The offshore oil industry has been tackling the problem of crevice corrosion in instrumentation piping clamps for years, using a variety of costly approaches. Now, a German company working in conjunction with its UK subsidiary has come up with a very promising solutionAt last month's Offshore Europe 2005, held in the city of Aberdeen, Stauff UK unveiled the results of a long-term investigation into crevice corrosion affecting pipe clamps on offshore exploration and production rigs. Operators have been struggling with the problem of crevice corrosion since the 1980s; it particularly affects clamps associated with instrumentation and lubrication pipe work. The basic applications are simple: 316 stainless steel tubing in metric and imperial sizes up to 12mm and 1/2in outside diameter, secured by plastic jaws in one of two standard materials (dependent on exposure to the elements ) with stainless steel plates and bolts.Crevice corrosion is a localised phenomenon that arises from a stagnant solution at the micro-environmental level. Such stagnant micro-environments tend to occur in crevices (shielded areas) such as those formed under gaskets, washers, fastener heads, insulating material, surface deposits, disbonded coatings, threads, lap joints and clamps. It is initiated by changes in local chemistry within the crevice - depletion of inhibitor in the crevice; depletion of oxygen in the crevice; a shift to acid conditions in the crevice, or a build-up of aggressive ion species (such as chloride) in the crevice.The most common manifestation is oxygen differential cell corrosion. This occurs because moisture has a lower oxygen content when it lies in a crevice than when it lies on a surface. The lower oxygen content in the crevice forms an anode at the metal surface. The metal surface in contact with the portion of the moisture film exposed to air forms a cathode. Figure 1 shows its full potential, with pinhole leaks occurring in as little as five years. Operator responses to the problem have been varied and have involved less than ideal solutions (BP used protective wax containing vapour corrosion inhibitor, British Gas used lead foil, BP/Shell selected 6% molybdenum super-austenitic stainless steel) or alternative costly replacement programmes.Stauff has worked with offshore operators over a number of years to find an answer that provides long-term integrity while maintaining practical application and commercial viability. The first attempts at a design that excluded the ingress of moisture did not provide the complete solution, so attention was turned to the material of the pipe clamp.Over the last two years, development has focused on devising a material that includes a corrosion inhibitor, while maintaining the essential qualities of the standard clamp product. This has now been achieved, and extensive testing has thrown up some very encouraging results. Clamps moulded from this polypropylene/corrosion inhibitor mix (designated PP-AC) have been successfully tested in salt spray cabinet trials according to DIN 50021, to ASTM B117, and they have also undergone additional SO2 tests.The Stauff Anti Corrosion Pipe Clamp, has already been welcomed by oil companies led by BP. It is available in both single standard series and twin-clamp series DIN 3015 Parts 1 and 2, in metric and imperial sizes up to 25.4mm.