T.D. Williamson explores the safety procedures during a squeeze off, the most common way to isolate polyethylene pipes.
Risk is an everyday part of life for pipeline operators, and controlling risk is a full-time job.
Consider how this might play out during a squeeze off, a common way to isolate polyethylene (PE) pipes.
Squeezing involves using hydraulics or mechanical tools to compress the pipe between two parallel, rounded bars.
The process has been applied safely in gas distribution networks for decades, but there’s a caveat – the technician must be careful to follow the prescribed procedure.
Any deviation can negatively affect pipeline integrity, people and the environment.
The importance of proper procedure
T.D. Williamson (TDW) engineers performed various squeeze offs on 4-inch medium-density polyethylene (MDPE) pipe and evaluated the impact on the pipe using microscopy.
The test began with an ASTM F1041-compliant squeeze. Before squeezing, the pipe had very smooth inner and outer walls and no visible deformities.
The wall thickness, roughly 10.8mm, was fairly consistent throughout. Consistent pipe wall thickness is critical to the structural integrity of the pipeline. Any significant decrease in wall thickness could constitute a weakness in the pressure properties and shorten the life of the pipeline.
After the ASTM F1041-compliant squeeze, there was a small amount of deformation on the inner wall as an approximately 3.7 per cent decrease in wall thickness, from about 10.8mm to 10.4mm. There was nothing to suggest the pipe suffered significant damage.
Next, TDW performed a non-compliant procedure on a different piece of the same type of pipe. Engineers squeezed and released the pipe twice as fast as prescribed.
This time, the results were very different from the first test.
There was significant plastic deformation on the inner wall of the pipe as well as a 3.8cm-long crack on the outer wall. The crack was approximately 1mm deep, or about 8.5 per cent of the total wall thickness.
In addition, the pipe’s wall thickness had decreased about 11 per cent, from close to 10.8mm to 9.6 mm.
This test confirmed that following the proper squeezing procedure is critical to the safety, integrity and life of the pipeline.
Engineered solutions
The squeezing procedure is somewhat tedious and requires diligence to execute properly. It can be easy to unknowingly deviate from the proper procedure.
For operators looking to further eliminate or reduce the risk associated with relying on human behaviours, there is another option: using an engineered physical solution.
According to TDW Senior Director Hot Tapping and Plugging (HT&P) Product Line, Ed Guidry, it’s generally better to apply a physical change or engineering control to a product than to simply assume that workers will follow a procedure.
“As a service provider and original equipment manufacturer, our goal is always to eliminate or reduce risk whenever possible, and local distribution companies are no different,” Guidry said.
“When we have the opportunity to move further up the strength of defences risk model TDW uses and reduce risk by adding engineering controls, we absolutely want to do that.”
Using an engineered solution doesn’t eliminate the need for proper procedures. In this case, the pipe must be prepared before the fitting can be successfully fused onto it. Preparation includes peeling or scraping the pipe with an approved tool to remove any oxidation on its outer most layers.
Thorough preparation should not be ignored; if the pipe is not peeled before fusion, it is usually because the operator has made an intentional decision to skip this step.
A suitable replacement for line squeezing
To allow an operator to perform PE isolation and branching activities through a fitting easily and safely, TDW developed the POLYSTOPP® Quick Connect system.
It incorporates multiple engineered safety features to keep the technician from using the equipment incorrectly.
For example, the tapping machine is designed with a positive stop that makes it impossible for the technician to accidentally tap through the bottom of the pipe.
In addition, redundant safety rings and locking collars prevent pipeline damage or personal injury should the technician deviate from the proper operating procedure.
As effective as the POLYSTOPP Quick Connect system is, Guidry said that, in the end, the primary concern should be the fitting.
“Since risk is all around us, safety and quality are our primary mandates,” Guidry said.
“By performing isolations with engineered solutions like the POLYSTOPP Quick Connect system, our customers can be assured that they will meet safety requirements and, more importantly, eliminate the risk of pipe damage and offer their teams the security of a truly safe work environment.”
For more information, visit the website.
This feature also appears in the September edition of The Australian Pipeliner.