Dr Baxter showed how the cost of different alloying elements influenced the price of stainless steel and influenced the cost of both corrosion and mechanical performance. The cost indices are significantly reduced by using the lean duplex stainless steel, LDX 2101^®. 

The corrosion performance of the grade was discussed with particular emphasis on its resistance to both general and localized corrosion. In general terms, LDX 2101^® considerably outperforms, for example, 1.4307 /type 304 stainless steel. 

The mechanical performance of the alloy was discussed. The proof strength is nominally twice that of 304-type stainless steel. The main implication of this is that material utilization is potentially improved, by as much as 30-40%. This can have attendant benefits associated with material cost and unit weight. 

Chris Baxter described how LDX 2101^® should be considered as a "tolerant" duplex stainless steel when welding it. 

The presentation finished by describing actual and potential applications for this grade of stainless steel. The common theme for applications is that LDX 2101^® is a high strength corrosion resistant alloy. As such, it is frequently considered a substitute for C-Mn steel, galvanized steel or painted systems. It is even considered an alternative in some 304 or ferritic type stainless steel applications, particularly where strength is an issue.

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2.2    'New Magnesium Alloy Technology', Nick Jeal & Paul Lyon (Magnesium- Elektron) 

Magnesium is used successfully on aircraft; including both military and civilian fixed wing and rotorcraft applications.  The main benefit of using magnesium is its low density, being only 2/3 that of aluminium. 

Lightweight is of significant benefit to not only the aerospace industry, seeking to improve performance and pay load capacity, but also other areas of transport.  Most noticeable growth over the last 15 years has been in the automotive industry who have embraced the use of Magnesium.  The growth has been driven by at least 3 themes:

·        Need to improve fuel economy and emissions

·        Improve vehicle performance

·        Reduce cost

Applications range from thin wall covers to gearboxes and most recently engine block applications. 

It is anticipated that magnesium usage will increase in aircraft, for similar reasons of environment (already seen in the automotive market) and payload performance.  The benefits of weight reduction being far more beneficial and valuable in the air transport market. 

So what are the barriers to change?  Two themes often arise when discussing Magnesium for new applications: Fire and Corrosion.  Fire is not an issue unless the melting point of the component is exceeded.  General corrosion resistance of Magnesium alloys has improved significantly as this attribute has been designed into the alloys.  Galvanic corrosion requires design input if the component is likely to be exposed to potential galvanic situations. 

The advent of new high temperature alloys (WE43, Elektron 21) have raised the melting point (further reducing potential for fire) and offer vastly improved general corrosion performance.  It is important that specifications and advisory notes recognise the improvements made in the last 20 years of alloy development and application.

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4.1      'Seawater Materials in the Oil and Gas Sector', Doug Stannard (Kellogg, Brown & Root) 

Seawater duties cover Cooling water, Firewater, Washdown, Injection water and Ballast water.  Equipment comes in the form of Seawater Lift Pumps, Seawater Filters, Heat Exchangers, Pipe and Fittings, Firewater Pumps, Deluge sets and Nozzles.  Typical conditions are:

• Inlet temperatures – 3-11^oC in North Sea
• Outlet temperatures – Dependent on Process but usually restricted to 40^oC
• Low pressures – around 20 bar  

Each of the following materials was discussed with respect to suitability:

• Carbon steel
• Austenitic Stainless Steel
• Copper – Nickel/Aluminium Bronze
• Duplex and Super Duplex Stainless Steel
• Super Austenitic Stainless Steel
• Titanium
• Nickel alloys – Alloy 400/K500, Alloy 625, C-276
• Glass reinforced epoxy (GRE)

In summary, none of the above materials is perfect for all applications, rather it is the case that different materials will prove more suitable for different applications.

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