Tips For Installing Flanges and Gaskets

The broad strokes of a successful installation include proper flange, gasket and bolt selection, as well as bolt torque pounds. Here are some more details on the process.

Tips For Installing Flanges and Gaskets

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The world of gaskets, flanges, and bolts is truly vast.

There are a hundred varieties taking into account material, manufacturers, sizes and patterns. Each class is as fundamentally important as the next. Do your own research with the available charts and engineering data to help you choose the right flange, gasket, and bolts for the job.

There is no question, though, that there are misconceptions about field repairs and retrofits. Pipe fitters and industrial plumbers generally have a thorough understanding of this subject matter, as they deal with it every day. Service plumbers who are going in to make repairs, however, often are ill-equipped to handle the art of flange, gasket, and bolt selection and installation.

There are four major factors for choosing a gasket: the type of flange, the temperature it's required to handle, the media that is flowing through the pipe, and the operating pressure. First, make sure that you are connecting same-faced flanges.  Generally, there are six types of flanges (flat, raised, male-female, ring joint, tongue/groove and groove to flat), but flat and raised are the most common.

A raised-face flange has an inner ring (inside the bolt pattern) that is raised. A flat-faced flange has a “mating” surface that is entirely flat. There are two conventional gaskets, the first being “full-face” gaskets. You have seen these before. They are gaskets with the bolt holes visible. The second is called a “ring gasket.” You probably have seen these. They are just a smaller ring without the bolt holes because they fit within the bolt-hole pattern. The full-face gaskets match up with flat-faced flanges, and the ring gaskets match up with raised-face flanges.

The broad strokes of a successful installation are proper flange selection, gasket selection, bolt selection and bolt torque pounds.


First, make sure that as you fit the pipe and flanges, the mating surfaces come together evenly and plumb, especially if you are working with cast iron flanges. If the flanges have a more considerable gap on one side than the other, you need to adjust your fitting to make it uniform. Undue stress on pipe through tightening the bolts to bring it together will lead to uneven torque pounds, unnecessary joint stress, future leaks, and cracked or broken flanges. 

Once the proper gasket is in place, the bolt holes are lined up, and the flanges have uniform gap spacing, bring the flanges together. Insert your gasket and “two-hole” the flange, which means getting at least two bolts in two bolt holes. Doing this will allow you to fine-tune the alignment for the rest of the bolt holes. If you are having a difficult time getting the holes to line up, purchase a spud wrench. The spud wrench has a sharp point on one side that you drive into the offset bolt holes and maneuver around until they line up to “hole” the flange.

Make sure you lubricate the bolts and tighten them before continuing. Contrary to popular belief, you should not lubricate most gaskets. Most manufacturers’ instructions say that gaskets should be dry without lubrication, fresh out of its packaging, and installed dry at room temperature. The gasket seals itself by even compression, not pipe dope, anti-seize or oil lubrication. Always read the instructions that come with the gasket.

The bolts should be tightened down to the manufacturer’s recommended torque rating, so you need to have a torque wrench. Tighten the bolts in a diametrically opposed pattern (star pattern) until you have reached proper torque on all bolts. Then complete it with a clockwise check of each bolt to verify torque.

As for the bolts themselves, many pipefitters and old-timers swear by “stud bolts.” Stud bolts are a piece of all-thread used in lieu of a hex-head bolt. It’s a piece of all-thread cut to length with nuts on both sides. Stud bolts are much easier to get off when you need to service something down the road because they are less likely to shear. You can also keep a few pieces of all-thread 7-footers on site and cut to length only stocking a box of nuts to match. You should use multi-purpose grease, lithium grease, anti-seize, etc. on the bolt threads so they can be easily removed for future service. 

Creep and Relaxation

Lastly is the issue of creep and relaxation. You must torque the bolts properly and cycle the system, re-evaluate and retighten if necessary, to make sure nothing leaks. It is possible to have a period where excessive heat or expansion will put tremendous stress on a joint. When the joint "relaxes" the tension, a leak will form. 

Taking great care in proper material selection and installation practices separates us from the hacks of the world. Make sure care is taken in the details and read the instructions that come with your material selections.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 23 years' experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 


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