An Overview of ASME’s B31.3 Code for Process Pipe Fabrication

An Overview of ASME’s B31.3 Code for Process Pipe Fabrication

The American Society of Mechanical Engineers (ASME) sets codes for safety standards in the fields of engineering, fabrication, and construction. For process pipe fabrication, ASME code B31.3 is the industry standard, and STI Group’s pipe fabrication services meet this standard. What follows is an overview of ASME’s B31.3 Process Piping code.

The Purpose of ASME’s B31.3 Process Piping code

ASME’s B31.3 Process Piping code provides specifications for the pressure design requirements of high pressure pipes to ensure that the pipes can safely meet the demands and stresses that will be placed on it. To this end, ASME B31.3 sets standards for material selection, support design, thermal expansion, examination, and testing, as well as additional factors that affect the strength and durability of process piping.

ASME B31.3 Process Piping was also created to meet the requirements of the ASME B31.3 Normal Fluid Service code. The specifications of ASME B31.3 Process Piping may thus be used for all Category D fluid services. However, for Category M fluid services some restrictions may apply and it is necessary to consult an engineering specialist to ensure compliance.

Corrosion Resistance

Corrosion resistance is a major consideration for pipe fabrication. The corrosion resistance required affects the pipe wall thickness needed as well as the selection of pipe materials and the materials of gaskets, valves, and other parts. ASME uses different subsections to address corrosion allowance for different piping specifications (PS). These are specified by the PS-number.

Hydrostatic Testing

Hydrostatic testing is crucial to ensure the integrity and performance of fabricated pipes. ASME B31.3 sets hydrostatic test limits that specify different minimum test pressure specifications for different design pressures and temperatures. Hydrostatic testing will also need to take elevation changes into account, for example if the pipe system runs from low to high elevations. Hydrostatic testing may need to be performed on fittings, valves, and instruments separately to ensure compliance.

Connections and Bends

Connections and bends in pipes are among the most common sources of failure. ASME B31.3 addresses what types of connections and bends are permitted and what type are not. It also addresses when welded branch connections will need to be reinforced and what types of welded fittings may be used. Fittings and flanges are also covered in ASME B31.3 with specifications for temperature requirements, materials, and pressures.

STI Group Process Pipe Fabrication for ASME B31.3

STI Group rigorously meets ASME B31.3 codes for process pipe fabrication as required with regard to material selection, welds, fittings, hydrostatic testing, corrosion resistance and all other ASME B31.3 requirements. Our fabrication shops have earned ASME’s “U,” “S,” stamps, and our welders and craftsmen are highly experienced and well trained in meeting ASME B31.3 codes.


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