Plant machinery and safety considerations are key components when it comes to the day-to-day running of an engineering or manufacturing enterprise. Continual improvement is something a lot of companies strive to reach. However, with some safety aspects there are sometimes different approaches, especially when it comes to process plant safety versus rotating machine safety.
The issue is not lost on Emerson’s senior sales manager Andy Kennard, who spends a lot of his time on plant safety issues and the differences between how process engineers and rotating machine specialists see their roles
So what is the difference between the two?
“Process plant safety is typically about gas explosions and hazardous areas, concerns like that,” said Kennard. “That’s typically handled by a safety instrument system (SIS). Whereas rotating machines are usually handled by the reliability people – so compressors, big fans, turbo machinery. And if that machinery goes off the rails you have tons of steel rotating at thousands of RPM that can cause massive damage. In both cases where failure occurs, there is severe physical impact, cost and production impact, as well a safety impact.”
Both sets of engineers can help each other, which is especially true when it comes to predictive maintenance and having to shut down plant – a course of action that can sometimes be avoided.
“Reliability engineers have traditionally understood the importance of condition-based monitoring or predictive diagnostics,” said Kennard. “That’s what they do for a living. Process control people should be able to learn from that and think: ‘I don’t have to shut the plant down’. If they’re smart about this, and use the predictive diagnostics that are now available in technology like smart devices, they can avoid false trips. When there is a real issue they need to shut the plant down. But if they’ve just got a faulty sensor, this shouldn’t happen.”
And sometimes it is something as simple as a faulty sensor that can cause an issue. Kennard cannot reiterate enough the importance of safety in plant, but also believes a common sense approach is needed. Plant shutdowns, due to false readings or sensors not doing their job properly, is something that is not only common, but costs a lot of money to the company involved.
“Some [process engineers] say, ‘if any doubt, shut down. That is the whole point of the safety system. It must be separate from the control system’. You can understand the mindset of plant managers,” said Kennard. “It’s always got to be failsafe because they think ‘if one of my instruments is faulty what can I do about it anyway? I just have to assume the worst case because I don’t really know if that instrument is really faulty, or is it a genuine trip’. However, it’s all about what smart devices can do for you. In the process control world people don’t always think in the reliability sense. But the rotating machine engineers do.”
Kennard gives the example of how its smart safety system, DeltaV SIS, might give users information twice on the same signal and how this can assist process engineers to make a more informed decision on whether to shut down plant or not.
“It might give you a traditional analogue 4-20 signal that tells you the pressure,” said Kennard. “Equally, it sends a digital signal at the same time telling the engineer what the pressure is. And process engineers think ‘Well, they’re always going to be the same aren’t they?’ Well, no, they’re not. This is often a cause for unnecessary trips. What can happen in the 4-20 scenario is that there might be a bit of earth leakage, or a dodgy connection. The current can be limited by the earth leakage. Some of the current will leak off somewhere else. If the temperature is at 75 per cent of maximum, it might only read it at 50 per cent thus incorrectly suggesting that things are safe. But the digital signal is not affected by things like earth leakage. It will give you the correct signal.”
Kennard said that smart sensors and the signals they send – along with the right analytical software – can help, especially if a sensor is giving a false reading. This means managers wouldn’t automatically make the decision to shut a plant down. They could flag it to an operator that maybe there is something wrong and they shouldn’t trust the signal. Perhaps if the engineer doesn’t hear from the operator, they shut the plant down. There is a lot of extra data and information and the analytics that go with it that allow people to take a view about safety that still maintains safety, or even improves it, but at the same time helps the availability by avoiding false trips. It gives process engineers more confidence in the safety system.
Emerson’s process control safety system – not the machine safety system – does exactly that. It uses the smarts inside smart devices to both warn when there is a false negative and keeps the plant running, or potentially allows you to keep the plant running. It also does this extra safety check when you don’t trust the 4-20 milliamp signal because perhaps there’s an earth leakage there. It just utilises the smarts inside the smart devices.
Kennard is at pains to point out, that while all this is designed to improve availability while ensuring plant is run safely, there is also an environmental aspect that needs to be taken into consideration.
“If a plant is closed down, things can solidify in the processes and that leads to environmental problems,” he said. “You have all this waste product. For example, when you look at a gas or chemical plant and shut it down, it doesn’t stop running – you might have to flare the gas. So it impacts environments as well as production and safety.”
Kennard said it not a case of engineers trying to protect their own territory. Ideally everybody will work together to get the best safety outcome for the plant and the people who work in it. If that can save money and take into account environmental concerns, then that is a great outcome all around.
“Trying to get both sides of the issue together should be easy,” he said. “They don’t need to be scared about this. Their aims are similar but they are approaching it from a different point of view. One says it is a safety issue based on reliability. The other says it’s a safety issue based on production. Well both are true. It’s two very different worlds. You rarely hear of the discussions between these people even in the same room.
“If you had to frame the discussion it would be something like this – these guys have more in common than they think even though they have completely different departments in completely different buildings. They’ve both got the same aim and could learn from each other.”