POWDER METALLURGY DESIGN Hot isostatic pressing proves value on complex subsea components

Powdermet Sweden has achieved new penetration of the offshore market for its high alloyed stainless steel grade components formed by Hot Isostatic Pressing (HIP).

Powdermet Sweden has achieved new penetration of the offshore market for its high alloyed stainless steel grade components formed by Hot Isostatic Pressing (HIP).

Complex components are being produced for subsea developments. Under a recent order from Framo Engineering, Powdermet is supplying two multiphase duplex steel swivel components for the Framo Rotation Connector (designed in collaboration with Powdermet) which is destined for a Statoil-operated field in Norway. Forming part of the swivel block, the 2 meter high pressure-disconnectable swivel weighs 7 tonnes and is capable of accommodating multiple flow paths. More orders from Framo are expected in the near future.

Powdermet components business area manager Carl-Gustaf Hjorth claims the company has gained a good reputation throughout this decade for its HIP techniques. "Statoil was the first offshore company to take HIP on board, so they are well acquainted with the concept and can appreciate what we are able to offer. Using HIP techniques, the very complicated internal passages needed for the swivel block are entirely maintenance-free."

Powdermet also received recently an order for manifolds for Norsk Hydro's Visund platform via Scomark Engineering in the UK. The order is for five high pressure manifold systems of different sizes with wall thicknesses up to 40mm. With bore sizes ranging between 8 and 16 inches, the manifolds will be made in 2 meter sections with the nozzles and flanges forming an integral part of the finished pieces.

Advantages for offshore components

For offshore applications there are numerous reasons why some contractors are now specifying HIP technology for components: with the world's largest hot isostatic press, Powdermet is well placed to capitalize on this trend. Materials used are duplex stainless steel (which has good corrosion resistance and relatively high mechanical properties) or high strength austenitic steels. Being prone to segregation during solidification, however, these steel grades are difficult to hot work without cracking. In the HIP process, gas atomized powders are used which allows rapid solidification without segregation.

The HIP process also permits considerable design flexibility in shaping the products, making it especially suitable for flanges, fittings, tees, valve bodies, manifolds, piping and pump components. Often requiring irregular shapes and small runs of each type and size, every component can be individually designed so that it is guaranteed to fit.

Depending on the series length and shape of the components, different methods of manufacturing the cans which form the finished product can be used. Flanges are made from sheet material produced by spin forming and then welding the elements to create the can.

An alternative method employs sheet elements which are formed by pressing in a fluid cell press. This allows considerable freedom in the geometric design of the finished product. For example, it is possible to make the wall thickness of the outlet on a manifold section thicker than the run pipe so that a lighter construction is possible at the end. Using traditional methods, an extruded outlet always gives a thicker run pipe than the outlet. It is also easy to make local changes in the wall thickness of the run pipe to accommodate different reinforcement requirements for integrated hubs.

Since Powdermet carries stocks of ready-mixed powders, delivery times for most components are relatively short with lead times of 10 weeks being achieved compared with up to 20 weeks for traditionally forged parts. Material properties are excellent and are equal to or better than forged products due to the homogeneity of the material and its isotropy. Using HIP, these alloys can also be ultrasonically tested while the microstructure of conventionally solidified material is too coarse.

Considerable weight savings

Recent developments in fabrication shaping at Powdermet have considerably reduced the weight of components with savings of up to 40%. According to Hjorth, one oil company has stated that for one manifold, a weight reduction of 20% was achieved using HIP technology.

"We can produce parts up to 10 tonnes if required, depending on the steel grade, and the fit for purpose design means that we can achieve near net shapes so that machining is reduced to preparing weld bevels and sealing faces. In some cases welding has been cut to a third of that required using conventional fabrication methods."

Powdermet Sweden has now established an agency with Prosessmetall in Norway and gained ISO 9002 certification in December.

For more information contact Carl-Gustaf Hjorth, Powdermet Sweden: telephone +46 220 34800 or fax +46 220 33188.

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