API Updated API-571 Exam Questions and Answers by jibreel

Erosion and erosion-corrosion are mechanical degradation mechanisms enhanced by fluid motion, and typically result in directional or flow-oriented metal loss patterns.

According to API RP 571 Section 5.4.2 (Erosion and Erosion/Corrosion):

“Erosion typically results in localized thinning, often described as grooves, gullies, or horseshoe-shaped patterns... The metal loss is directional and may occur in elbows, tees, reducers, and pumps.”

Hence, Option C (grooves and gullies) most accurately describes erosion and erosion-corrosion characteristics.

API RP 571 on Chloride Stress Corrosion Cracking (Cl-SCC) clearly states:

“Austenitic stainless steels such as 304 and 316 are highly susceptible to Cl-SCC when subjected to tensile stress and exposed to chloride-bearing environments.”

“Susceptibility is greatest in non-stress-relieved weldments or cold-worked areas.”

Brass and carbon steels are not typical Cl-SCC candidates; low alloy steels such as 1.25Cr-0.5Mo are also not commonly affected.

Thus, option C is the correct answer.

From API RP 571 Section 5.3.3.2 (Caustic Corrosion):

“Caustic corrosion, also known as caustic gouging, occurs in boiler systems when caustic concentrates in under-deposit areas or due to improper steam drum and boiler water design. Good design and water treatment practices are key preventive measures.”

Temperature control or acid injection are not practical or effective mitigation techniques. Design considerations—such as proper water flow, material selection, and minimizing deposits—are essential.

Hence, the correct answer is Option C.

API RP 571 emphasizes under Hydrogen Stress Cracking – Hydrofluoric Acid (HF):

“Cracking in carbon steel is influenced by high hardness and tensile stress in the presence of wet HF acid.”

“Controlling weld and heat-affected zone hardness to below 200 BHN is a key mitigation measure, as higher hardness significantly increases susceptibility.”

Steel hardness and strength are thus critical for cracking in HF environments, making option C correct.