Nickel magazine, Jun. 02 -- Austenitic stainless steels are widely used in the manufacture
of contact surfaces for the food and dairy industries, and high-quality welds are key to maintaining a high
level of sanitation and cleanability.
In 1999, the 3-A Sanitary Standards Committee asked the American Welding Society (AWS) for help in establishing a standard for sanitary tube welding. The society responded by issuing two documents: AWS D18.1: Specification for Welding of Austenitic Stainless Steel Tube and Pipe Systems in Sanitary (Hygienic) Applications and the companion document: AWS D18.2: Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tube.
At the AWS's second "Welding in Food Applications Conference," held in St. Louis, Missouri, U.S.A., April 17-18, NiDI consultant Richard Avery reported that a document titled Welding Vessels, Tanks and other Equipment is being prepared.
Following are some highlights from the conference:
Edwin L. Wolf of Swagelok Company, an American manufacturer of fluid system components, says: "With the introduction of D18.1 and D18.2, contractors and owners are trying to meet new standards. The use of orbital welding equipment and new purging techniques can greatly simplify the meeting of these new standards."
Attendees to the AWS conference were introduced to AWS specifications, including procedure qualification, performance qualification and visual examination requirements. These were outlined by James R. Hannahs of Edison Community College, who described how to apply the specifications and discussed the limitations of the documents.
The important properties of austenitic stainless steels were reviewed and discussed by NiDI consultant Roger Covert, who stressed that stainless steels are ideally suited for food industry applications.
Joseph McSwiggin of Rodem Inc. discussed standards for the design and welding of food processing equipment. "Welding of food processing equipment should be a science, not an art," he stated, and proceeded to explain the various types of weld joints encountered, the types of welding equipment and procedures used, and the types of post-weld treatments that are beneficial to corrosion resistance and cleanability of welded joints.
Richard Campbell of Purity Systems pointed out that there is a wide range of acceptance criteria for welds in the food service industry. "Inspection methods and techniques depend on these criteria," said Campbell, who outlined various inspection methods and techniques that may be applied to the inspection of the equipment.
Technical details of the requirements necessary to prepare high purity/hygienic stainless steel tubing for orbital and manual welding were presented by Mike Porter of TriTool Inc. In a related talk, Jerry Miller of International Training Institute discussed some of the difficulties encountered with the application of gas tungsten arc welding to meet acceptance criteria in the industry.
Clean-in-Place (CIP), an automated technique used to remove residual product soil from process equipment
without major disassembly of parts, is commonly used in the food processing and pharmaceutical industries.
The equipment used to manufacture food and pharmaceutical products is typically constructed of stainless
steel and is a fabricated weld assembly. The methods to clean food product from a welded surface were
discussed by Larry Hanson of Sani-Matic Systems.
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