The inherent design features of current PIPIP (pipe-in-pipe-in-pipe) technology allow LNG (liquefied natural gas) to be transferred both subsea and buried onshore safely and securely, with minimal risk to the environment. This ability is enhanced by an associated integrity monitoring system that provides rapid and sensitive leak-detection capabilities. ITP InTerPipe's PIPIP technology received DNV's Certificate of Fitness for Service in 2007. Leaks are primarily detected by monitoring pressure in the annulus. Because the inner annulus is closed, arbitrarily small leaks can be detected via pressure measurement; the only variable being how much time is required. The leak-detection capability in the PIPIP system is orders of magnitude better than can be achieved with conventional leak detection. For example, a leak of 0.002 m3 LNG/hr (0.00004 % of the flow rate) can be detected in about 18 hr. The case study presented shows the ability to detect leaks when about 40 l. of LNG had leaked in the annulus. Since the inner annulus pressure is less than thr triple point of methane (117 millibara), pure methane cannot exist as a liquid in the annulus. Leaks will consist primarily of a mix of vapor and solid methane, with the solid methane subliming after continued contact with the inner pipe. Leak location can be detected by fiber optic methods for all leaks large enough to affect the temperature of the intermediate pipe. Annulus pressure monitoring will detect a small leak more quickly. A leak in the intermediate pipe can be distinguished from a leak in the inner or outer pipes by either the fiber optic measurement or the rates at which the pressures of the inner and outer annuli change.
PIPIP technology aids LNG transfer
Oil and Gas Journal ; 106 , 20 ; 46-51
2008
6 Seiten, 5 Bilder, 2 Tabellen, 8 Quellen
Article (Journal)
English
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