Pipeline Integrity - Part 2
The How & What of Maintaining our Pipes

June 1, 2011

Corrosion (External/Internal)

Managing external corrosion through inspections and maintenance comprises over 50 per cent of TransCanada’s corrosion budget. Failures from internal corrosion represent approximately 25 per cent of all failures on TransCanada’s system. The good news is, as pipelines are inspected more often, corrosion is becoming less frequent.

“We began inspecting the Alberta System in 1975 after a failure resulting in a fatality occurred in 1974,” says David Chittick, Director, Pipeline Maintenance. “Those were the early days of inspection technology. We’ve come a long way since then.” That said, Chittick admits that in last decade, TransCanada has experienced a number of failures on previously inspected pipelines.

“We attribute those to the quality of inspections. In the early days it was low resolution, now we use high resolution, high-definition tools able to define the features in pipeline. The technology continues to improve.”

Inspections begin process and save maintenance costs

Since 1990 the majority of TransCanada’s larger diameter lines have been inspected as part of a risk mitigation process in the Pipeline Maintenance Programs.

“We inspect approximately 4,000 miles of pipe a year,” David explains. “The intervals can be as low as every three years up to 10 or 15 years, depending on the specifics of the pipeline. In some pipes the number of anomalies is so great we need to inspect them every three years.”

David adds that some pipes within the Alberta System are only 4 to 8 inch-diameter telescopic lines and cannot be inspected because they are too small to accommodate a launcher or receiver required for inspections for internal corrosion.

External corrosion can be assessed using above ground measurements to determine where examination can occur.

Inspection reports give the TransCanada Pipeline Integrity team the depth and length of a particular feature. Failure to comply with the acceptance criteria triggers an investigation and excavation.

Excavation when necessary

If it does comply the feature is allowed to grow forward within the assumed growth rate, which is calculated from multiple inspection data pads along system. That determines when the feature will be excavated.

“Frequently, we haven’t had the anticipated growth rate, so excavations weren’t required,” Chittick says. “This is important because the cost of excavations continues to climb, whereas the cost of inspections continue to drop. We strive to do fewer digs and more inspections.”

That said, TransCanada does between 200 and 300 excavations each year on the Canadian system. In 2010 in Peace River we excavated 91 times from the end of January to mid March.

Other tests and protection

By installing an electoral current against the pipeline, cathodic protection works as a defense against external corrosion.

To detect internal corrosion, TransCanada can use a hydro test, a complex process that involves injecting water into the pipe and pressurizing the system higher than what it would normally operate at.

Stress Corrosion Cracking

“Stress corrosion cracking (SCC) is the most challenging pipeline integrity issue we have,” says David Chittick, Director, Pipeline Integrity. “We don’t yet have luxury of inspection tools as we do with corrosion defect management where we are able to inspect, identify the feature and manage it.”

TransCanada has more than 4,6000 kilometres (2,500 miles) of pipe susceptible to SCC. Based on their knowledge of the pipe, soil, terrain and other factors that may lead to cracking, the Pipeline Integrity team develops models on which to base rigorous maintenance programs.

SCC testing

SCC is detected most effectively with a hydro test, which injects pressurized water into the pipeline. To date TransCanada has completed more than 400 hydro tests.

“This extensive and costly process is becoming increasingly more complicated to complete,” Chittick says. “It’s difficult to have access to water and to dispose of water, yet it’s the only reliable means we have to effectively manage the risk of SCC on the pipeline.”

He adds that TransCanada has been developing inline inspection tools since the 1980s. Tools to define cracks in liquid pipelines aren’t effective tools for gas pipelines as they aren’t able to identify a crack from a non-injurious feature like a lamination.

“We’re getting closer,” says Chittick. TransCanada has used an ultrasonic tool when hydro tests aren’t feasible on a couple of occasions on pipes in Alberta that have too much elevation change to do a hydro test. “It’s very complex and very costly and we don’t want to have to do it too often.” Chittick says.

EMAT

TransCanada partnered with respected inspection company Pipetronics in 1998 to develop the latest SCC inspection technology, Electro Magnetic Acoustic Translucers (EMAT). The tool is at the point where it can now be introduced to a controlled market.

“It’s taken 13 years to get to where we are with EMAT today,” Chittick says.  “We are now able to use it, and it’s looking effective, but it will take another 5 to 10 years for the process to truly be complete.”

Recoating

When pipelines on the Canada Mainline are susceptible to SCC, maintenance crews often recoat the pipeline to protect against cracking.

SCC History

TransCanada began the SCC management program in 1986 after the first SCC incident on the Canada Mainline the year before. A flurry of SCC failures in the early 1990s prompted the National Energy Board (NEB) Transportation Safety Board to launch an inquiry and incorporate SCC management practices in its guidelines. TransCanada adopted those practices and has since enhanced them.

Geotechnical threats

A common threat to pipeline integrity is unstable terrain, such as on a slope.

“We monitor the terrain and create sophisticated models of the interaction between the movement of the slope and pipe,” says David Chittick, Director, Pipeline Integrity. When strain relief is required the pipe is pulled out of position, exposed, allowed to spring back into shape and pulled back into place.

Streams and river crossings where high spring flows expose pipes to moving rocks and boulders also pose a challenge. To avoid this, pipes are frequently buried.

Mechanical-Third Party Damage

Events like unauthorized excavation on pipelines pose the deadliest threat. Fortunately, mechanical and third party damage incidents are not frequent. Yet this is an area where TransCanada continues to invest a great deal of time and resources.

 “We attempt to manage mechanical and third party damage through an integrated public awareness program with municipalities, contractors and other stakeholders,” comments David Chittick, Director, Pipeline Integrity. “We want to make sure people are aware of where the pipelines are and that they know to where to call to find out before they dig.”

TransCanada also uses inline inspections to look for dents and gouges due to third-party activity. Often to prevent an unauthorized excavation incident in an area where there is activity that could threaten the pipeline, maintenance crews simply place a cement slabs on top of the pipe to clearly mark the spot and protect the pipe.

Air patrols proactive

Aerial control over pipelines is an important component of limiting mechanical and third party damage.

“We’re not necessarily looking for someone in the act of doing something, we’re also looking for a third party who might have been there,” Chittick explains.

“We’re concerned about failures in the future. Often the pipeline won’t not rupture initially, but over time a gouge in the pipeline will lead to a crack and either a leak or a rupture.” He points to the 2004 incident in Belgium where 24 people died when a pipeline blew up five days later after it had been hit.

Construction & Manufacturing

Construction and manufacturing practices have improved considerably since the early days of the pipeline industry when failures were often attributed to low standards.  

“Today we have high quality seals and rigorous quality management systems,” says David Chittick, Director, Pipeline Integrity. “At TransCanada we have many stringent procurement practices for pipe and all of our manufactured products.”

 

 

Further Information