EXPLORATION • DRILLING • FIELD SERVICES
Fig. 1 In situ testing was conducted on two link types
Fig. 1(a) L
Fig. 1(b)
ifting operations in a marine environment pose several challenges, of which corrosion and the potential embrittlement of steel chain-based
components are among the important ones from a material integrity perspective. Corrosion reactions are not only damaging to the surface of the components, which can lead to stress raisers and a reduced service life, they can also promote hydrogen embrittlement (HE), especially on components that operate in offshore or other corrosive environments. Te use of Grade 8 steel alloy chain and components is currently acknowledged as the preferred option when it comes to lifting applications in a marine environment. Tis grade of steel alloy not only complies with the strength/ design requirements for safe lifting but also assists in minimising the risk of embrittlement type failures such as HE.
REAL-WORLD CASE STUDY Historically, products such as steel alloy lifting chain and components such as master links and quad assemblies have been manufactured with various types of corrosion protection, including paint, powder coating, electro plating and hot dipped galvanising. However, once placed into service these coatings are prone to breakdown and erosion due to mechanical stressors. Recent research by McKinnon Chain and William Hackett Lifting Products has considered the suitability of sherardising as a premier corrosion protection method – especially for products used in harsh applications and corrosive environments. Sherardising is a process recognised to be environmentally friendly with
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Fig. 1(c)
Rod Bell discusses the use of corrosion protection measures to extend the service life of lifting chain and link components
CONFRONTING CORROSION
extremely low levels of waste and a zero risk of hydrogen embrittlement. Te hard, abrasion-resistant coating doesn’t interfere with the metallurgical properties of the base material, and it has spark- resistant properties. A further benefit from a testing perspective is that the coating doesn’t interfere with non-destructive
Fig. 2 (a). ‘Untreated’ (painted) chain sling after 20 months service
testing methods such as eddy current and magnetic particle testing (MPI). To inform and support decision- making in relation to the design and development of various Grade 8 lifting products, several tests were commissioned that focused on: corrosion resistance; adhesive properties; anti-spark properties;
Fig. 2 (b). ‘Treated’ (zinc thermal diffused and powder coated) chain sling after 20 months service
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