Gas sampling system (photo: Martek Marine)

Maritime industry technology specialists Martek Marine are setting the bar high when it comes to offshore gas safety. The company has developed a first-of-its-kind gas sampling system for a new moored floating production unit, which forms part of the Jangkrik Complex gas fields development in Indonesia. The system has been developed to dramatically improve offshore crew safety through the use of advanced gas sampling technology.

Following drilling at three exploration wells, Jangkrik 1,2 and 3, a feasibility study completed in July 2011, led to selection of the most appealing concept for development of the area. The chosen approach is based on a subsea development with 10 wells and full treatment facilities on a spread moored floating production unit (FPU). The FPU has an export line to shore at Sapi Landfall.

Global maritime technology company Martek Marine specified a gas sampling system for the FPU which is the first of its kind. Based on the company’s well reputed MM5001 Gas Sampling System, the bespoke setup comprises of 4 independent systems. The systems are designed for the sequential sampling of hydrocarbon gas, as well as sequential sampling and continuous monitoring of oxygen. The sampling activities are focused on the ballast and condensate tanks in addition to continuous monitoring of supply headers within the FPU.

“The system will play a vital role in ensuring the safety of those onboard, by giving crew the means to effectively monitor gases within enclosed spaces and ensure that levels maintain within safe parameters,” says Martek Marine Project Engineer, Steve Austwick.

The first sampling system is a split system, designed to sequentially sample hydrocarbon (22 Point) in water ballast tanks. Equipped with the latest dual Non-Dispersive Infra-Red (NDIR) sensors, the equipment is faultless when it comes to monitoring increasing levels of methane (CH4).

Being a split system, the pump, solenoids and sensors are housed in the monitoring side of the system installed in a cabinet on deck. Benefiting from an EExe enclosure and EExd internal components the unit is explosion-proof.

The human machine interface (HMI) and programmable logic controller (PLC) are housed control side in the cargo control room (CCR). In a conventional gas sampling system, the control and monitoring equipment is mounted in a single cabinet which is installed in a safe area, usually the CCR.

“The important benefit to a split system, is that the need to run sample piping into the CCR is avoided,” adds Austwick.

The second system supplied is a 6-point system used for sequential sampling of oxygen in condensate tanks. In addition to benefitting from the design features of the sequential hydrocarbon gas sampling system, the addition of advanced paramagnetic sensors enables levels of oxygen to be monitored in the inert gas blanket of condensate tanks.

Paramagnetic sensor technology provides unbeaten performance and longevity.

“The sensors use no consumable parts, meaning they excel in terms of durability,” says Austwick. “Offering world-class precision over a range of 1% to 100% oxygen, they are able to measure the oxygen concentration not only in flammable gas mixtures, but also in low concentrations and with high precision.”

Two further gas sampling systems were supplied under the contract, both continuous oxygen gas sampling units. Both single point systems, the first is designed for use in the inert gas supply header and the second, in the high purity nitrogen header.

Both systems benefit from paramagnetic oxygen sensors to monitor oxygen enrichment. Both the sensor and the pump are installed in a single cabinet.

“Having only one sample line ensures the headers are continually monitored and no front-end control is therefore required,” says Austwick. “A signal from the system analyser is connected directly to the distributed control system (DCS) on the vessel, ensuring optimum reliability through localised control functions near the equipment.”

All gas sampling systems are now installed and the naming ceremony of the Jangkrik Floating Production Unit (FPU) vessel took place on March 21, 2017 at Saipem Karimun Yard, Tanjung Balai Karimun, Indonesia. The FPU then sailed to its final destination at the Jangkrik Complex in preparation for gas processing and export, which is expected to reach a capacity of up to 450 million standard cubic feet per day (mmscf/d).

Tags: Martek Marine