It is important to recognize that not all bolt tightening sequences are created equal. Since the 1930's, the Star Pattern has been used as the primary sequence for bolted flange joint assemblers. It has been used for pipe flanges on both ASME B16.5 and ASME B16.47 flanges (NPS 26 inch and above), heat exchangers, and other applications such as butterfly valves. This sequence is applied to all types of gasket materials and flange types, including Raised Face (RF), Ring Type Joint (RTJ), Double-Jacketed, Spiral Wound Gaskets, and even newer gasket types like the Kammprofile gasket.

However, the Star Pattern is not necessarily the best bolting pattern for every type of flange or gasket. To choose the best tightening sequence, one must consider the gasket type and arrangement of the flange connection. Therefore, this article is intended for supervisors, engineers, or anyone else who oversees bolted flange assembly or maintenance, and we will discuss different torque sequences.

It is important to note that there is no “silver bullet” bolt tightening sequence ideal for torquing every type of flange or gasket. In fact, in ASME PCC-1, which is the world’s leading guideline covering the assembly of bolted flange joints, an entire appendix is dedicated to bolt tightening sequences. This includes the Star Pattern, which is labeled the “Legacy Pattern” because the technique has been around for so long, and several other options, which are classified as “Alternative” bolting patterns.

The alternative bolting sequences are included to demonstrate more efficient ways to assemble flange connections. They can be used with just about any tightening method from hydraulic torque to pneumatic torque to manual torquing with a clicker wrench.

In this article, we will cover the Legacy (a.k.a. “Star”) Bolting Pattern in depth, as well as the Modified Star Bolting Pattern, which is referred to as “Alternative Assembly Pattern #1” in ASME PCC-1. We will explain how to perform both sequences and provide recommendations on which pattern to use based on the size and type of flanges.

It is important to keep in mind that while bolt tightening sequences are crucial, other important elements of bolt tightening procedures must be addressed, such as flange alignment, gasket installation, torque values, torque tables, how bolt torque needs to change for different materials (like stainless steel bolts), and so on.

TO BE CONTINUED...