Don't Neglect Pressure Gauges

Inadequate attention can make plants vulnerable to mishaps

By Jason Deane, WIKA Instrument

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The simple pressure gauge is an often-overlooked defense mechanism for preventing accidents. However, in auditing more than 250 plants, WIKA Instrument discovered that up to 25% of all pressure gauges were broken, damaged or misapplied — this represents an average of eight deficient gauges located within 20 feet of each employee.

A failed gauge compromises a plant's ability to detect a problem before a safety incident occurs. Malfunctioning gauges also can lead to media leaks, fugitive emissions and a fire or explosion, taking a toll on safety and reliability.

Even minor accidents can cause employee injury and lead to downtime. Any accident or leakage also puts staff sent to fix the problem into harm's way, which, of course, can lead to further employee injury and lost hours.

Many causes contribute to this dangerous situation with gauges. Fortunately, they can be prevented.

CAUSES OF GAUGE FAILURE
Through its evaluation of more than 150,000 gauge installations, WIKA has identified eight common causes of failure. So, let's look at each, along with the solution.

1. Vibration. Many pieces of equipment vibrate. However, excessive vibration can lead to gauge failure and may indicate a problem with a component. Solution: install a gauge that will resist vibration better — i.e., a liquid-filled or direct-drive gauge with only a single moving part.

2. Pulsation. A rapidly cycling medium within a pressure system can make a gauge pointer move erratically and eventually can lead to breakdown of internal parts. Solution: install a restrictor and liquid-filled case to dampen pulses on a standard gauge or replace with a direct-drive gauge that lacks gears and linkages.

3. Temperature. Extreme temperatures cause sweating and loosening in metal joints and eventually can cause them to crack. Solution: install a gauge with a fully welded diaphragm seal and consider adding an on-board cooling element to combat the highest temperatures.

4. Overpressure and pressure spikes. Frequent pegging against the stop pin can bend the gauge pointer and compromise the integrity of the Bourdon tube or sensing element and, ultimately, lead to rupture. Solution: install an overpressure protector to inhibit readings that exceed gauge capacity.

5. Corrosion. The highly corrosive media often found in process plants can damage the sensing material in gauges. Solution: install a diaphragm seal that's constructed from material that will withstand the corrosive.

6. Clogging. A medium that contains suspended particles or is viscous or can crystallize can clog the pressure system and make gauge readings unreliable. Solution: install a diaphragm seal with a clog-preventing barrier.

7. Steam. Some media produce steam or other vapors that can damage the internal parts of gauges. Solution: install either a mini-siphon with an internal chamber to reduce surges or a full siphon, making sure to include a coil for horizontal applications and a pigtail for vertical ones.

8. Mishandling and abuse. Even properly installed gauges will start to malfunction if mistreated over time. Solution: conduct regular safety and maintenance training for all employees who come into contact with or proximity to gauges.

Unfortunately, many plant personnel aren't properly equipped or experienced enough to recognize and address all these problems. That, however, doesn't reduce the importance of doing so.

TACKLING THE PROBLEMS
When beginning to address instrument shortcomings, keep in mind that studies show that fewer than 0.25% of piping components account for greater than 80% of controllable fugitive emissions. Installing gauges with welded diaphragm seals on these components creates a dual containment device, which is required by the U.S. Environmental Protection Agency. This means plants can correct a major source of violations and fines by addressing a very small percentage of connection points. For many facilities, this is an excellent place to start to get meaningful results quickly.

Another fairly straightforward step that's simple to implement but can yield powerful results is standardization of gauges. This reduces the number of replacement parts that must be kept in inventory — and confusion by technicians. In other words, when replacing an old or faulty gauge, employees more likely will select the correct gauge rather than resorting to like and kind replacement. This also helps ensure the storeroom maintains proper inventory, helping cut costs.

Plants that don't have the resources to identify and correct faulty and misapplied pressure measurement instruments can get outside help, such as from WIKA's FAST Team. Any audit team should:

• Visually evaluate the plant's gauge population and look for issues that need to be addressed.
• Diagnose gauges that pose threats and uncover the causes.
• Formulate a strategic plan to address all the discovered issues.
• Audit the storeroom and streamline inventory, reducing redundant part numbers and guesswork.
• Provide dependable processes to prevent misapplying instruments in the future, and coordinate employee-training programs.

Given the complexity of managing the operations of a process plant, it's easy to understand how smaller components such as mechanical pressure instruments can be overlooked. However, using gauges as early warning devices can improve uptime, safety and profits. Money spent on the humble gauge very well could be the best investment a processing plant can make.



JASON DEANE is a senior instrumentation engineer for WIKA Instrument, LP, Lawrenceville, GA. E-mail him at jason.deane@wika.com.


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  • I think it is an insult to outside operators to say they don't know about what service or size a pressure valve should be. I think many of the problems is budget as many of these valves are expensive to replace. Some times management balks at paying to keep such an inventory. When an order goes through to order more pressure gauges it most like goes through a parts coordinator that can be the bottleneck. I think if I am qualified to operate my area of the plant, I know what gauges are used i.e. stainless, oil filled etc. I also know that I need a gauge that will surpass the service pressure. Now a days there is a trend to have back up or redundant pumps in service. It is cheaper to build plants with just one pump as opposed to Pump A and Pump B for same service. Also they used to put in bypass valves in control loops in case a control valve fails, but not anymore. Plant designers need to ask the folks who will have to operate the plant what is best, and safest, not the cheapest.

    This kind of looks like it was written by a gauge manufacturer.

    Frank Fox 40.2 years in Chemical Processing Texas

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  • Thanks for the article Jason. I'm a young engineer and found it really useful.

    Reply

  • Thank you two for the feedback. It’s interesting to see the takeaway from someone with 40 plus years of experience vs. someone just starting out in the industry. After decades of working in plants – sometimes at the same facility – it’s understandable that some tasks become second nature and knowledge seems practically innate. But more experienced workers are retiring, and the young engineers who are assuming these responsibilities don’t have that historical perspective or the proper documentation to ensure gauge compliance with process media, etc. A young reliability engineer with Honeywell, recently discussed this exact challenge with me in a webinar. I encourage everyone to watch a complimentary recording of "Gauging Reliability – Rethinking Instrumentation to Improve Uptime, Lower Costs" on the Hart Energy website. Based on what I am seeing at various plants across the country, his challenges are commonplace. If anyone has more insight or would like to discuss this topic further, please email me and the FAST team at info@wika-fast.com. Here is a link to the webinar: http://video.hartenergy.com/webinars/vid151.php Jason Deane

    Reply

  • This is a helpful article Jason. Do you have statistical data on failure rate of gauge protector? The reliability of this mechanical over pressure protection device seems to have been overlooked and in high pressure toxic and flammable gas service applications it could potentially pose serious risks.

    Sunowo Dwijanarko

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