What to Watch for with Flexible Piping

When you’re looking to buy flexible piping, what should you look for? Joe Hartmann shares his on-the-job experience and informal research findings.

A straight line may be the shortest distance between two points, but is it the best way of getting there? By now most of you have heard about the latest in flexible underground piping systems for fuel distribution systems. You may have seen—or tripped over them—snaking their way through the trade show floors, and you’re probably intrigued by their potential. Will they cut down on installation time and total cost? Are they secure? Will they last for 20 years or more? How will they affect delivery rates at the nozzle?

In this article I will describe the testing required to become approved for service station applications and the three main types of flexible piping systems available. I will also point out key factors to consider when looking to buy flexible piping systems, and compare certain aspects of this new technology with that of traditional piping.

Leaking the story
So, why all the attention to flexible piping systems? Well, for one thing, the EPA has named piping as the culprit in nearly 80 percent of the leaks from underground storage systems. Most piping leaks occur at fittings and swing joints, and are caused by corrosion and improper installation practices. Stories of cleanups costing hundreds of thousands and even millions of dollars don’t even raise an eyebrow anymore—unless, of course, you’re the one who has to pay the bill. The ideal system would be one with no permeability; would be compatible with all liquids; would last 30-plus years; would have no (or a minimum of) fittings, and then only where they could be visually inspected and tightened; and which would cost less than any other option.

In response to these problems, and in an attempt to improve the reliability of fuel system installations, manufacturers developed flexible piping systems in the early 1990s to replace steel and, in some cases, fiberglass pipe for fuel system installations.

This is a flexible piping arrangement for a typical service station installment.

Thermoplastic flexible hose has been used for years to replace traditional materials such as copper and aluminum tubing in the automotive, aerospace and food industries. However, it took pioneering entrepreneurs like Bufalo Environmental Products and Total Containment to make flexible piping compatible with, and economically feasible for petroleum products. They accomplished this by developing the co-extrusion process and new thermoplastic materials, such as fluoro-polymers and polyethylenes. Other companies, such as Advanced Polymer Technology, utilize an inline laminar extrusion process to manufacture their flexible pipe. As with any new technology, flexible piping systems are undergoing almost continuous development. Today there are six manufacturers of flexible piping systems.

Making a new connection
Flexible piping systems feature continuous lengths of pipe between tank and dispenser containment chambers. All fittings are installed inside these contained spaces; this reduces the chance that a fitting leak will enter the environment, and it allows all connections to be inspected after backfilling.

Both the National Fire Protection Association and the Uniform Fire Code require piping systems to be UL Listed and tested before they can be designed into a fuel system installation. Seven flexible primary piping systems have gone through UL testing and carry the UL 971 Listing. In the July/August ‘96 issue of PE&T, Underwriters Laboratory’s Tom Skowera describes some of the many tests a flexible piping system must pass to achieve the UL 971 Listing. These tests include: sustained pressure, leakage, immersion, “air oven aging,” permeability, tensile, torque, bending, low-temperature bending, crush testing, tensile strength, burst test and product compatibility.

While some flexible piping systems passed third-party testing with flying colors, others barely passed certain aspects of the testing process. It is important to keep in mind that the UL testing provides a minimally acceptable safety testing standard for piping used in petroleum equipment applications.

In general, there are three types of flexible piping systems: single-wall, carrier pipe and co-axial. Following is a description of each of these systems.

This is an example of a flexible pipe installation with sweeping turns between dispenser containment sumps.

Primary (“single-wall”) pipe
The term “single-wall” is a little deceptive for flexible piping systems because the “pipe” is made by co-extruding multiple layers of different materials. Each layer serves a different function. The hose that is made into flexible piping is manufactured from proprietary materials. Typically, the inner hose is made of a thermoplastic such as polyurethane, and lined with a thin layer of a fluoro-polymer for chemical resistance and permeability. The next layer includes braided polyester or nylon to add strength, and then a durable outer layer of polyethyline or nylon to protect against abrasion, UV deterioration, contamination and other environmental conditions.

In 1994, Smith Fiberglass Products, Inc. introduced a flexible stainless steel primary pipe that can maintain a very high pressure, or high burst strength. Similar to a flexible connector, this primary pipe is contained within a polyethylene containment pipe.

When determining which pipe to use for a particular application, check with the manufacturers to make sure their products are compatible with the installation requirements. For instance, some piping will not work with suction systems; others are designed for very high pressure (as with motor oil pumping systems); others are not listed for use with alcohol or other chemicals. And while installation test pressures range from 50 to 60 psi, the burst pressures have a wide range, between 150 and 1,000 psig.

The primary flexible pipe is pulled through the carrier pie, which serves as secondary containment

Carrier pipe
Another version of flexible piping incorporates the same single-wall primary pipe; however, it is pulled through a corrugated secondary containment “carrier” pipe, which is typically 3-4 inches in diameter. The carrier pipe provides three advantages over primary single-wall pipe. First, there is added protection against a release to the environment. Second, it is a convenient means of monitoring the primary pipe for leaks. A liquid sensor in the tank containment sump will detect leaks from the primary piping. And third, some manufacturers state that if, at some time in the future, the primary pipe fails, it can be pulled through the carrier pipe and replaced without excavating.

