This is an excerpt from the January/February 2014 issue of InTech magazine by Guillermo Pacanins, P.E., a certified TÜV Rheinland functional safety expert. To read the full article, please see the link at the bottom of this post.
Smart instrument installed in the field.
Any process plant that handles products, feedstock, or fuels that are the least bit hazardous (flammable, toxic, or otherwise environmentally dangerous) has safety concerns. Operating in compliance with regulations and standards is a way of life for oil, gas, petrochemical, biofuel, and many commodity chemical producers. But beyond compliance, companies want and need to protect their people, equipment, and the surrounding environment.
Applicable standards include ANSI/ISA84.00.01-2004 Parts 1-3 (IEC 61511 Mod) and IEC 61508, along with facility-recognized best procedures and practices. Compliance with these standards ensures that the plant is not simply within the letter of the law; it helps the plant operate with minimal potential for incidents and injuries.
Undertaking this effort begins with plant hazard and operability studies and the layer of protection analysis (LOPA) methodology. Some situations may call for a quantitative risk analysis, as provided by the Center for Chemical Process Safety and indicated by ANSI/ISA84.00.01-2004 Part 3, Appendix F.
Performing a LOPA helps identify which identified hazards require safety instrumented functions (SIFs) and the required probability of failure on demand for each to lower the risk to a tolerable level. Performing a LOPA is a main step toward ensuring that requirements under ANSI/ISA84.00.01-2004 Parts 1-3 (IEC 61511 Mod) are met.
Once the safety instrumented system (SIS) is designed and implemented according to the safety requirement specification, its operation must be maintained and monitored to ensure integrity of the SIF, and to ensure ongoing compliance with standards. Any changes to the hardware, such as new equipment, new field devices, different products, or different specified operations and processes must be taken into account using a management of change procedure. Any malfunctions or other process issues must also be accounted for, typically by proof testing and monitoring the SIS along with its associated field devices, such as sensors, instruments, valves, and logic solvers
Real-time safety monitoring software improves the integrity of process safety systems and ensures compliance and safe operation. Companies can enhance the results generated by the software with the information supplied by SISs, plant automation systems, and their associated smart field devices. All these systems and their associated components must be maintained, a task that can be eased by using smart field devices.
Safety systems need maintenance too
In a process plant that runs well, the safety system can fade into the background, because it has a low daily demand rate. Nonetheless, field devices connected to an SIS still need maintenance. Many plant accidents have been caused by a neglected safety system field device not working properly when called upon in an emergency.
The reality of thinly staffed process plants is that the operations and maintenance professionals charged with this time-consuming and complex task also have to watch over the other plant assets that support regular production. They are responsible for availability, productivity, and so on. Since the SIS does not affect these areas under normal circumstances, it can become a secondary concern, or slide even further down the list of priorities.
To make matters worse, field devices that are part of the SIS do not always employ the latest technologies. They often do not have the capability to provide information to the main plant automation system, an asset management platform, a computerized maintenance management, or other related systems. There may be no alternative to sending an individual to a given field device and inspecting it where it is installed, a task that is often postponed.
All SISs depend on field devices for their information, many of which are discrete (on/off), plain 4-20 mA analog, 24 VDC, or some other analog signal type. Each device provides its primary variable and nothing more. This does not have to be the case, because smart field devices can produce extensive diagnostic and other information.
Many field sensors, instruments, and valve actuator positioners installed in the past 10 or even 15 years have some diagnostic capability built in. In other cases, dumb field devices can be upgraded to smart ones, either through retrofit or replacement. In either case, an SIS that is capable of gathering more diagnostic information from each field device greatly improves the quality of data available from these systems, and ultimately makes life easier for the process automation professionals responsible for the SIS.
However, even if all needed data is available, users must still make sense of the information. Volumes of raw diagnostic data must be transformed into useful information that guides maintenance efforts and promotes correct operation of the SIS and other related systems. This is not an easy task, as the relatively small number of plants that operate effective asset management programs indicates. Still, there is a way to improve safety system operation without unduly burdening plant personnel, and it starts with smart field devices.
To read the full article on improving safety system performance, click here.
About the Author
Guillermo Pacanins, P.E., holds a B.Sc. in electrical engineering. He is a certified TÜV Rheinland functional safety expert and has more than 27 years of experience with process controls and functional safety in process industries. He serves as a system designer, workshop presenter, and trainer for ACM Facility Safety, where he holds the title of safety lifecycle leader/educator.
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