Duplex Stainless in Pulp and paper, Chemical engineering and Nuclear Energy

Pulp and paper

The Pulp and Paper industry is very competitive, and reducing costs a priority. In spite of it, or because of it, this industry has been one of the earliest ones to recognise the value of duplex stainless steels.

For example, S32205 (EN 1.4462),S32304 (EN 1.4362) and S32101 (EN 1.4162) can be used in digesters, pressure vessels and liquor tanks as well as in paper machines. For more aggressive environments, such as bleaching, super duplex S32750 (EN 1.4410) is needed.

The properties that led to this development are the overall low life cycle costs,     the high strength (reduction of weight), the increased corrosion resistance (particularly to SCC) and the higher surface hardness. The latter property is important to resist the abrasion of wood chips and pulp (particularly in digesters). The optimum material choice today is a selection of austenitic, duplex and super- austenitic stainless steels that complement each other.

Chemical engineering

Duplex stainless steels are used along with other stainless steels to process/ produce a wide variety of chemicals: fertilisers, polymers, pharmaceuticals, etc. Their corrosion resistance and high strength make them particularly valuable for key process equipment such as

ƒpressure vessels,

ƒheat exchangers,

ƒcondensers,

ƒstorage tanks,

ƒdistillation columns,

ƒand all the ancillary equipment: tubes, pumps, valves, fittings, filters, fasteners, agitators, ….

Presence of impurities such as chlorides or fluorides, abrasive solids and of course elevated temperature increase the aggressiveness of the medium.

Nuclear Energy

In this industry with very high safety standards, any change in materials specifications takes a very long time. Nevertheless, duplex stainless steels are being specified in some new build and in decommissioning uses.

Their high SCC corrosion resistance ensures long term safety (up to 150 years), while the high strength allows a simpler design. In addition, a better thermal performance is obtained thanks to a relatively low thermal expansion and higher thermal conductivity compared to austenitic stainless steels. In new built plants, duplex stainless steels are used in the piping of the secondary water cooling circuit of the power plants.

In decommissioning, they are now one of the preferred materials for boxes in which slow-decaying radioactive materials are placed for geological storage. An example is provided by the Pile Fuel Cladding Silo at Sellafield, one of the world’s oldest nuclear storage sites, which will need a total of 2200 duplex stainless containers, weighing 1.3 tons each, to keep the nuclear waste for at least 500 years. Other applications are canisters for transport and storage of nuclear fuel.