Flexible gas piping’s evolution, path to solutions

February 18, 2016 By    
Metallically shielded CSST (courtesy of Titeflex Corp.)

Metallically shielded CSST (Photo courtesy of Titeflex Corp.)

Flexible gas piping, often referred to as CSST for its base material composition of corrugated stainless steel tubing, has gone through significant product construction changes for the U.S. market.

Gas fitters have installed flexible gas piping systems in the U.S. for about the last 25 years. The flexible steel piping is sold in coils, typically 250 feet in length. Mechanical fittings are attached to the CSST wherever the CSST is cut to length, and they provide a pipe-thread interface back to system components such as gas valves or black iron pipe components. CSST is continuous in length and is installed similarly to pulling electrical cable, which results in significant labor savings and fitting joint reductions when compared to rigid black iron gas pipe installations.

Conventional yellow CSST

Challenges developed for the CSST industry in the 2000s with claims of damage to conventional yellow CSST resulting from lightning strikes to homes.

A class-action lawsuit related to enhanced warnings was brought and settled with the industry in 2005-06. As a result of the lawsuit, and by 2006, all CSST manufacturers had incorporated a direct bonding requirement for new installations of yellow CSST systems. Direct bonding of CSST to the electrical grounding system reduces the magnitude of electrical potential differences between bonded metallic systems. This leads to reduced chances for electrical arcing between bonded systems and an improved level of defense from indirect lightning activity.

Product construction advances

Most industries do not plan to deal with lightning damage claims to their products. But several CSST manufacturers have taken the challenge as an opportunity to make flexible gas piping systems that can withstand ever-increasing levels of lightning energy, which can find its way into homes.

Beyond installation safeguards, such as direct bonding, manufacturers have moved the challenge to one of product construction – the ability of a tubing jacket to withstand higher levels of electrical arcing energy.

The newer category of CSST products is termed protective-jacketed CSST. The design premise utilizes a jacket to protect the CSST underneath from electrical arcing to the pipe’s exterior. Protective jackets and protective jacket systems are conductive in nature – they seek to spread the electrical arc and dissipate the charge to prevent damage to the underlying CSST.

A further advancement to product construction involved the aircraft industry – and understanding how aircraft are designed to withstand direct lightning attachment. Lightning experts and laboratories that aid in testing and certifying aircraft components have contributed their expertise in this area.

The result was a metallically shielded flexible gas piping system, with the technology having been used in composite aircraft parts to prevent damage from direct lightning strikes. This protective jacket system is composed of three layers. The metallic shield is the workhorse when it comes to dissipating and mitigating unintended arcs to its surface. The shield is sandwiched between two layers of plastic jacketing, which also perform significant product functions. Additionally, the system design incorporates a metallic shield-to-fitting connection to establish electrical continuity throughout the piping system for optimal performance.

Responding to challenges

The U.S. flexible gas piping industry, some gas utilities and builders have gone through a challenging decade with CSST and lightning experiences. But the industry has responded, developing knowledge of lightning interactions with its products that few other construction products’ industries have ever considered.

From their experiences, CSST manufacturers have developed arc-protective jacketing systems and have even borrowed from the aircraft industry to ensure protection for gas piping systems in homes.

The same CSST product benefits that builders have always enjoyed still apply – scheduling improvements, gas fitting-joint reductions and design flexibility. Now, even greater reliability has been built into protective-jacketed CSST products with respect to lightning protection, a worthwhile approach for dealing with gas piping systems.

 

Mark Harris is in business development at Titeflex Corp. He can be reached at mharris@gastite.com or 615-325-1103.

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