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E Carson and Sons has secured the New Zealand agency for an internal pipe sealing system that allows leaks to be repaired quickly, without having to expose the pipe. BY MARY SEARLE
Actually, it doesn’t have to be any more, thanks to a revolutionary system that has recently become available in New Zealand. Wellington-based contracting firm E Carson and Sons has become the agent for Amex, an internal sealing system for accessible pipes. Director Eddie Carson says one of the company’s first projects using the system was to fix 40 joints in the 18 kilometre long, 1350 diameter sewer pipe in Eastbourne, Wellington, and to test a further 300 joints using Amex Seals. The traditional approach to this project would be to dig up the pipe and apply an external wrap to reseal the leaky joints – a huge job which would cause great inconvenience to locals through traffic disruptions as the pipe is along the only road in and out of Eastbourne. Instead, using the Amex system, the pipe was repaired internally, with no digging or disruption required – and in a much quicker timeframe too, each joint can be sealed in just 40 to 60 minutes. Amex seals can be installed in wet or dry conditions. The latest project involved installing Amex seals under the Waikato River to repair the main sewer outfall pipeline for Hamilton City.
The Amex internal sealing system comprises a PVC liner, a rubber seal and stainless steel retaining bands. It can be fitted to any pipe that a person can get in to, up to eight metres in diameter. An added advantage of the rubber seal is its flexibility, ideal in earthquake prone locations. In an elasticity test a pipe was deflected up to 3.7 degrees then repressurised and the Amex seal held. Installing the seal
Then stainless steel bands are put in position at the edges of the rubber seal. The diver, using a hydraulic jack, puts a little pressure on the band (20 bar) to hold it in place. He then checks that it is aligned in the groove on the rubber seal, using a small nylon hammer and a stainless steel drift pin to tap the steel ring into position. Once perfectly aligned, the pressure on the steel ring is jacked up to 250 bar. The diver then taps the band with his hammer so it conforms to any lumps and bumps in the pipe. He then jacks it up to 250 bar again and repeats the tapping and pressurising until the band no longer looses any pressure after tapping. A wedge is placed in the band and the hydraulic jack removed. Three or four hours later they’ll go back and retension the seals as there is a bit of give in the rubber. “We often have to replace the wedge – we’ll find a 100mm wedge will have to be replaced with a 106 or 108 mm wedge,” says Eddie.
Up until now, the German manufacturer would send its experts around the world to install the system, a somewhat ridiculous and expensive proposition when it comes to New Zealand. So instead, the Carsons was trained by the German experts install all the dry seals (where pipes can be drained) and Carsons has gone on to train eight divers from underwater construction firm, NZ Diving & Salvage, to undertake the submerged seal installation under its supervision. The divers on duty the day Contractor visited Hamilton were Rangi Walker and Mike Pascoe, their supervisor taking care of their safety was Glenn Hunter. Eddie Carson was on site to oversee the installation of the seals. Rangi was down the pipe when I arrived. Taking a seat in the control room I could see his every move on screen as he worked – his red gloved hands moving through the murky water, positioning the bands and wielding the hammer. Although divers with dredges had cleared 20 cubic metres of sand and sludge out of the pipe before Carsons started the project, the water is still murky, with visibility of between one and 1.5 metres. But that’s a vast improvement on the first dive, where visibility was just 50mm – the supervisor couldn’t see anything on the monitor – and each seal took three hours to install, but now, with a bit of practice and clearer water, the divers seal a joint in as little as 40 minutes. It’s not a career for the claustrophobic, swimming in the dark and murky waters of an outfall pipe. But if peace of mind is needed, the diver has four different air supplies – there’s the air compressor, plus two high pressure backups and the diver has a tank on his back for an absolute emergency if all the other lines get severed.
However, unlike other divers working underwater, Rangi doesn’t have to worry about his dive metrics (depth, time, air, etc), that’s Glenn’s responsibility. “His job is sealing the pipe,” says Glenn. “He’s my little robot.” Eddie keeps a close eye on Rangi’s progress too, ticking off each step of the job on a checklist. “It’s too easy to forget stuff underwater.” Joint 19 is the one Rangi’s working on and it has a nasty offset, making it difficult to fit the seal – on other joints the seal just seems to snap on. He has to put a shim – a very thin piece of stainless steel – under the joint to protect the rubber band from the joint’s sharp edges. After wrestling with it for some time, he finally gets it into place. The Hamilton job is only eight metres deep, so the work in this pipe is limited by diver fatigue, rather than diving issues. And after several hours underwater and underground Rangi finishes his shift and Mike dons his rig to head down the pipe for his turn. “It’s pretty straightforward,” says Mike. “The hardest part of the job is getting up the ladder at the end of a three-hour dive.”
Contractor Vol.34 No.6 July 2010 |
Fixing damaged and leaky underground pipes is a time consuming, messy and expensive project, right?
The team to do this involves a diver in the pipe doing the hard yards. He has a video camera on his head and is able to communicate with onshore staff each step of the way. In the control room, monitoring the diver’s depth, time and air, is the dive supervisor. There is also a second diver in the pipe, positioned near the entry point, looking after the various cables going to the diver installing the seals.
Inside the pipe, the first step is cleaning to get rid of any detritus. The diver then puts up the PVC liner, which is there to protect the seal against sharp edges. Next, the rubber seal goes on – this is capable of sealing up to water main pressure (20 bar). Made of EPDM rubber, the seal has ridges on its outside edges to improve its watertightness. The standard width is 240mm, but seals are also available in 360mm and up to 500mm for repairing cracks (although the pipe must be structurally sound).
Carsons invited Contractor to a Hamilton City Council project to see the new system being installed on a 1500mm diameter sewer outfall. On this particular stretch of pipe, all 31 joints on its 120 metre length needed repairing.
There’s the second diver in the pipe too, taking care of all the cables, and, in case of an emergency, there is a standby diver on shore, dressed and ready to go in a full lifting harness if a rescue is needed.