SPED Materials Selection & Specification 3

Question 1

The maximum allowable hardness for carbon and low-alloy steel in NACE MR0175 sour service is:

Accepted Answer

HRC 22 (approximately 237 HBW)

Answer

NACE MR0175/ISO 15156 limits carbon and low-alloy steel hardness to HRC 22 (≈237 HBW) to prevent sulfide stress cracking.

Question 2

Galvanic corrosion risk is greatest when two dissimilar metals are:

Accepted Answer

In electrical contact in the presence of an electrolyte

Answer

Galvanic corrosion requires both electrical continuity between the metals and an electrolyte to complete the electrochemical circuit.

Question 3

SA-335 P91 alloy steel pipe is primarily used in which service?

Accepted Answer

High-temperature, high-pressure steam service above 1000°F

Answer

SA-335 P91 (9Cr-1Mo-V) is a creep-resistant alloy specifically developed for high-temperature steam piping in power generation applications.

Question 4

Which type of corrosion involves selective dissolution of one component of an alloy, commonly seen in brass in ammonia service?

Accepted Answer

Dealloying (dezincification)

Answer

Dezincification is the selective leaching of zinc from brass, leaving a porous copper matrix; it commonly occurs in stagnant or slow-moving water and in ammonia environments.

Question 5

When specifying a material for piping in hydrofluoric acid (HF) alkylation service, which alloy family is most commonly selected?

Accepted Answer

Monel (Ni-Cu alloy, UNS N04400)

Answer

Monel alloys (Ni-Cu) are the industry-standard material for anhydrous HF service due to their excellent corrosion resistance to this highly aggressive acid.

(SPED) Society of Piping Engineers and Designers Certification Practice Test

(SPED) Society of Piping Engineers and Designers Certification Practice Test

SPED Materials Selection & Specification 3