Plastics, limitations from corrosion

Protect the balance from corrosion. Objects to be placed on the pan should be limited to nonreactive metals, nonreactive plastics, and vitreous materials. 

Only Continental and Inner-Tite offered protective sleeves to their customers as an option. None of these manufacturers has published installation recommendations to limit shear and bending forces on the plastic pipe that connects to their steel tapping tees. On another issue related to protective sleeves. Safety Board examination of a protective sleeve offered by Continental to its customers revealed that the sleeve that did not have sufficient clearance to allow the application of field wrap (intended to protect the steel tee from corrosion after it is in the gronnd) to that portion of the steel tee under the sleeve. This observation was confirmed by a Continental representative. 

The membrane is usually made from one of several materials. Woven polyester or cotton, the most commonly used and least expensive material, is adequate for temperatures up to 150°C. Siatered plastic is used where a low cost, washable surface is desired. This material is temperature limited by the polymer material to about 60°C and the flow of some powders may cause a static charge build-up on the membrane that could be hazardous ia some operatioas. Wovea fiberglass fabric or porous ceramic block is used for temperatures up to about 425°C. Siatered stainless steel powder or bonded stainless mesh is used for corrosion resistance, and for temperatures up to 530 to 650°C. Additional information can be found ia the Hterature (38,39). 

Plastic Pipe In contrast to other piping materials, plastic pipe is free from internal and external corrosion, is easily cut and joined, and does not cause galvanic corrosion when coupled to other materials. Allowable stresses and upper temperature limits are low. Normal operation is in the creep range. Fluids for which a plastic is not suited penetrate and soften it rather than dissolve surface layers. Coefficients... 

Table I shows the chemical composition limits of various aluminum alloys presently used for packaging applications (3). In general, these alloys have good corrosion resistance with most foods. However, almost without exception, processed foods require inside enameled containers to maintain an acceptable shelf life (4, 5). Moreover, when flexible foil packages are used for thermally processed foods, the foil is laminated to plastic materials that protect it from direct contact with the food and also provide heat sealability as well as other physical characteristics (6,7).

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