Creating solutions in collaboration Annual report 2013

Asset management 

Pipe fracture in the seabed

27 June 2013Research

To supply the island of Texel with water, water company PWN uses two sag pipes: water pipes that are buried in the seabed. In June 2013 a break occurs in one of the sag pipes. The inhabitants of Texel are immediately informed, but noticed no, or practically no, change in its water provision: the drinking water suply continues.

“The infrastructure is designed in such a way that each part can be missed”

On 27 June 2013, a break occurs in one of the sag pipes in the seabed between the mainland and Texel. The water continues to flow, so there’s no reason for panic. “That’s pretty good, eh?” says George Mesman, who leads the research into the cause of the fracture for KWR. “The infrastructure is designed in such a way that any part can fail and the water will go on flowing at a specific, minimum level. If a part fails, the consumer hardly notices any reduction in supply.”

High season

Ilse Dingerdis, team leader of Mains Management at PWN explains why this is: “Two pipes transport water to Texel. Normally, one pipe is sufficient to supply everyone on the island with water, even during the summer months of July and August, when the population quadruples because of the tourism. But on account of the persistent heat wave at the end of July, we decided not to run any risks: over a couple of days we shipped extra drinking water to the island in special tank trucks.” But the population hardly noticed a thing. “The drinking water provision was not endangered. We did however advise people to be a little more economical with their water and not to water their gardens,” says Dingerdis.

Cause

Abrasian of a pipe causes a fracture

Abrasian of a pipe causes a fracture

PWN of course wants to know what mechanisms led to the fracture, to avoid a repetition in the future. Mesman works with Paul Wesselius of PWN to find the answer. In mid September they complete their investigation. On 1 November the pipe is back in operation. Mesman explains the fracture’s cause: “Very occasionally it happens that part of the sag pipe becomes exposed. Because the polyethylene of the pipe and the fresh water are lighter than seawater, that part of the pipe floats slightly above the seabed. The ebb and flow movement of the tide then sometimes causes the underside of the pipe to rub against the ground leading to the pipe’s abrasion. The pipe fractured on its underside.”

Technical challenge

Dingerdis is very pleased with the investigation. “We now know a lot more. The location where the fracture occurred is very dynamic: the influence of the tides there is significant. Over the course of a couple of years, the bottom can descend by 3 to 4 meters. We’ve increased the frequency of our inspections of both sag pipes from once every six months to once every quarter.” In the situation as it now stands, the event could therefore reoccur. But PWN will not leave it at that. “We’re busy working on a permanent solution,” says Dingerdis. “Our preference is to bore a pipe underground. It would be the first time that such a long pipe, 4.6 km, would be bored in the Netherlands. It certainly presents a technical challenge!”

© 2017 KWR Watercycle Research Institute

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