# Do you know your SDR?

What is SDR and why is it important?

Pipe SDR is the abbreviated term for standard dimensional ratio. This simply refers to the mathematical relationship between the pipe outside diameter and its wall thickness. The SDR will refer to a wall thickness dimension which has been calculated to reflect the maximum operating pressure of the pipeline.

SDR is critically important when:

• calculating the internal pressure of a pipe system.
• the ID of the pipe is critical for example pumping mains to calculate pressure drops or volumetric data, or when inserting an item into the pipeline, such as an electric cable.
• calculating the pipe tensile strength when putting under considerable installation stress, for example, HDD drilling.
• Calculating the compressive strength of the pipeline to determine the depth of burial or compaction of backfill material.

How do I check the SDR or wall thickness of a pipe?

• Simple mathematical equation. Pipe OD / the wall thickness of the pipe = SDR
• Simple mathematical equation. Pipe OD / SDR11 = wall thickness
• Physical measurement (if you have access to an open-end) with a bullnose micrometer.
• Product markings

Example:

250mm (OD pipe) / SDR 11 = 22.72mm (wall thickness)
250mm (OD pipe) / 22.72 (wall thickness) = SDR 11

What if itâ€™s already installed in the ground?

If the pipeline is already installed or you are trying to identify the SDR/wall thickness of an existing pipe in the ground, there are a few ways to do this.

1. All pipes manufactured to industry-recognized water, gas and power standard are marked with 1 or 2 print lines which should remain fully visible and recognizable once installed. The markings will identify the SDR of the pipe and some even detail the wall thickness of the pipe too.

Example of pipe markings.

BS EN 12201 PEAK PIPE SYSTEMS (PPS1) BUREAU VERITAS 1144/001 225 X 20.5 MM SDR11 PE100 PN 16 B1 BATCH NO. DATE/TIME POLYMER CODE E.G. (B9L) W/P; MO. No.

• You can either use an ultrasonic measuring device which measures the wall thickness of the pipe accurately, you can then determine the SDR of the pipe by using the calculation above.

What industry SDR are standard and readily available?

Over time the development of polyethylene materials and standard pipe SDR has changed and been developed in accordance with the MOP (max operating pressures) required for the pipe networks. Ensuring the suitability and longevity of the networks throughout the systems life cycle.

Below is a list of standard industry available SDR and how commonly they are stocked within the UK market.