Onshore pig trap valve replaced at operating pressure using tetherless intelligent pressure isolation plugs.
Leaking pig trap valves present serious safety concern for pipeline operators who frequently use these systems to launch both standard and intelligent pigs. The potential for fire, pipeline content discharge or the overexposure of maintenance workers to pipeline contents demands the replacement of these valves to comply with industry safety standards.
Traditional maintenance procedures often require a hole to be cut into the pipeline wall for stopple isolation installation, or the entire pipeline system to be depressurized and taken out of service to facilitate these changes. In comparison, the use of tetherless intelligent pressure isolation plugs (e.g. The PSI SmartPlug[TM]) has been proven to be a cost-effective method of completing valve maintenance projects by minimizing pipeline downtime while not affecting pipeline integrity.
Approximately 85% of all pipeline repair projects completed around the world using intelligent pressure isolation plugs have involved the repair or replacement of leaking pig trap valves. The most economical use of this system onshore, when comparing its value with alternative methods, is to isolate multiple locations with the same plug.
The primary advantage of using intelligent pressure isolation plugs as a method of pipeline pressure isolation is the ability to minimize pipeline downtime. The following advantages of this system have also resulted in project savings:
* No hole or future leak path is left at the isolation location by eliminating the need to hot tap and stopple (non-evasive).
* Greatly reduces or eliminates the flaring of gas.
* Transmission and production continues during pipeline repairs.
* Eliminates the need to displace pipeline contents or conduct pipeline purges.
* Reduces the time and cost to de-commission (bleed down) and re-commission (refill and re-pressurize) pipelines.
* Reduces the disposal of hydrates, chemicals and contaminated hydro-test water.
* Isolates multiple sections of pipeline anywhere in the pipeline system.
* Minimizes refinery, chemical plant, gas processing facility, and storage terminal outage due to pipeline downtime.
The same project savings realized by many of the world's largest oil and gas production companies can also he found in the onshore applications listed below.
Pig Trap Valve Replacement Or Trap Reconfiguration
The use of intelligent pressure isolation plugs for live pipeline pig trap valve replacement and pig trap reconfiguration are the most cost-effective applications for these tools because the entire trap and isolation valve can be removed and replaced without transmission interruption. Pig trap reconfiguration is typically required because of the need to launch and receive intelligent tools that are longer than the original trap was designed to accommodate.
The standard method of using intelligent pressure isolation plugs for this application involves several simple steps. The first step is to purge the pig trap using nitrogen or water. A temporary reduction in pipeline pressure may be required if the valve only leaks at high pressures.
The intelligent plug is then launched using either water, nitrogen or pipeline product until it reaches the desired location. The isolation plug is then activated as described below and self-locked into position by differential pipeline pressure.
The pig trap is then depressurized and construction can begin once the integrity of the isolation plug seal is verified. Verification is via the onboard pressure gauges with real time data transmitted through the pipe wall and pressure gauges on the pig trap.
Navigable Water Isolation (lakes, rivers). Intelligent pressure isolation plugs can be used to isolate directionally drilled pipelines or pipelines that are laid across navigable waterways. Applications include crossing isolation valve installation, valve replacement, or tying in new replacement crossings. Two intelligent isolation plugs can be pigged into position with a batch of water between them to flush and flood the submerged pipeline in preparation for cutting, and to prevent the pipeline from floating.
Installing valves at navigable waterway crossings enables the crossing to be quickly isolated and avoids the accidental discharge of petrochemical liquids into inland or coastal waters in the event of a pipeline rupture. These plugs significantly reduce the amount of pipeline downtime by isolating only the new valve location, thus avoiding the need to purge the entire pipeline system across the waterway or back to the nearest isolation valve.
Midline Valve Replacement or Installation. Intelligent pressure isolation plugs can be used to isolate multiple midline valves for replacement or repair and multiple midline locations for new valve installation. In most cases, construction can be completed without the need to reduce pipeline pressure. The availability of alternate product flow routes may also allow the entire pipeline system to continue product transmission during construction.
