Duplex stainless steels - shipbuilding

One of the most important areas of duplex stainless steel applications is shipbuilding. Most of the chemical tankers are designed for the transportation of a variety of chemicals. More and more aggressive chemicals and hazardous or toxic materials have to be shipped imposing ever higher demands on materials selection. In many cases duplex has replaced the use of austenitic stainless steels due to its better performance with regard to pitting and crevice corrosion resistance in chloride containing media. Moreover duplex grades have much higher mechanical properties compared to austenitic stainless steels. The following articles are generally available through the trade press, we regret we cannot supply them in their through our site.

Duplex stainless steels for chemical tankers

Authors: Jacques Charles - Bruno Vincent, Creusot-Loire Industrie - France, originally presented at the 97 Duplex Maastricht Conference, the Netherlands, paper number D97-018.

Abstract

Material selection for chemical tanks is of prime concern when considering building costs, and maintenance costs. This paper outlines why duplex stainless steels have been more and more selected instead of 316 LN or 317 LN grades for the erection of new chemical tankers. The main advantages of duplex stainless steels, including their resistance to different corrosion mechanisms, their high mechanical properties which allows the designer to reduce weight when properly used, and their good weldability are emphasised. The paper gives also some practical advises when selecting duplex stainless steels, i.e. how to specify and how to weld them. Finally, some practical experience gained from the use of the material in marine chemical tankers is summarised.

Duplex at 60 knots

Author: Miel Bingen - Stainless Steel World.

Abstract

There is more to duplex and shipbuilding than just chemical tankers. The combination of corrosion resistance and mechanical strength make it an ideal material for the most demanding parts of waterjet propulsion systems. Stainless Steel World visited market leader John Crane-Lips to get to grips with the ins and outs of the use of corrosion resistant alloys in this innovative field of marine propulsion systems.

Waterjet systems are often used in very demanding applications. Seawater for instance is a highly corrosive medium. Furthermore reliability plays an important role. If you combine this with the mechanical requirements of waterjet systems one can imagine advanced materials are needed and stainless steels naturally qualify. At present a typical system is constructed for no less than 30 per cent out of duplex, 60 per cent out of 316L, and 10 per cent non-metallic materials, with a typical system weighing no less than 14 tons.

In general the most demanding parts are made out of duplex, or 2205 to be more exact. Duplex is a very interesting material because of its excellent mechanical characteristics, corrosion resistance and availability. Furthermore the material is easily repaired as it has a good weldability. Especially the mixed flow impeller has a very heavy duty due to debris in the water and an extremely high number of revolutions. Next to the mixed flow impeller duplex is used for the impeller seat ring and the shaft. Especially the shaft is a demanding piece of equipment as it is forged and has to be manufactured to the most exacting specifications on the verge of what is possible today.

It looks as if duplex will not be limited to use in the above mentioned applications though. With weight playing a vital role in shipbuilding and operators willing to invest an extra 100,000 USD for every ton of weight that can be saved the material offers significant potential. As duplex has a considerably higher mechanical strength than more conventional stainless steels replacing the later for duplex can reduce overall weight as less material is needed.

Developments in Welding of Duplex Stainless Cargo Tanks for Chemical Carriers

Authors: Jörgen Strömberg, Solveig Rigdal, Leif Karlsson ESAB AB, Sweden, Frank Lake, Esab Welding and Cutting Products, P O Box 517, Hanover, PA 17331 USA, originally presented at the Duplex America 2000 Conference, Houston, USA, paper number DA2-016.

Abstract

This paper will present welding technology and welding consumables for the welding of duplex stainless steel cargo tanks. For assembly welding both SMAW and FCAW are being used and special flux-cored wires have been developed to optimise welding performance in vertical and overhead welding positions. Most of the prefabrication of tank sections is made with submerged arc welding. Procedures using a suitable backing flux and submerged arc flux for one-sided welding are presented. High productivity is combined with high quality of the weld. Procedures using tandem arc welding are compared with single arc welding. In a chemical tanker there are many welds between stainless and carbon steels and processes, including gravity welding, procedures and consumables are discussed.