The pipeline coating is the first line of defence against corrosion and cathodic protection is
used to control corrosion risks at sites of coating damage. However, some coating systems
show failure modes that interfere with the effectiveness of the cathodic protection and create a
new corrosion risk. These risks include CP shielding, microbial corrosion and external stress
corrosion cracking.
This paper describes and defines failure modes for pipe and field joint coatings and identifies
which failure modes create the conditions for CP shielding.
Comment is then made on sampling patterns for excavation and direct examination and on
additional tests that may clarify the long term behaviour of the coating systems.