API 510 Corrosion Mechanisms and Monitoring 3

Question 1

Which nondestructive examination (NDE) method is best suited for detecting hydrogen-induced cracking (HIC) in plate steel?

Accepted Answer

Automated ultrasonic testing (AUT) with phased array

Answer

AUT with phased array ultrasonics can detect the internal, planar HIC blisters and step-wise cracking that occur within the steel plate, which surface methods cannot find.

Question 2

Naphthenic acid corrosion in refinery equipment is characterized by which distinctive feature?

Accepted Answer

Pitting and grooving at areas of high turbulence and velocity

Answer

Naphthenic acid corrosion produces characteristic pitting and grooving at high-turbulence locations because the corrosion product (iron naphthenate) is soluble and is swept away by flow.

Question 3

What does the term 'short-term corrosion rate' mean in the context of API 510 remaining life calculations?

Accepted Answer

Corrosion rate measured over the last inspection interval only

Answer

The short-term corrosion rate in API 510 is calculated from the most recent inspection interval, reflecting current operating conditions more closely than the long-term rate.

Question 4

Which condition is required for chloride stress corrosion cracking (Cl-SCC) to occur in austenitic stainless steel?

Accepted Answer

Tensile stress, chloride ions, and temperature typically above 140°F (60°C)

Answer

Cl-SCC requires the simultaneous presence of tensile stress, chloride ions, and elevated temperature (typically above 140°F/60°C) to initiate and propagate cracks.

Question 5

In high-temperature service above 750°F (400°C), what corrosion mechanism causes carbon steel to lose strength and ductility through carbon removal from the steel matrix?

Accepted Answer

High-temperature hydrogen attack (HTHA)

Answer

HTHA occurs when hydrogen reacts with carbon in the steel to form methane gas, which decarburizes the steel and creates internal fissures, reducing mechanical properties.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Corrosion Mechanisms and Monitoring 3