I agree fieldbus is good for modular construction, which is not just for floating production storage and offloading (FPSO) [InTech July/August 2013 Web Exclusive]. Projects in the process industries are increasingly turning to modularized construction to reduce escalating construction costs and to use construction resources where they are available instead of where they are scarce. Fieldbus and modularization are industry trends seen for ships such as FPSO and floating liquefied natural gas floaters, but also for onshore plants everywhere from oil and gas to metals and mining—on the even larger scale of mammoth modules.
Fieldbus fits well with modularization, because the instrumentation can be tested on the module in the yard and when the module arrives at the site. In the yard, all instrumentation is installed and hooked up on the module, fully commissioned and tested. Thanks to the digital bus architecture, fieldbus reduces the amount of tray to install, cable to lay, and wires to cut, strip, label, ferrule, and connect on the modules. Device commissioning is faster. The traditional five-point loop check associated with 4–20 mA is not required. Once a module arrives on site, minimal wiring has to be connected. System integration is simply a matter of plugging the module into the established power and fieldbus leading back to the system in the equipment room. Fieldbus makes the instrumentation and control (I&C) part of the modules easier to assemble, reducing the I&C connections to a minimum. Because the “topsides” consists of process modules fabricated in different yards, fieldbus enables these modules to be connected with the rest of the ship using only a few cables; this is a “plug-and-play” concept ideal for fast-track projects.
Using fieldbus has many secondary benefits, one of which is the ability to automatically monitor device diagnostics from a central location. Device diagnostics from the intelligent device management software part of the asset management solution mean that physical inspection of the device is rarely required. Subsequently, devices do not need to be installed in conveniently accessible locations, but can instead be directly mounted, on the pipe or equipment, without impulse lines. This simplifies installation on compact modules and also eliminates the risk of plugged impulse lines.
Another benefit of fieldbus is the ability to place analyzers on the module in the field or on deck, connected directly to the process sampling point, without having to run long sampling lines with heat tracking off the module to an analyzer shelter. This may include gas chromatographs and other analyzers. This greatly facilitates the completion and integration of modules at the site. The analyzer shelter may not be required, reducing weight—important on offshore vessels and installations. Note that these are field-mount analyzers in their own suitable enclosure. The analyzers connect to a fieldbus running back to the distributed control system and AMADAS.
Fieldbus eliminates the problems associated with hardwired I/O and is an ideal fit for modular construction. The reduced footprint and weight is important on a crammed FPSO. As devices these days are no longer integrated with just one signal each, the system I/O counts are higher than in years gone by. But a fieldbus system is designed based on device count instead of I/O count, so 6,000 I/O instead becomes 2,000 devices.