Sheffield Forgemasters approved for new nuclear work

Sheffield Forgemasters is set to become one of the few UK companies able to fabricate safety-critical cast components for nuclear power stations, after passing a final audit for ASME NPT (nuclear partials) status.

Forgemasters siteAs a result of the audit, Sheffield Forgemasters will receive an accreditation certificate which will allow it to take on a whole new strand of civil nuclear manufacture, complementing its status as an ASME-certified nuclear materials organisation. Forgemasters is an established supplier of civil nuclear castings and forgings, and a founding member of the Nuclear AMRC.

Forgemasters’ NPT status will allow the company to weld-fabricate the components it currently supplies – a part of the nuclear assembly process that few organisations can undertake, and one with significant challenges posed by weld-joining different materials.

The ASME code is the most comprehensive series of guidelines for civil nuclear manufacture in the world and all other codes, including the French RCC-M code, operate to similar compliance requirements. Forgemasters has held its Nuclear Materials Organisation status since 1992.

Group quality director David Street said: “Forgemasters currently enjoys ASME status as a materials organisation, an accreditation for which we have had to pass a similar audit and a full quality systems survey every three years, working closely with the Hartford Steam Boiler Company to reach the audit stage.

“The audit to gain NPT status is a significant landmark for the company, which is the culmination of several years of work to establish enhanced requirements and disciplines embracing all our processes, employees and sub suppliers. This is to ensure we meet the exacting construction requirements of the ASME code, which are some of the most stringent demands in modern engineering.”

Once Forgemasters secures NPT accreditation, it will sit with one of its key customers, Rolls-Royce, as one of the only UK companies qualified for main component fabrication within the heart of a civil nuclear power plant.

Street added: “The programme to retain our existing accreditation and to gain the higher NPT accreditation has required an investment of approximately £140,000, but the new accreditation will undoubtedly create new revenue streams as we start to tap into nuclear assembly work for a global client base.

“The implications of the ASME codes are vast for any company wishing to enter the UK civil nuclear supply chain with precise requirements which need comprehensive understanding to ensure compliance and avoid code violation. Businesses will need to understand how to engage with this process and at the moment, very few UK companies do.”

SFIL has an unparalleled understanding of the ASME code within the UK and, as a tier one member of the Nuclear AMRC, is poised to play a crucial part in establishing quality assurance requirements for businesses aiming to enter the UK civil nuclear supply chain.

“The code is an absolute requirement with no scope for concessions,” Street said. “Manufacture must be ASME code compliant to avoid non-acceptance and rejection. That’s where our involvement with the Nuclear AMRC should enable our expertise in this field to reach a much broader market.”

SFIL will now continue its work on manufacturing major nuclear island forging components for the UK’s nuclear submarine programme, as well as civil nuclear projects worldwide.

100mm weld promises deep benefits

Nuclear AMRC welding specialists have successfully joined 100mm thick steel plates with a single weld. The landmark result means that welding time for large pressure vessels could be reduced from weeks to hours.

ebeam 100mmThe team used electron beam welding, which is capable of joining much thicker components in a single run than other welding technologies while maintaining high material quality. The technique has become accepted in the aerospace and automotive industries, but is not yet used in nuclear manufacturing.

“Parts which would traditionally be welded in weeks could be welded in one day,” says Bernd Baufeld, power beam technology leader at the Nuclear AMRC. “E-beam welding has a major advantage in cutting costs for pressure vessels and other large nuclear components by reducing the time of production.”

Pressure vessel walls are currently joined by multiple tungsten inert gas or submerged arc welds – between 20 and 80 runs for a 100mm thick section –  with repeated non-destructive evaluation (NDE) to ensure material quality. With an electron beam, it takes just one weld and one round of NDE. Electron beam welding also reduces the requirement for pre-weld machining, as it requires a simple butt rather than a v-shaped weld prep.

Baufeld’s team used the Nuclear AMRC’s Pro-Beam K25 to demonstrate the techology’s feasibility for nuclear applications. They achieved a 100mm depth of weld using SA508 grade 3 steel, commonly used in civil nuclear pressure vessels, at a rate of 18cm per minute.

“100mm is at the border of what’s traditionally done in the e-beam world,” Baufeld notes.

One of the biggest challenges was dealing with the several cubic centimetres of liquid metal produced by the electron beam. “You can’t weld with a vertical beam because you’d lose metal through dripping,” says Baufeld. “You have to weld with a horizontal beam, and you still have to keep the metal contained.”

Initial tests show that the join has excellent material properties, comparable to the plate material. The team has also achieved 80mm single-pass joins in stainless steel and 85mm in nickel-base alloy.

Baufeld and the team are continuing to develop the technique to produce larger demonstration parts, and apply the lessons learned on the K25 to the Nuclear AMRC’s giant new K2000 e-beam chamber.

ebeam 17DecWith a 208m3 chamber, the K2000 is over 80 times the volume of the established K25 facility, and believed to be the largest e-beam chamber in the UK. Its gun was fired for the first time (pictured) in late 2013, and the cell will be fully commissioned and available for collaborative research from the end of March.

The Pro-Beam K2000 gives the capability to complete very intricate joins on large components using nine axes of movement – four for the component and five for the electron gun. It can be used to weld gas turbine parts up to three metres in diameter, with fully automatic joint following and variable thickness programming – capabilities found in only a handful of machines worldwide.

  • See the latest edition of Nuclear AMRC News for more on our welding and cladding research, including details of the new diode laser cell and the latest news on additive manufacturing for the energy sector.