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How to Choose the Right Fastener?

Oct. 12, 2020

In processing industries such as oil, gas, and petrochemical products, choosing the right fasteners for the right applications is crucial. For example, bolts used to connect mating flanges, or screws used to connect pipe standards to load-bearing walls, or nuts and bolts used to connect the dished ends of the reactor, are critical to production. Choosing the right fasteners is also critical to the safety of the process and factory workers. Picking the right fasteners will not attract attention. However, if the right fasteners are not selected for the application, it can cause problems ranging from small leaks to catastrophic failures, and it will definitely attract attention. We will study how to choose the right fastener every time.

There are so many applications for industrial fasteners that even a list is beyond the scope of this article, but the types of fasteners and their applicability to applications and services are usually the same in many applications. Whether to use mild steel or chromium-molybdenum alloys or even strange things, will depend on the requirements of the application.

 8.8 Grade Hex Flange Bolt

8.8 Grade Hex Flange Bolt

Choose the type of fastener suitable for the application

Here are some basics. Are your fasteners suitable? Sometimes more than one type of fastener appears. Here, the experience of you and your fastener supplier will help you determine the right fastener for the application. Generally, a bolt consists of a head, a shaft of a certain length, and a threaded end.

The head of the bolt can be a hexagon head, screw head, socket head, or other designs. The design of the bolt head is very important for the amount of torque the bolt bears and other issues, so the correct selection of the bolt head is very important. The length of the bolt depends on the application. For example, the length of flange bolts must be long enough to fix the gasket, flange, flange gasket, matching flange, another gasket, and nut, and leave a few threads to ensure safety.

The thread is also part of the application. Whether it is a coarse thread (UNC), fine thread (UNF), or 8 thread (UN commonly used in oilfield applications), threads need to be selected to provide the best load handling characteristics. There are also Metric standard threads, BSW (British Standard Whitworth), and others. Thread selection is important: coarse threads can speed up assembly. The assembly time for fine threads will be longer due to the number of revolutions that have to go through the same distance as the coarse threads. However, they provide better thread engagement and more mating surfaces are in contact, which provides a stronger connection and can accommodate greater pulling forces.

Building materials

Almost all fasteners use carbon steel. It has the widest range of workability and strength characteristics. There are even low-carbon steels, such as ASTM 307 Class B, for heavy-duty hexagon bolts and stud bolts used for flanged connections in piping systems with cast iron flanges. Medium carbon steel can be heat treated to improve its load-bearing capacity. ASTM A193 standard covers alloy steel and stainless steel bolt materials used in high temperature or high-pressure working conditions. This specification includes fasteners intended for use on pressure vessels, valves, flanges, and fittings.

The most commonly used fasteners are grade 2, 5, and 8 hex heads. Grade 2 is standard hardware grade steel. This is the most common steel fastener and the lowest price. Grade 2 bolts are usually used where high strength is not required, such as handrail installation and on pipe clamps and hangers. Grade 5 hex head bolts are hardened to increase strength and are the most common bolts used in automotive applications. 8.8 Grade Hex Flange Bolt is stronger than a Grade 5 bolt. As a result, they are stronger and can be used in demanding applications such as car suspension and equipment assembly.

Hexagon socket bolts are usually alloy steel. Alloy steel bolts are made of high-strength steel alloy and undergo further heat treatment. Alloy steel bolts are usually not plated, resulting in a dull black surface. Alloy steel bolts are very strong but very brittle. If zinc plating is required, the socket head should be used with care. When these fasteners are plated, hydrogen embrittlement may occur, which may cause fastener failure. Alloy steels with manganese content exceeding 1.5%, copper content exceeding 0.6%, and chromium content below 4% are very useful in a large range of strength and ductility. Alloy steels with appropriate concentrations of molybdenum, vanadium, or other elements can be used in areas where corrosion may occur, such as heaters, boilers, and other equipment.

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