1. National standards for flanges, such as ANSI B16.5 and AWWA C-207, were developed many years ago. This was long before the sophisticated computer analytical tools available today, which can be utilized to design flanges. As a result, IPP has shown that the standard flanges called out were either over-designed, in the case of ANSI, or not applicable for modern piping materials such as thermoplastics, as is the case for AWWA.
2. Historically, engineers have been under the impression that the only method to reduce the cost of standard flanges was to make them thinner. As a result flange-sealing performance has suffered.
3. Standard back-up flanges utilized on high density polyethylene (HDPE) piping stub-end applications were assumed to safely perform at the stated AWWA pressure ratings. IPP research has shown that the AWWA piping industry standards are not applicable to HDPE pipe.

Caution! Do not use this procedure to align and/or pull the joint together.

The American Water Works flange standard ratings for class 150 flanges, AWWA C-207 Table 2 Class D (formerly known as the 1-D) are based upon how flanges behave when welded onto steel pipe. When bolted together, the opposing forces neutralize each other via the full-faced gasket, and there is a marked absence of deflection. This creates a stable joint and assures a safety factor of 2.

On HDPE applications, however, the free-floating rings are able to uplift at the pipe wall. They cantilever and rotate at the edge of the flange adapter, creating a rotational force in an axial direction around the edge of the adapter. This creates stress levels at approximately twice the magnitude of a welded 2-D flange, which exceeds the yield point of the flange material.

Unknowingly, many design engineers have specified the flanges in AWWA C-207 on HDPE piping applications thinking the stated pressure ratings were applicable.

IPP employs sophisticated engineering computer software to design its products. Finite Element Analysis (FEA) is used to determine primary levels of hoop, axial, radial, shear and von Mises stresses. This design tool is recognized for accurate stress analysis and allows for results that are verifiable and reproducible. FEA represents the ultimate in structural analysis for the most sophisticated systems to ensure long life and safe operation.

IPP has used FEA to evaluate each and every flange shown on AWWA C-207 Table 2 Class D and Table 4 Class E up to 63″ (see Performance of Standard Flanges on HDPE Flange Adapters), and has concluded that, “C-207 is misused in specifying flanges for HDPE piping applications at the stated pressure ratings, if a traditional safety factor of 2 is desired, as it is for steel pipe applications.”

Moreover, AWWA C-207 for HDPE Pipe specifically states:

The pressure ratings displayed in ANSI/AWWA C207 apply only when the flanges
are welded to steel pipe in a typical slip-on fashion. These pressure ratings do not
apply to loose or floating back-up flanges on thermoplastic piping stub ends. Do Not
assume pressure rating correctness from AWWA C207 tables; they do not apply to
HDPE piping systems.

Therefore, in many cases you will find that traditional flanges will not hold the adequate pressure necessary for a successful seal. While the comparative weights of IPP Deltaflex® flanges are lighter than conventional lap joint flanges, their innovative geometry is designed to meet or exceed pressure requirements with a safety factor of 2.

Typically, an engineer strives to design a system that fits the client’s needs and is functional, safe and cost effective. As you can see, C-207 flanges will not accommodate all of these criteria. The misapplication of C-207 and the pressure of market forces have caused thinner and thinner flanges to be selected, leading to systems that are held together by strain-hardened materials operating at stress levels between yield and tensile break points. The reduced section modulus of these flanges increases the potential for accelerated stress corrosion and ultimate joint failure.

Improved Piping Products has patented a unique design, trade named IPP Deltaflex®. It is the modern high-performance backing ring for HDPE piping systems because the total mass of the flange, compared to a 2-D flange, is reduced by 30 percent or more and redistributed in a patented configuration that outperforms the 2-D flange.

Note the unique cross sectional design and the manner in which it seats to the HDPE flange adapter and mates with its counterpart. The unit is lightweight, easy to manipulate and install, and incorporates the following important features:

• The I-beam principle for weight reduction.
• Redistribution of mass to the critical load bearing areas for maximum strength and reduction in the joint.
• The Belleville washer principle is utilized for storing energy in the bolts, eliminating the need for re-torqueing.
• Better corrosion resistance due to the IPP Deltaflex® being made of ductile iron as opposed to the 2-D which is made of carbon steel.

In order to make the backing ring selection process less confusing, IPP has designed its products in conjunction with the most commonly used SDR pipes in the industry. Our standard lines include SDR7 in sizes 1/2″ through 24″ and SDR11 in sizes 2″-47″ with many more to choose from, and all are designed with a safety factor of 2.

A simple calculation provides the answer. For purpose of illustration, let’s assume 12″ SDR 9 pipe has been specified, but IPP can only offer SDR11 or SDR7 backing rings in this size. You can choose to use the SDR11 backing ring; however, the safety factor will be less than 2.

The calculation for determining the safety factor is simple. Take the pressure rating of the backing ring, in this case 160 psi, and multiply it by its safety factor of 2 (320). Dividing 320 by the operating pressure, 200 psi, yields a safety factor of 1.6. Using SDR7 backing rings would yield an ample safety factor of 2.67 (267*2/200=2.67). If you were to use the AWWA C-207 Class D flange with an actual rating of 60 psi, you would yield a safety factor of 0.6.

Now you can make a decision about which safety factor is more appropriate for your application. Choosing the proper safety factor will eliminate joint failure, leakage and the need for bolt re-torqueing.

IPP Deltaflex® backing rings have gained acceptance into a wide segment of the overall piping market and are being used in the following applications:

• Water and Waste Water
• Gas
• Mining
• Landfills
• Shipbuilding (NASSCO Approved for U.S. Navy Coast Guard – Fast Deployment Fleet)
• Factory Mutual
• And many more

One look at the list of customers and projects IPP has supplied will show that IPP Deltaflex® is recognized worldwide as the preferred backing ring for use on HDPE Pipe.

Millions of our backing rings are in use worldwide. Including IPP Deltaflex® in your master specification as the preferred backing ring will ensure safety and peace of mind while helping to keep you within budget.

Contact us for more information, or request a quote.