|Launcher valve removed while system remains pressurised. (Photo courtesty of STATS Group)|
STATS Group were recently retained by a major operator in Australia to provide isolation of a pressurised 10” LPG natural gas pipeline at a plant in Victoria. The isolation was required to allow a launcher valve to be safely replaced while the system remained live and at an operating pressure of 41 bar.
It was the first time the pipeline technology specialist has deployed their hot tap installed ANSI Class 600 BISEP™ on an Australian project. The BISEP™ provides a fail-safe, fully proven double block and bleed (DBB) isolation and was deployed through a welded split tee fitting, without the need for additional hot taps to bleed or vent.
The BISEP™ isolation is provided by a spherical dual seal plug, deployed from a pressure competent launcher through a slab valve and rotated towards the pressure threat. The spherical head houses twin compression seals and provides a facility to bleed the seal annulus (void), providing a zero-energy zone between the fully proven seals. The annulus bleed port is initially used to test each seal at 110% of the isolated pressure, it is then used to constantly monitor the isolation during the intervention work.
The elastomeric seals are activated by a hydraulic cylinder inside the plug, which compresses the seals. The resultant radial expansion pushes the seals out against the pipe bore. Venting the pressure downstream of the plug causes a piston effect on the plugging head, which acts to further energise the seals providing leak-tight isolation, even in corroded or pitted pipework. A differential pressure across the plug enhances the hydraulic actuation and maintains both seals, even with no hydraulic pressure present. This self-energisation feature makes the isolation fail-safe with dual redundancy in activation, providing the specified minimum differential pressure is maintained.
After performing validation tests on the BISEP™, STATS technicians confirmed successful double block isolation and an isolation certificate was issued to the client. Nitrogen was then flushed through the BISEP™ launcher to purge the system and create safe worksite conditions to allow removal of the launcher valve. Once the new valve had been fitted, nitrogen was again used to perform a joint re-instatement leak test of the newly installed valve against the back of the set BISEP™. A unique feature of the tool is the ability to withstand pressure in the reverse direction, which can make reinstatement of the isolated system easier when compared to traditional line stop systems.
After a successful leak test of the reinstated valve the pipeline pressure was equalised, the BISEP™ was then unset and recovered into its launcher. The slab valve was then closed, allowing the BISEP™ launcher to be depressurised and removed. The hot tap machine was then reinstalled to allow a completion plug to be deployed and set into the flange of the welded fitting. With the completion plug set and tested, the hot tap machine and slab valve were removed from the pipeline and a blind flange was installed onto the welded fitting.
STATS supplied personnel and equipment which included split tee fittings, hot tapping machine, DBB slab valve, BISEP™ and completion plugs. All hot tapping and line isolation work was carried out by STATS technicians. Upon client request, a System Integration Test was conducted at the Victoria facility prior to BISEP™ deployment onsite.
STATS Group has invested more than £3 million in developing a range of hot tapping machines. The SureTap™ propriety range comprises four models with cutting capacities ranging in size from 3” to 48”, to provide safe and reliable hot tapping operations on a range of pipeline materials and mediums up to 2220 psi/153 bar (ANSI Class 900). This latest investment underlines the group’s commitment to developing industry leading solutions and expanding its global reach.