Corrosion Prevention Exploring the Advantages and Limitations of Nickel Alloys
Just because titanium has a reputation as a highly corrosion-resistant material does not mean it is better than nickel alloys in every application, said Dr. Helena Alves of materials supplier VDM metals (Hall 11.0, Stand E51). Alves was co-chairing a congress session Wednesday on the use of nickel alloys, titanium and zirconium.
Dr. Thomas Wellauer, a corrosion specialist with DSM Nutritional Products (Sisseln, Switzerland) spoke about his experience with vitamin precursors. In one case, nickel alloy C-22 was needed to prevent corrosion in a filter. A stainless steel version corroded badly in just two weeks, despite previous successful laboratory tests. It turned out that under real process conditions, hydrolysis of the product produced 150 ppm of chlorides and took the pH down to 2.
Dr Ralph Bäßler of the Federal Institute for Materials Research and Testing (BAM) presented the results of tests on titanium alloys (grades 2 and 12) and nickel alloys in various acids at 200 °C. After finding that a gold-plated autoclave could not withstand the conditions, the BAM team were forced to use a test vessel lined with 50 microns of tantalum using the Tantaline process (Hall 11.0, Stand B74).
The Limitations of Titanium
Titanium performed well in 5 % phosphoric acid, but could not resist higher concentrations. p-toluene sulfonic acid at 200 °C completely dissolved titanium grade 2 in two days.
Comments from the audience highlighted titanium’s sensitivity to fluoride, which is often a significant contaminant in phosphoric acid. At applications below boiling point, Alloy 31 is a better choice for phosphoric acid service, several experts said.
How the Right Material Reduces Lieftime Costs
NeoNickel (Hall 11.0, Stand E71) supplies stainless, duplex and super-duplex steels, nickel alloys, and titanium from locations in the UK, Germany, France, and the Czech Republic. Sales manager Stephen Pollard agrees that demanding process conditions may require engineers to use more-expensive alloys. Given the range of costs involved, however – up to EUR 200/kg for the rarest alloys – he says some companies are also seeking to replace costly alloys with cheaper solutions.NeoNickel is unusual in having its own laboratory for application testing.
Sandmeyer Steel Company (Hall 11.0, Stand A81) is a U.S. stockist well-known in North America for its ability to source hard-to-find items, says marketing manager Gary Orr. Sandmeyer adds value for its customers in the U.S. and abroad by using laser and water-jet cutting, milling, and other operations to produce near-net shapes.
Sandmeyer vice president John M Curley, IIIµ points out that better materials can reduce lifetime costs. However, he regrets the lack of wide acceptance of super-duplex stainless in North America, compared to Europe. but