Flying by the seat of your pants?

If you want to fly without using appropriate instrumentation, I’ll walk, thank you. The same goes for your process.

06/18/2013


There was a time in the history of aviation when “flying by the seat of your pants” had real meaning given the relative lack of gages in an early airplane’s cockpit. Yet, in many ways we still operate our plants this way. We instrument what we consider to be critical measurements based on historical operation, but we don’t necessarily perform a detailed analysis of the process to determine if there are other things that might be just as important to the operation in terms of throughput or quality or, possibly even more importantly, to uptime and equipment longevity. Even those organizations that don’t have a “run it till it breaks” mentality don’t necessarily make the best use of the instrumentation they have, while more thoughtful companies install things that could be beneficial in improving uptime and operation of the facility.

While there’s something to be said for the ability of the human body to detect small changes in things, like vibration or the sound of a piece of equipment, there’s no substitute for good measurement to detect it before it becomes bad enough for a human to detect. Heuristic capabilities built into some instruments have extended this human capability for sensing problems so they can be detected well before an operator can. One manufacturer, for example, has built a plugged sensing line detection capability into their transmitters that uses the noise signature of the process. When it decreases by a threshold amount, it generates an alarm. Sensing these changes in process noise can also be used to detect other problems like pump impeller wear, which can also create pressure fluctuations that then cause a valve to cycle excessively leading to an early failure. Digital valve positioners can analyze the motions of the valve that would go unnoticed by an operator to alert maintenance to the need for service before the valve fails. This use of heuristics can be applied to any number of other situations to prevent failures before they happen.

So why aren’t more plants taking advantage of these kinds of diagnostic capabilities? The problem is that organizations are in many ways constrained either externally or internally from deploying these technologies. One key constraint is financial. Some of what’s required to perform the analysis falls into the realm of capital expenditures, which in most cases requires a payback. If the system does its job so you keep from having the outage and down time that would have cost you the money you justified buying it on, then without the down time you can’t show that you actually saved any money, making the successful system a failure. Talk about a “Catch-22.” Another constraint is cultural. One engineer for a major U.S. corporation has said that his company won’t buy some of these technologies because to use them effectively would require rewriting their maintenance procedures, which they won’t do. A competitor of theirs has stated that having the plugged line sensing technology would have prevented an explosion that occurred at one of their refineries. That means the first company is unwilling to install something that would prevent an explosion because they would have to change a procedure that is meant to prevent explosions. Really? What Catch-22s have you run into that have prevented you from implementing something that logically should have been implemented?

This post was written by Bruce Brandt. Bruce is a technology leader at MAVERICK Technologies, a leading system integrator providing industrial automation, operational support, and control systems engineering services in the manufacturing and process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, and business process optimization. The company provides a full range of automation and controls services – ranging from PID controller tuning and HMI programming to serving as a main automation contractor. Additionally MAVERICK offers industrial and technical staffing services, placing on-site automation, instrumentation and controls engineers.



Anonymous , 12/23/13 08:53 AM:

I personally agree that more instrumentation is needed and that the instrumentation should have more and smarter diagnostics. The article appears to really be about type 4, 3, and 2 diagnostics for better situational awareness.

Most plants were built years ago with a minimal amount of instrumentation necessary required to safely operate the process, because 4-20 mA and on/off signals are expensive due to the large amount of cable, conduit, junction boxes, cable tray, installation labor, marshalling cabinets, system cabinets, and I/O cards etc. Improving process unit utilization, energy efficiency, reducing maintenance costs, and mitigating safety and environmental incidents to stay competitive requires additional automation, but the necessary data is not available. These are missing measurements. But ageing plants can be modernized.

The article speaks of what is commonly referred to as ‘type 4’ diagnostics (Process Equipment Diagnostics) to improve process equipment reliability, reducing downtime, while minimizing maintenance cost and more effectively scheduling turnarounds by continuously diagnosing which equipment require maintenance and which don’t. Potential equipment includes heat exchangers, pumps, blowers, air cooled exchangers (fin-fans), unmonitored compressors, and cooling towers etc.

Additionally, plant modernization should cover automatic energy monitoring to drive energy conservation measures for generation, consumption, and loss to improve energy efficiency thus reducing cost. Automatic HS&E monitoring to reduce personnel exposure, detect hazards, record emissions, and provide operators increased situational awareness thus benefitting health, safety, and environmental as well as for associated regulatory compliance should also be part of modernization.

