The effective sealing of flanged pipe and fitting joints would be a relatively simple matter if all installations were free of misalignments and offsets, and if all pipe and fitting flanges were precisely machined flat and to the exact angle specified. But based on the occasional joint leak we hear of, and the number of custom flange fillers, manufactured to a specific angle as sometimes required, it is apparent that manufacturing and installation have still not reached the degree of perfection that can be shown on an engineering drawing. When faced with less-than-perfect conditions, the choice of gaskets can make the difference between a successful assembly or fighting a leak. The selection of gaskets for flanged ductile iron joints falls into three categories: full-face flat gaskets, ring gaskets, and specialty gaskets. Let’s discuss the attributes of each of these. Full-face gaskets are relatively inexpensive in that they are often cut from low-quality sheet rubber where the “drop” can be used to manufacture gaskets for smaller diameter flanges. Thicknesses of full-face gaskets vary, but 1/8” has become fairly standard and 1/16” gaskets are not recommended. Compression of the gasket material in the full-face design is greatest near the bolt holes and decreases with distance from the bolt holes. If the flanges are installed in less than ideal conditions, which is often the case, some misalignment and/or offset results in induced beam and shear loads on the flange, threads, and pipe. Under these conditions, it is easy to see that compression of the gasket is not uniform around the bolt circle, and induced loads could be severe enough to open a leak past the gasket or through the threads. Increasing bolt torque may stop such a leak, but in tightening the bolts, the gasket compression is increased more near the bolt holes than where it is most needed, which is at the pipe-flange/thread line interface. So, although the full-face gaskets are inexpensive and easy to center in the joint, they suffer from non-uniform compression in less than ideal applications. The ring gasket has two advantages over the full-face flat gasket: It is less expensive and compression is greater. The compressive loads are greater because the same number of bolts are compressing less material. This gasket design provides an effect that is similar to a raised-face flange since the bolt torque localizes compression of the gasket to the area between the pipe ID and the bolt circle. However, in less than ideal installation conditions the ring gasket is still susceptible to non-uniform compression due to misalignment of pipe, and high bolt torques result in cupping of the flanges so that more compression occurs on the gasket OD than the ID. Furthermore, due to the lack of bolt holes in the gasket, it can be somewhat harder to center. The advantages of ring gaskets are higher compression and lower cost. Specialty gaskets, such as AMERICAN’s Toruseal® gasket, provide a unique combination of advantages at a modest increase in cost. The Toruseal® gasket is molded from the same high-quality SBR rubber compound used for push-on gaskets. The design consists of a 1/8”-thick, full-face portion with bolt holes and a single or double torus (bulb) on the ID edge of the gasket that is 1/4” in diameter. The bulb’s location and diameter provide two functions. First, the bulb is located to provide sealing on or inside the thread line diameter of the pipe-flange interface. Secondly, the bulb diameter is larger than the thickness of the flat portion of the gasket, which results in very high compression in the critical sealing area of the pipe-end face. These two design factors have increased the sealing ability of flanged joints so that AWWA C111 now states that 4-inch through 24-inch flange joints may be rated for 350 psi when using specialty gaskets of this design. Successful testing of flanged pipe with Toruseal® gaskets for Underwriter’s Laboratory and Factory Mutual has confirmed high pressure ratings with a substantial factor of safety. In lab tests and hundreds of field applications under almost every conceivable installation condition, Toruseal® has demonstrated a significant improvement in performance of the flanged joint when compared with other options. When your job calls for flanged piping, specify and use AMERICAN’s Toruseal® gasket for optimal performance.

Gene Oliver, Technical Director, American Cast Iron Pipe Company PHOTO BY SYLVIA CASWELL