Two intelligent plug trains are pigged into position with nitrogen, water, or pipeline product between them. Both plugs are activated at the set location and the fluid or gas between them is drained or vented to allow construction to begin. Upon construction completion, the tools are unset and pigged to the next location or locations for additional isolations, or removed from the pipeline at the plug launch site or a downstream pig receiver.
General Midline Construction. The category of general midline construction contains the greatest number of applications for the use intelligent pressure isolation plugs. These applications include, but are not limited, to the isolation of midline pipeline sections to:
* Remove unwanted pipeline connections (tees, stopple fittings, illegal taps, etc).
* Cut out and replacement of anomalies found by inline inspection tools.
* Lower pipelines for depth of cover requirements in the area of new construction.
* Re-route pipelines to remove it from close proximity to buildings or houses.
* Remove ruptured or leaking pipeline sections.
The intelligent pressure isolation plug can be stopped on both sides of an isolation location and construction can begin within two to three hours of arriving. Additional advantages include not having to displace large volumes of pipeline contents or nitrogen purges just to work in one small location. Pre-tested pipeline segments can be welded in and x-rayed in order to quickly return the pipeline to service and reduce the time and cost of commissioning activities.
Midline Hydro-test and Leak Detection. Intelligent pressure isolation plugs can be used to isolate multiple midline sections of pipeline for hydro-testing while the pipeline system remains at operating pressure or full of pipeline product. The system enables the testing of shorter pipeline sections and reduces test water disposal cost. The intelligent plug system also eliminates the need to cut test headers and jumpers into the pipeline for test section isolation and water movement. Other hydro-test applications include but are not limited to:
1. Hydro-testing pipelines with large changes in elevation. Isolating sections of pipeline ensures that the entire system can be tested to the same test pressure and prevents over-pressuring sections at the lower elevations.
2. Hydro-testing offshore pipeline beach approaches. These areas are defined as high consequence area (HCA) because of their potential impact on the environment should a leak occur. An intelligent isolation can be pushed with water from the shore or by pipeline product from offshore with a slug of water and positioned as required for pressure testing.
3. Identifying leaking sections of pipelines during a hydro-test. This system will avoid the need to cut the pipeline into multiple sections or install multiple stopple fittings to identify the leaking section. The use of SF6 tracer gas or dye in hydro-test water in combination with the intelligent pressure isolation plugs will increase the speed of identifying the leak location.
Intelligent pressure isolation plugs can be used to abandon pipelines segments that are no longer required or pipelines that cross restricted above ground construction areas without taking the entire system out of service. A single plug train can be pigged to the intended end of the operating system and activated.
Once the isolation is certified, the pipeline can be cut and a valve added at the new termination point to facilitate the retrieval of the plug into a temporary receiver. The operating line can then be blinded for future construction.
Features of the Piggable Intelligent Isolation Plug. The tetherless intelligent pressure isolation plug train is bi-directionally piggable, typically through 1.5D bends, and can isolate any pipeline medium. The standard maximum differential isolation pressure is 200 bar (3,000 psi) for all pipeline diameters 10 inches and above.
A typical isolation plug train consists of two independent plug modules, each activated by the onboard micro-hydraulic activation system. Each plug module is independently capable of isolating the full pipeline pressure, thus providing a double-block isolation with 100% redundancy of all components and essential systems.
In some cases, one plug module is sufficient to isolate the pipeline pressure and contents for construction activities when comparing the features of the system to a standard hot-tap and stopple. Unlike stopples, intelligent pressure isolation plugs are leak free and isolate pipelines with a 0% leak tolerance.
The Actuation System
The actuation system includes a hydraulic reservoir, battery package, hydraulic pump, valves and valve controllers. The tool is positioned by stopping pipeline flow and immobilized the plug by the use of "slips," or threaded metal segments made from hardened steel.
The slips are activated by pressurizing the "set-side" of the internal hydraulic cylinder. This results in the piston moving from right to left, which forces the slips to slide up the bowl and expand radially.
The slips' surface is threaded to enable the slip teeth to penetrate the surface of the pipeline inner wall a few thousandths of a millimeter. Thus the tool is not dependent on surface friction to secure it in place. The slip penetration is well within API tolerance for new pipeline surface roughness.
