multibolt

Multibolt is a term used in engineering to describe a fastener assembly that secures a joint with multiple bolts rather than a single fastener. The approach distributes clamping force around the joint, reducing stress concentrations, improving fatigue life, and providing redundancy in critical applications. Bolts are typically arranged in a regular pattern around a flange or joint face, with the arrangement specified by a bolt circle diameter (BCD) and bolt count.

Common applications include pipe and equipment flanges, turbine housings, aerospace structures, and other machinery where airtight, watertight, or high-strength joints are required. Design considerations encompass bolt size and material grade, target preload, tightening sequence, lubrication, and gasket or seal design. Accurate torque or preload control is essential to achieve uniform clamping and to prevent leakage or bolt yielding.

Advantages of multibolt assemblies include improved load distribution, reduced risk of joint failure if one bolt loosens, and easier maintenance or replacement of individual fasteners. Disadvantages include longer assembly times, stricter alignment and seating requirements, and higher total cost. Potential failure modes include bolt shear, loosening from vibration, excessive gasket compression, or uneven clamp loads from improper pattern or torquing.

The term does not refer to a single standardized product and is used across industries to describe many different multibolt configurations. See also: flange, bolt circle, fastener, preload, torque, gasket.