API 510 Corrosion Mechanisms and Monitoring 2

Question 1

What type of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?

Accepted Answer

Galvanic corrosion

Answer

Galvanic corrosion occurs when dissimilar metals are electrically connected in an electrolyte, causing the more anodic metal to corrode preferentially.

Question 2

Which monitoring technique uses the rate of change in electrical resistance of a metal probe to measure corrosion rate?

Accepted Answer

Electrical resistance (ER) probes

Answer

Electrical resistance (ER) probes measure corrosion rate by detecting changes in the probe's cross-sectional area as metal is lost to corrosion.

Question 3

Polythionic acid stress corrosion cracking (PTA SCC) primarily affects which material in refineries?

Accepted Answer

Sensitized austenitic stainless steel

Answer

PTA SCC affects sensitized austenitic stainless steel when exposed to polythionic acids formed from sulfur compounds, water, and oxygen during shutdowns.

Question 4

What is the primary driving force for under-deposit corrosion in pressure vessels?

Accepted Answer

Concentration of aggressive species beneath accumulated solids

Answer

Under-deposit corrosion is driven by the concentration of corrosive species (chlorides, acids, sulfur compounds) trapped beneath deposits, creating a localized aggressive environment.

Question 5

In API 510 inspection practice, which corrosion mechanism is most commonly associated with crude oil distillation overhead systems?

Accepted Answer

Hydrochloric acid (HCl) dew point corrosion

Answer

HCl dew point corrosion is the dominant mechanism in crude distillation overhead systems, where HCl condenses from hydrolyzed chloride salts and attacks carbon and low-alloy steels.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Corrosion Mechanisms and Monitoring 2