Technical Presentations at the July 2000 Meeting

Coming to a Sheet Pile Near You… The Bug of the Millennium- A Wholly Practical Guide to Actual Holes',
Mike Hodgson (John Martin Construction Ltd) and Tom Shelley (Felixstowe Dock & Railway Co.).

The abstract was not supplied.

High Pressure Air cylinders reducing through-life costs', Ritchie Brown (BAESEMA).

HP air cylinders are used to store air at 276 bar and are used in naval vessels as an energy store for a wide number of applications. These are seamless steel cylinders swaged and machined at each end to allow installation of end fittings. Any catastrophic failure of the steel will result in explosive energy release with the potential for causing considerable damage or fatalities. Revalidation every 10 years involves cylinder removal, shot blasting, pressure testing and visual examination. This is a time consuming and costly process and the revalidation intervals do not tie in with docking periods.

No cylinders have failed a pressure test in the last 40 years which means that the historical safe operation has been based on visual examination.

Fracture mechanics calculations have established that no linear defects detectable with 99.9% confidence at manufacture can grow to cause failure in a life of 30 years. The implication is that defects that can cause failure can only grow by a corrosion (pitting) mechanism. This is borne out by service experience where there is no evidence that cracks have ever been detected.

A safe life of 20 years has been calculated assuming chain pitting down the length of the cylinder initiating a crack. The size of defect for the remaining required 10 years life can be detected with high confidence by visual examination. Cost reductions can be achieved by in-situ revalidation based on chemical cleaning, visual examination using CCTV combined with ultrasonic/eddy current sizing of any defects found. Failure probability can be demonstrated to better than 10-6.

The development and properties of 25%Cr superduplex stainless steel wirelines, strands and ropes', Keith Bendall (Advanced Metals International Ltd).

Highly alloyed 25% chromium super duplex stainless steel has been widely, successfully applied in many different product forms for three decades. Demanding applications for such material are found in a wide range of industry sectors and the high resistance to corrosion proven in offshore oil and gas, chemicals processing, pulp and paper, FGD (Flue Gas Desulphurisation), architecture and defence.

The successful processing of wire from FERRINOXR 255 PRE n >40 super duplex steel rod coil has enabled the production of AMINOXTM 255 wirelines, strands and wire ropes. AMINOX 255 strands offer mechanical strength up to over 50% higher than Type 316 stainless steel. Conventional and compacted construction strands are available. Extensive testing of AMINOX 255 wires and strands has demonstrated the excellent combination of properties.

A wide variety of applications requiring high mechanical strength and reliable, predictable resistance to corrosion in acid media and/or chloride ion containing environments can benefit from the deployment of the super duplex wires, strands and wire ropes which have been developed. Typical applications would include wirelines and well-service strands, mast rigging strands, architectural support and restraint structure strands, swimming pool support structures, marine environment towing/mooring/equipment deployment, architectural/corrosive environment balustrades, lifting equipment/pulley systems/support structures in chemical process industry environments and civil engineering structure components.

'The commercial use of corrosion resistant metals and their alloys subsea - a marine manufacturers perspective',
Phillip Walsh and David Somerville (CRP Marine).

As a designer and manufacturer of products for use in the marine environment CRP has endeavoured to utilise materials that offer an optimum performance in conjunction with commercial availability. The company looks to organisations such as the Marine Corrosion Club to advise on new material development and also monitor performance of existing materials in corrosive environments.

The presentation focused on-

(i) Who is CRP?, (ii) UraductÒ and associated banded products- presented by Phillip Walsh, (iii) The use of corrosion resistant materials in the development of CRP's internal clamp- presented by David Somerville

• Who is CRP?

  CRP Marine was established in 1970 in the new town of Skelmersdale in Lancashire. Initially the company produced simple marine products such as lifebuoys and lifejackets manufactured from polyurethane foam and elastomer. This proved to be an extremely successful venture and subsequently surface buoys and small boat fenders were added to the growing product range. In 1980 the company initiated a major diversification with the manufacture of syntactic foam. This material is used in the construction of subsurface buoys, ROV buoyancy and flexible riser buoys. The use of this material precipitated the company's entry into the offshore market. CRP continued to expand throughout the 80's, establishing a reputation for engineering excellence and high quality products and on the 1st January 1990 moved to a new purpose built factory, also located in Skelmersdale. It was shortly after this time the company received BS 5750, Part 1/ISO 9001 certification. The relocation of the company produced two further developments.

