Preventing Joint Gap Failures and Leaks
By Alan Siebenthaler
HK Marketing/Territory Manager
Conversations regarding joint gaps in concrete pipe are a necessity for a number of reasons, but the allowable size of that gap varies depending on the state and specification within which you are working.
The joint gap refers to the gap between two pieces of pipe once they are assembled in the field.
“Often we get calls from customers wanting to know the allowable joint gap opening,” says Randy Reimer, director of Sales for Hamilton Kent. “What they are really asking is, ‘the joint is open, so how much of an open joint can be allowed before we lose deformation on the gasket?’”
Lost deformation in a joint means a potential joint failure or leak, but the allowable joint gap depends on the pressure requirement of the joint.
One of the national standards, ASTM C443, requires a joint to withstand 10 psi while it is under ½” deflection. Most states follow this standard, which is convenient for suppliers and contractors doing work in multiple states. To meet leak resistant performance of the joint, it is safer to specify a maximum ½” joint gap for up to 27”. For 30” and larger, a gap of ¾” could be allowable.
There are some U.S. states, such as Florida, that require contractors to follow different standards. The Florida Department of Transportation (FDOT) has an open gap pressure rating of 5 psi.
Florida’s average elevation is just 100 feet above sea level, meaning the groundwater table is much closer to the surface than other regions – sometimes it’s less than three feet below the surface. FDOT has the strictest requirements for these types of drainage and infrastructure projects, holding producers and installers to higher standards, including video inspection of every installation and proven watertightness to handle the greater potential for leaks.
Regulators don’t come by these numbers by chance. The allowable joint gap is based on a mathematical calculation based on the specification, safety factors, the maximum opening and the pressure rating required when joint gaps are present. A contractor can ignore these minimum standards at his or her peril, because doing so increases a joint’s potential to fail.
“Often during installation, if a contractor is using a new crew or is not at the top of their game that day, they could leave larger joint gaps, which could lead to a lot of problems,” says Reimer.
Many state DOTs now insist on video inspection after installation, and open gaps can be easily seen with this method. Sometimes leaks are spotted as well. This is something every contractor wants to avoid at all costs, explains Reimer. He adds that if open gaps or leaks are present post-installation, there are limited options. Contractors can grout the joints – an expensive and difficult task, especially in smaller diameter, non-human-entry pipe that is grouted using a sealing packer and a CCTV camera. Pipes large enough for human entry can be grouted manually. Or, a contractor can install internal repair couplings or inject a leak repair product into the joint. Last of all, the project owner may require the contractor to completely excavate the site and reinstall the pipe properly, which is a prohibitively expensive solution.
“These kinds of problems lead to big claims that are often disputed between producers, contractors and owners,” Reimer says. “Sometimes even the gasket companies are called in, which is why all of Hamilton Kent’s gaskets are designed with the specification in mind.”
These gaskets are designed to meet pressures from 2 psi silt-tight applications all the way up to hundreds of psi. Hamilton Kent designs many different shapes, using state-of-the-art materials and the means to confine gaskets in the joints so they fit any application.
Under pressure, rubber can become like a sheet of paper and be forced right out of the joint. Think of a mouse getting in your house through a tiny hole that seems much smaller than its body, Reimer says.
“Keeping this in mind, we meet the specifications for which the joints are designed,” he says. “Sometimes this is a balancing act. You want a safety factor in case the joint gaps are present post-installation, but you don’t want such a large safety factor that you’re putting so much rubber in the joint that you drive the price up. The balance is performance versus safety factor versus cost.”