The construction team for the San Andreas Pipeline No. 2 Replacement Project in San Bruno employs different techniques for replacing the more than 90-year-old pipeline to minimize impacts to neighbors and communities.

One way is the simple dig a trench, cut the deteriorating pipeline out, replace it with a like section only newer and better. Another way, used to cross major roadways, is called “slip-lining,” where the old pipeline stays in place, but the crew inserts a new smaller diameter pipeline through it. And another difference: while the exteriors of the new pipelines in the trenches can be connected by welding on the exterior surfaces, the slip-lined pipeline joints need to be prepared and welded from the inside. That’s quite a feat given the crowded interior space. SFPUC Photographer Robin Scheswohl captured the process in pictures.

First crews dug a pit and then they dug a second one … on opposite sides of the road. They pushed and pulled a 42” pipe through a 54” pipeline from one side to the other. Then they welded the new, smaller section together for a seamless pipeline. The above shows the smaller pipe “slipped” into the larger one. The photo below shows the opposite end where the pipe pokes through. Note the fan to assure a supply of fresh air to those working inside of the pipe.

Here is how the two pipelines fit together: Shims guide the smaller one through and keep the pipes separated. Also one can see it is very close quarters inside this 42” diameter pipeline for this welder to link pipeline sections together.