat temperatures for the materials covered are more conservative than either ASME or NAVSEA, so a margin of "safety" can be incorporated when higher preheat is utilized for joints that are restrained, etc.
Best regards - Al
