Rapid Crack Propagation (RCP): What Does It Mean for PE Gas Pipeline?

Although the PHMSA has noted pipeline safety has improved in recent years, corrosion continues to be a major contributor to pipeline failures, according to the administration. Corrosion could lead to dangerous explosions and fires.

When natural gas pipelines exhibit weaknesses, the pipes may be more prone to corrosion, according to the American Gas Association. Companies may want to be on the lookout for rapid crack propagation (RCP), or when a brittle crack in a material grows and results in fractures, as one of the red flags for pipeline failure, Pipeline and Gas Journal said.

Since the risk of RCP is high for metal pipes, pipeline and utility companies are increasingly choosing durable polyethylene (PE) pipes for upstream and midstream systems.

Rapid Crack Propagation: What Does It Mean for PE Gas Pipeline? The risk of rapid crack propagation (RCP) is high for metal pipes. Durable polyethylene (PE) pipes may be a solution for upstream and midstream systems.

The risk of rapid crack propagation (RCP) is high for metal pipes. Durable polyethylene (PE) pipes may be a solution for upstream and midstream systems.

Why Pipeline Operators Are Choosing PE Pipe

According to Alliance for PE Pipe, PE pipe is not only durable, but it's also flexible. The properties of PE pipe allow this material to withstand corrosion and chemicals while underground.

Since plastic pipes can endure corrosion better than metal, PE is often used for natural gas pipelines because the process used to make PE pipe makes it less prone to leaks.

Utilities could choose PE piping systems when overhauling underground infrastructure, which may protect them from corroded pipes and joints that could lead to leaks, according to the Plastics Pipe Institute (PPI).

"PE pipes, as well as the heat fusion joints in PE piping, greatly resist the propagation of an initial small failure into a large crack—a major reason for the overwhelming preference for PE piping for gas distribution applications," the report by the PPI said. "And, PE piping retains its toughness even at lower temperatures. In addition, PE piping exhibits very high fatigue resistance. Potential damage by repetitive variations inoperating pressure (surges) is highly resisted."

Factors That Raise Risk of RCP

Pipeline and Gas Journal outlined numerous factors that may contribute to the risk for RCP cracks.

One risk is the size of the pipe; the pipe's diameter may influence cracking. The publication notes that as the diameter of the pipe grows, the risk for RCP also increases.

Another factor is the operating temperature of the pipe. Pipeline operators may want to make sure pipes are protected from lower temperatures because frigid conditions could cause RCP.

Pressure is also a significant factor because a pipeline pressure pulse may contribute to RCP. Companies may want to be aware that there is a higher chance of RCP when the stress in the pipe wall rises. In the event RCP occurs, the consequent pressure waves may result in fragmentation, causing pieces to travel at a high velocity and distance.

What to Look for in RCP

When replacing their existing pipeline and underground infrastructure, pipeline operators may want to look out for warning signs that indicate RCP cracks. Although PE pipelines are more durable against such cracks, they also can appear in this type of material.

According to Pipeline and Gas Journal, an RCP crack is usually presented by a sinusoidal crack within the pipe. Other signs of an RCP crack include the crack going into two directions and butt fusion joints, or when cracks are arrested by electrofusion couplers.

As companies determine what is the best pipeline material for their transmission and distribution operations, they should look into PE pipes for their strength and ability to withstand several factors that could lead to RCP.

Although PE is still vulnerable to RCP, there are a variety of ways pipeline operators can prevent these cracks in PE pipes. If operators choose PE pipeline, they should test the pipe for the amount of pressure it can endure to make sure they limit the chance of RCP.

Reference :  http://solutions.borderstates.com/rapid-crack-propagation-rcp-what-does-it-mean-for-pe-gas-pipeline