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An up to date review of pickling processes for stainless steel including immersion, spray, localised and anodic. It emphasises the benefits of pickling on the corrosion resistance of stainless steel. Author – John Swain of Anopol first published in Stainless Steel Focus Issue 03/2007.
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Summary information on eight popular welding processes used on stainless steels is given. The welding processes covered are: gas tungsten arc welding, (GTAW or TIG), plasma arc welding, (PAW), shielded metal arc welding, (SMAW or MMA), gas metal arc welding, (GMAW or MIG/MAG), flux cored arc welding, (FCAW or FCW), submerged arc welding, (SAW), electric resistance welding, (ERW), and Laser welding.
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Should heat tint discolouration in the heat-affected zone of stainless steel welds be removed? In cases where the application involves an ‘aqueous’ corrosion hazard, the local reduction in sub-surface chromium can affect the corrosion resistance of the steel. The removal of weld heat tint from stainless steel fabrications using acid pickling or electrolytic methods not only improves the overall appearance but is vitally important for restoring the full corrosion resistance of the finished product. As a general rule, if you can see a discolouration on the surface due heat tint, this should be removed as part of good post weld cleaning practice for any stainless steel welded joints. (37)
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Practical advice on the “hows” and “whys” of post weld surface treatments. Why removal of weld heat tint should be be the norm for stainless steel.
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Welding of stainless steel is a critical operation in ensuring that the material is in an optimum condition for its intended service. This photo guide shows examples of good and bad practice.
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BS EN 1600, BS EN 12072 and BS EN 12073 cover electrode selection for coated or uncoated rods and wires for, GMAW, (MIG), GTAW, (TIG), PAW, (plasma arc), and SAW, (submerged arc), shielded welding and flux cored methods. A table of suggested consumables, (fillers), for welding a range of stainless steel grades is given and the electrode compositions to BS EN 1600.
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This article covers how to design stainless steel bolts, (fasteners), subject to shear and tension forces. Shear and tension capacities for bolts of property class 50, 70 and 80 from diameter M10 to M24 are given. (207)
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Soldering is often used for joining stainless steel in applications such as roofing and water tubing, (plumbing). Prior cleaning, the correct selection of flux, (phosphoric acid based), and thorough post solder cleaning are important steps for the successful soldering of stainless steels. Tin-lead or tin-silver solders can be used, but care is needed with solder selection to avoid bi-metallic, (galvanic), corrosion in service. Joint strengths are not as high as welded or brazed joints.
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BS EN ISO 3506 replaces BS6105. Part 1 covers bolts, screw and studs, part 2 nuts and part 4 tapping screws. The chemical compositions are common to the various parts. Austenitic grades A1, A2 and A4 are shown and compared to bar grades 303, 304, 349S17, 316 and 394S17. Mechanical properties for property class 50, 70 and 80 austenitic bolts and studs and property class 20H, 25H, 30H and 40H tapping screws are tabulated and the fastener designations, such as A2-70 and A4-25H described. Duplex FA, (ferritic-austenitic similar to 1.4462, (2205), of EN 10088-1), is a likely future grade for inclusion in the standard. Fastener grade selection is covered in annexes to the standards. The standards lists grades 1.4439, 1.4539, (904L), 1.4529, (6% molybdenum austenitic), and 1.4462, (2205) as suitable for reducing the risk of chloride induced stress corrosion cracking failures in applications such as indoor swimming pools.
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This review examines recent developments in inert gas purging and demonstrates where significant cost savings can accrue through the use of specialist contemporary purging equipment when welding pipes and tubes.
This review is by Dr Mike Fletcher of Delta Consultants.
