DSS084: Are Explosion Isolation Flap Valves Safe? Recent Test Results from Fike with Jim Vingerhoets

In this episode of the DustSafetyScience Podcast, we talk to Jim Vingerhoets, Global Product Manager at Fike Corporation in Antwerp, Belgium, about explosion isolation flap valves and recent tests that Fike ran to assess their safety.

Jim has over 13 years’ experience with Fike, almost 10 of which have been spent as an explosion protection scientist. As Global Product Manager for explosion protection, he has two primary responsibilities: to ensure that Fike products meet customer and industry standards and to address any knowledge gaps in either equipment or industry processes.

In today’s interview, Jim answers the following questions:

What are flap valves?
How are they typically tested?
What were some of the test findings?
What recommendations arose from this testing?

Much of the material discussed in this podcast episode is from a white paper recently published by Fike:

Are Explosion Isolation Valves Safe?

What are flap valves?

Although they have been around for a long time, flap valves weren’t used as explosion isolation devices until 2010. Prior to that, they were used on dust collector air inlets to prevent dust from accumulating in the inlet pipe.

This function raised the question: if they close off during flow reversal in the dust collector, why wouldn’t they close when faced with explosion pressure, which also induces flow reversal? From that point on, work went in to determining if they could be adopted as explosion isolation devices.

How are they typically tested?

Because flap valves were a relatively new explosion protection technology, standardization committees and experts had to develop ways to test them, Fike included. Fike also developed its own flap valve and published a white paper titled “Are Explosion Isolation Flap Valves Safe?“

In 2014, the European standard EN 16447 was developed to present the general requirements for flap valves used for dust explosion isolation. The same year, NFPA 69 included flap valves as exploding isolation devices, although it did not specify the test protocols required.

At present, testing is done using an explosion test vessel, a duct length, and a flap valve. Some key points:

The explosion test vessel must be small enough to cover the intended use: if you test on a one cubic meter vessel, the flap valve will be certified for one cubic meter and up.
The length of the pipe is important. If a three-meter pipe is installed and the test is successful, the installation distance of the flap valve is three meters.
Although testers are encouraged to keep the valve open using a fan and blower, they are not easy to use in an explosion test because they can be destroyed during testing. Therefore, the standard allows other methods to keep the flap artificially open until it would close in a real situation.
You must test as intended on the explosion vessel. If you intend to use flap valves with a vented vessel, you test with a vented vessel. If you intend to use flap valves with a suppressed vessel, you can suppress it.

What were some of the test findings?

Jim mentioned that he noticed three issues that complicate test results.

The first issue is testing with only the vessel side ducting included and not the protected side. This changes the dynamics of the air and material flow during the deflagration from what would be seen when the device is in use in a real system.

For example, when the flap-valve slams shut, the air and material on the protected side continues moving causing a vacuum on the back side of the valve. This can cause very strong pressure oscillations and forces on the flap valve and assembly that are not accounted for in the test. In the worst case the valve may distort allowing the flame to pass through the safety device to the protected side.

The second issue concerns lack of an accurate release mechanism. There is a provision in the current test protocol which allows testers to keep the flap open artificially without process flow in the test and release it at the correct time of flow reversal.

“First of all, those are the words of the standard. The standard is not wrong there. It is correct,” Jim said. “The standard says release at the time of flow reversal, but we have noticed that not every test lab knows exactly how to do that and it is also not easy to do. How would you measure flow reversal? You would need all kinds of measurements.”

He has seen tests being done using a weak fishing line in the hope that it would break as soon as flow reversal occurs. Fike’s test protocol involved a well-controlled pneumatic actuator. After the dust injection and ignition, the flap is released.

“There are much higher closure velocities because there is already an explosion pressure when the flap is released,” Jim said. “Also much higher pressures in the bolts, unprotected and protected pipeline. And this flap failed. There was, again, mechanical damage, failure. What we ask is that the standards not only say, “Make sure you hold it until flow reversal. It should describe the correct technologies and mechanisms that you can validate that the test was valid.”

The third issue involved correlating explosion vessel arrangements- venting, suppression, containment- with the intend use of the flap valve. In most cases, a flap valve is used with a vented vessel in industry, and nearly all testing is restricted to that setup.

“We have seen that the test houses for ATEX certification use open ports and not a vent panel,” Jim pointed out. “They probably do that to avoid the dust injector creating overpressure, which already starts closing the valve prematurely. So they leave the ports open. So that dust injection is there and it doesn’t create overpressure. But what happens if you initiate the explosion? The flame immediately finds the open port and that is its preferential propagation path.”

If the flap valve is closed after, the explosion doesn’t want to propagate through it: instead, it might propagate halfway in the pipeline between the explosion test vessel and the flap valve. There is less pressure because venting starts immediately instead of after bursting a vent panel. The seal and installation distance are not challenged correctly. This method could result in overly optimistic certification values, both on the pressure side and installation distance, which then leads to dangerous situations in the fields.

What recommendations arose from this testing?

Jim pointed out that many explosion flap valves that have been certified may not have been tested correctly, making them potentially unsafe.

“So what we ask is a change in the testing standards of EN 16447 to include additional elements that reflect the real world in the testing protocols. On the other hand, we should look at all flap valves available and installed and check if they are tested correctly or not. Have they been tested to see if they can protect their own pipelines? Have they been tested with the flap held in an open position until ignition or after? Or have they been tested with a blower? Have they been tested with vent panels or foils instead of open ports?”

If the answer is yes to all, the flap valve can be relied upon. But Jim warned that if any of the answers is no, the flap valve has to be rested to confirm that it is safe.

Fike has presented its findings to the European Standardisation Committee responsible for standards on the explosion protection systems, but it may be two or three years before any changes are made.

“In the meantime, we have to be careful and check every flap valve to see if it has been tested correctly, and if not, retest it,” Jim said.

Conclusion

Flap valves are a relatively new technology compared to more traditional explosion isolation systems, although they have been used for other purposes for years.

“The fact that we may have been a little bit too fast in accepting (new technologies) is maybe a lesson learned from industry,” Jim said. “The scientific community was almost forced to give rapid advice because it was already in use. And then you may not have all the findings. Maybe we should be a little bit slower in accepting explosion protection technologies, so that there may be lessons learned for the future.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Jim Vingerhoets directly:
Email: [email protected]
LinkedIn:https://www.linkedin.com/in/jimvingerhoets/

If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.