An ambitious expansion project of a Liquid Natural Gas (LNG) terminal in China aims to double the capacity for importing and regasifying LNG.
This will significantly bolster the terminal's annual gas transportation capacity to meet the growing demand for natural gas in northern China. To ensure the safety and reliability of the LNG terminal, G.M. International has been tasked with providing SIL 3 certified products.
CHALLENGE
One of the customer's requests was the availability of Safety Instrumented Function (SIF) loop verification. This process is used to calculate the performance of the SIF to determine whether it meets the targeted Safety Integrity Level (SIL). The SIL for each SIF loop is typically specified during the SIL classification performed at the design stage. The verification of a SIF involves reviewing the loop design and gathering the required information to calculate the probability of failure on demand (PFDavg) for the loop, and it is an essential tool to reduce the probability of undesired events. The types of information required during SIF loop verification include, but are not limited to, hardware failure rate, percentage of common-mode failure, and proof test coverage. The LNG terminal environment also exposes electronics to salt, moisture, and changes in temperature. These vulnerabilities create a considerable risk of corrosive attacks and a high probability of failure for electronic components. This harsh environment should prompt further evaluation and result in specially designed and packaged equipment for offshore applications. In this specific case, a device shall be conformally G3 coated and suitable for operating in harsh environments, including providing an extended operating temperature range. Furthermore, the end user expressed interest in a solution capable of reducing wiring costs and footprint.
SOLUTION
The solution provided by G.M. International included SIL certified safety barriers, safety relays, power supplies and surge arrestors. In the installation, GMI Barriers (D5000 series) and isolators (D6000 series) are mounted on a customized system termination board. Various models, depending on the barrier/isolator, are involved in such applications, including models TB-D5016-YOK-006, TB-D5016-YOK-007, and TB-D5016-YOK-008. These termination boards are directly connected to Yokogawa Prosafe I/O cards SAI143 (AI), SDV144 (DI), and SDV 541 (DO). The direct and easy connection between the PLC and the GMI modules is provided by a single dedicated system cable. This solution significantly decreases engineering, wiring, and maintenance costs. The galvanic isolation between the safe and hazardous areas is provided by the D5000 Series associated apparatus. The dual-channel D5014D module is a power supply and isolating repeater. It is a high-integrity analog input interface suitable for applications requiring SIL 3 level. The D5014D module can be used as a duplicator, providing the possibility to obtain two separate output signals completely isolated from each other. This ensures galvanic isolation between DCS and SIS to avoid any interference between the two systems. Then, the SIL 3 proximity detector and repeater D5031D module is used to monitor the health of sensors installed in the field.
The D5090S relay module is then used for switching safety circuits up to SIL 3 level. The choice has been made because that compatibility between the safety relay and the DO card pulse test is guaranteed.
The 24Vdc power supply module PSW1250, besides being a SIL 3 solution, is also suitable for Zone 2 / Division 2 installations. A single module can provide up to 50A and can be wired for redundancy or paralleled to increase the output capability when required. In this case, the PSW1250 is responsible for powering the entire batch of termination boards, barriers, and isolators, playing a crucial role in the application. Moreover, this power supply module provides a cumulative fault contact output, which is triggered in case of malfunctioning of the installation, including itself. Undervoltage and overvoltage protection is also provided to ensure the safety of the equipment.
The D9420S, included in this installation, is a super slim, SIL 3 surge arrestor. The device provides two-stage surge protection for floating I/O signals of measurement and control, as well as safety systems. With its 6mm width, it can be easily fitted into any marshalling cabinets or distribution cabinets.
BENEFITS
G.M. International provided local technical and after-sales support for developing and testing the solution. The utilization of GMI TBs significantly reduced the wiring costs for the customer. Adopting SIL 3 products not only enhances reliability and availability but also reduces financial costs. The lower probability of faults, spurious trips, and undesired shutdowns, along with extended product lifecycles, results in decreased maintenance costs and reduced plant downtime. Additionally, G.M. International offered the added benefit of safety-related trainings through their professional personnel.
