Recently several classification societies have redefined and made more stringent their requirements for coupling bolts. Different bolting methods and their requirements have been further defined. This includes fitted bolts, non-fitted bolts and combinations thereof. For fitted bolts, the term fitted has now been defined as “The accuracy of fit is to be zero or negative clearance” or similar, requiring a verified zero to interference fit. The theoretical requirements and submittals for non-fitted bolt have been further defined as well. These new requirements will result in either larger connections or require coupling bolts that can achieve the required interference fit in a verifiable way. Traditionally, fitted bolts that require an interference fit have been installed after being cooled down with CO2 or liquid nitrogen. There are concerns about this practice due to the rapid temperature change and its effect on the bolt material. There is also the problem of how to remove a bolt fitted with an interference fit without damaging flange holes and bolts, especially after being in operation for some time. Fortunately there are established and new solutions to these updated requirements such as expandable bolts that both create the required fit and are easily removed .The alternatives also include solutions where the flanges are removed and removable couplings are used.
The paper will discuss the design, maintenance and operational aspects of these rules and the different solutions.
