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Providing coverage of Alaska and northern Canada's oil and gas industry
August 2006

Vol. 11, No. 35 Week of August 27, 2006

SPCO reports on North Slope pipelines

Annual report shows Alaska North Slope common carrier oil pipelines have some corrosion but are generally in good shape

By Alan Bailey

Petroleum News

On Aug. 16 the Alaska State Pipeline Coordinator’s Office published its annual report on its surveillance between July 1, 2005, and June 30, 2006, of Alaska common carrier pipelines (other than the trans-Alaska pipeline). On Aug. 4 the agency notified BP of the results of a June 1 surveillance of BP’s monitoring and surveillance program for the company’s North Slope common carrier oil lines — that report showed BP’s surveillance and monitoring to be satisfactory.

State-regulated common carrier lines cross state rights of way and, as oil transportation systems, have to be available for use by anyone who needs to use them. SPCO, an agency within the Alaska Department of Natural Resources, administers the state’s pipeline right-of-way leases. Lease administration includes surveillance of the safe operation of the common carrier pipelines.

SPCO does not oversee field gathering lines, such as the Prudhoe Bay transit lines where BP has found severe corrosion problems. Field gathering lines are considered to be part of an oilfield infrastructure, rather than a common carrier oil transportation system, and typically lie within the boundaries of an oil and gas lease or unit.

On the North Slope ConocoPhillips subsidiaries operate the Alpine and Kuparuk common carrier oil lines. BP subsidiaries operate the Badami, Endicott, Milne Point and Northstar common carrier oil lines.

Focus on corrosion

In surveillance visits to the pipelines since June 2005 SPCO’s compliance oversight team has particularly focused on corrosion issues and has reviewed the pipeline operators’ corrosion monitoring and prevention procedures. The team observed several aspects of pipeline corrosion monitoring, including the operation of smart pigs and the assessment of corrosion coupons. A smart pig is a device that passes down the inside of a pipeline and carries instruments to measure certain characteristics of the pipeline wall. A corrosion coupon is a small piece of metal placed in the pipeline fluid flow to assess the rate of internal pipeline corrosion.

All of the pipeline operators have run smart pigs through their lines in the past three years and all use ultrasonic testing, a technique that is similar to a medical sonogram and that enables the internal condition of a pipeline to be assessed from the outside. Other testing techniques include radiographic testing and magnetic flux leakage. Operators also conduct regular ground and aerial inspections of the external conditions of the pipelines. Each pipeline has a leak detection system that compares the volume of fluids entering the pipeline with the volume of fluids delivered from the pipeline — a mismatch in the volumes can indicate a leak.

The recent problems at Prudhoe Bay have raised particular concerns about the older components of the North Slope infrastructure. Of the common carrier oil pipelines, the Kuparuk, Endicott and Milne Point lines date back to relatively early North Slope development. The Badami, Northstar and Alpine lines are more modern.

The Kuparuk pipeline went into operation in 1981 and carries oil from the Kuparuk River field and neighboring fields to the trans-Alaska pipeline. Only certain portions of the pipeline can accept a pig and ConocoPhillips cleans these portions monthly with a maintenance pig. The company also runs a smart pig through the same portions of the line every three years, the last run being done in June 2003. The company uses a photographic technique called tangential radiography to test unpiggable sections of the line, as well as using techniques such as ultrasonic testing and corrosion coupons.

As part of its aerial surveillance ConocoPhillips also uses an infrared detector to check for leaks on the line.

The most significant corrosion issue on the Kuparuk pipeline appears to be external corrosion, especially at weld packs where water can seep into the pipeline insulation. ConocoPhillips monitors this corrosion using tangential radiography. And, although there is some internal corrosion in the pipeline, corrosion coupon testing suggests that the corrosion rate is quite low.

The Endicott pipeline, built in 1987, carries oil from the Endicott field to the trans-Alaska pipeline. It is possible to run pigs through the entire length of the pipeline and BP last ran a smart pig through the line in the fall of 2005. The pig run discovered some metal-loss anomalies but BP has stated that “… no features were reported that would compromise safe pipeline operation.” In summer 2006 the company is conducting field verification of the data from the smart pig, and will schedule any necessary repairs. “Pigging in 2005 indicated mostly external corrosion-related anomalies,” the SPCO annual report said.

