The code for stainless steel seamless pipe is ASTM A312. This code is an international material standard for the manufacture of stainless steel pipe, developed by the American Society for Testing and Materials (ASTM). The ASTM A312, which covers austenitic and ferritic stainless steel pipe, has been in existence since its first publication in 1945.

History and Development of ASTM A312

ASTM A312 stainless steel seamless pipe: Requirements

ASTM A312 stainless steel seamless pipe: Material range and classification system

This standard covers over 50 different grades of austenitic stainless steel, primarily divided into the following series:

ASTM A312 stainless steel seamless pipe: Manufacturing process and technical requirements

1. Manufacturing Methods

The standard specifies three manufacturing processes: Seamless pipe (SMLS) uses a non-welding process; Welded pipe (WLD) uses an automatic welding process without the addition of filler metal; and Heavy Cold Worked Pipe (HCW) requires cold working with a minimum thickness reduction of 35%.

2. Heat Treatment Requirements

All steel pipe must be supplied in the heat-treated state. Heat treatment temperature requirements vary by grade:

ASTM A312 stainless steel seamless pipe: Key points for chemical composition control

The standard has strict regulations on chemical composition.

Key element control includes:

Carbon content control: L series requires a carbon content of ≤0.035%, H series requires 0.04-0.10%

Stabilizing elements: 321 contains titanium, 347/348 contains niobium, and Ti ≥ 5 × (C + N) or Nb ≥ 10 × C is required

Molybdenum: 316 series contains 2-3% molybdenum to improve pitting corrosion resistance

Nitrogen: N series uses nitrogen to improve strength

ASTM A312 stainless steel seamless pipe: Mechanical performance requirements

When specifying ASTM A312 stainless steel pipe, it is important to consider strength requirements. The appropriate strength requirements are stated in the ASTM A312 based on the intended application of the pipe. For instance, stainless steel pipes used for pressure vessels should be able to withstand high pressures.

On the other hand, stainless steel pipes used for general piping should allow for some flexibility in order to maintain their integrity during normal operation. Additionally, ASTM A312 requires that all pipe be ductile enough to handle mechanical loading, thermal cycling and vibration without fracturing or losing their integrity.

The standard specifies tensile property requirements for different grades, primarily divided into three strength grades:

ASTM A312 stainless steel seamless pipe: Corrosion resistance

ASTM A312 stainless steel seamless pipe: Testing and quality assurance

1. Nondestructive Testing Requirements

Each steel pipe must undergo hydrostatic testing or nondestructive electrical testing (eddy current or ultrasonic). For pipe NPS 10 and above, the hydrostatic testing requirement may be waived with the agreement of the manufacturer and purchaser, but the letters "NH" must be included in the marking.

2. Intergranular Corrosion Testing

The standard refers to ASTM A262 Practice E for intergranular corrosion testing. Low-carbon and stabilized grades require testing under sensitized conditions; other grades are tested in the as-delivered condition.

3. Cryogenic Service Applications

The standard specifically addresses cryogenic service applications: When the impact test criteria are 15 ft·lbf energy absorption or 15 mils lateral expansion, certain austenitic stainless steel grades (such as TP304, TP304L, and TP347) are accepted by the ASME Pressure Vessel Code at temperatures as low as -425°F without impact testing.

ASTM A312 stainless steel seamless pipe: Maintenance requirements

Conclusion

In conclusion, the code for stainless steel seamless pipe is ASTM A312. This code sets out the specifications for the manufacture of stainless steel pipe and outlines requirements for strength and ductility, corrosion resistance and maintenance, etc. The ASTM A312 also contains recommendations for maintenance practices to keep the pipe in good condition over time.