Technical Bulletin # P-07

Clamp Type Pipe Construction --- Making Sure Your Pipe
Service Life Is Not Cut In Half During Installation

THE PROBLEM:

     Groove clamped type piping construction is becoming more frequently employed in a variety of applications. Once primarily used for fire sprinkler service, groove clamped construction is now commonly found in condenser water piping from large 24 in. diameter main risers to smaller 2 in. distribution lines, at chill and secondary water systems, and for domestic water applications.

     The groove clamped pipe system, most commonly know by the manufacturer names Victaulic or Grinnell, offer faster installation, lower installation costs, tremendous flexibility, among other benefits. While in many aspects viewed as equal to welded black iron pipe, there are a few critical considerations to remember.

     In many examples, we have documented advanced failures of groove clamped systems which would not have occurred if certain precautions were followed.

THE SOLUTION:

     The most important consideration for a groove clamped installation, from our perspective, is the method of producing the groove itself - whether it be rolled or swagged into the pipe to leave a ridge on the interior surface, or cut or milled from its outer wall. From its appearance alone, it is difficult to identify the method of groove formation, although the exterior side wall of a rolled groove will sometimes appear with a slight radius.

Rolled Groove - New	Roll Concealed Under Rust

     The below close-up photo of the groove illustrates its depth into the outer pipe wall. Where cut, this represents an unnecessary loss of wall material, and therefore the weakest point along that pipe length.

     If rolled or swagged, no actual wall loss at the pipe occurs, and the displaced pipe wall material still exists in the form of a ridge at the pipe interior. However, if cut or milled from the pipe, significant wall loss results. For small diameter piping, 0.098 in. of pipe is lost when the groove is cut. With a specified groove depth of 0.124 in. for most larger diameter pipes, this wall loss can amount to 33% of the pipe itself, but as much as 55% of its allowable pipe loss. Often used as an alternative to threading small diameter pipe and the threading losses which occur, cutting a groove into pipe can produce similar result.

     Generally, a look inside the pipe is necessary in order to determine whether the groove has been cut or rolled. A protruding ridge on the pipe interior shows that the groove has been rolled, whereas the absence of any ridge, shown in the photograph below, shows that it has been cut. While some construction specifications will define the method of grooving, most do not - thereby leaving it up to the piping contractor.

     From our discussion with various steam fitters, we have been advised that cutting the pipe is an easier and cheaper installation method - especially for larger diameter pipe. This may possibly explain why some of our clients have been surprised to find the groove cut when the piping specification clearly called for a rolled groove.

     The below photograph shows the absence of a roll groove protrusion where the iron oxide deposits have been scraped away. In this case, the cut out loss of 0.124 in. of material from the outside of an initial 0.375 in. pipe wall, combined with a 15 MPY corrosion rate over 12 years, has reduced the remaining service life of this piping system to zero.

     Another potential threat involving the use of cut grooved piping has to do with it being unevenly cut. We have identified some installations where the groove was cut eccentrically into the pipe - with the depth of the groove at 0.050 in. on one side, and 0.200 in. at its opposite wall. This not only removes significant pipe material in one area, but produces a weakened joint due to inadequate and uneven clamping. Such a condition can only be attributed to poor workmanship by the contractor, and is all but impossible to detect once the pipe is in place.

     Clamped pipe construction places far more emphasis on maintaining a top quality water treatment program, and for open water condenser systems - relatively clean water requiring good filtration. Unlike welded pipe, crevices exist at each clamped joint where dirt and bacteria can accumulate. While the chemical resistance of the rubber gasket is high, oxidizing biocides and cleaning agents always offer the potential to cause deterioration and cracking over extended time.

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