Iron Pipe Joint Development down through the Years - Part 4 of 5

This is an edited version of a presentation made at the American Society of Civil Engineers' 2017 Pipelines conference, and is the fourth in a series of five brief articles. On the sixth week, it will publish in its entirety with a complete list of references.  It's getting really interesting now as we examine how thrust-resisting iron pipe joints were developed and perform.

The Second Boltless Breakthrough

Last week, we ended with tie-rods being used to restrain joints. They were expensive, labor intensive, and subject to failure over time. The necessity of an alternative resulted in the development of joints that were self-restraining.  

Just as non-restrained joint development began with bolts and labor and advanced to boltless and efficient, so did restrained joint development. An early joint in the 1960s used a push-on gasket inside a bell having a non-sealing flange and bolt holes. A follower gland with bolt holes was placed over the barrel of the connecting spigot. A substantial alloy bar was welded to the spigot barrel against which the loose follower gland engaged. Bolts between the follower gland and the non-sealing flange ensured restraint. Slight deflection could be set prior to tightening the bolts, but none was available after the joint was made. This was an improvement over flanged joints, and strong positive restraint was accomplished; but it was costly, heavy, labor-intensive, and required significant pre-construction planning and design. AMERICAN’s brand was Lok-Fast. I quoted, sold, and produced shop drawings for many Lok-Fast projects. Figure 9 shows the joint cross-section and you can see its heft and complexity. 

Figure 9. The exceptionally strong but equally heavy, expensive, and labor-intensive Lok-Fast joint. The number of bolts equaled mechanical joint. Field adaptability and post-installation deflection were not an option. (American Pipe Manual, 2004)

Product development and innovation efforts now turned toward removing the bolts and adding flexibility. This was accomplished with deeper bells having a cross section that accepted a locking wedge and mated against a weld-ring on the pipe spigot. The bolts were gone and reasonable flexibility was gained. Conventional push-on gaskets were also used. Product development progressed from the smaller through the larger diameters. AMERICAN's brand name is Flex-Ring, and it is shown in Figure 10. 

Figure 10. Flex-Ring, a boltless, easier-to-assemble, restrained joint offering flexibility. (Author's personal collection.)

The combination of strength and joint flexibility allows Flex-Ring to be used in moderate-profile water crossings in place of the more expensive ball and socket pipe and has more recently been introduced to horizontal directional drilling applications. A project cited in an ASCE Pipelines 2016 paper was a 1,640-foot, 36-inch diameter HDD installation. (Carpenter, 2016) Each joint of that diameter has 2-degrees deflection, and the pulling capacity of the joint is 310,000 pounds; but with the use of bore hole lubricant, the maximum load reached in that project's pull was only 110,000 pounds.

At this stage of restrained joint development, bolts had been designed out, deflection had been designed in, and innovative product development engineers turned their attention to welding and field adaptability.  By placing high-strength, hardened steel wedges with serrated teeth into push-on gaskets, the industry was able to combine joint restraint, joint deflection, boltless, easy and fast assembly, and field adaptability into a complete restrained joint product. Brand names include AMERICAN's Amarillo Fast-Grip shown in Figure 11.  The bright yellow color distinguishes this from conventional non-restrained gaskets.

Figure 11. AMERICAN Amarillo Fast-Grip restrained gasket, left; and a cross-section showing tooth profiles. (www.american-usa.com).

At this point, restrained joint innovation had progressed from heavy, bolted, rigid, expensive, pre-engineered, and time-consuming assemblies to standard-weight, boltless, flexible, affordable, field-adaptable, and easily-assembled connections. To make it even better, AMERICAN's Flex-Ring is available on valves, bringing further value to a pipeline project.

Next week, we will see the climax of this joint technology in the AMERICAN earthquake joint which deflects, telescopes, and has tremendous end-wise strength. To invite others, Share and Like this post, and please ask any questions.