Piping Piping Materials and Specifications 1 — Questions and Answers
Question 1: What does the ASTM designation 'A106 Grade B' specify for pipe?
- Stainless steel seamless pipe for cryogenic service
- Seamless carbon steel pipe for high-temperature service (Correct answer)
- Electric-resistance welded carbon steel pipe for general service
- Chrome-moly alloy pipe for boiler applications
Correct answer: Seamless carbon steel pipe for high-temperature service
ASTM A106 Grade B is a seamless carbon steel pipe specification commonly used in high-temperature process piping up to 750°F (399°C).
Question 2: What is the primary advantage of using austenitic stainless steel (e.g., 316L) over carbon steel in piping?
- Higher tensile strength at all temperatures
- Superior corrosion resistance, especially in chloride and acidic environments (Correct answer)
- Lower cost per foot
- Greater resistance to hydrogen embrittlement
Correct answer: Superior corrosion resistance, especially in chloride and acidic environments
Austenitic stainless steels like 316L offer excellent corrosion resistance due to their chromium and molybdenum content, making them suitable for corrosive process fluids.
Question 3: What is the purpose of the ANSI/ASME pipe schedule number system?
- To identify the pipe material grade
- To indicate the pipe wall thickness relative to the outside diameter (Correct answer)
- To classify the pipe's pressure-temperature rating class
- To specify the pipe end preparation type
Correct answer: To indicate the pipe wall thickness relative to the outside diameter
Pipe schedule numbers (Sch 40, Sch 80, etc.) define the wall thickness as a ratio, where higher schedule numbers indicate thicker walls for higher pressure service.
Question 4: What does 'NPS' stand for in pipe specifications?
- Nominal Pipe Size (Correct answer)
- National Pipe Standard
- Net Pressure Specification
- Non-Pressure Service
Correct answer: Nominal Pipe Size
NPS (Nominal Pipe Size) is a dimensionless designator that approximately indicates pipe size; actual OD does not equal NPS for sizes 14 inches and below.
Question 5: Which material is preferred for piping in hydrogen service to minimize hydrogen embrittlement?
- High-carbon steel
- Austenitic stainless steel or specially treated low-alloy steel per Nelson curves (Correct answer)
- Cast iron
- Pure aluminum
Correct answer: Austenitic stainless steel or specially treated low-alloy steel per Nelson curves
The Nelson curves (API 941) guide material selection for hydrogen service by identifying safe operating limits for carbon and low-alloy steels to avoid high-temperature hydrogen attack.
Question 6: What is the primary use of chrome-moly (Cr-Mo) alloy piping such as P91?
- Cryogenic service below -100°F
- High-temperature, high-pressure service in power and refinery applications (Correct answer)
- Chloride-containing corrosive service
- Underground buried piping
Correct answer: High-temperature, high-pressure service in power and refinery applications
Chrome-moly alloys like P91 (9Cr-1Mo-V) have excellent creep strength and oxidation resistance at elevated temperatures, making them ideal for high-temperature steam and process service.
Piping Piping Materials and Specifications 1
What does the ASTM designation 'A106 Grade B' specify for pipe?