Going super critical

July 1, 2016

Pipeline flushing is being given a breath of fresh supercritical CO2, thanks to technology developed by Denmark’s Ocean Team.

A SCCO2 unit from Ocean Team. Photo from Ocean Team.

Pipeline operators have been suffering from a problem – how to flush and clean systems incorporating several kilometers of small inner diameter pipeline.

According to Noria, an American authority on machinery lubrication and oil analysis, 80% of breakdowns in fluid systems are caused by contamination problems.

It’s a problem in subsea systems, which often contain umbilicals and controls lines up to 30km-long and with internal diameters less than 10mm and no efficient cleaning options currently exist, according to Denmark’s Ocean Team.

A break down in a fluid system, which could be a hydraulic control line, could have serious impacts. Ocean Team highlights that of eight different safety systems that failed during the Gulf of Mexico Macondo incident, two were most likely due to system contamination, which could even have been introduced into the system prior to installation.

Espen Kähler Amundsen, head of engineering at Ocean Team, says contamination in hydraulic lines also results in hydraulic fluid leaking into the environment during venting due to excess pipeline pressure.

Flushing the lines using conventional method (laminar flow) does not prove efficient witnessing a too high-pressure loss. The turbulent flow required to flush material out just drops out, so the fluid is cleaned but not the pipe system, says Ocean Team. To be able to maintain the pressure needed to fully clean the pipeline would mean having to handle pressure losses above 30,000psi, the firm says.

After receiving a number of enquiries post-Macondo, Ocean Team set to work on a solution. The firm has developed cleaning method, using CO2 in a liquid super critical state, which it thinks would also be useful for the nascent decommissioning industry.

The supercritical liquid state CO2 (SCCO2) is able to maintain a turbulent flow inside pipes as narrow as 1/4in in diameter and longer than 30km, says Ocean Team, degreasing and removing contaminated sludge as it goes. CO2 in a liquid and supercritical state has a viscosity 10X lower than water and a carrying capacity similar to oil, says Ocean Team.

After proof of concept, Ocean Team ran two tests on a 6.5km-long dual 1/4in outer diameter control-line with several third party supervisors from a major North Sea operator present.

Flushing through a 13km, 1/4in outer diameter control-line shows a pressure drop of only 150 bar at a Reynolds no. of 19000. Together with the separation effect inside the Ocean Team’s SCCO2 unit, the method reached a cleanness of NAS1638 Grade 3/AS4059 Class 3 (Normally, a new oil has a standard purity of AS 4059 Class 8-12, yet, a purity level of NAS 1638 Grade 6/AS4059 Class 6). The process removed all wax in the pipes, which had come from the manufacturing process, and it was performed in 24 hours.

In October last year, a Danish operator had Ocean Team work on a blocked wax inhibitor line, which was stopping a well producing on the Danish Continental Shelf. “Historically, the well would have to be changed,” Amundsen says. “The well-owner desired to avoid including huge costs when the company had tried to unblock the pipes for three months. The SCCO2 technology flushed a small hole in three days. The operator was saved a huge amount of money not changing the well.”

“In the last 4-5 months we have also done a lot of flushing of coils, mostly for tests, where we are going to build some SCCO2 plants for some costumers,” Amundsen says. “These costumers are some of the biggest within tube/pipe manufacturing for the on and offshore industries, also the medical and aerospace industry.”

Following the successful tests, a dedicated unit for commercial use is being built and the firm is in talks with an oil major about a subsea pilot project – sadly no names right now. This would be the first SCCO2 subsea project in the North Sea. “That can change everything,” Amundsen says. Ocean Team is also going to be carrying out tests at the facility of an umbilical tube manufacturer in August, Amundsen says.

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