In June 1996 there was a leakage in an isolation coupling of a gas pipe line. Because of this we did develope a method to determine corrosion and monitor its growth.

Isolation joints and flanges are intended to keep the currents of the cathodic protection separated from eachother. A pipe line leading to or from an installation (above or below ground) has a cathodic protection. As soon as there is moisture in the insulation coupling and / or dirt accumulates, a galvanic process will start and the material of the coupling will dissapear.

Because some parts of a coupling are very thick, radiography is often not possible.

Isolation coupling 
Affected coupling
Isolation spool
Testing a coupling