  First, CRP Polymer Engineering was established to develop the company's interests in the onshore general engineering markets.

  Second, CRP Marine expanded its project management and engineering capabilities in order to successfully complete an increasing number of turnkey engineering contracts. CRP Polymer Engineering and CRP Marine both now operate within the corporate structure of the CRP Group Ltd. In 1998 CRP further extended their overall site which now covers approx. 8 acres, more than doubling the factory floor space, incorporating full span overhead cranes and a dedicated product testing area as well as Europe's largest hydrostatic pressure vessel for the testing of deepwater buoyancy modules. CRP Group now employs over 200 personnel predominately located in the UK, but also in an expanding CRP Group Inc. organisation based in Houston, Texas USA.

• CRP's UraductÒ and associated banded products - presented by Phillip Walsh

  CRP manufactures and markets a Cable & Flowline protection system called UraductÒ that is used in the Oil & Gas, Submarine Telecommunications and Submarine Power Cable markets to protect exposed areas of cables & pipelines from impact and abrasion damage. The essence of the system is that Polyurethane half-shells are banded onto the outside diameter of the core product to form a long lasting protective sheath. The banding used must exhibit good tensile strength and very good resistance to corrosion, as the systems typically require a design life of 20 to 25 years subsea.

  UraductÒ has been marketed for over a decade and is in use all over the world. Through the use of careful material selection, material testing and constant monitoring CRP only use Titanium grade 2 or Alloy 625 banding materials. Alternatives such as Stainless 316 and Monel 400 have not proved suitable as they suffer from crevice corrosion.

  CRP commissioned a test to discover the extent of the problem in 1997. The test and subsequent report was prepared by DRA. The test compared four banding materials; Stainless 316, Monel 400, Alloy 625 and Titanium. The bands were assembled, as is the case with the UraductÒ product. Each sample was immersed in seawater for a 7-month period and the resulting report showed conclusively that both the Alloy 625 and Titanium were free from any crevice corrosion.

• The use of corrosion resistant materials in the development of CRP's internal clamp - presented by David Somerville

  CRP have been involved for a long time in the development of subsea buoyancy for the oil industry and for oceanographic and ROV purposes.

  One of their main products over the years has been the distributed buoyancy module used to support sub-sea risers. These modules provide buoyancy at discrete positions along the riser's length, and may be positioned to generate the correct configuration for the riser.

  A typical distributed buoyancy module comprises two outer half shells, filled with buoyant material, surrounding an internal clamp. The clamp acts as a key for the module locking it in place on the riser.

  A number of years ago, the industry standard was for the use of aluminium clamps. While these had advantages such as their low weight compared to steel and the avoidance of cathodic protection, they had a number of disadvantages relating to their weight, their ability to comply with variations in riser diameter and the effect they could have on the sheath of a flexible pipe.

  CRP have developed a composite clamp using a titanium alloy securing strap. The composite provides buoyancy and an envelope around which the strap could function. The titanium alloy provides a much better strength to weight ratio and corrosion resistance in seawater, using a commercially available material.

  Flexible pipes because of their construction have large manufacturing tolerances with regard to diameter. During installation and in service, the internal and external pressures, the pipe tension and the geometry of the pipes' configuration can influence the diameter of the pipe. The clamp must accommodate all these and still maintain its capacity to keep the buoyancy module in place.

  The ability of CRP's internal clamp to achieve all these was demonstrated and discussed, along with a typical test programme used to validate the clamp's functional and structural integrity. CRP have also developed test programmes on various lubricants for their internal clamps to ensure that their use will not affect the corrosion resistance of the clamp.

  As industry demands become increasingly onerous, so the internal clamp's design has evolved. This will continue with a keen eye on the use of new materials, which meet the functional requirements and corrosion resistance needed for long term sub-sea service.