Simon Bell, iNPIPE PRODUCTS, UK, describes the cassette arrangement, enabling multiple pigs to be loaded into a launching trap at any one time.
Pipeline cleaning is of paramount importance to maximise the lifetime of the hugely expensive pipeline asset, minimise maintenance and energy costs, and consequently ensure maximum commercial returns to the operator. Unfortunately, history tells us that the design of piping systems has not considered the need for regular pipeline cleaning. This means that there has been no consideration for seamlessly introducing pipeline cleaning tools known as pigs into the pipeline, without stopping or interrupting production flow through the pig launcher. Similarly, the receiver must be designed to accommodate the removed debris, together with the emerging cleaning tool. This design fault may be based upon the common misconception that the pipeline may not need cleaning, or that the design of launchers and receivers ‘appear to be simple pressure vessels’ that can be easily retrofitted if needed. Often, the planning, engineering and procurement of launchers and receivers is left to the last minute, or takes place years after production commences, with little thought of the function of the launchers/receivers over the lifetime of the pipeline system or the integration into the system.
There are lots of examples of ‘unpiggable pipelines’: pipelines designed and commissioned without any consideration for future cleaning or inspection. Once constructed, commissioned and supplied, their ongoing maintenance becomes the responsibility of others. Experience has proven that the majority of cleaning problems could have been easily avoided had the cleaning systems been considered and designed with the same care as the pipeline itself. In simplistic terms, the design of the launchers and receivers should be dictated by the pigging frequency and types of cleaning pigs to be used, together with the intelligent pigs needed for periodic inspection of metal loss/potential failure modes. It should also be considered that the type of cleaning tools may change over a 25 year lifetime, or more. For example, some pipelines in the UK were originally constructed with an expected 25 year operational lifetime but are now over 50 years old and still profitably operating. Throughout extended pipeline operation, the type of deposition and amount of deposition may vary greatly, as the reserve product and rate of flow changes. This may mean that different types of cleaning tools will also be required: a gas pipeline may initially use spheres, which may lead to bi-directional pigs and, finally, as flowrate diminishes, there may be a requirement for bespoke low flow pigs to be designed. The one constant requirement over the course of the evolving pipeline is the need to design a pig launcher that can handle, load and launch different cleaning tools quickly and efficiently, and then to receive these tools together with varying amounts of debris, with minimal disruption to production.
Undoubtedly the successful financial operation of the pipeline over the commercial lifetime expectation is wholly dependent on the efficiency and frequency of the cleaning regime, which includes pig handling, and launching and receiving the pipeline cleaning tools (pigs) that travel the pipeline for cleaning, pipeline inspection or stabilisation purposes. Entrusting the design of these vital systems to non-specialists, who often come with no practical, hands-on experience, armed only with a few proprietary catalogues, can be a short-sighted economy. This is particularly true as pipelines become larger, which can mean trying to remove hundreds of cubic metres of debris if not regularly cleaned.
Pig trap definitions
Pig launchers and receivers (often referred to as ‘traps’) can be referred to by many different names; some of which describe their nature and orientation, e.g. pig, scraper, vertical, inclined, declined, subsea or temporary.
Although the definitions are simple, in reality it is quite different, because a cleaning tool launcher or receiver is a pressure vessel that, when wrongly designed, badly manufactured, poorly maintained or incorrectly operated, can be the cause of operational problems. If the system design is not carefully considered and fool-proof to use, it may compromise the concept and simply not be used, which in itself will create a multitude of additional issues within the pipeline. Scale of size is also a significant variable in design, when it is considered that we are discussing launchers and receivers that accommodate tools from typically 2 - 120 in. in diameter and tools can vary in weight from a few kilos up to 8000 kg.
- A more detailed definition of a pig trap is a pressure vessel designed with the following features necessary for safe operation:
- Provides safe access to or from a pipeline.
- Provides a means by which this access can be safely closed between the surroundings and full pressure capability of the pipeline – major oversized barrel for easy tool insertion.
- Provides for the access to be opened, or closed, with speed, convenience and safety – rapid opening closure.
- Provides an internal holding or storage position in which the cleaning tool may rest until desired travel movement is achieved, or after travel is terminated.
- Provides a means of converting the cleaning tool from its free expanded state into its compressed travelling state – reducer from the major barrel through to the minor barrel/line pipe.
- Includes, or is associated with, the means of controlling flow, pressure and/or mechanical movement to give the cleaning tool a positive driving force into or out of the pipeline – valve system and kicker.
- Incorporates a properly engineered, safe and practical provision for connecting to the pipeline.
- Is properly supported in a way which will neither impose excessive strains on the pipeline nor will accept more force than it is safe or desirable from the pipeline and its associated systems.
Existing launchers and receivers are generally designed to accommodate the launching of an online inspection tool. Inspection tools are considerably longer than a standard cup or disc pig; consequently the main barrel of the pig launcher is able to accommodate multiple numbers of standard pigs if required. Typically, four pigs are used, but any number can be accommodated dependent upon..
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Read the article online at: https://www.worldpipelines.com/special-reports/20092023/successful-launching-and-receiving/
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