An MJ or mechanical joint bolt set is typically used when a flanged joint is not possible or not desirable. They offer greater flexibility for alignment than a flanged joint, which makes them ideal for underground joints, but they are also used in other locations as well.
The benefit of MJ joints over flanged joints for underground installations is the concern with the shifting or movement of the pipe. With the MJ there is allowable movement, while the rigidity of the flanged joint poses problems if the supporting ground until the pipe was to settle or to move for some other reason.
The MJ bolt set is used with the MJ joint. There are different options in these sets depending on the specific application and the concerns for corrosion and other factors.
There are several different options in an MJ bolt set. All are designed to meet specifications, including those outlined by ASTM and AWWA requirements. It is important when purchasing any sets to ensure they are designed to the latest requirements, as these can and do change over time.
The set contains a gasket, six bolts, and the corresponding nuts. The bolts and nuts are made of stainless steel, with or without a coating. The most common coating used in these sets is Xylan, which is a family of coatings. The use of these fluoropolymer coatings boosts corrosion resistance. It is also a coating that is highly resistant to wear, which allows for a significantly longer life cycle for bolts and nuts.
Gaskets used in an MJ bolt set will be produced from SBR or vulcanized styrene-butadiene rubber. This material has a long-life cycle, is more resistant to abrasion than natural rubber and offers greater flexibility, even at low temperatures. It is also rated as very good for resistance to heat and heat aging, making it a top choice for a gasket.