The carrier pipe is a continuous length of corrugated polyethylene. As with the primary pipe, all connections (or terminations) of the secondary pipe are made within the contained spaces beneath dispensers and in tank sumps. If the secondary pipe is to be used for interstitial monitoring, the corrugated inner surface of the pipe may lengthen the time it takes to recognize a leak. For this reason, some manufacturers provide a smooth channel at the bottom of the corrugated pipe to allow product to flow freely back to the underground tank.

Ameron’s secondary containment system incorporates fiberglass reinforced plastic containment piping with mechanical connections and sweeping turns. The mechanical connections are quicker to install than the chemical joints made with traditional fiberglass piping, and yet the joints are strong enough to maintain the required test pressures.

Regardless of the system employed, the secondary containment pipe should be capable of maintaining the minimum of 5 psi test pressure, and preferably 10 psi to ensure integrity of the installed system for its entire service life. A means of post-installation testing should be incorporated into the design of the secondary pipe.

This man is tapering lengths of fiberglass pipe prior to installation.

Co-axial double-wall pipe systems
The next generation of flexible piping is a coaxial double-wall piping system. Here’s how it works. Basically, the single-wall flexible pipe is wrapped with an integral “loose” outer layer. Standoffs or channels are incorporated into the design in order to maintain the interstitial space for product to flow. When the pipe fittings are attached, the secondary containment pipe may also be sealed. If so, the secondary pipe must be capable of meeting the same test pressures as the primary pipe, usually 50 psig.

Some manufacturers have developed methods of tapering into the secondary piping for interstitial monitoring. They also bridge piping between dispensers so that all piping can be monitored and tested from a single point in the system. One way to improve the reliability of line leak detection is to continuously monitor the interstitial space of the product piping.

This is an example of a co-axial double-wall pipe system.

Fitting decisions
Here are some things to consider when deciding which type of pipe to install at a particular location:

• The flexible pipe is provided on standard, pre-determined lengths of coils from 250-1,400 feet, and is measured and cut to length in the field.

• The inside of some piping systems are smooth, while others are corrugated; whatever the surface, this will affect flow rate, bending radius, elasticity and test procedures. Generally, smooth inner walls provide better flow rates.

• There are fewer fittings with flexible piping systems than with conventional fiberglass or steel installations; and these fittings are typically made of brass or nickel-plated steel, with an integral swivel end. (Various methods are used to connect the fittings to the flexible pipe. Some systems require special machines to swedge the fittings onto the hose, some require special cutting tools, while others require nothing more for installation than a socket wrench and a utility knife.)

Piping comparisons
The cost of material for 2 to 4-inch fiberglass pipe lists at between $2.50 - $4.50 per foot, and fittings range from $8.00-50.00 each. The cost for flexible pipe ranges between $9.00 and $15.00 per foot. Fittings range from $20.00 to $110.00 each, but there are fewer required than with FRP systems. A typical FRP pipe installation takes several days to complete, while flexible pipe for a typical service station can be placed in a day. Testing of both systems takes about the same amount of time.

We recently compared the total installation cost using flexible pipe verses rigid FRP pipe on a couple of the tank installations we are in the process of designing. The total actual cost of the installations were about the same.

Look beyond the up-front material cost and installation time savings. Yes, flexible pipe is more expensive, and yes it is quicker to install than fiberglass pipe; but other factors on a project may increase the total installation cost. For example, a small odd shaped site may require an irregular tank orientation or burial depth that can affect the amount of pipe required for an installation.

Flow rate calculations can be a little tricky. There are a number of factors that affect the flow rate on any installation, such as, tank burial depth, product specific gravity, pipe diameter and pump size. Most flexible pipe systems are available in 3/4 inch, 1-1/2 inch and 2-inch diameters, primary fiberglass pipe is typically two to three inches in diameter.

Because of the sweeping turns (typically 18-36 inch radius) and fewer fittings, the smaller diameter flexible piping may in some instances, be capable of maintaining or exceeding the flow rate of fiberglass pipe. Equipment manufactures and design professionals should be consulted on each installation to determine the appropriate equipment necessary to achieve a specific flow rate. (See Sullivan D. Curran's)

Before you buy
Take the time to check the capabilities of each before selecting a flexible piping system to specify, distribute and install. Review the installation methods and instructions to see how the pieces go together. Discuss the product with other users and installers who have worked with the product. Then compare the total installation cost on a project-by-project basis to determine if flexible piping is the way to go.

Finally, while flexible pipe may reduce the amount of skill required for pipe installation, do not jump to the conclusion that fuel system installation is “no brainer” work. The petroleum equipment industry will always be involved with installing equipment to safely store and distribute flammable and combustible liquids. We will always need to carefully handle materials and properly set and backfill tanks. We are still cutting threads for steel pipe risers. Excavating, trenching, sloping, tank burial depth, cathodic protection, testing and calibration are all critical to installing a secure fueling system.

This work requires a great deal of skill and training. Regardless of the piping to be installed, installers must be trained by the manufacturer on installation methods and test procedures. So don’t abandon your training programs, and be sure to check the next issue of PE&T for an article on how to properly install these flexible piping systems.

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