Lessons Learned in the Design and Use of Stainless Steel as an Alternate to Carbon Steel Bolts and Tie Rods

摘要

Flanged and mechanical coupled joints are often a necessary component of water transmission pipelines. These joints utilize threaded materials, or fasteners, in the form of bolts, studs and harness rods which must be designed for a number of stresses. Threaded carbon steel is commonly used as a fastening material but in a buried application can be prone to corrosion even with protective coatings. Stainless steel fasteners are sometimes used in lieu of carbon steel with the expectation that stainless steel is inherently less susceptible to corrosion. Nevertheless, stainless steel bolts and tie rods can still corrode under certain conditions. Furthermore, stainless steel fasteners generally have less strength than carbon steel. This can become problematic when specified for applications such as flanges and harness rods because the general design framework of common American Water Works Association (AWWA) standards and design manuals assumes the strength of carbon steel. This paper compares the relative merits of carbon and stainless steel material when used in threaded form for bolts, studs, and harness rods to connect carbon steel water pipe components. Corrosion aspects of both carbon and stainless steel are considered as are strength differences between the two materials and how it relates to design. Examples are provided to illustrate the potential conflicts that can result when stainless steel fasteners are incorporated into an AWWA design framework.