Several companies have recently added a disclaimer to their literature for wedge action restraints for use with Ductile Iron Pipe. The disclaimers essentially provide that the exterior hardness of Ductile Iron Pipe must be below a Brinell value of 230 (BHN) for their teeth to engage the pipe and ask that decades-long industry standards change to accommodate the designs of their restraints, which seem to be experiencing performance issues on AWWA-compliant ductile iron pipe. These disclaimers are self-serving and in some ways distorting.

Some of the disclaimers imply that ductile iron pipe with hardness above 230 BHN likely fail to meet the AWWA standard ANSI/AWWA C151/A21.51 (C151). There is no hardness requirement in C151, which the disclaimers do not refute. These disclaimers, however, speculate that pipe with a surface hardness above 230 BHN may have difficulty meeting the 10 percent elongation requirement as stipulated in C151. Their suggested correlation between hardness and elongation is misplaced and misinforming because these companies are only testing a surface property and trying to extrapolate it to the properties of the entire pipe wall as specified in C151 physical property requirements.

Brinell hardness testing from the top layer to a depth of 0.05” (as suggested by some of the disclaimers) would not yield an accurate BHN, as the Brinell hardness testing procedures for ductile iron pipe require that the surface layer of pipe be ground to a smooth surface. Further, utilizing other methods, such as Vickers or Rockwell testing, and extrapolating to BHN, as suggested by some of the disclaimers, would yield inconsistent and subjective results. We have tested multiple pieces of random production pipe following the international standard, ISO 2531 – “Ductile Iron Pipe, Fitings, Accessories and Their Joints for Water Applications”, which has a hardness requirement and has procedures for measuring hardness, which requires grinding the surface layer to a smooth surface. The results showed hardness well below 230 BHN on all samples tested.

It is also noteworthy that wedge action restraints are not standardized by AWWA, so the companies that produce them are not obligated to share their design criteria (like tooth sharpness). The companies offering a disclaimer appear to utilize a similar design that has worked on smaller diameters for years, but have seemingly had difficulty replicating positive results on larger diameters. It is possible that their design struggles in larger sizes are due to the higher forces associated with larger diameters. In fact, U.S. Pipe’s own Field Lok 350® gaskets are only available up to 24”, as we have found it is difficult for frictional restraints to handle the higher pressures associated with larger diameters. We do not have a disclaimer for pipe hardness with these gaskets, only that the pipe meets the requirements of C151. That said, at least one other company has a unique design for wedge action restraints and has not offered a pipe hardness disclaimer presumably because they have not experienced significant product failures.

In summary, U.S. Pipe is celebrating its 125th anniversary in 2024. We have been producing 3” – 64” Ductile Iron Pipe that meets or exceeds the requirements of AWWA C151 since its inception in 1965. We stand behind our products and do not recommend using products that offer a disclaimer due to surface hardness for any diameters.

If you require additional information, please contact one of our Sales Managers or a member of our Technical Resource team.

Click here to see the official U.S. Pipe Technical Bulletin.