Posted at 14-Aug-2018

Taking the Long View on Safety with Festo

Paul Skade
By Mark Carpenter
Product Manager, Industrial Hose

I am a former Engineer on Submarines in the Royal Navy and got in to the Hose industry in 2010 becoming the UK Sales Manager for Norres in 2014, ERIKS was my majo...

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When your new product R&D can take up to 15 years, you want actual production to be as fast and reliable as possible. And when your entire production system is classified as potentially explosive Zone 1 and Zone 2, then you also want it to be as safe as possible. Which – if you’re Bayer Crop Science – means asking for advice, support and solutions from Festo.

 

Bayer’s €110 million investment in a multi-purpose production system brought their ingredient development and manufacturing, laboratory processing, sampling, piloting and production all under one roof, in Dormagen, Germany.

With process development requiring the use of flammable operating fluids, frequent process changeovers, and numerous interfaces and intervention points, the whole system is designated as potentially explosive zones 1 and 2, in accordance with explosion prevention and protection measures.

So, knowing that the probability of an incident depends largely on the reliability of the system components and individual processes, Bayer realised the importance of choosing reliable process control instrumentation and technology.

The efficiency bonus

Instrumentation and control technology components certified in accordance with IEC 61508 make an essential contribution to safety. They help to prevent dangerous plant conditions such as overpressure, and can detect future trends and initiate suitable preventive measures. For example, by calculating the temperature gradient they can detect a runaway reaction so that automatic measures – together with alerts if necessary – can be activated  to prevent a safety risk incident.

Reliable availability of coolant water, electricity, emergency stop and stress-relief devices, pumps, mixers and process valves minimises safety risks.

The bonus for production plants is that all these factors also optimise the economic efficiency of the process. Today’s process engineering systems are so highly optimised, the only sure way to increase output is to ensure a reliable, highly productive system with minimum downtime. This leads to reduced inspection cycles and inspection times, as well as avoiding equipment idleness or downtime due to unscheduled repairs.

Safety first – but flexibility second

The Bayer Crop Science multi-purpose system is designed to be highly flexible in its connectivity and operation – allowing subsystems and equipment such as dryers, centrifuges, distillers, stirrer tanks and other reactors to be connected and utilised in a variety of ways.

An in-house pipeline with adaptable piping handles material flows, while the decentralised process control system is distributed over a total of 67 automation systems, to enable highly flexible and adaptable adjustment.

To ensure safety, extensive instrumentation and numerous control technology devices are used to switch dosing, exhaust, steam and other valves to failsafe positions, with actuators activated by solenoid valves. If an emergency situation arises, the valves quickly exhaust the actuator and close the process valve.

Placed between the positioner and the actuator, the solenoid valves are required to have at least the same SIL classification as the entire safety loop they sit in, with single-channel architecture.

The impossible valve

The Festo solenoid valves VOFC and VOFD can be supplied with TÜV certification up to SIL 3. This guarantees a failure probability rate of 2.41 E-4, and a safe failure fraction of 75%. Or in simple terms, used correctly, there will be a maximum of one faulty operation in 2,410 switching cycles.

If the safety loops have an annual failsafe inspection – as most will – then a faulty operation will occur only once in 2,410 years – making it virtually impossible for a valve not to switch when it should.

However, what makes conditions especially challenging for a solenoid valve in a safety loop is that it’s in “low demand mode”. Built for several million switching cycles, a valve only switched on in case of emergency will be permanently energised – perhaps for decades – but almost permanently idle. Even so, it has to be ready and able to shut down immediately and reliably when required.

That’s why Bayer chose Festo solenoid valves VOFC – and installed over 1,500 of them in safety- and non-safety related circuits in their multi-purpose system.

1 valve. Dozens of applications

Bayer’s requirement was for one solenoid valve to suit all applications, and to be compatible with the requirements for actuation in intrinsically safe circuits (Exi) in zone 1.

Many of the VOFC valves on their site are used in the multi-purpose system for actuating ball valve units in tank systems, reactors and media supply systems. But others are used across the site for a wide range of applications – some to control large actuators and some to control small, some indoors, some outdoors.

Specifically developed to meet process industry criteria, the VOFC range features piston poppet valve technology, with no dynamic seals. This allows switching operations to be made by a diaphragm, with no friction which might otherwise negatively affect switching performance. The solenoid coil power rating is comparatively low, at just 1,8W (or less than 200mW for the intrinsically safe variant). The valve itself has outstanding flow characteristics, and these have a positive effect on the safety valve’s closing time. 

Even the harsh ambient conditions within Bayer’s facility are no challenge for the VOFC, which has proven Ematal corrosion protection, exhaust ports with special non-return devices to prevent penetration of rainwater or outdoor air into the solenoid valves or downstream actuators, and also lacks venting holes which could allow unwanted ingress.

The compressed air supply lines for the solenoid valves have also been designed for reliability and efficiency, with zero leakage. Made from polyurethane tubing they utilise NPQH push-in fittings featuring an integrated sealing ring. The lines are highly flexible, quick and easy to install, and highly resistant to UV radiation and chemicals. Available in a choice of colours, they eliminate the need for additional identification of the nitrogen and compressed air lines used in the system as a pressure medium.

Lastly the use of bulk packs eliminates the need for connection screws for large tubing lengths, which reduces to a minimum the number of possible sources of leaks.

Festo forever

During 15 years of operation in Bayer’s multi-purpose system, not a single one of the 1,500-plus intrinsically safe Festo solenoid valves with TÜV certification up to SIL 3 has malfunctioned.

When 14 of them were removed and extensively tested in the climatic chamber at Festo, they provided statistics for comparison with earlier laboratory test results from the German Technical Control Board TÜV-Rheinland.  As a result, the TÜV has now issued certification with no limitation of the valve’s service life.

This means that the operating company responsible for installation, operation and maintenance can specify service life for itself. Festo is the first company to receive this unlimited service life certification for solenoid valves.

When new product R&D can take up to 15 years, like Bayer Crop Science’s, you tend to take the long view. With Festo solenoid valves VOFC, you can afford to.

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