OS-C501
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Offshore Standard DNV-<strong>OS</strong>-<strong>C501</strong>, November 2013<br />
Sec.4 Materials - laminates – Page 61<br />
5.3.1 The effect of seawater is generally less severe than the effect of fresh water.<br />
5.3.2 The effect of distilled water is more severe than the effect of fresh water.<br />
5.3.3 The combination of water and high temperature may be worse than the individual effects of temperature<br />
and water.<br />
5.3.4 Aramid fibres shall not be exposed to the combination of water and temperature cycles above and below 0°C.<br />
5.4 Effect of chemicals<br />
5.4.1 The compatibility of a laminate to the exposure to chemicals shall be demonstrated.<br />
5.4.2 In a qualitative way most chemicals tend to have similar effects as water on a composite. The degradation<br />
rates shall be obtained for the actual materials in question. In addition, chemicals may break down the matrix,<br />
attack the matrix / fibre interface or destroy the fibres.<br />
5.5 Effect of UV radiation<br />
5.5.1 UV radiation can break down the polymers and reduce their strength. The resistance of surface layers to<br />
UV radiation shall be documented and quantified if necessary.<br />
5.5.2 Glass and carbon fibres are very resistant to UV radiation.<br />
5.5.3 Aramid fibres are not resistant to UV radiation and shall be protected.<br />
5.5.4 Polyesters tend to have a good UV resistance.<br />
5.5.5 Epoxies tend to have a bad UV resistance.<br />
5.5.6 Vinylester tend to have a variable UV resistance.<br />
5.6 Electrolytic Corrosion<br />
5.6.1 Carbon fibre laminates shall be isolated from direct contact with all metal parts to prevent electrolytic<br />
corrosion.<br />
5.6.2 It is recommended to check the quality of the isolation by resistance measurements.<br />
Guidance note:<br />
Electrical connection between carbon fibres and steel in submerged conditions (with or without anodes) will cause<br />
cathodic protection of the carbon fibres where they are exposed to sea water (in cracks, cut surfaces etc.). When<br />
polarised the local pH at the fibre surface will be increased to ≈ 13 and salts from the sea water will precipitate on the<br />
fibres. The associated volume increase will force the crack to open more (“The wedging effect”). As a result, the<br />
mechanical properties of the laminate may be reduced, due to the gradually increasing loss of adhesion between the<br />
carbon fibres and the matrix.<br />
5.7 Combination of environmental effects<br />
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5.7.1 The combination of environmental effects on materials, like combined humidity and heat, may be worse<br />
than the individual effects.<br />
5.7.2 Test data should be obtained of the combined effect of environments on the material properties if<br />
relevant. The worst relevant combination of environments should be used for testing.<br />
5.8 Blisters/osmosis<br />
5.8.1 Some matrix systems develop blisters after some time of water exposure. Matrix systems should be<br />
chosen that have been proven to be blister resistant. A proper mixture of hardener and curing agent is also<br />
important to prevent blistering. Blistering can also be related to weak bonding between gelcoat and laminate.<br />
Blistering is also sometimes referred to as “Osmosis”.<br />
6 Influence of process parameters<br />
6.1 Introduction<br />
6.1.1 Composite laminates can be produced in many ways. Changes to the process parameters may influence<br />
some or all-material parameters.<br />
6.1.2 Process parameters are seen here in a wider sense. Change of void content or fibre fraction are part of<br />
this section, even though these changes are a results of other changes of more fundamental production<br />
parameters.<br />
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