Increased corrosion in Milne Point

The Milne Point pipeline was built in 1984-85 to transport oil from the Milne Point field to the Kuparuk pipeline, for delivery through the Kuparuk pipeline to the trans-Alaska pipeline. As with the Endicott line, pigs can be run through the entire length of the line and BP ran a smart pig through the line in the fall of 2005. The smart pig data indicates that the 10 most significant pipeline corrosion defects are external. However, the pig data also appears to indicate an accelerated rate of internal corrosion since the previous smart pig run four years earlier.

“Four years prior, the pipeline was said to have had only one internal anomaly identified. Now there are well over a thousand identified and, of these, 144 were identified as being in the 40 percent to 50 percent and 50 to 60 percent depth range,” the compliance oversight team leader reported, following a review of the smart pig data. “We were told that the oil producing formation is similar to the one that has contributed to problems with the GC-2 pipeline.”

The major Prudhoe Bay oil spill in March resulted from a corrosion-related leak in the Gathering Center 2 transit line and BP has theorized that solids from viscous oil production had absorbed some corrosion inhibitor that would otherwise have provided some protection to that line. In its report on the June 1 SPCO surveillance of the BP Milne Point pipeline monitoring program, the SPCO team said “we were told that some flour sand is being contributed to the system in a similar fashion (to GC-2). They have increased the (pigging) frequency to quarterly pigging for cleaning purposes.”

The newer Badami pipeline came on line in 1998, to transport oil from the Badami field to the Endicott pipeline for transportation to the trans-Alaska pipeline. Production from Badami was suspended in 1999 because of reservoir problems at the field. The field came back on stream in September 2005. The entire pipeline is piggable and BP ran a smart pig through the line in 2003. Prior to restarting the line in 2005 the company conducted field verification of the 2003 smart pig data and determined that none of the corrosion features found by the pig run threatened safe pipeline operations.

In September 2005 the SPCO compliance team conducted a field surveillance of the Badami and Endicott pipelines, in part to observe the Badami restart. And, as part of the June 1, 2006, SPCO surveillance of BP pipeline monitoring, the compliance team leader inspected data from the Badami smart pig run. The data indicated some internal corrosion-related metal loss anomalies in the pipeline but the compliance team signed-off BP’s corrosion monitoring program as satisfactory.

Alpine shows no significant corrosion

The Alpine oil pipeline has been operating since November 2000 and connects the Alpine field to the Kuparuk pipeline for transportation of the Alpine oil to the trans-Alaska pipeline. ConocoPhillips cleans the pipeline monthly using a utility pig and uses smart pigs to detect corrosion and pipeline integrity problems — the last smart pig run occurred in June 2005. During regular aerial pipeline inspections an infrared detector scans for pipeline leaks. The SPCO report does not indicate any significant corrosion problems in the Alpine oil pipeline.

The Northstar oil pipeline, connecting the Northstar field on Seal Island in the Beaufort Sea with the trans-Alaska pipeline, was built in 2000-01. The northern six-mile section of the 17-mile pipeline is buried in a trench in the floor of the Beaufort Sea. The pipeline wall of the subsea section is thicker than the wall of the on-land section. Additionally, “the Northstar oil pipeline is equipped with a sophisticated leak detection system capable of sensing hydrocarbons that could be emitted from a subsea leak,” the SPCO report says. The entire pipeline is piggable and BP last ran a smart pig through the line in 2003. The company plans another smart pig operation in the summer of 2006, the report says. BP is also trying to implement a new “guided wave” technology in the Northstar line, to detect defects such as corrosion related wall loss and cracks.

SPCO has not conducted surveillance on the Northstar oil pipeline in the period since Jan. 1, 2005. However, the compliance oversight team has reviewed BP’s surveillance reports on the pipeline. And, as part of the June 1, 2006, SPCO surveillance of BP pipeline monitoring, the SPCO team leader examined the 2003 smart pig data. This data indicates some metal loss anomalies but even the more significant of these anomalies were so small as to be barely within the detection limits of the pig instrumentation.

The SPCO annual report can be found at http://www.jpo.doi.gov/Publications/publications.htm.






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