PVC wrapping effect on cathodic protection shielding

[midris]

Hello,

STOPAQ PVC outerwrap is being considered for aeging underground CS piping which is protected by an impressed current CP system. The current drain test was performed on the piping and the required current for protection has been determined. Will the PVC wrap result in CP current shielding?

Thanks,

 

[brimmer]

If there is a holiday or coating were to become disbonded, any PVC wrap will shield current

 

[SJones]

The outerwrap should be the second layer in a two layer Stopaq system. CP current will only be required where the metal substrate becomes exposed to the soil, so shielding is not an issue in that case. Shielding becomes an issue when the coating disbonds from the substrate and electrolyte finds its way into contact with the steel whilst CP current is denied access through the intact coating. The Stopaq system has been tested for disbondment and the data should be available to you. In its simplest form it will state compliance with EN 12068. An overview of a detailed test programme for Stopaq, undertaken with Shell, is given at:

A Bessant, Putting An End To Coating Disbondment: Viscous-Elastic Coatings For Transportation Pipelines, Corrosion Management, Jan/Feb 2009, pp 15 - 18

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.