Technical Presentations at the January 2002 Meeting

'Development of Titanium/Steel Composite Risers', Phil Jaques (Oil States Industries Ltd.).

Advanced composite materials offer unique properties such as lightweight, high strength, good thermal insulation and excellent fatigue and corrosion resistance, which make composites attractive to deep water applications. The successful application of composite risers require key technical issues to be addressed which are unique to the composite components, design, manufacture and performance.

Projects currently in progress to qualify composite production risers and drilling risers are the aforementioned Heidrun composite drilling riser, the NIST-ATP (US Department of Commerce National Institute of Standards & Technology - Advanced Technology Program) project on composite production risers and the Norske Conoco A/S and Oil States Composite Steel-Titanium Interface connector project.

The Heidrun titanium drilling riser has been in operational use for 4 years. Drilling operations have seen the successful completion of 20 new wells. The risers are inspected after each retrieval, random checks are conducted on the titanium riser welds, pipe material and titanium studs by industry approved NDE methods. The titanium materials have shown no detrimental defects. Periodic repairs have been carried out on the internal rubber wear liner. Damage mainly due to initial operational start-up procedures, revised drilling procedures have seen limited damage to the rubber liner. Booster line pins have seen wear caused by abrasion, mud being trapped between the pin and box elastomeric seals. Coating the titanium pin surface with Tungsten frame spray technique has rectified this operational damage.

Although titanium Ti-6Al-4V ELI alloy offers the optimum combination of elastic modulus, strength and weight for drilling riser applications, titanium is quite expensive. Therefore efforts are underway to evaluate carbon fibre composites as an alternative solution. The proposed design of composite joints incorporating titanium liner and connectors suggest that composite drilling risers will cost approximately 50% than that of titanium risers. Specific drawbacks to acceptance are cost. On a direct component-to-component replacement basis composites and titanium in general are more expensive than their steel counterparts. However, when applied to deep water floating systems the reduction in weight and improvement in fatigue performance of individual composite components, such as a riser, can provide significant cost and performance benefit at the systems level. This translates into a much lower systems cost for newbuild Spars or TLP's.

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'Stainless Steels for Marine Environments', Jan Olsson (AvestaPolarit Ltd.).

As a starter, modern and classical poetry reflecting on marine corrosion is presented. The concept of marine environments is shown to cover two of the classical elements, air, i.e. atmospheric corrosion, and water, the latter included fully immersion and the area between, the splash zone. The discussion includes the possible use of stainless steel in natural marine environments, i.e. at ambient temperatures and without any additions to the water. This is justified by showing the influence of chlorination or a slightly elevated temperature on the corrosion potentials of different stainless steels in seawater.

It is established that 1.4401 (type 316) is good enough for most, but not all atmospheric conditions. It is also established that there are stainless steels which can cope with natural seawater, but only the most highly alloyed, i.e. 6Mo austenitic grades and superduplex grades should be considered in such cases. Examples of installations exposed to atmospheric conditions covers stainless steels for wall claddings, storage tanks, export pipe lines, hand railings, bridges, cable ladders on offshore platforms and prestigious monuments. One example of a successful industrial application is also emphasised, seawater reverse osmosis (SWRO).

Material Selection for Corrosion Prevention, Roger Francis (Weir Materials & Foundries Ltd.).

In the modern world, industrial equipment must be reliable, and this includes resistance to corrosion. However, there is a continuing pressure to reduce costs without sacrificing performance. This paper uses the selection of materials for pumps to show all the factors that must be considered to make a cost-effective choice. Corrosion resistance is discussed for a range of materials and environments, along with other factors, including metallurgical and economic. The importance of adequate information and the experience to utilise this is demonstrated. The identification of the key requirements for a specific application is essential and requires a close relationship with the customer to ensure adequate information exchange. Only by a careful consideration of all the relevant factors can a cost-effective material selection be made.