Automation & IT / Fluid Handling / Reliability & Maintenance / Instrumentation

Don't Neglect Pressure Gauges

Inadequate attention can make plants vulnerable to mishaps

By Jason Deane, WIKA Instrument

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.