Printer Friendly

New Mexico gas study of PE 4710 resin leads to increased use of HDPE pipe.

Special To Pipeline & Gas Journal

Since New Mexico Gas Co. completed its research study on PE 4710, the company has added some 28,000 customers and installed more than 1,200 miles of pipe made from the state-of-the-art grade of polyethylene. An in-house team investigated bimodal PE 4710 compounds to determine the resin's compatibility with other, older pipe resins and evaluate its performance in terms of longevity, strength and confidence level.

According to Tony Radoszewski, executive director of the Plastics Pipe Institute, Inc. (PPI), "The research and development teams of pipe and resin manufacturers continually work to produce new products such as PE 4710 that will benefit the industry. The commercialization of PE 4710 allows for the maximization of pipe performance in gas systems, bringing an excellent level of environmental stress crack resistance and enabling a piping system to be operated at high pressure without sacrificing safety or service life.

"PE 4710 produces a very efficient pipe, which leads to savings in materials, transportation and installation," he continued, "plus, sections are heat-fused together which make a pipeline leak-free. The experience of the New Mexico Gas Co. with bimodal PE 4710 pipe offers invaluable insights for gas utilities across the nation."

For New Mexico Gas, the decision to permit the use of PE 4710 pipe was not automatic as the company embarked upon a thorough investigation to approve the material for its pipe.

"We conducted extensive laboratory and field evaluations to ensure that the material could be easily fused to the existing pipe network and in the dramatic mix of New Mexico's topography," said Angela Serrano de Rivera, manager, gas system engineering, New Mexico Gas Co., who led the effort.

"After all, New Mexico has deserts and snow-capped mountain ranges punctuated with canyons, mesas, and river valleys. This rugged terrain, extreme diurnal temperature range, and seasonal temperatures from over 114[degrees]F (46[degrees]C) in the summer to -21[degrees]F (-29[degrees]C) in the winter combine to make New Mexico one of the most challenging territories for delivering natural gas," she said.

New Mexico Gas Co. (NMGC), based in Albuquerque, provides natural gas to more than 500,000 customers in 345 urban and rural communities throughout the state via 12,000 miles of pipeline, comprised of 1,600 miles of transmission pipe and nearly 10,500 miles of distribution mains.

Concurrent with advances in plastic material science, the company began to transition from the predominant use of steel pipe to polyethylene pipe in the late 1970s and early 1980s. Today, approximately 57% of the pipelines maintained by the company are polyethylene.

According to Serrano de Rivera, the potential benefits of using advanced bimodal PE 4710 gas pipe first drew the attention of NMGC in 2005. Prior to that, unimodal PE 3408 pipe was used.

Faced with limited pipe supply due to Hurricane Katrina in 2005 and the challenge of delivering gas safely and cost-effectively under an extremely wide range of operating conditions, engineers at NMGC were intrigued by industry buzz indicating bimodal high density polyethylene (HDPE) resin's excellent resistance to slow crack growth (SCG) and rapid crack propagation (RCP), critical criteria for any gas pipe material.

These attributes lead to higher pressure capabilities while maintaining PE's long service life expectancy and versatility of installation, which includes trenchless procedures.

In late 2005, NMGC initiated an internal evaluation of bimodal PE 4710 pipe. These extensive laboratory and field evaluations included not only SCG and RCP tests but also critical heat-fusion joining tests: it was vitally important to ensure that the material could be easily heat-fused to the existing pipe network. Following is an overview of those tests conducted by Serrano de Rivera and her New Mexico Gas team, and the results.

[ILLUSTRATION OMITTED]

[ILLUSTRATION OMITTED]

Material Testing Of Bimodal PE 4710 Pipe

Fusion Test:

Tests were conducted on pipe sizes ranging from 1/2-inch CTS SDR 7 to 6-inch IPS SDR 11 and grouped into the following categories:

--Like materials, PE 4710 to PE 4710 fused with NMGC's fusion procedure;

--Unlike materials, PE 3408 to PE 4710 fused with NMGC's fusion procedure;

--Like materials, PE 4710 to PE 4710 fused with PPI's generic butt fusion procedure (TR-33/2005), and

--Unlike materials, PE 3408 to PE 4710 fused with PPI's generic butt fusion procedure.

[ILLUSTRATION OMITTED]

All fused samples were tested in accordance with the manufacturer's testing procedures, using both visual and destructive testing. Three joints were made of each pipe/ fusion procedure combination. Times and bead sizes were recorded for each of the following steps in the fusion process:

1. Time to get indication of melt bead and soak time;

2. Bead size per side at the time of heater removal;

3. Total bead size after fusion (visual exam), and

4. Cooling time under pressure. The fused samples were cooled under pressure until cool to the touch, then allowed additional cooling time before being cut into specimens for destructive testing. Four test specimens approximately 9 inches long and 1 inch wide--were cut from each sample at opposite quadrants. Each specimen was then tested according to the manufacturer's destructive test procedures, in accordance with ASTM D2513.

A total of 16 fused samples were evaluated with 100% positive results.

