Pavis1968
The ASME B31 Codes for Pressure Piping are voluntary consensus Codes. ASME cannot make the law; your local government will do that. The law will result in regulations and one form of those regulations is a Building Code. Usually, (in most places where the ASME Codes are used) the LOCAL BUILDING CODE will set MINIMUM STANDARDS and in many places in the world the local building Codes will mandate that one or more of the ASME B31 Codes for Pressure Piping be used ONLY THEN DO THE ASME CODES HAVE THE FORCE OF LAW.
You ask:
1- Is it required the thickness for steam lines in refinery to be calculated as per ASME B31.3 or not?
Is it required by whom? You must ask your local jurisdiction what Codes and Standards are REQUIRED by them (by you local jurisdiction). Usually, the owner's specifications and standards will be written in compliance with the requirements of you local jurisdiction (in compliance with the LOCAL LAW). You will notice that B31.3 states that it is the responsibility of THE OWNER OF THE FACILITY to specify what ASME Code should be used for the physical plant - the owner may mandate the more than one Code or Standard be applied to the design of various units in the refinery (usually, the OWNER's requirements for which Codes and Standards are to be used in the owners refinery are expressed in the company specifications and standards. It is common practice (in most but not in all) in refineries for the OWNER to specify that the ASME B31 Code for Pressure Piping, B31.1, Power Piping be used for all the piping in the steam / water loop in the boiler house (NOTE that some boiler piping will also have to comply with the ASME Boiler and Pressure Vessel Codes). The OWNER"S specification for all piping in the refinery outside the battery limits for the boiler house be designed, fabricated, erected, examined and tested in compliance with the ASME B31 Code for Pressure Piping, B31.3, Process Piping (there may be some exemptions for some area in which there is Transportation Piping that complies with either B31.4 or B31.8 (or it may be that there is none of this type of piping within the refinery).
You have stated that the OWNER'S specification requires the application of the B31.3 Code for Process Piping throughout the refinery except for the piping associated with "steam generating equipment". So, there is your answer. The OWNER has written a specification / standard that calls for B31.3 to be used for all piping except for steam / water loop piping.
The B31.1 Code includes (in B31.1 Appendix "A") values for allowable stresses to be used in the design of pressure piping. These allowable stresses are GENERALLY based upon a factor of safety of four. The B31.3 Code includes (in B31.3 Appendix "A") values for allowable stresses to be used in the design of pressure piping. These allowable stresses are GENERALLY based upon a factor of safety of three. GENERALLY then, pressure design of piping designed in accordance with B31.1 will require thicker wall piping for the same pressure/temperature service. The B31.1 Code Committee is of the opinion that Power Piping should be designed (et. al.) to more conservative standards - THAT is the reason for the difference in the factors of safety.
Pavis1968, there is NO SUBSTITUTE for sitting down and reading the Codes that are required by your local jurisdiction. It is the RESPONSIBILITY of the piping engineer to completely understand the laws of the local jurisdiction and to completely understand the rules and the design philosophy of the Codes that are required by your local jurisdiction.
John.
