1.What are the mechanical properties of A691 steel pipe?
Answer: The mechanical properties depend on the specific grade and heat treatment. For example, Grade CM-1Cr typically has a tensile strength of 415-585 MPa (60-85 ksi), yield strength of 205 MPa (30 ksi) min, and elongation of 20% min. Properties are verified through tensile tests, hardness tests, and impact tests as per ASTM standards.
2.What heat treatment is required for A691 steel pipe?
Answer: A691 steel pipes typically require post-weld heat treatment (PWHT) to relieve stresses and improve mechanical properties. This involves heating the pipe to a specific temperature (e.g., 1200-1350°F for CM-1Cr) and holding for a period, followed by controlled cooling, as specified in the ASTM A691 standard.
3.What are the welding considerations for A691 steel pipe?
Answer: Welding A691 steel pipe requires careful procedures due to its alloy content. Preheating and post-weld heat treatment are often necessary to prevent cracking and ensure weld integrity. Welding materials should match the base metal composition, and qualified welders must follow codes like ASME Section IX.
4.How does A691 steel pipe differ from other similar pipes, like A335?
Answer: A691 is an electric-fusion-welded pipe for high-temperature service, while A335 is a seamless ferritic alloy-steel pipe for similar applications. A691 is welded, making it more economical for large diameters, whereas A335 is seamless and often used for higher pressure applications where weld integrity is a concern.
5.What testing and inspection requirements apply to A691 steel pipe?
Answer: A691 steel pipes must undergo various tests, including hydrostatic testing to check for leaks, non-destructive examination (e.g., radiography or ultrasonic testing) of welds, chemical analysis, and mechanical tests (tensile, hardness, impact). Inspection is done per ASTM A691 and often includes certification and marking.
