FAIRBANKS, AK – June 20, 2000. Engineers at Alyeska Pipeline Service Company believe they have determined the cause of a shift in a section of above ground pipe near Atigun Pass.  The shift caused several parts of the assembly that anchors the pipe in place to move significantly and affected about a mile long length of the pipeline.  Engineers believe the pipeline movement occurred as a result of a pressure wave generated by the collapse of a vapor pocket in a low section of the pipe near mile post 170 during a pipeline restart on April 17^th.

The result of that vapor pocket collapse was discovered on May 15^th when an Alyeska crew conducting a routine ground reconnaissance discovered seven above ground anchor assembly’s had tripped allowing the pipe to move 21 inches.

“All of the safety mechanisms put in place to keep the pipeline from suffering severe damage worked exactly the way they were supposed to” says Alyeska Senior Vice President Bill Howitt.  Howitt says though the shift was dramatic and steel bolts were actually sheared off because of the extent of the force on the pipeline, “the support members behaved the way we designed them, they absorbed the impact and kept the pipe itself from suffering any damage”.

Crews from Fairbanks, Pump Station 4 and Pump Station 5 were mobilized to work on the problem immediately after it was discovered.  Temporary cribbing was put in place to maintain the pipe stability until the anchors were reset and the shoes those anchors sit on were returned to their correct position.  The repositioning of the pipe was completed on May 26^th.

Regular ground surveillance has been conducted on the affected area, the last being on February 26^th.  No abnormalities were discovered at that time.  Regular aerial surveillance apparently did not detect the condition.

Howitt says, “This incident taught us a lot.  We will modify our surveillance procedures by doing everything from lower altitude surveillance fly-overs to painting orange alignment stripes on the pipeline anchors to make sure the pipe is positioned where it is supposed to be.  We are also in the process of reviewing other pipeline locations where the presence of a vapor pocket could lead to a similar situation”.

“The good thing is we learned a lot from this incident, the great thing is the support system for the pipeline worked exactly like it was supposed to”.

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