PolyPipe LLC


PolyPipe LLC is dedicated to the specialized natural-gas distribution (NGD) pipe market in the United States.

In April 2021, we paused the shipping and sale of small-diameter NGD pipe – pipe of 1½ inch diameter of less – because of inconsistent wall thicknesses found in some samples. NGD polyethylene pipe is certified for outdoor, underground installation only and is not approved for use inside or underneath buildings.

We have had no reports of failures associated with this issue.

We have now determined that this issue was limited to production of a small portion (less than 1% of coils and less than 0.002% of total feet) of the small-diameter NGD pipe coils manufactured at Dura-Line Corporation’s Gainesville, Texas plant. Therefore, small diameter NGD pipe produced at Gainesville remains on the inventory hold.

The Company has released from the hold all small NGD diameter pipe produced at Erwin and recommenced production of small diameter pipe at its Erwin, Tennessee plant at the end of June 2021. We have now concentrated our NGD pipe business at the Erwin plant—Gainesville is no longer producing NGD pipe.

This issue does not affect NGD pipe sizes 2” diameter and larger, NGD pipe manufactured at PolyPipe’s Erwin facility or any of Dura-Line LLC’s Datacom conduit products.

We will keep this site updated with the latest information for our customers. Our most recent customer update addressing this issue is available here.

A message from leadership . . .

As a company dedicated to serving the unique needs of the NGD market, we take our responsibilities very seriously.

We value the trust you place in us and our partnership together.

PolyPipe LLC


NGD Pipe Update

All PolyPipe NGD pipe is now manufactured at the company’s facility in Erwin, Tennessee and a repository of all customer updates and fact sheets are posted here.

Update Summary

Root Cause Summary

The wall thickness issue we observed in certain small diameter NGD pipe produced at Dura-Line’s Gainesville, Texas plant was caused by an irregular pull on the manufacturing line that can be generated by coilers used to wind the pipe into coils when operated without maintaining slack in the line. We refer to this as “coil whip.”

Coil whip can occur when the pipe is being wound onto a coiler. When one pipe coil is finished and removed from the coiler, excess pipe can accumulate between the end of the line and the coiler. Once the end of the accumulated pipe is attached to the coiler, the winding speed of the coiler must be increased to take up the slack.  If the speed is not reduced before the slack runs out, the coiler can force the pipe to speed up the puller for a moment, transmitting a force up the line. Under certain circumstances and conditions, the force may be able to stretch molten plastic at the beginning of the extrusion line, causing a thin wall to form on a short segment of the pipe.

The vast majority of the small diameter NGD pipe produced at the Gainesville plant was not impacted by coil whip. Pipe would only potentially be impacted by coil whip if the coiler speed was not reduced by the operator before the slack was taken out of the line, and not every instance of coil whip would result in a wall thinned below ASTM specifications.  Additionally, some coilers are less likely to cause coil whip due to differences in operating speed and controls. For additional information, see Customer Update 13, which is accessible here.

Before April 2021, our ultrasonic wall monitors did not always detect when the wall thicknesses of affected pipe dropped below specification in localized sections. Because the monitors were averaging wall thickness measurements collected over brief time intervals, the thinned segment was too short to cause the calculated average wall thickness value to fall below specification and thus an alarm was not triggered.


Inventory Note

Erwin Not Affected; Erwin Small Diameter NGD Pipe Released from Hold

We have determined that coil whip was not a recurring issue at our Erwin plant.   To the contrary, we identified only one isolated instance where Erwin produced and shipped pipe that had a localized thin wall below ASTM specifications. The pipe had a visible deformation (the outer diameter was reduced in a localized section resulting in an “hourglass” shape), and was not properly contained.  Erwin had (and continues to have) robust processes and controls in place to prevent any recurring issue, including: (i) the use of different coilers and coiler configurations, including the ability to more precisely control the take-up speed for excess slack; (ii) process differences between Erwin and Gainesville which minimized slack accumulation between coils, including the use of two operators during coil changeout and the ability to manually control the coiler speed; (iii) positioning of equipment on the plant floor; and (iv) the training and experience of operators at the Erwin facility.

Based on this conclusion, the company released pipe produced at Erwin from the inventory hold announced on April 20.  You can find the plant of manufacture on the pipe’s print line.

A Small Portion of Gainesville Small Diameter Pipe was Impacted; Gainesville Small Diameter NGD Pipe Remains on Hold

We have determined that this issue was limited to production of certain small diameter NGD pipe at Dura-Line’s Gainesville plant.

This coil whip issue occurred intermittently and impacted only a portion of our small-diameter NGD pipe produced at Gainesville. When a coil whip event occurred, it could cause a single, short section of thin-walled pipe on the coil.

We estimate significant coil whip events resulting in a reduction in wall thickness more than 10% below specification may have occurred in less than 1% of the small diameter pipe coils produced at Gainesville (and less than 0.002% of total feet of Gainesville’s small diameter NGD pipe). We have also detected coil whip events that resulted in wall thickness reductions less than 10% below specification for a segment of less than 5 inches in length. We are not able to estimate how frequently these less significant events occurred, but we believe they were similarly sporadic.

Unfortunately, because of the sporadic nature of coil whip in Gainesville and despite our best efforts, we are not able to identify which lots or batches of Gainesville’s small diameter NGD pipe were impacted or say with confidence that the issue was limited to a specific time frame.

Please continue to quarantine small-diameter NGD pipe (1 ½ inch diameter or less) produced at Gainesville or return it to PolyPipe. You can find the plant and date of manufacture on the pipe’s print line. For information about how to return your pipe, click here. Please also send our communications on to your customers.

If you have additional questions about the inventory hold or how to read the print line of your pipe, you may contact your NGD sales representative or send your questions to: NGD@duraline.com

Answers to Your Questions

Visitors are invited to use the form below to submit additional questions for consideration. You may also contact your NGD sales representative or send your questions to: NGD@duraline.com.


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