At TesTex we hold quarterly Engineers Breakfast Meetings where we meet with local engineers to discuss issues they may be facing and work together towards solutions to this. One of the recent subjects was ‘Managing Pipework Integrity’. As part of this heading there was further debate into how to protect buried pipework and the methods currently available for this one of which is looking at the options for field applied external coating.

About Field Applied External Coating

The Majority of buried metallic pipework need to be protected against corrosion. Buried pipework systems are normally protected by a combination of a protective coating; the factory applied coating is the primary source of protection and cathodic protection (CP).

Any uncoated pipes and fitting or those with coating damages should be protected by a field applied coating. A wide range of factors should be considered before the selection of the appropriate material and processes for the coating and/or repair in the field those being the following:

• Operating temperature.
• Type of existing coating (factory applied)
• Ground conditions.
• Type of labour available.
• Complexity of shape to be coated.
• Ambient conditions during application.

There are a wide variety of field applied coatings ranging from cold applied self-adhesive overwrap tapes to multi-component liquids and fusion bonded epoxy powders, added to this there are multi-component liquid coating and wraps for damp surfaces and as stated great care should be considered with regards to selection of and the appropriated system and materials.

The condition of the surface to which a coating is to be applied will directly affect its performance and surface consideration should include any existing pipe which requires overlapping and area of exposed metal to be coated.

Existing pipe coatings which are to be over lapped shall be:

• Checked for existing adhesion.
• Assessed to determine appropriate removal method.
• Contoured to eliminate crevices or sharp steps.
• Identified to the most appropriate compatible material (coating) group.
• Cleaned and primed where applicable in accordance with the manufactures recommendations

There are two basic methods of surface preparation for metal surfaces, these are, in order of effectiveness:

• Blast cleaning.
• Wire brushing (mechanical or hand).

The choice of preparation method will be dictated by technical and environmental considerations, the type of coating to be used and by economic consideration related to the size of project.

Part 2 will continue in more detail and will be added to the blog shortly, in the meantime, if you would like more information on this subject or to speak with one of our specialists, please get in touch, email us aims@testexndt.co.uk or call 01469 541586.

Written by Dave Tiley – TesTex Inspector