US federal safety regulators have instructed Cheniere Energy to remove two of the five 160,000 m3 storage tanks at its Sabine Pass LNG export terminal from service following leakage incidents.
One of the units, Tank S103, suffered liquid leakages through cracks in its outer wall while vapour leaks were later discovered at various points around the base of the second affected unit, Tank S102.
Cheniere stated that despite the closedown order on the two tanks by the US Pipeline and Hazardous Materials Safety Administration (PHMSA), LNG exports would continue as normal utilising the three unaffected tanks. Located in Louisiana, adjacent to the Texas border, Sabine Pass has been exporting LNG since February 2016 and has four liquefaction trains in operation. A fifth is under construction.
The leak of LNG from Tank S103 was discovered visually and by means of gas detection alarms on 22 January. Liquid had escaped through four cracks, ranging from 0.3 to 2 m in length, in the outer tank wall and collected in a surrounding containment ditch where it began to vaporise.
The tank was taken offline within minutes and the surrounding area was closed off to limit potential ignition sources. No injuries were reported as a result of the incident. It is estimated that approximately 17 tonnes of LNG escaped from Tank S103.
Tanks S103 and S102 were kept virtually empty and in a cold state after 22 January and no further gas escapes have been noted. PHMSA has ordered that the two tanks be fully emptied, warmed up and certified gas-free so that a full investigation as to the cause of the leakages, followed by repairs, can be carried out.
The source of the leaks will have to be identified and repaired before the affected tanks will be allowed back into service. Cheniere will require permission from the US Federal Energy Regulatory Commission (FERC) as a final all-clear.
Sabine Pass was initially built as an LNG import terminal and came onstream in 2008. However, the early development of shale gas deposits in the US Gulf at around the same time obviated the need for imports and prompted Cheniere to reconfigure the facility by giving it a bi-directional capability and the opportunity to export LNG.
The first three Sabine Pass storage tanks were commissioned in 2008 while the final two units entered service in 2009. Tanks S103 and S102 are among the inaugural batch of three.
All the Sabine Pass tanks are built to the single containment design, with 9% nickel steel inner tanks, perlite insulation and a low-temperature steel outer shell able to withstand temperatures down to -25˚C.
The outer shell of a single containment storage tank is primarily for the protection and retention of the insulation and to contain purge gas pressure. It is not designed to contain LNG in the event of liquid leakages from the inner tank.
The industry will be awaiting the results of the Cheniere investigation and the remedial action taken with interest. At no time has there been any indication that the integrity of the inner wall on the two affected Sabine Pass tanks has been compromised.
Cheniere has a two-year jump over its rivals in the development of a US LNG export capability and, in a sense, Sabine Pass is the flagship project, setting down a marker by highlighting the country’s potential as an LNG exporter. As of late January 2018, Sabine Pass had dispatched 230 LNG cargoes to 25 countries.
Interestingly, full containment storage tanks were chosen for Cameron LNG and Freeport LNG, two projects also built originally as import terminals but now being given a bi-directional capability to enable exports.
Cheniere itself has opted for full containment tanks for Corpus Christi LNG, its greenfield export terminal now being built in Texas. With full containment tanks both the inner and outer shells are capable of holding LNG.