PCS Coating Failure Analysis and Remediation 3

Question 1

White powdery deposits on the surface of a zinc-rich primer before topcoat application most likely indicate what condition?

Accepted Answer

Zinc corrosion salts (white rust) from normal weathering

Answer

Osmotic blistering of the primer

Answer

Chalking due to UV degradation

Answer

Cathodic disbondment of the primer

Question 2

Mudcracking (also called mud cracking) in a coating film is most often caused by which application error?

Accepted Answer

Applying an excessively thick wet film in a single coat

Answer

Substrate contamination with chloride salts

Answer

Application over a damp or wet surface

Answer

Incompatible topcoat applied over primer

Question 3

Which instrument can detect corrosion beneath an intact coating without removing the coating?

Accepted Answer

Ultrasonic thickness gauge

Answer

Dry film thickness gauge

Answer

Holiday detector

Answer

Magnetic pull-off gauge

Question 4

What does the pull-off adhesion test (ASTM D4541) specifically measure in a coating failure investigation?

Accepted Answer

Tensile strength of adhesion between coating and substrate

Answer

Wet film thickness of the applied coating

Answer

Type and pattern of the coating failure

Answer

Density of holidays in the coating film

Question 5

Sagging or runs in a freshly applied coating film are most commonly attributed to which cause?

Accepted Answer

Over-thinning of the coating or applying an excessive wet film thickness

Answer

Substrate surface profile that is too coarse

Answer

Excessive ambient temperature during application

Answer

High relative humidity above 85%

Question 6

In coating failure terminology, 'intercoat delamination' specifically describes which failure mode?

Accepted Answer

Separation occurring between two successive coats within the coating system

Answer

Separation of the coating system from the steel substrate

Answer

Cohesive failure within a single coat due to solvent entrapment

Answer

Separation exclusively at the primer-to-topcoat interface

Question 7

Which surface contaminant, if not removed before coating application, is most likely to cause osmotic blistering in a marine or immersion environment?

Accepted Answer

Soluble chloride salts

Answer

Oil and grease residues

Answer

Rust scale loosely adhering to the substrate

Answer

Abrasive blast media residue