A Cautionary Tale about Unextended Proprietary Restrained Joints for Ductile Iron Pipe

The ductile iron pipe industry offers a variety of proprietary restrained joint products. (In this paper, the abbreviation PRDIP is used for proprietary restrained ductile iron pipe.) As with any product, optimum performance of PRDIP results when the manufacturer's installation instructions are followed. However, when these instructions are not followed, problems may result. Many miles of pipe were successfully installed for the project presented in this paper. At some vertical diversions, problems occurred where proprietary restrained joints were not fully extended. This paper is a generic investigation of a 36-in. (900 mm) pressure pipeline project, but the information presented in Section 3 is based on an actual installation. One of the problem locations from that project is examined in detail. Vertical diversions in this project were particularly sensitive to the pipeline expansion that occurs if the PRDIP is not fully extended. Most designers and installers are aware of this issue and extend the joints whenever pipeline expansion would harm the pipeline or surrounding structures. Ductile iron pipe manufacturers have recommendations in their product literature for how this may be accomplished. To provide proper context, the paper begins by describing the issue. It then discusses in broad terms how the issue may be easily addressed and eliminated as a concern.