In a conventional installation, each process control device has to be individually wired with up to five or more connections. An installation of 300 automated on/off valves would typically require 1,500 wires, 1,200 I/O points, and considerable labor hours and staff. Installing networked process control valves would require only 20 (two-wire) cables and one person can be assigned to this task, dramatically reducing installation time and materials costs plus saving additional costs in other infrastructure.
Requirements of the sea
To make the transition to valve communication networking, shipbuilders and ship owners have had to overcome real and perceived problems that exist on land but are magnified for seagoing installations. Particularly, in a shipboard emergency, such as a collision or fire, it is essential to protect shipboard valve networks that rapidly actuate valves to predetermined safety positions. Without network redundancy, a cut cable or short circuit can result in immediate device loss on a shipboard field network. In addition, any solution used on ships must be extremely durable and well suited for use in corrosive, heavy washdown and high seas environments. It must also have short circuit protection and fulfill explosion-proof requirements.
Answering seagoing concerns
Valve communication and control devices may be used individually or in combination to address all of the above-mentioned concerns of shipbuilders and ship owners. For example, by using a valve communication terminal (VCT), pneumatic override signals can be remotely activated to manually reposition any or all valves to safe positions. Network redundancy can be addressed through “loop topology” in conjunction with an AS-Interface network, which allows field devices to continue to communicate and operate normally, even in the case of a cut cable. Short circuit protection can be provided to ensure that short circuits are identified and isolated, enabling the process control network to function normally and in an uninterrupted manner. Moreover, explosion-proof requirements are met through the use of stainless steel enclosures.
Exceeding shipbuilders’ expectations
Shipbuilders worldwide have begun adopting valve communication networking and are realizing the benefits. Hundreds of vessels are now equipped with shipboard valve communication networks above and below deck in a wide range of ship types and applications.
Conventional control systems require miles of cables and wires, and considerable I/O. An AS-Interface network, however, dramatically reduces the need for wiring, I/O, cabinets and infrastructures, making it significantly less expensive. It is important to note that the labyrinth of wires on industrial ships that rely on conventional control systems also severely limits the available space on board. By reducing the number of wires required per valve, the AS-Interface networking solution reduces the wiring space burden by over 80%.
Another advantage of valve networking compared with a conventional control system is that instead of taking several hours to install and test a single valve, it takes less than an hour. Moreover, during a launch date crunch, bus communications makes it much more efficient to isolate problems in valve networks. The ease of installation eliminates the need of sending hundreds of people into a frenzy to examine individual valves, size components, install various systems, weld connections and do the wiring.
Adapting proven technology
Most of the technology for device valve communication networking used in ships was transferred from land-based industrial applications, where it has been used for over a decade. Once it was adapted to shipboard use, various enhancements were added to further improve redundancy, safety and installation productivity in very confined shipboard spaces.
There are many maritime applications, including military, in which shipboard bussing of valves and other devices can yield substantial cost benefits along with improved operational efficiencies, maintenance cost reductions, and safety.
Well stimulation vessels, as well as various offshore service vessels and platform supply vessels, are increasingly embracing shipboard valve communication solutions due to their numerous benefits, including, among others, minimal space requirements, increased efficiency, and decreased downtime.
Read Dale Ruckman’s Valve World article