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steel pipe coating

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BRIS

Civil/Environmental
Mar 12, 2003
525
We are designing a major pipeline over steep terrain supplying raw water for irrigation- The majority of the pipeline is ductile iron but because of high pressures (pressures over 25 bar in valley sections) some short lengths will be steel - Diameters are 800mm to 1400 mm -

Steel pipe is not my field of experience but I have to prepare a specification for the corrosion protection system.

I have no corrosivity data other than the site is in a limestone area and Ph is above 8.0.

Because of the rough terrain and difficult access I am proposing a polyurethane coating and lining rather than epoxy coating and cement mortar lining. I understand polyurethane is more flexible and resistant to impact damage/poor handling.

Also because of the difficult access and remote location we want to avoid the provision of cathodic protection. will a 3 layer polyurethane system give adequate (50 year) life without cathodic protection.

The obvious reply is to do the job properly - consult a specialist - undertake resistivity surveys and chemical analyses and design the system - but we now don't have time - I need to produce a specification by the end of the week.


Any advice on the suitability of polyurethane coatings and their advantages welcome

 
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Several years ago I did testing to qualify coatings for federal underground piping distribution. We made district heating distribution systems. The outer casing saw no pressure but was in contact with the soil.

For what its worth we evaluated both urethane and epoxy. The testing was focused on neutral pH but very wet conditions.

The urethane was far superior in corrosion resistance and ease of application. We put it on in a single coat and holiday tested after installation.

Single coat was selected because of the intermediate surface prep required and holiday testing showed no apprecialbe difference.

 
Dear BIRS,

I think you are right in supposing that a Polyurethane coating is more flexible than an epoxy but I still doubt that this will help you to rule out corrosion problems caused by bad handling or bad soil preparation.

As inliner has more chances to survive (depends of the water)but I think you will like to make field welds and therefore you will need to paint inside/outside and here you are again facing some problems: the polyurethane coating needs certain conditions (Temperature, humidity, dust etc).
Kind regards
 
Thanks for the response.
My problem now is finding a defining the minimum physical properties for Polyurethane pipe coating for the pipe specification. e.g

Peeling resistance, Impact resistance, cathodic disbondment etc.

Are these covered by any standard?

Brian
 
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