NTSB Safety Recommendation P-98-019

NTSB safety recommendation P-98-019.

THE NTSB RECOMMENDS THAT THE INNER-TITE CORPORATION: Develop and publish recommendations and instructions for limiting shear and bending forces at locations where your steel tapping tees are used to connect plastic service pipe to steel mains.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 1998-04-30

Adopted Date: 1998-04-23

Overall Date Closed: 1998-10-21

Synopsis: Despite the general acceptance of plastic piping as a safe and economical alternative to piping made of steel or other materials, the Board notes that a number of pipeline accidents it has investigated have involved plastic piping that cracked in a brittle-like manner. For example, on October 17, 1994, an explosion and fire in Waterloo, Iowa, destroyed a building and damaged other property. Six persons died and seven were injured in the accident. The Board investigation determined that natural gas has been released from a plastic service pipe that had failed in a brittle-like manner at a connection to a steel main.

Probable Cause: None

Ntsbnumber: DCA95MP001

Report Number: SIR-98-01

Addressee Name: Inner-Tite Corporation

Addressee Status: Closed - Acceptable Action

Addressee Date Closed: 1998-10-21

Addressee Organization Type: P-Private Industry

Communication Date: 1998-05-20

Communication Type: Official Correspondence

Communication Contents: (Letter Mail Controlled 5/22/98 12:26:14 PM MC# 980661) -From George W. Davis, P.E., President: This is in response to your letter dated April 30, 1998; part of which stated, "Develop and publish recommendations and instructions for limiting shear and bending forces at locations where your steel tapping tees are used to connect plastic service pipe to steel mains." Our preliminary response to your letter and recommendations is as follows: I. We feel that we are qualified to develop and publish instructions for limiting shear between rigid mechanical fittings and polyethylene gas service tubing. As you may be aware, Inner-Tite Corp. pioneered the use of rigid protection sleeves to bridge the gap between the metal transition fitting and the old steel service pipe where polyethylene tubing was used for service renewals. We probably had written instructions in the 1960s and 1970s, but frankly, this is such an old matter that the practice of installing protection sleeves on service renewals (at the street) is taken for granted. It is simply a I. routine practice, inasmuch as all of our customers – Cont. as far as I know -- more than 50 gas utilities – use bridging pieces to guard against shear in service renewals. 2. Your recommendation is specific to plastic service pipe and steel tapping tees (presumably restricted to steel pipe). Why limit your investigation and recommendations to steel tapping tees? In the Northeast, for example, there is a very large amount of cast iron pipe with rigid threaded iron or brass service tees having a transition fitting incorporated into the service tee. For all intents and purposes, the same exact shear conditions would occur with these cast iron installations as might occur with steel tapping tees. It is equally possible that the same conditions could occur with copper tubing, pipe, and fittings. 3. Your recommendations infer that Inner-Tite should promulgate instructions regarding the bending radius for polyethylene and other plastic piping materials joined to our transition fittings. Frankly, we are reluctant to pursue this course of action. Our Posilock transition fittings are used with a number of different types and different manufacturers of polyethylene. These various polyethylenes, and the compounds from which they are made, have widely varying physical properties. While we are not conversant in the intimate detail of these physical properties -- we are aware that the flexural modulus, for example, varies considerably. An appropriate minimum bending radius for one polyethylene, might be unfair or 3. (Cont.) unsuitable for another. We, therefore, feel that any recommendations regarding a bending radius should rest with the manufacturer of the compound, and certainly with the extruder of the polyethylene tubing or pipe. I hope you will agree that lnner-Tite Corp. should develop and publish recommendations for limiting shear by use of bridging pieces (or protection sleeves) where our Posilock transition fittings are used to connect polyethylene tubing to steel, cast iron, copper, or any other rigid gas piping fittings.

Addressee Organization Type: P-Private Industry

Communication Date: 1998-07-10

Communication Type: Official Correspondence

Communication Contents: (Letter Mail Controlled 7/17/98 3:21:05 AM MC# 980893) -From George W. Davis, President: As a follow-up to our earlier correspondence, I am enclosing, herewith, Inner-Tite Corp. Recommended Practice for Limiting Shear and Bending Forces on Flexible Gas Tubing, supplemented by Inner-Tite drawings X0694B, X0694D, X0694E, X0694A, and X0694C. I trust that these written instructions comply with your directive to lnner-Tite Corp. Thank you for your cooperation on this matter.

