INTRODUCTION
Although fasteners are low cost items, when fastener failures occur they can have a severe impact on the economics of plant operations. It is increasingly important to deal effectively with materials and corrosion problems even for low cost items such as threaded fasteners because of changes due to: equipment upgrades; higher capital costs; water recycling; and, more aggressive process conditions. This paper relates primarily to the use of stainless steel and specialty alloy threaded fasteners in pulp, paper, biomass conversion and other industrial facilities, but references to carbon steel and low alloy steel threaded fasteners are also included since these materials are used extensively throughout the industries. This paper discusses threaded fastener failure modes, design criteria of connections, specifications, standards and identification markings. The term threaded fasteners is used in this paper to indicate all forms of fasteners including bolts, studs, socket head cap screws, nuts, washers, etc.
This paper is the first of two papers on threaded fasteners by the author. In this paper, failure modes of fasteners, design criteria of connections, common standards and specifications and fastener identification markings are discussed while the second paper will discuss the installation of threaded fasteners and guidelines for the use of threaded fasteners. Although fasteners are low cost items, when fastener failures occur they can have a severe impact on the economics of pulp, paper and biomass conversion operations. It is increasingly important for mills to deal effectively with materials and corrosion problems even for low cost items such as threaded fasteners because of changes such as equipment upgrades, higher capital costs, water recycling and more aggressive process conditions. Failure of a fastener costing less than a dollar on a paper machine can result in huge losses due to equipment damage and production downtime. As an example, if a failed fastener passes through a press roll nip, the roll cover will likely have to be replaced or in the worse case scenario the roll may be damaged beyond repair. Threaded fasteners are used to mechanically join or clamp parts together and transmit loads. In gasketed joints, the purpose is to prevent leakage while in most other joints the clamping force transmits loads and prevents the parts from separating or vibrating loose. In normal joints, the clamping force should equal or exceed the working load while in gasketed joints, tightening should only be adequate to prevent leakage. This paper relates primarily to stainless steels and specialty alloys in the pulp, paper and biomass conversion industries, but references to carbon steel and low alloy steel threaded fasteners are included since these materials are used extensively throughout the chemical process industries. The term threaded fasteners is used in the following sections of this paper to indicate all forms of fasteners including bolts (1), studs (2), screws (3), cap screws, nuts and washers.
