Design Life and Coating Selection and Application

[imans]

Dear Forum's members,

Does any one know what is the influence of design life on coating selection and its application? For example if I want to make an offshore structure with 5 years design life, would the coating specification be different with the one has 20 years design life? What is the different?

Thank for your attention and help.

 

[JoeTank]

When one considers what a coating system intended for 10-15 years looks like after just a few years, I shutter to think what the contractor would do if only a five yesar life were expected. Unless you had resident observation of the coatings work by an independent inspector (such as one with NACE certication) you very well could end up with a five year coating anyway. Sad, but true.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[mshimko]

Offshore structures are not always painted - at last the submerged portion.

Back to the original question specifically: there's always a trade off of the total service life of the structure, minimizing maintenance costs, and minimizing acquisition costs. The challenge is saving money NOW is always more attactive to those who have to pay for it.

Only once did I spec out the paint system for a short service life structure. This was a test structure that was planned to be used for only 3-4 years (and hence the owner didn't want to spend much). I spec'd out a "minimal" low-cost paint system that I thought would last 5 years, and be easily touched-up or recoated later if required - a slight overkill p[robably. 10 years later, the test structure is still in service!

 

[windguy]

Service life and environment has a big influence on the coating type and required dry film thickness.

For further reference, have a look at ISO 12944 'paint and varnishes - Corrosion protection of steel structures by protective paint systems'. For large projects (in Europe anyway) this is normally specified.

This standard covers the the through life coating system, and breaks the application into environment (ie corrosive, industrial, submerged) and durability (in years). Depending on these variables, it gives detailed recommended coating systems.

For the offshore projects I've been involved with, the submerged zone must be either coated OR cathodically protected, as well as a corrosion allowance in the steel supplied. Further guidance refer to NORSOK M-501.

Hope that helps.

 

[robsalv]

What a question. Sounds valid but loaded.

A "normal" coating system that would get 15yrs life in an industrial environment might only make it to 5yrs in an offshore situation.

IMHO a decent multicoat system is cheap insurance. I would hold fast to recommending a "proper" system and it will be less susceptible to failure prematurely if the applicator messed up somewhere that the QA/QC didn't pick up.

Cheers

Rob