All these improvements are possible without adding any control loops and without migrating the control system. The additional automation only requires more sensors. However, opening junction boxes and cable trays to lay additional cables to hundreds of new transmitters would be disruptive and carry a great risk of damaging the existing installation. A new innovative solution was required.

The primary layer of automation which already exists in the plant uses hardwired or fieldbus signals to the control and safety systems covering functions on the P&ID with millisecond response time supervised by operators in the control room. The second layer of automation uses wireless sensor networks mainly to the asset management system for monitoring of missing measurements with pervasive sensing going beyond the P&ID with update period of seconds, minutes, or an hour for maintenance, reliability, HS&E, and energy personnel in offices beyond the control room. By eliminating wires, deployment is accelerated and low risk, possible during a turnaround or even while the plant is running.

Wireless sensors and software enable plant personnel to become more effective – by no longer having to fly by the seat of their pants.

Interestingly, most of the new data does not go to the control or safety system operator consoles in the control room. Most additional data goes beyond the control room, for instance to the maintenance and reliability office, presented as KPI and equipment dashboards, not as an animated P&ID. The raw data from wireless instruments is aggregated in essential asset monitoring software with pre-engineered modules for pumps, heat exchangers, air cooled exchangers, cooling towers, blowers, unmonitored compressors, filters & strainers, as well as pipes & vessels. Multi-parametric algorithms embedded into the software provide easy-to-understand process equipment diagnostic information.

Once wireless sensor networks have been deployed plant-wide, the plant is prepared to quickly and easily add more automation as needed in the future as industry demands inevitably change.
New plants should be built including wireless sensor networks from the very beginning. Do not design in traditional operator rounds.

IEC 62591 (WirelessHART) is the international standard for wireless in process applications. Thanks to a multi-path multi-hop mesh topology, reliability >99% can be achieved inside a plant environment full of steel, and a single (optionally redundant) gateway can be mounted at the edge of the plant areas eliminating the need to run the networking and power supply into the process units themselves thus reducing risk. Update period can be set from 1 second to 1 hour for individual devices as required by each application. That is, a single common network infrastructure for all applications: steam trap monitoring, relief valve monitoring, and process equipment monitoring etc.

WirelessHART enables existing sites to be modernized & sustained in ways previously not possible, benefitting both operations and maintenance. Start by requesting the user’s guide to how to modernize and sustain an old plant using a second layer of automation for pervasive sensing of missing measurements found beyond the P&ID. The guide covers the modernization process from justification and audit to commissioning and handover. The guide can also be used for new projects to deploy plant-wide wireless infrastructure, to make sure the new plant is not built to be run & maintained the old way.

Learn more from this blog:
http://community.emerson.com/process/emerson-exchange/b/weblog/archive/2013/10/03/why-are-there-missing-measurements.aspx

The article goes on to talk about ‘type 3’ diagnostics (Process Connection Diagnostics). This is the diagnostics performed by the device to detect plugged impulse line, valve, or actuator failure etc.

The article then continues to talk about ‘type 2’ diagnostics (Device Diagnostics) also performed by the device itself (self-diagnostics) to detect is own internal problems with electronics (e.g. memory) or internal mechanical parts or power supply etc. Using FOUNDATION Fieldbus you get diagnostics not only from transmitters and control valves (traditionally 4-20 mA devices), but also from discrete devices such as on/off valves and electric actuators / motor operated valves (MOV) (traditionally on/off signal devices) etc. as well as complex devices like gas chromatographs and tank gauging systems (traditionally Modbus or proprietary) – and this diagnostics get integrated into the same intelligent device management (IDM) software part of the asset management system as the transmitters and control valves.

Learn more about FOUNDATION fieldbus here:
http://www.fieldbus.org/images/stories/technology/aboutthetechology/overview/fieldbus_brochure.pdf

Users that need guidance on rewriting their work processes can get help from the guideline found here to make sure diagnostics becomes a natural part of daily maintenance and turnaround planning:
http://www.eddl.org/DeviceManagement/Pages/DeviceDiagnostics.aspx#Institutionalizing

Lastly, although not mentioned in the article, there is ‘type 1’ diagnostics (Signal Diagnostics) which includes “power advisory” problem with 4-20 mA signal or communication statistics and signal strength for fieldbus and WirelessHART.
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