What tests are required for ASTM A335 P5 steel pipes before shipment?
Mandatory inspections include chemical composition analysis (spectrometer), mechanical property testing (tensile strength, hardness), hydrostatic testing (1.5 times the working pressure), and nondestructive testing (ultrasonic or eddy current). High-temperature pipes also require impact testing (such as Charpy V-notch). All inspections must comply with ASTM A335 and ASME SA335 standards and produce a third-party certified report.
How can defects in P5 steel pipes be detected through nondestructive testing (NDT)?
Ultrasonic testing (UT) can detect internal cracks and inclusions; radiographic testing (RT) is suitable for volumetric defects in welds; eddy current testing (ET) is used for surface cracks; and magnetic particle testing (MT) is only suitable for ferromagnetic materials (P5 requires magnetization). When selecting a method, consider the defect type, pipe diameter, and wall thickness. Automated phased array UT can improve inspection efficiency and accuracy.
What is the difference between ASTM A335 and ASME SA335 standards?
ASTM A335 is a material standard, and ASME SA335 is its equivalent, adopted version of the Boiler and Pressure Vessel Code. The technical content is essentially the same. However, the ASME version adds additional requirements for special applications such as nuclear power plants (such as more stringent impact tests). The intended use must be clearly specified when purchasing. If the pipe is to be used in ASME-certified equipment, the SA335 mark must be applied.
What are the hardness testing methods for P5 steel pipe?
Commonly used are Brinell hardness (HBW, which produces a large, representative indentation), Rockwell hardness (HRC, suitable for thick-walled pipes), and Vickers hardness (HV, suitable for thin-walled pipes or small areas). Surface oxide scale must be removed before testing, and the test points should be avoided along welds. The standard requires a hardness of ≤250 HBW; a hardness exceeding this value may indicate a risk of brittleness.
How can one determine whether P5 steel pipe has deteriorated due to high-temperature service?
Metallography can be used to observe carbide aggregation or spheroidization. A decrease in hardness (e.g., below 20% of the initial value) indicates creep damage. Ultrasonic thickness measurement can reveal localized thinning. Composite metallography can also be used to measure the oxide layer thickness. When the pipes are severely deteriorated, they need to be replaced to avoid pipe burst accidents.
