It is capable of hot tapping, line plugging and pipe freezing, thus allowing pipeline repairs and modifications to be undertaken without disrupting operation.
Hot tapping and line plugging can facilitate a range of offshore maintenance and modification requirements to be undertaken on-line which, given the high cost of downtime, inevitably draws interest and attention among offshore operators for the value it represents.
Furmanite Australia General Manager Colin Bickerstaff explained that “Pipeline intervention procedures allow a section of line or plant to be isolated, whether to enable emergency or planned repair work to be carried out, a malfunctioning valve or other equipment to be changed out, instrumentation to be installed (from flow meters and sampling points to pig indicators or internal visual surveillance equipment) or to enable modifications involving tying in new branch connections or re-routing a line to be undertaken – all with no disruption to operation.”
Furmanite now offers pipeline intervention services onshore, offshore and subsea, at large diameters (to 72 inches), high pressures (over 100 bar), high temperatures (to 370°C) and on large scales requiring multiple simultaneous operations.
Most importantly, this enhanced capability now lies alongside services such as leak sealing, joint integrity, in-situ machining, maintenance of ancillary equipment such as valves, and SmartShim technology to protect conductors and caissons from fatigue damage, in an impressive portfolio of services and technologies geared to helping offshore oil and gas operators maximise asset uptime, from a single-source contractor.
“The ability to mobilise multi-skilled technicians able to provide a range of specialist on-line and in-situ services is often a key consideration when working offshore, facilitating valuable manning economies and time and cost efficiencies.
“The extension of our hot tapping and line plugging capabilities is a logical move and a potentially valuable one to operators,” said Mr Bickerstaff.
While the principle of these pipeline intervention services is not new and the techniques are well-proven, on-going development and improvements to the technologies and capabilities are seeing competence boundaries extend. Subsea hot tapping, for example, is an area of growing interest, particularly given the increasing move towards subsea processing.
On-line pipeline intervention
Hot tapping involves a welded or mechanical fitting which is installed on the pipeline together with an appropriately-rated full-bore valve. A manually, pneumatically or hydraulically operated drilling machine (depending on diameter size, and suitable where intrinsically safe equipment is required) is then used to remove a section of the existing pipe, using a pilot drill to break through the pipe wall.
The product content fills the void beneath the drill, and air is expelled through the drilling machine purge valve, which is then closed to retain the pressure. The drilling process continues to complete the cut, and the cutter and coupon (the disc produced by the process, which is retained by a positive retention device fitted to the cutter pilot drill) are withdrawn into the void above the valve.
Factors such as pipeline product type, temperature, line pressure, line and branch nominal size, wall thickness and operating conditions are all taken into account.
“The choice of cutters and pilots, machine and swarf clearance measures will be determined by material and size.
“While pressure and connection configuration will decide the adapter to be used, temperature affects the machine’s seals and whether cooling spools are needed, and product and chemical constituency will clearly impact in terms of corrosion, flammability, toxicity and so on and the measures that need to be taken accordingly,” Mr Bickerstaff added.
Line plugging operations also begin with a hot tap and temporary valve through which a mechanical plugging head is inserted into the line, rotated and locked into position. The line plugging head is fitted with a sealing element which is activated in the line under pressure, achieving a temporary seal and stopping pipeline flow or re-directing it through a by-pass.
Once the repair, alteration or relocation is complete, the plugging head and equipment is removed, a completion plug installed and locked into position, and a blind flange is installed on the hot tap connection to complete the seal. The process can be reversed and the hot tap connection re-used to repeat the line plugging operation in future if required.
Subsea challenges
A subsea pipeline intervention may create further challenges, Bickerstaff acknowledges “A number of factors make subsea hot tapping and line plugging more complex, from practical issues such as visibility (highly visible colours are used on the equipment to aid the divers), and use of hydraulic actuators for ease of installation, to consideration of external water pressure and the need to keep the pressure balanced across the machine.”
Furmanite IPSCO, has the capability to perform hot taps and line stops subsea, at depths to 300 m, with work undertaken to date including both single line stops and double line stops with bypass, typically to 24 inch lines at pressures to over 150 bar on high pressure natural gas and crude lines, generally working with ANSI 600 and 900 RTJ flanged configurations.
“Experience to date has included what is believed to be the world’s largest subsea double hot tap on a 36 inch main sour gas line at 150 m depth, through ANSI 900 ball valves.
“The project was completed in around eight hours from launch of equipment and fittings to hot tap completion, with no interruption of service. Similarly, the largest subsea line stop project undertaken by Furmanite IPSCO to date has been a double 20 inch line stop with 12 inch bypass on high pressure gas lines at over 200 m depth.”
He also highlighted one of the more unusual subsea hot tapping projects which involved multiple hot taps to float a submerged fuel storage cell in 650 feet of water. “The taps were made to float the unit, as well as balance the fuel cell on the way to the surface,” he explained.
Bespoke solutions could also be engineered if required. For example, Furmanite enabled one major operator to avoid lost production by installing six high pressure self-sealing hot tap tee-clamps over a 115 m length of a main crude oil pipeline on the seabed, while the line remained in operation. This allowed solvent injection to dissolve and release a flow restriction caused by a build-up of deposits which had been hindering production.
“Shutdown to carry out a repair would have been extremely costly with potentially days of lost production, but Furmanite was able to provide structural self-sealing (for simpler subsea installation) hot tap tees, designed for pressures of 170 barg and tested to 255 barg, that could be fitted by divers while production continued uninterrupted. With the clamp installed an interspace test was used to confirm seal integrity. A valve was then installed and a drilling machine adapted for subsea deployment used to drill into the pipeline. This enabled a connection to be made to allow the solvent to be injected into the line to dissolve and release the restriction.”
“With the combined strength of experience, equipment manufacturing and in-house design, plus the engineering expertise to develop bespoke solutions for specific applications that we now offer, we can provide offshore operators with a service and competence to rival any in the field,” said Mr Bickerstaff.