Prevent Water Ingress - Increase Instrumentation Reliability

Easy Steps to Dramatically Improve Instrumentation Transmitter Reliability

Did you know that a typical name brand instrumentation transmitter has a typical MTBF (mean time between failures) of around 80 years!

Is that what you are seeing at your plant???

If NOT, – continue reading…

80 years MTBF is accurate, documented data for one of the most common pressure transmitters used in North America. MTBF is based on the statistical average, so it doesn’t mean every single transmitter will last 80-years, but it’s still an impressive number considering the environments where instrumentation is often used. 

That MTBF number is valid even for transmitters that are installed in very demanding environments, such as an offshore facility located in a hot, humid area! As long as the transmitter is installed and maintained PROPERLY they can (and do) achieve the statistical lifespans.

But many plants complain that their instruments are failing at a much higher rate than the published data. And each of those instrument failures translate into plant trips, downtime, lost revenue, reduced safety margins, and massive headaches and lost sleep for applicable managers and technicians!

If you follow my blogs, I may start to sound like a broken record here, but…

The solution, is the part about the instruments being properly installed and maintained…

Sadly – a very large percentage of the instruments at most plants now days are NOT installed correctly and are NOT maintained properly (if at all).

Moisture is the enemy of instrumentation circuits of any kind, and frankly causes problems on about anything made of most metals (circuit board runs, contacts, wires, etc.). When moisture gets into a transmitter housing, it is GOING TO shorten the lifespan of the instrument dramatically below the MTBF stats, period.  

You may be wondering - How can moisture get into an instrument that has downward angled conduit and doesn’t get hit by rain, etc.? Many people assume the only way for moisture to enter an enclosed space is by draining into it… But moisture finds ways in… For example; here is one common path for moisture ingress into an instrument:

Tiny air gaps in the transmitter housing cover threads and/or imperfect gland seals on the cable connections will allow trace amounts of ambient air to be pulled in at night when the air inside the transmitter contracts due to cooling. That ambient carries moisture vapor with it (humidity). Some of that moisture condenses as the transmitter cools. As the transmitter warms the next morning, some of the air will flow back out of those miniscule holes and gaps – but it will leave some condensed moisture behind. This cycle repeats and over time the transmitter internals accumulate a surprising amount of moisture.

Fact: Moisture causes corrosion, which wreaks havoc on any electrical circuit over time and shortens the MTBF dramatically.

Lesser-known fact: Moisture can also cause partial short circuits in the 2-wire 4-20mA signal line, which causes some interesting and challenging problems. If you’d like to learn more about how moisture can throw off instrument loop accuracy, check out this blog:  Brain Teaser: Instrument Techs - 4to20 mA Faults | Orion Technical Solutions (orion-technical.com)

Once someone understands how moisture can sneak in with the air, they typically to do a much better job on the tasks that involve sealing things up…

Note - We cover this topic in our I&C courses, along with the many other real-world problems and issues that occur in the field that are typically not covered in textbooks and schools.

So – here is the low hanging fruit:

Steps to boost instrumentation reliability:

Instrument Techs should do the following tasks EVERY SINGLE TIME they work on an instrument:

• Check and note if a housing cover is not fully tight when they begin working on a transmitter – If it was NOT adequately tight, find the reason (or the person) responsible, and correct the issue.

The reason for transmitter covers being under-tightened is often because they simply didn’t understand how important it is to have a perfect seal - or more often, because they didn’t have the right tool for the job… The best tool I’ve seen for this is a transmitter cover wrench: Cover Wrench - R1 (CWR1) – Automation Tech Tools. 

It fits between the notches on the covers and works on nearly any common round transmitter or housing cover on any brand of instrument from PT’s, TT’s, LT’s, to I/P’s, valve positioners, screw-on sensor heads, and so on. The same company offers some other some other items along this line that are worth looking at, including an adapter for a torque-wrench for those who need to adjust the cover to a specification (nuclear industry, etc.).

• Inspect the transmitter housing and covers for:
  1. Good threads on housing and cover (not galled, corroded, or dirty/grimy)
  2. Good O-rings (lubricated and in good condition) 
• Check inside the transmitter for evidence of moisture ingress into the housing. If you find ANY evidence of moisture, report it, and then try to find and fix the source of the problem.
• Clean the housing and cover threads with non-metal brush (toothbrush), and apply thread lubricant.
• Ensure the cover O-ring is in good condition and properly lubricated prior to replacing the housing cover.
• Carefully screw the housing cover on a few turns by hand, and then tighten it adequately with appropriate wrench / tool. If the cover doesn’t screw on smoothly and easily for at least the first several threads, it may be galled, corroded, or damaged - so respond accordingly. Be sure to tighten the cover appropriately!

Note – A systemic cause of instrumentation failures via moisture ingress is caused by technicians who tend to ‘under-tighten’ the housing covers. They do this because they know how hard it is to remove the covers next time if properly tightened… This problem is going to happen pretty often if they are trying to use ‘long screwdriver method’ to catch on the tabs of the housing, or are trying to use other inappropriate tools to remove / replace the covers. Just get them a transmitter cover wrench noted earlier, and the problem goes away.  

The simple steps above will have a dramatic impact on the reliability of your instrumentation, which will translate into better uptime, better operations, increased safety margins, and less headaches and lost sleep.

It often surprises me how few organizations take the time to fix the little things like this (among many others) that can have a huge impact on overall operations. Many organizations are so busy implementing various ‘improvement’ projects and programs or putting out fires – that they fail to see the low hanging fruit right in front of them. This one is a no-brainer for anyone with ears to hear.

I try to post on things like this that get overlooked or that can have a substantial impact. Follow me and/or Orion Technical Solutions for more.

Feel free contact me for more information, or if you have input, perspective, or ideas to contribute to the cause.