Four Ways to Perform a Joint Test: A How-to Guide

By Alan Siebenthaler
HK Marketing/Territory Manager

Last month we discussed why consistent joint testing is a crucial and sometimes overlooked steps. This month, let’s get practical and outline some common ways you can joint test, break down the benefits and drawbacks of each, and summarize the steps involved. To start, there are essentially four ways to joint test.

• Hydrostatic Testing
• Internal Joint Testing
• Traditional External Joint Testing
• HK Coupling by Straub – External Joint Testing

Each of the different styles of testing have unique benefits and drawbacks. They also apply differently depending on the size, material and shape of the pipe being tested.

Regardless of testing method, you’ll want to make sure you have two well-manufactured pipes with clean, smooth joints and a good fit on the gasket before you begin testing, otherwise you’re going to waste a lot of time, money and effort. Additionally, during any of these four tests, pressure is slowly brought up until it reaches the required level in ASTM standards, project specifications or state and local requirements. No leakage should be observed through the joint during these timed tests. 

Hydrostatic testing

Hydrostatic testing is straightforward and one of the most common methods of testing. Install the gasket, home the pipe, seal the ends with pipe plugs or watertight bulkheads, and then restrain the pipe together with beams and either chains or come-along winches to keep the pipe joint from opening up when pressure is applied.

Once you’ve done all that, fill the pipe, making sure to carefully bleed the air. This process can take a long time – a really long time. You’ll also need a lot of water on hand. We suggest limiting this type of testing to 18” and smaller pipe because of the time and water requirements, but larger pipe can also be tested.

Internal joint testing (IJT)

IJT offers a lot of benefits over hydrostatic, if you’re willing to foot the bill and have the resources on hand to manage the process. Common brands like Cherne and Plug-It offer equipment that allows a much more focused test. IJT is feasible only on pipes that measure 21” or more in inside diameter, as a person must be able to fit inside the pipe. Consider that before choosing this method.

First, the round, metal frame with inflatable bladders is rolled inside the pipe until it is centered over the joint. The pipe is restrained similar to hydrostatic testing. Air is used to fill the bladders until they have an adequate seal on the pipes on either side of the joint, and then water is pumped in between the bladders to test.

IJT is a great testing option, but the cost can be off-putting as you must purchase a different frame and bladder setup for each size of pipe, in addition to the hoses and control board. You also need to have both pressurized air and water on site, which can be a hassle for some manufacturing locations and for many jobsite installations.

External joint testing (EJT)

EJT is a tried and true method of joint testing, but as anyone who’s done EJT can tell you, it does have its challenges. EJT involves drilling two holes in the bell of one pipe, installing nipples with epoxy in both, installing a secondary gasket and primary gasket, homing the pipe, restraining them together, filling the joint between the gaskets with water, closing the exhaust valve and pressurizing.

The benefits of EJT are that it’s usable on any size and shape of pipe including box culverts, and you’re testing according to the more common jobsite conditions where there is more likely to be external hydrostatic pressure on the joint.

There are three negatives for this test. First, you’re drilling two holes in one pipe, which is semi-destructive, though those holes can be repaired. Secondly, getting a good seal between the secondary gasket and the bell can be difficult, especially for box culvert testing. Thirdly, it can be challenging to test with the joint opened, the secondary gasket needs to be adjusted. The important thing to keep in mind is leakage around the secondary gasket does not constitute a failed test. As long as pressure can be maintained on the joint and there is no leakage inside of the pipe or box, then the test is considered successful.

HK Coupling by Straub

HK Test Coupling is an external joint testing technique that takes all the simplicity and benefits of the Cherne and Plug-It internal testing and applies more realistic jobsite conditions. Coupling testing is very new and somewhat limited to straight wall round pipe and manholes only. It also comes with a higher price tag than a standard EJT might, but the costs are much lower when compared to bladder style mechanisms and generally balanced out by the time and effort saved.

With the HK Test Coupling, there’s no drilling and no need for a secondary gasket, eliminating the risk of external leakage. The process: slide the coupling unit over one piece of pipe, home and restrain the pipe, slide the coupling unit over the joint so it’s centered, tighten with a ratchet (no air needed), fill and pressurize.

The ease of use, time saved and enhanced accuracy of the results, along with the realistic conditions, make the HK Test Coupling test a great choice, even with the limitations to pipe sizes with straight wall.

Testing is an important step in the installation process, but so much of it may seem daunting or costly. Hopefully this overview helps encourage you to test more regularly, easily and accurately in the future.