Chemical Attraction

A recent highly successful NZSSDA seminar focussed on surface finishes on stainless steel – with particular regard to the growing popularity of chemical treatments. Held at HERA House in Manukau City on 30 June 2010, this important seminar attracted a high attendance. The day’s proceedings started with the surface finish requirements, followed by the possible options for treatment, and concluding with the legal requirements for compliance with the HSNO Act.
Smooth Talking
Les Boulton of the Nickel Institute gave a review of the need for a smooth surface finish to preserve the corrosion resistance of the metal. Common defects like heat tint, arc strike, scratches, grinding burrs, undercut and weld dressing were described – with a special emphasis on embedded iron and rust which have serious consequences when the material is in service. Tea staining and chloride contamination were also dealt with in detail.
As these are all vital considerations that need to be addressed day-to-day in our industry, it’s worth repeating the summary of this presentation here:
• Good stainless steel surface finishing is important to ensure plant and equipment is fit for purpose in service.
• Specifications for stainless steel equipment and plant should always include surface finish requirements such as Ra (or surface roughness).
• Specifications need to be clear regarding requirements for stainless steel parent material and for fabricated sections. For example, providing the grade of weld finish required.
• Many specifications should include a requirement for pickling and passivation of welded stainless steel joints.
Quality and Safety
Following on, Russell Thorburn of Tata Steel International reviewed how the welding and fabrication can damage the passive film and described the various chemical treatments on the market. There were a number of interesting comments on workshop practice in particular the need for tight control on chemical treatments for both quality and OHS reasons. And the need for training and proper signs and data sheets available at the work site. The toxic nature of these chemicals was commented on at length – a worthy reminder.
Safety and the Law
Finally, Mike Saunders of Sandvik (NZ) Ltd outlined the requirements of the Hazardous Substances & New Organisms (HNSO) Act of 1996, and dealt in detail with the assessment of pickling paste and the necessary compliance activities. Of note was the need for workshops to have trained and certified “handlers” of paste at all stages – from the appointment of approved delivery companies to receipting, storage, record keeping, and comprehensive training of personnel. This popular Seminar provided an up-with-the-play insight into the state of chemical cleaning and its implications for the industry in New Zealand. It also demonstrates just one way in which the NZSSDA has a vital role to play in training industry personnel on important technical issues such as stainless steel surface finishes.