Minimum DR for CIPP Lining

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“What is the thinnest liner I can get? I have a job that I think I’d like a very thin liner as all I want to do is provide corrosion protection.”

Groundwater At Invert of Pipe

Fully Deteriorated Pipe

If there is no groundwater above the pipe invert, the minimum DR is 100. So what exactly does that mean you ask? Dimension ratio is the outside diameter of a pipe to the wall thickness. For example, if a pipe is 4″ in diameter and the DR is 40, then my wall thickness is 0.1″ or 4 divided by 40. So let’s look at how thin we could make the wall of a liner to a host pipe and meet the ASTM standard for wall thickness of material. According to ASTM F-1216-16, the minimum dimension ration for a liner at a DR of 100 would mean we’d take the diameter of the pipe and divide it by 100. In the case of our 4″ pipe, that number would be 0.04″. This can be found in ASTM F-1216-16, X1. Design Considerations, Note X1.2 There is a reason for a minimum DR and that reason is due to the pipe wall collapsing under its own weight if applied any thinner than that.

So what does that mean for a your job? If there is no groundwater, and the pipe in still structurally sound, then a liner in the DR100 range may solve your issues. We see thin liners and coatings in pipe buried in walls of buildings as there isn’t any loading, no groundwater issues, and most of the defects are caused by corrosion scale in the pipe. While the minimum may be all you need for your project, many installer will, if not officially directed, give themselves margins of safety. We see most roof drain projects lined or coated at a level of about 2mm of thickness for the materials applied.

But what about a fully deteriorated pipe condition. First, let’s look at what partially deteriorated pipe. A pipe in this condition as described in X1. Design Considerations of ASTM F-1216-16 may have longitudinal cracks and up to 10% distortion of the diameter if the rehabilitation can survive surcharge loads. Piping above ground has no surcharge loads, so many of these types of situations would be eligible for lining or coating to a thickness of DR 100. Point repairs may need to be performed to get the pipe back to the partially deteriorated condition, then lined or coated. For a fully deteriorated pipe condition, then we need to perform the evaluation of the pipe and pipe conditions including soil modulus (if applicable), backfill materials used (if applicable), groundwater, ovality, pipe diameter, and any pressures on the pipe.

So, there you go. Divide diameter of pipe by 100 as your minimum. From there, protect yourself by adding extra thickness to insure you are protected by unknown issues. Finally line or coat your pipe to the thickness that fits the pipe condition. For additional details call 888-354-6464.

 

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