Each plug module has one packer, made from a Viaton or Bunan elastomeric material. The packer is set by applying additional hydraulic pressure to the "set side" of the internal hydraulic cylinder. This compresses the packer between the pressure head and the bowl and causes the packer to expand radially to form a pressure seal with the ID of the pipeline.
Once a plug has been actuated, it is "self-locked" by the differential pipeline pressure across each plug module. Additional differential pressure across a plug module will only maintain or intensify its sealing and gripping ability. Once the plug is self locked by differential pressure, the internal hydraulics no longer are required to maintain the plug in the set position.
The intelligent isolation plug systems are failsafe with delta pressure across the plug modules. Even if all communication fails, the plug will continue to isolate the pipeline as long as there is a differential pressure across the plug modules.
The intelligent pressure isolation plugs are unset by equalizing pipeline pressure across the plug modules. An internal bypass valve within each plug module or re-pressurizing the "low pressure" side of the plug by use of an external pipeline pump can be utilized to equalize pipeline pressure. The pressure in the set side of the hydraulic cylinder is then vented by a command give to the communication system, and the unset side of the cylinder is pressurized, causing the piston to retract. This may be achieved by opening the bypass valve in the plug train or by applying pressure from an external source.
The tool can be unset and recovered without the communication system once the pipeline pressure is equalized. This forces the pressure head to relieve the set on the packer and the actuator flange to pull the slips off of the slip bowl ramp, thereby releasing the module. Each individual plug module is factory tested and receives a third-party certificate by DnV.
Pipeline Stress Analysis
Each isolation location is given a pre-job pipeline stress analysis to ensure that the plug will only apply safe levels of internal pipe wall stress at the intended isolation pressure. Should the analysis determine that an excess amount of pipeline stress would be induced by the intelligent pressure isolation plug, there are several options to ensure a safe installation with the system:
* Reduce pipeline pressure to an acceptable differential pressure.
* Install a temporary PSI external pipeline reinforcement clamp/sleeve (approximately 30 minutes to install).
* Identify a location that contains a sufficient grade of pipe to resist internal forces.
Because these forces are defined as temporary by applicable standards, much like the forces induced by stopple fittings, the use of reinforcement clamps has not been required, to date.
Control & Communication System
The control and communication system is divided into three sub-systems--the surface control center, external antenna, and onboard micro-hydraulic system. The control center allows the operator to send commands and display received data from the intelligent isolation plug train on a standard laptop computer monitor. The maximum communication distance between the antenna and the intelligent pressure isolation tool inside the pipeline is approximately 10 meters (30 feet). Therefore, no excavation is required for most isolation locations at typical burial depths.
Intelligent pressure isolation plugs are tracked and positioned using a proprietary electromagnetic pig tracking system that is integrated into the onboard communication system. This tracking system allows the operator to determine the location of the intelligent isolation plug with an accuracy of 5 cm (2 inches).
The same tracking system is available for use in standard pigs so that multiple pigs and isolation plugs can be tracked and each individually and uniquely identified as they are positioned in the intended isolation location.
Remotely controlled and operated intelligent pressure isolation plugs use field-proven technology and have been used worldwide by most major pipeline operators. It is a fail-safe device that dramatically reduces pipeline downtime and opens the way for the performance of pipeline maintenance and repairs in ways previously impossible.
Authors: Ralph Parrott is North American Sales Manager. He has more than 12 years of experience in the petrochemical and pipeline maintenance industries. He is a graduate of Purdue University and holds a B.S. degree in construction engineering and management.
Edd Tveit is Director of Business Acquisition. He is a founder of PSI and has more than 18 years of experience in the development and deployment of special pipeline equipment, pigs, and remotely operated pipeline plugs. He holds a B.Sc. degree in mechanical engineering
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|Comment:||Onshore pig trap valve replaced at operating pressure using tetherless intelligent pressure isolation plugs.|
|Author:||Parrott, Ralph; Tveit, Edd|
|Publication:||Pipeline & Gas Journal|
|Date:||Aug 1, 2005|
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