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Monday, September 15, 2014

Pipeline Coating Overview

Pipeline Coating Overview

     Looking through some old files, I ran across some notes taken at a pipeline coating / corrosion course not too long ago.  This course was taught by one of the leading experts in pipeline corrosion prevention in recent years. 
     Corrosion is simply the loss of chemical and/or physical integrity of the pipeline.  Corrosion is caused by four things: 
1) Primary chemical reactants (water and oxygen).
2) Secondary chemical reactants (including biological)
3) Physical damage, either before or during service
4) Electrical anomalies
     There are 10 properties required of all pipeline coatings (or: the 10 qualities of good pipeline coating).
1) Must have good adhesion to steel
2) Must be an effective barrier to water
3) Must be chemically stable
4) Must be resistant to mechanical damage
5) Must have long term physical stability
6) Must be amenable to field repair of joints and holidays
7) Must be a good dielectric
8) Must be available and cost effective
9) Must be environmentally benign
10) Must be accepted by the pipeline industry
     Next we went through generic names of different pipeline coatings along with an explanation of what they are.
1. Bituminous Enamels - Coal tars or asphalts reinforced with glass fibers and covered with an outer wrap.
2. Bituminous Mastic - a thick mixture of asphalt, aggregate, and glass fibers.
3. Extruded Polyethylene - two or three layer coatings of PE over butyl rubber, epoxy or bituminous materials.
4. Fusion Bonded Epoxy or Thin Film Epoxy - Epoxy applied as a powder to a heated pipe.
5. Liquid Epoxy - epoxy applied as a liquid; pipe is often heated before or after application in order to speed curing.
6. Extruded Rubber - premixed rubber extruded on pipe and cured in a steam heated autoclave.
7. Liquid Urethane - urethane applied as a liquid to a heated pipe.
8. Tapes - pressure sensitive, cold applied or hot applied laminates of various thermoplastic polymers.
9. Heat shrinkable plant applied - generally a spirally wrapped two layer heat shrink system which is plant applied and offers excellent high temperature corrosion prevention.
10. Viscoelastic - applied using a PE or heat shrinkable outer wrap.
     Important factors in pipeline coating applications:
1) Substrate must be clean with an adequate anchor pattern
2) Coating material must be properly mixed or otherwise uniform in consistency
3) Coating materials must be applied at the proper temperature and at the proper speed
4) Substrate must be at the proper temperature and the materials applied at the proper thickness
5) Materials must be properly quenched or cooled to the ambient temperature
6) Coating must not have any holidays or otherwise any other non-conformities
7) Coating must have adequate adhesion with no delaminations
     Commonly used pipe coating tests:
These tests are used to qualify new materials as well as to determine application quality:
1) Resistance to impact
2) Resistance to bend
3) Resistance to cathodic disbondment
4) Adhesion (peel test, etc)
5) Resistance to shear
6) Presence of holidays
7) Resistance to hot water permeation (where appropriate)
8) Thermal characteristics (where appropriate)
9) Material uniformity (where appropriate)
10) Thickness
      Pipeline coating application guideline:
1) Carry out a rigorous, though realistic, inspection program.
2) Make sure your pipeline inspectors are knowledgeable. 
3) Make sure application is strictly according to specifications.
4) If specification variation is necessary, make sure all interests are protected.
5) Do not accept job until satisfactory.
6) Maintain records on materials, application and performance.
7) Don't let application get you in a time bind.  Provide ample time for contingencies.


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