Cost Justification and Reliability Benefits of Multi-Jackbolt Tensioners

Multi-Jackbolt Tensioners are bolt tightening devices that have been around for over a decade. They are widely used on critical equipment in most heavy industries including Petrochemical. Although the concept is relatively simple, these tensioners have many benefits that are not commonly known. They have proven to be economical in terms of cost and in terms of equipment reliability, which will be the focus of this paper.

Multi-Jackbolt Tensioners (MJT) come in many variations including nut style, thrust collars (unthreaded) or bolt style devices. Due to the wide variety of components available, the MJT system can be retrofitted into the same area as a standard OEM nut or bolt. This paper focuses on the nut style tensioner (FIG. 1) as this is the most commonly used. However, most of the benefits are applicable to the other designs.

The MJT system is composed of a round nut body with an internal thread identical to a standard fastener. In between the thread and the outside diameter is a series of drilled and tapped holes designed to accept hardened jackbolts that pass through the entire nut body. A hardened washer is always used under the jackbolts to protect the bearing area of the equipment that is being worked on (FIG. 2).