Benefits of Using Flexible Piping In Vent-Pipe Applications

Flexible vent pipe
Photograph courtesy of OPW

For the owners and operators of retail-fueling sites, the current difficulty in obtaining fiberglass-based piping and fueling-system components, which is being driven by an ongoing resin shortage, has made it hard to acquire vent pipe for use in underground storage tank (UST) installations. Since vent pipe is a required component in the fueling setup, as it is run from the UST to the system’s pressure vacuum vent, these shortages are holding up the installation of new or upgraded systems.

Vent pipe is critical to UST-system operation because it allows the tank to vent should its internal pressure or vacuum exceed a certain point, basically allowing the tank to “breathe.” While the fiberglass shortage is undoubtedly troublesome, there is a readily available–and proven–solution for the problem: flexible vent pipe.

Frustration-Free Vent Pipes
OPW offers a complete array of flexible vent-pipe sizes and lengths, all of which are designed and approved to offer a number of advantages when used with all varieties of motor fuels currently available in the petroleum market.

The benefits of flex pipe

Flexible pipe has been used in fuel system installations for more than 25 years, mainly to provide connection points between USTs and fuel dispensers. In addition, in 2004, UL/ULc added a “Normal Vent Pipe” designation to its UL-971 “Standard for Safety Nonmetallic Underground Piping for Flammable Liquids,” making flex pipe a go-to option in fueling-system installations for both the handling of liquid product and venting applications.

The advantages that flex pipe has when it is used as UST vent pipe are the same as when it is utilized in fuel-delivery applications:

  • Eliminating the need to hand-build joints in the field
  • No cutting, fitting, gluing or welding of underground fittings
  • Termination points can be contained inside sumps; no need to bury joints underground
  • Reduction in or elimination of potential leak points
  • No need to use adhesives or hard-to-handle glue kits to connect fittings
  • A wider forgiveness window with less chance of cracks, leaks, or intrusion paths will develop
  • Installable in any type of weather conditions

Flex pipe also provides advantages when compared to other materials used in the manufacture of vent pipe:

  • Rigid fiberglass pipe: Rigid fiberglass piping can be challenging to work with, especially when weather conditions are less than perfect. What’s more, it requires specialized glue kits and equipment to install, with the joints needing time to cure properly, which lengthens the installation period. Since the process involves literally installing glass in the ground, ground shifts, frost heave and changes in weather conditions can cause rigid fiberglass piping to crack, leading to UST water intrusion.
  • Semi-rigid pipe: This pipe needs to be welded with joints that are buried in the ground, which is a costly and time-consuming process. Also, when a fused joint is mechanically connected to a sump wall, the attachment force required can create fine cracks in the sump, which can lead to the formation of leak points.

Flexing their muscles

OPW Retail Fueling, Smithfield, NC, introduced its FlexWorks product line in 1996. Since then, more than 10 million feet of flexible piping—which was UL-listed for use as vent pipe in 2007—has been sold for use with motor fuels, high-blend fuels, concentrated fuels and aviation and marine fuels around the world.

Available in single-wall and double-wall configurations, OPW flex pipe is also available in multiple lengths on a reel or in 25-, 33- and 40-foot flat “sticks,” and in diameters of 1.5, 2 and 3 inches. The flat-stick configuration aids the fuel-site installer, allowing vent piping to be installed straight with no dips or low spots – using “straighter is greater” as a guide – according to PEI/RP 100-20 “Recommended Practices for Installation of Underground Liquid Storage Systems.” OPW actually goes further than the PEI/RP 100-20 recommendation by suggesting that the vent piping be sloped 1/4-inch per foot back to the tank, rather than the PEI-recommended 1/8-inch per foot.

Flexible vent-pipe connections should be constructed of stainless steel and can be contained in a transition chamber or sump, especially in states that require the use of double-wall pipe. If stainless-steel fittings or a transition sump are not available, the connections should be wrapped in Densyl™ tape (also known as grease tape or wax tape) to protect against corrosion.

In the 25 years since its creation, OPW has upgraded its FlexWorks flexible piping, including increased flexibility that requires less force to bend for easier installation; reduced pipe weight for lower shipping costs; significantly reduced pipe memory for quicker connections and the ability to lay the pipe flat in the trench; and the use of enhanced Kynar® ADX (PVDF) Pipe Liner that is denser and more permeation-resistant, making it ideal for both liquid and vapor exposure.


After decades of proving its worth as a component in underground fuel-delivery systems, flex pipe is rapidly becoming a first-choice option for vent-pipe applications, and the current fiberglass crunch is another reason that makes flexible vent pipe a reliable alternative to rigid or semi-rigid fiberglass pipe.

Visit opwglobal.com to learn more about OPW’s full portfolio of flexible vent-pipe products.

This post is sponsored by OPW Retail Fueling

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