Squeeze-off Test:

Squeezers were used to test the squeeze-off ability of the pipe in accordance with ASTM F1563. The pipe was squeezed off under pressure (60 psig) using NMGC's squeeze-off procedure for periods of 4 and 24 hours. After the 4- and 24-hour tests, the pipe was released and allowed time to return to its original shape. After 48 hours, from both the 4- and 24-hour tests, the pipe returned to 90% of its original shape. Next, the squeeze area was cut in half to examine the internal walls. The squeeze-off test results were 100% acceptable.

Material Testing Of Bimodal PE 4710 Fittings

Fusion Test:

Tests were conducted on 2- and 4-inch SDR 11 elbows, 3-way tees, and caps grouped into the following categories:

--Like materials, PE 4710 to PE 4710 fused with NMGC's fusion procedure;

--Unlike materials, PE 3408 to PE 4710 fused with NMGC's fusion procedure;

--Like materials, PE 4710 to PE 4710 fused with PPI's generic butt fusion procedure (TR-33/2005), and

--Unlike materials, PE 3408 to PE 4710 fused with PPI's generic butt fusion procedure.

[ILLUSTRATION OMITTED]

All fusion samples were tested in accordance with the manufacturer's testing procedures, using visual and destructive testing. Fittings were tested with all PE 3408 polyethylene pipe NMGC had installed over the years.

Three joints were made of each pipe/ fusion procedure combination. Times and bead sizes were recorded for each of the following steps in the fusion process:

1. Time to get indication of melt bead and soak time;

2. Bead size per side at the time of heater removal;

3. Total bead size after fusion (visual exam), and

4. Cooling time under pressure.

Two-and 4-inch manifolds were built using the sample fittings and cooled under pressure until cool to the touch. The samples were then allowed additional cooling time before being pressurized to 95 psi (0.66 MPa) and Igepal soap-tested. No leaks were found. Next, the sample fittings were cut into test specimens for destructive testing.

Four test specimens--approximately 9 inches long and 1 inch wide--were cut from each sample at opposite quadrants--some of the specimens were shorter because of fitting size. Each specimen was then tested according to the manufacturer's destructive test procedures.

A total of 24 fusion samples were evaluated. The results were 100% positive.

Material Testing Of Bimodal PE 4710 Service Tees Fusion Test:

Tests were conducted on 2-, 4-, and 6-inch SDR 11 ; and concave and convex service tees made from bimodal PE 4710 and fused with:

--NMGC's fusion procedure, and

--PPI's generic butt fusion proce dure (TR-33/2005).

All fusion samples were tested in accordance with the manufacturer's testing procedures, using visual, destructive, and hammer tests. Each service tee was fused to a manifold pressurized to 60 psig and tapped under pressure with the results recorded on a data logger. Times and bead sizes were also recorded for each of the following steps in the fusion process:

1. Time to get indication of melt bead and soak time;

2. Bead size per side at the time of heater removal;

3. Total bead size after fusion (visual exam), and

4. Cooling time under pressure.

The fused samples were cooled under pressure until cool to the touch, then allowed additional time to cool before being cut into specimens for destructive testing. Three test specimens--approximately 9 inches long and 1 inch wide--were cut from each sample at opposite quadrants. Each specimen was then tested according to the manufacturer's destructive test procedures.

A total of 24 fusion samples were evaluated. The results were 100% positive.

Field Testing Of Bimodal PE 4710 Pipe

In addition to extensive laboratory testing, the bimodal PE 4710 pipe was field-tested for scratch resistance by tying samples to the back of a truck and dragging them on asphalt and in gravel. To evaluate toughness, a sample was run over six times by a 3-ton pickup truck. The pipe was then removed and evaluated by sustained pressure tests in accordance with ASTM D2513. All bimodal PE 4710 pipe samples tested passed the field test with no resulting leaks.

Results And Conclusion

Based on the extremely positive results of the evaluation, NMGC began field installation of bimodal PE 4710 gas pipe in December 2005. To date, a total of 1,200 miles of PE 4710 pipe has been installed across New Mexico's challenging terrain, in urban and rural locations, including 224,741 feet of replacement pipe in 2008 alone. The installed pipes range from 1/2-inch CTS to 6-inch IPS and 7 to 11 SDR.

Serrano de Rivera offered an overview of the study's results. "After more than six years of impressive experience with PE 4710 pipe used in the extreme conditions of New Mexico without incident, New Mexico Gas Co. is pleased to report that bimodal pipe is proving to be an enduring solution and is the only plastic pipe approved to be used in New Mexico Gas Co.'s gas system."

[ILLUSTRATION OMITTED]

PPI is the major trade association representing all segments of the plastic pipe industry. For more information visit www.plasticpipe.org.
COPYRIGHT 2013 Oildom Publishing Company of Texas, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Comment:New Mexico gas study of PE 4710 resin leads to increased use of HDPE pipe.
Publication:Pipeline & Gas Journal
Geographic Code:1U8NM
Date:May 1, 2013
Words:1709
Previous Article:Arctic Fox LLC.
Next Article:Oliver C. Klinger III, publisher of Pipeline & Gas Journal, announced the addition of two new editors and the promotion of a third.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters |