GPT Corrosion Control & Cathodic Protection

Question 1

What is the minimum pipe-to-soil potential reading (measured with a copper/copper sulfate reference electrode) that indicates adequate cathodic protection on a buried steel gas pipe?

Accepted Answer

-0.85 volts

Answer

NACE SP0169 specifies that a minimum negative 0.85 V (CSE) pipe-to-soil potential indicates adequate cathodic protection for buried steel pipelines.

Question 2

Which type of cathodic protection system uses an external DC power source to drive protective current onto a buried pipeline?

Accepted Answer

Impressed current system

Answer

An impressed current cathodic protection (ICCP) system uses a rectifier as an external DC power source to supply current through an anode to protect the pipeline.

Question 3

Magnesium and zinc anodes used in sacrificial anode cathodic protection systems work because they are:

Accepted Answer

Less noble (more active) than steel in the galvanic series

Answer

Sacrificial anodes must be anodic (less noble, more active) relative to steel so they corrode preferentially, supplying protective current to the pipeline.

Question 4

What does a 'holiday' refer to in the context of pipeline coating inspection?

Accepted Answer

A discontinuity or defect in the protective coating

Answer

A holiday is any gap, pinhole, or defect in a pipeline's protective coating that exposes bare metal to the corrosive environment.

Question 5

Stray current corrosion on a buried gas pipeline most commonly originates from:

Accepted Answer

DC transit systems or cathodic protection systems on adjacent structures

Answer

DC stray current from transit systems (electric rail) or neighboring CP systems can discharge from a buried pipe and cause accelerated anodic corrosion.

(GPT) Gas Pipe Technician Certification Practice Test

(GPT) Gas Pipe Technician Certification Practice Test

GPT Corrosion Control & Cathodic Protection