Good Practices

THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS

November 2004
Volume 20, Number 1

INSTALLERS OF AUSTENITIC stainless steel equipment can benefit from the 'good practices' that have been developed over the years working with this material.

SPARKS CREATED BY GRINDING nearby carbon steel can become embedded in the surface of stainless steel causing unwanted corrosion.

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A new online training module summarizes how austenitic stainless steels should be transported, stored, cut formed, welded and cleaned. By Patrick Whiteway

Nickel Magazine, November 2004 -- The operator of a wastewater treatment plant in the U.S. recently installed some stainless steel equipment and piping only to find that after just six months of operation, pitting corrosion occurred around some of the pipe joints. An inspection by a qualified corrosion engineer revealed that the corrosion happened because, at the time of fabrication, the heat tint around the internal weldments had not been removed. As a consequence, the operating life of the system would be significantly shortened, with large amounts of maintenance required to stop the leaks and extend the life of the equipment.

This could have been avoided had the fabricator and installer been familiar with "good practices" when working with stainless steel. While this is just a hypothetical example, in reality such events happen regularly in all geographic regions of the world.

"When fabricating austenitic stainless steels, certain practices need to be followed to maintain the material’s inherent corrosion resistance," says Dr. David Jenkinson, Director-Australasia for the Nickel Institute. "Failure to do so can result in unwanted corrosion of critical engineering components."

To help materials specifiers, fabricators and users of stainless steel prevent such problems, the Nickel Institute has created an on-line training module that outlines the "good practices" that should be followed to achieve the long, low-maintenance service life and aesthetic appeal in stainless steel.

Building on the success of the Nickel Development Institutes face-to-face workshops and print publication ("Guidelines for the Welded Fabrication of Nickel-containing Stainless Steels for Corrosion Resistant Services," NiDI series No. 11007), the on-line module uses interactive techniques to explain how austenitic stainless steels should be transported, stored, cut, formed, welded and cleaned.

Information on the welding and fabrication of stainless steels is frequently requested by users of the Nickel Institute website, so the on-line module will fill an important void.

The module will provide practical advice on, for example, how to avoid contamination of stainless steel during transport and storage; how carbon steel strapping can contaminate the surface of stainless steel during transport (and how this can be avoided); how storage indoors or under cover from the elements can help to maintain the condition of stainless steel; and how sparks created by the grinding of nearby carbon steel can become embedded in the surface of stainless steel.

Mechanical and thermal methods of cutting stainless steel are listed, and also some pointers on "springback", with the emphasis on the differences between stainless and carbon steels.

The most extensive portion of the module deals with welding. All types of welding, including shielded metal arc, gas tungsten arc and gas metal arc, are discussed, along with their advantages.

Cleaning procedures prior to welding are reviewed in detail.

Differences in the welding characteristics of austenitic stainless steels compared to carbon steels, such as the effect of a higher coefficient of thermal expansion, weld joint design, choosing appropriate filler materials, and the welding of dissimilar metals are also discussed.

Considerable attention is given to post-welding cleanup, in particular the removal of arc strikes, heat tint and surface contamination, which might not be a cause for concern with carbon steels. Details on how to properly pickle and electro-polish stainless steels, and the consequences of not doing so, are illustrated. Heat tints in the internal surfaces of piping are specifically discussed.

The module is recommended for all materials specifiers, fabricators and users of stainless steels.

Patrick Whiteway is Editor of Nickel Magazine.