1. Is post-weld heat treatment (PWHT) mandatory for A358 pipe?
No, it is generally not required for the austenitic stainless steels covered by this specification. These steels are typically used in the "as-welded" condition because they remain ductile and do not harden in the same way carbon steels do. However, PWHT may be specified for certain applications or grades (like 321) to restore corrosion resistance or relieve stresses.
2. How does ASTM A358 differ from ASTM A312?
The main difference is the manufacturing process.
ASTM A358 is for welded pipe produced from plate or sheet.
ASTM A312 covers both seamless and welded (made from skelp/coil) austenitic stainless steel pipe. A312 welded pipe is often produced using a continuous welding process without filler metal, unlike A358.
3. What non-destructive tests (NDT) are required?
The required NDT depends on the class:
Class 1 & 2: Require 100% radiographic examination (RT) of the weld seam.
Class 3: Requires a hydrostatic test or a non-destructive electric test (like an eddy current test). RT is not required.
All classes require a hydrostatic pressure test unless an alternative NDT is agreed upon.
4. What are the typical applications for A358 pipe?
It is commonly used in demanding applications such as:
High-temperature and high-pressure piping in power plants and refineries.
Chemical and petrochemical processing plants.
Pharmaceutical and food processing industries where corrosion resistance and cleanability are critical.
Large diameter piping systems where seamless pipe is not available or economical.
5. Does A358 pipe require filler metal for welding?
Yes, unlike some continuous weld processes (like those used for A312 pipe), the electric-fusion-welding process defined in A358 is performed with the addition of filler metal. This generally results in a weld joint with properties more closely matching the base metal.