Addressee Organization Type: P-Private Industry

Communication Date: 1998-06-24

Communication Type: Official Correspondence

Communication Contents: The National Transportation Safety Board has received your May 20, 1998, letter regarding Safety Recommendation P-98-19, which was issued to the lnner-Tite Corporation on April 30, 1998, as a result of the Safety Board's Pipeline Special Investigation Report - Brittle-Like Cracking in Plastic Pipe for Gas Service. The Safety Board asked that the lnner-Tite Corporation develop and publish recommendations and instructions for limiting shear and bending forces at locations where your steel tapping tees are used to connect plastic service pipe to steel mains. The Safety Board recognizes that lnner-Tite pioneered the use of protective sleeves to bridge the gap between metal transition fittings and the old steel service pipes where polyethylene tubing was used for service renewals. The Safety Board is pleased to learn that, as far as you know, all of your steel tapping tee customers use protective sleeves at these connections; the Board is aware of a number of gas pipeline operators who do not. Our report documents that, for some applications, MidAmerican Energy had no design criteria covering certain important parameters for sleeves. Unless steel tapping tee manufacturers recommend precautions, gas pipeline system operators may not realize the importance of determining these parameters. The Safety Board notes your concern that other types of service connections to mains may have the same issues involved as do plastic connections to steel mains that employ steel tapping tees. Given the scope of our study, we limited our intensive examination to plastic connections to steel mains via steel tapping tees. You advised that an appropriate minimum bending radius for one polyethylene tubing or pipe might be unsuitable for another. You also suggested that action on any recommendation regarding a bending radius should rest with the manufacturer of the compound, and certainly with the extruder of the polyethylene tubing or pipe. The Safety Board notes that ASTM 0277 4 recommends that bends near tap connections should generally occur no closer than 10 pipe diameters from a fitting and that manufacturers' bend limits should be followed. The Safety Board understands that several plastic pipe manufacturers publish similar bend radius recommendations at connections to fittings. Moreover, a number of gas pipeline operators have included the most conservative of these bend radius recommendations as their standard for bends at fittings. Compared to plastic piping manufacturers, steel tapping tee manufacturers may have less technical expertise regarding certain characteristics of plastic pipe. Nonetheless, steel tapping tee manufacturers, who have designed their rigid steel tees to connect to flexible plastic gas pipe, have a responsibility to provide recommendations for the safe use of their products. Steel tee manufacturers know the specific geometry of their tees. If a steel tee manufacturer believes that installation options depend on the type of plastic to be connected and that these options can be addressed only by the pipe manufacturer, the tee manufacturer has a responsibility to state that in its literature and to provide the gas system operator with directions for using its product safely. The Safety Board encourages lnner-Tite to develop and publish recommendations for limiting shear by use of bridging pieces (or protection sleeves) when its Posilock transition fittings are used to connect polyethylene tubing to steel, cast iron, copper, or any other rigid gas piping fittings. In addition, the Safety Board believes that lnner-Tite should provide guidance to its customers that they need to obtain information on the "bending" properties of plastic pipe from the manufacturer. Pending further response from lnner-Tite on the status of these efforts, Safety Recommendation P-98-19 has been classified OPEN—ACCEPTABLE ALTERNATE RESPONSE. Thank you for your prompt reply.

Addressee Organization Type: P-Private Industry

Communication Date: 1998-10-21

Communication Type: Official Correspondence

Communication Contents: The National Transportation Safety Board has received your July 10, 1998, letter regarding Safety Recommendation P-98-19, which was issued to Inner-Tite Corporation, as a result of the Safety Board's Pipeline Special Investigation Report - Brittle-Like Cracking in Plastic Pipe for Gas Service. The Safety Board asked that Inner-Tite Corporation develop and publish recommendations and instructions for limiting shear and bending forces at locations where its steel tapping tees are used to connect plastic service pipe to steel mains. The Safety Board is pleased that Inner-Tite developed and published a recommended practice for limiting shear forces by use of bridging pieces (or protective sleeves) when its Posilock transition fittings are used to connect polyethylene tubing to steel, cast iron, copper, or any other rigid gas piping fittings. The Safety Board further notes that Inter-Tite Corporation has published a recommended practice for bending limits, identical to ASTM D2774, and advises its customers to obtain information on the bending properties of plastic pipe from the piping manufacturer. Accordingly, Safety Recommendation P-98-19 has been classified CLOSED—ACCEPTABLE ACTION. Thank you for your prompt reply.