Backpressure Control System Back On-line

The backpressure control for Thompson Pass was brought back on-line Monday, February 21, 2000, after repairs were made to the system. The system was taken off-line on January 31 because a restriction in the piping or valves was causing a higher than normal backpressure. Investigation of the situation revealed that pieces of a pipeline cleaning pig, which had arrived at the Valdez Marine Terminal the day before, were in the system.

The backpressure control system was isolated, drained down, completely disassembled and inspected. Cleaning pig pieces were retrieved from the piping and valves. All missing pig pieces have been accounted for. Of the five backpressure control valves, two were undamaged, two incurred some damage and one was severely damaged. The system has been cleaned and bolted back in place and is currently operating on two valves. An incident investigation is underway.

Work will continue over the next several weeks to repair and reinstall one of the damaged valves, complete hydraulic upgrades, fine-tune the system and re-insulate the piping. The other two valves will be shipped to the manufacturer for repair. The backpressure control system was installed in 1997 to eliminate vibrations in the pipeline on the south slope of Thompson Pass. The vibrations experienced while the system is off-line do not create a risk to pipeline integrity. Residents of the neighborhood near the pipeline in this area were notified of the situation and kept informed of the repair schedule.

Crude Oil Storage Tank Flushing Practices Resumed

Alyeska Pipeline resumed the practice of tank flushing during crude loading from oil stored in tanks at the Valdez Marine Terminal this week. The tank flushing process mixes paraffin and other sediments back into the crude oil; the paraffin is a natural product that settles out of the crude oil as it cools in the tanks. To flush a tank, oil is drained down to a minimum level. Oil is then flowed into the tank at about 75,000 barrels per hour. After the tank is filled to approximately the 10-foot level, the crude oil is immediately transferred onto a tanker during the loading process. During the 45-minute tank filling process, the force of the inflowing oil helps to stir tank bottom sediments into the crude oil.

The tank flushing process was implemented in 1996 and has been used successfully as part of tank preparation prior to tank cleaning. It was temporarily suspended in 1998 when the Tanker Vapor Control System was brought online. At that time, the Tanker Vapor Control System could not manage the vapors from the flushing process with existing procedures. Procedural changes were made to the operation of the Tanker Vapor Control System during the latter part of 1999 to allow the tank flushing process to resume.

Tank bottom sediments are comprised of 98 percent organic material (paraffin, etc.) and water. Alyeska will continue the tank flushing process and monitor the tanks to determine if re-suspension operations have impacted sediment levels in tank bottoms. Tank sediments became a concern last year when it was discovered that sediment in at least one tank had clogged part of the tank’s fire suppression system.

U.S. Department of Transportation Conditionally Approves Alyeska’s Corrosion Control Management Plan

The U.S. Department of Transportation has conditionally approved Alyeska Pipeline Service Company’s Corrosion Control Management Plan. Formal approval is pending upon publication of the plan’s final procedures, due for release on April 1, 2000. The plan is designed to provide the highest level of corrosion protection and environmental safety on the Trans Alaska Pipeline System.

The Corrosion Control Management Plan consists of five parts. A Corrosion Data Management system includes a repository of data and helps support monitoring and maintenance decisions. Corrosion Protection Monitoring uses “coupons,” close interval survey and conventional test stations to assess the level of corrosion protection on TAPS. Action is taken if corrosion protection is not adequate according to established criteria. Integrated Monitoring combines pig data, corrosion protection data and maintenance history to help decision-making on additional corrosion protection including pipe refurbishment. Enhanced Cathodic Protection uses pig data and corrosion protection data in projections to determine the estimated future cost of maintenance. This helps determine where supplemental protection is economically justified. The Pipeline Integrity component uses corrosion pig data to find and repair any corrosion defect that could potentially impact the integrity of TAPS and acts as a safety net for other plan components.

Alyeska’s Corrosion Control Management Plan meets requirements of the U.S. Department of Transportation pipeline safety regulations. It has been recognized by the National Association of Corrosion Engineers and was featured in the November 1999 edition of its publication, Materials Performance.

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