Stainless steel helical coil is widely used in food industry, including food heat treatment process and beer brewing. In food industry, one of the most important thing is food safety. As a metal part that have direct contact with food, stainless steel helical coil has to meet restrict requirement for food safety purpose. Here, we are going to discuss some general requirement of stainless steel helical coil for food industry.
All specifications call for the common grades 304, 304L, 316 and 316L. Most specifications allow some other stainless steel grades as well.
2. Tube Specification:
Here we will compares the alternative specifications, all of which have from time to time been considered alternatives for food industry service. These specifications include:
· ASTM A249 “Specification for welded austenitic steel boiler, superheater, heat exchanger, and condenser tubes”
· ASTM A269 “Specification for seamless & welded austenitic stainless steel tubing for general service”
All specifications require fusion welded tube without filler metal (in practice this permits standard tube production using TIG or plasma welding). A269 and A270 also cover seamless product, if requested, although this is rarely required.
·A249 and A269 both require surfaces “free of scale” – annealing of the tube is normally done in a controlled atmosphere and this “bright annealed” finish is considered acceptable.
·A270 requires selection of both internal and external surfaces. The possible conditions range from a "mill finish" (i.e. the strip's 2B finish, without any subsequent polishing), to abrasive polishing with 80, 120, 180 or 240 grit, to special polishing and electropolishing. Surface finishes may also be specified in terms of Ra values, but no limits are given in the specification.
The food industry generally requires a tube with no weld bead remnant on the inside surface if the intended service is handling product.
·A249, A269 and A270 all require that “all material shall be furnished in the heat treated condition”. Heat treatment is annealing (also referred to as solution treatment or solution annealing). In practice this is not a common requirement for food industry tube unless it requires significant bending or flaring.
·A249 is intended for critical environments in boilers or heat exchangers, and hence extensive mechanical testing is required. Full tensile and hardness testing is standard, as are flattening, flange and reverse bend.
·A269 requires no tensile testing, but does require hardness tests, plus flange, reverse flattening.
·A270 requires a reverse flattening test only.
·ASTM A249 is written for a quite different application area. It does specify weld bead removal, but this requirement can be met from other standards, without unnecessarily calling up the stringent mechanical properties of A249. The annealing mandatory in A249 will also not be required in most food applications. A high cost option.
·ASTM A269 again requires tube in the annealed condition. Conversely, it does not specify internal weld bead removal, which generally is a food industry requirement. A269’s main positive aspect is that it is frequently a stock item. It will prove uncompetitive against un-annealed tube.
·ASTM A270 is the specification that commonly used in food industry. However, the finish options available in this specification are very comprehensive.