SPED Materials Selection & Specification 2 — Questions and Answers
Question 1: Which ASME material specification covers seamless and welded austenitic stainless steel pipe?
- SA-312 (Correct answer)
- SA-106
- SA-333
- SA-335
Correct answer: SA-312
SA-312 covers seamless, straight-seam welded, and heavily cold worked welded austenitic stainless steel pipe.
Question 2: What is the primary reason duplex stainless steel is selected over austenitic stainless steel in chloride-containing environments?
- Lower cost per pound
- Superior resistance to stress corrosion cracking (Correct answer)
- Higher elevated-temperature strength
- Better weldability without filler metal
Correct answer: Superior resistance to stress corrosion cracking
Duplex stainless steels have a two-phase ferritic-austenitic microstructure that provides significantly better resistance to chloride stress corrosion cracking than standard austenitic grades.
Question 3: SA-333 Grade 6 pipe is specifically intended for service at:
- Elevated temperatures above 900°F
- Cryogenic and low-temperature service (Correct answer)
- Sour gas (H₂S-containing) service
- High-pressure steam service above 600 psig
Correct answer: Cryogenic and low-temperature service
SA-333 Grade 6 is a low-temperature carbon steel pipe specification with a minimum impact test temperature of −50°F.
Question 4: Which corrosion mechanism is most critical when selecting piping materials for a wet H₂S service application?
- Galvanic corrosion
- Crevice corrosion
- Sulfide stress cracking (SSC) (Correct answer)
- Intergranular corrosion
Correct answer: Sulfide stress cracking (SSC)
Wet H₂S environments produce atomic hydrogen that diffuses into steel and can cause sulfide stress cracking (SSC) in high-hardness or high-strength materials.
Question 5: According to ASME B31.3, the basic allowable stress for a piping material is primarily derived from:
- The material's yield strength at room temperature only
- The lesser of fractions of ultimate tensile strength and yield strength at temperature (Correct answer)
- The material's hardness Brinell number
- The pipe wall thickness divided by the outer diameter
Correct answer: The lesser of fractions of ultimate tensile strength and yield strength at temperature
ASME B31.3 sets allowable stress as the lesser of specific fractions of the tensile and yield strengths at design temperature, among other criteria.
Question 6: What is the purpose of solution annealing austenitic stainless steel pipe after welding?
- To increase hardness and tensile strength
- To dissolve chromium carbide precipitates and restore corrosion resistance (Correct answer)
- To relieve residual stresses for sour service compliance
- To convert austenite to martensite for improved wear resistance
Correct answer: To dissolve chromium carbide precipitates and restore corrosion resistance
Solution annealing heats the steel above the carbide solvus temperature and quenches it, dissolving sensitizing carbides and restoring corrosion resistance.
Question 7: Which material is preferred for piping that handles anhydrous ammonia due to its compatibility and cost-effectiveness?
- Copper alloy (e.g., admiralty brass)
- Carbon steel (e.g., ASTM A106 Grade B) (Correct answer)
- 304 stainless steel
- Hastelloy C-276
Correct answer: Carbon steel (e.g., ASTM A106 Grade B)
Anhydrous ammonia is compatible with carbon steel; copper alloys are prohibited because ammonia attacks copper, and stainless or exotic alloys are unnecessary and costly.
SPED Materials Selection & Specification 2
Which ASME material specification covers seamless and welded austenitic stainless steel pipe?