Seamless tire hyperbaric pigs reduce inflation time in pipelines

Nov. 1, 1999
Offshore Greece, a complex diver-based maintenance program was just completed successfully by Stolt-Comex from the Seaway Discovery vessel.

Offshore Greece, a complex diver-based maintenance program was just completed successfully by Stolt-Comex from the Seaway Discovery vessel. It was simplified and facilitated by the use of specially-designed composite-bodied hyperbaric pigs, which were developed by International Pipeline Products (IPP) Ltd of Catterick, Yorkshire, UK.

Stolt-Comex had been contracted by Hellenic Petroleum to carry out maintenance on a 40-in. crude oil import line from a subsea pipeline and manifold (PLAM) about two miles from shore. The principal design parameters that IPP faced were ensuring 100% safety and reliability, ease of operation in a difficult environment, stability and sealing ability during the welding process, and the ability to successfully pig the line.

Seamless tires

By building its patented seamless tires into the pig, the company removed the need for any filling or venting operations, greatly reducing the subsea inflation time, and the number of critical, stressed components by 75%. In addition, the use of a buoyant core at the heart of the hyperbaric pig allowed a greatly reduced weight in water, thus improving its subsea handling characteristics. These two design developments alone significantly enhanced the integrity of the system and its fast, safe operation along with greatly reducing the cost of a difficult subsea maintenance job.

In order to complement these improve-ments, a new design, quarter-turn hyperbaric valve was incorporated into the product. Benefiting from CNC manufactured components, all of which are interchangeable, the operation of the new valve could not be simpler. The inflation tool is located in the tapered valve housing at the front of the hyperbaric, pushed forward and turned through 90°, opening the valve and engaging the locking mechanism. The pressure-balanced valve design prevents inadvertent opening due to external pressure, thereby removing the risk of over-inflation. The system employs a positive spring-loaded valve which provides positive location of the tool during inflation, thus preventing inadvertent dislodging. This is especially important in conditions of zero visibility.

Reducing downtime

Finally, the new design employs low-friction, long-life PTFE-based seals, all contributing to an advance in subsea servicing operations with enhanced safety. Historically, hyperbarics have been subject to lengthy inflation times and costly downtime for the operator. More importantly, diving operations have their own safety and cost criteria. The new system optimizes all of these - inflation time is less than one-tenth of that of a standard hyperbaric pig and the weight reduction is dramatic. A 16-in. hyperbaric pig weighs 3kg in water, and 15kg for the 42-in. version, against 200kg for a traditional type.