API Updated API-571 Exam Questions and Answers by angelina

According to API RP 571, under the section "Corrosion in Aqueous Environments – Cooling Water Corrosion", one of the key contributors to corrosion in carbon steel and other materials used in heat exchangers is the presence of dissolved oxygen. API RP 571 states:

"Oxygen is a primary contributor to corrosion in cooling water systems. Systems open to the atmosphere are typically more corrosive than closed systems due to the continual replenishment of oxygen."

"Corrosion rates are highest where oxygen concentration is the greatest, especially in systems using untreated or poorly treated water."

"Carbon steel corrodes in the presence of oxygen and water, forming corrosion products that may or may not adhere to the surface."

(Reference: API RP 571, Section 4.3.1.1 – Cooling Water Corrosion)

Therefore, increasing oxygen content directly increases corrosion activity in exchanger tubes, making option C the correct and documented answer.

According to API RP 571 Section 5.1.2.6 (Carbonate Stress Corrosion Cracking - CSCC):

“The cracking is usually intergranular and is most commonly detected using wet fluorescent magnetic-particle testing (WFMT) after surface cleaning. PT may not be sensitive enough to detect fine cracks formed by this mechanism.”

Because CSCC cracks are typically surface-connected and very fine, WFMT offers the best visibility, especially after proper surface prep.

Therefore, Option D is correct.

API RP 571 – Hydrogen Stress Cracking – HF Acid Service:

“HF acid environments can cause hydrogen stress cracking (HSC) in carbon steel, particularly in areas with high hardness or residual stress.”

“This is distinct from general corrosion and requires specific inspection focus.”

So, option A is correct.

In API RP 571, under the section Polythionic Acid Stress Corrosion Cracking, it is stated:

“Sensitization of austenitic stainless steels occurs when the material is exposed to temperatures in the range of 800°F to 1500°F (427°C to 816°C), which causes chromium carbide precipitation at grain boundaries, depleting the adjacent areas of chromium.”

“Once sensitized, the steel becomes susceptible to attack in the presence of polythionic acids, particularly in environments containing sulfides and oxygen.”

(Reference: API RP 571, Section 4.2.2.5 – PTA SCC)

This makes option B (750°F to 1500°F / 400°C to 815°C) the most accurate and standard-aligned answer.