API 653 Welding & Metallurgy 3

Question 1

Which metallurgical phenomenon occurs when carbon migrates from the base metal to the weld deposit during welding of dissimilar steels?

Accepted Answer

Carbon migration (decarburization/carburization)

Answer

Carbon migrates from the lower-alloy steel toward the higher-alloy weld deposit or vice versa at elevated temperatures, creating a decarburized zone susceptible to creep.

Question 2

Per API 653, when is a welding procedure qualification test required before making repairs to a tank in service?

Accepted Answer

When the repair involves a new base metal, filler metal, or process not previously qualified

Answer

API 653 requires a qualified welding procedure specification (WPS) supported by a procedure qualification record (PQR) whenever the combination of variables falls outside previously qualified ranges.

Question 3

What is 'lamellar tearing' and what plate orientation makes it most likely to occur?

Accepted Answer

Subsurface cracking caused by through-thickness tensile stress in plates with low short-transverse ductility

Answer

Lamellar tearing occurs when restrained welded joints place through-thickness tensile stress on plates containing elongated MnS inclusions with low ductility in that direction.

Question 4

In API 653 tank inspection, what is the significance of a 'heat affected zone' (HAZ) in the context of corrosion?

Accepted Answer

The HAZ can have altered microstructure and residual stresses that increase susceptibility to certain corrosion mechanisms

Answer

The thermal cycle during welding can sensitize stainless steels, harden carbon steels, and introduce residual stresses in the HAZ, all of which can accelerate corrosion under certain conditions.

Question 5

Which electrode classification would be selected when making low-hydrogen welds on A516 Grade 70 carbon steel in accordance with AWS A5.1?

Accepted Answer

E7018

Answer

E7018 is a low-hydrogen electrode (H8 designation) suitable for structural steels with higher strength and/or thickness, where hydrogen-induced cracking is a concern.

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

API 653 Welding & Metallurgy 3