^ It is Mr. Meliefste’s sincere hope that the WIB’s recommended practice will make a major contribution to safety and reliability in when it comes to actuated valves in process facilities
Article By David Sear
Describing the creation of the WIB’s new recommended practice, Mr. Meliefste compares it to a hurdle race. “We had to address a lot of challenges,” he said. “To start with many different disciplines and parties were involved with unclear responsibilities and often using different terminologies. Then there was the lack of standard datasheets addressing application requirements (on/off valve sizing datasheet), as well as a lack of clear and unambiguous definitions for valve torque data, factors and coefficients. And the list of hurdles continues, as we also had to contend with a lack of quality valve torque data including ‘on demand correction factors’. And even today there are still gaps in relation to data sheets, valve torque data, etc.”
But why was this new recommended practice deemed necessary in the first place? To answer that question, Mr. Meliefste simply has to start showing the huge number of photos he has collected over the years. These reveal the almost haphazard way that actuators are sometimes mounted to valves. “Do these assemblies look safe and reliable to you?” he asks. “Valves and actuators have been bolted together at the lowest possible cost. I have numerous examples of AV assemblies with multiple brackets, misalignment, poor engagement of the stem, exotic brackets and the like. What makes matters worse is that these actuated valve assemblies are often used as part of a Safety Instrumented System, meaning that a failure could have catastrophic consequences.”
What is needed, stresses Mr. Meliefste, is a sea-change in perception. “An AV assembly is an engineered product and should be treated as such. So all the components that are selected – the valve, the actuator, the bracket, the solenoid, the switchbox, etc – should have been built to the same high standard and should be compatible with each other. A chain is as strong as the weakest link, so there’s no point using a flimsy bracket to mount a heavy actuator.
Discussing how the WIB set about this initiative, which was to take thirteen years’ hard work and involve many individuals and companies, Mr. Meliefste notes that: “key objectives were to identify any missing pieces in the current international standards, to specify those missing pieces and to reference applicable sub-clauses from the current standards. ISO 12490 and EN 15081 were used as a base.”
The resulting document – which contains an amazing wealth of information and runs to 67 pages – is freely available for use, by both WIB members and anyone else involved in the specification and application of industrial AV assemblies. The entire document is broken into sections such as terms & definitions, assembly sizing & selection / torque test procedures, dimensions, AV assembly inspection & routine testing, marking, assembling, sizing data sheet & valve torque input form, dynamic torque.
The recommended practice should go a long, long way to improving the safety and reliability of actuated valve assemblies. Nevertheless, communication remains key, stresses Mr. Meliefste. “As stated, AV assemblies really are engineered products. This means that proper communication is required. End users should therefore provide all the necessary process and application data. Similarly, valve manufacturers must provide all the required valve torque data and ODCF (on demand valve torque correction factor). Missing or vague data from either party is unacceptable.
Finally, asked if he believes there will ever be an end to the ‘hurdle race’ Mr. Meliefste is optimistic. “Oh yes, if we all cooperate in using the recommended practice and promote better consultation between end-users, EPCs, valve manufacturers and AV assembly contractors then that is the best way forward to realising safe and reliable actuated valve assembles.”
That cooperation is already starting to take shape. “For example, Bray is helping to produce tested data for so-called Long Stand Still, which will hopefully trigger other valve vendors to follow suit and provide helpful data,” says Mr. Meliefste.
He further adds that the WIB is communicating with electrical actuator vendors such as Auma and Rotork to append electrical actuators to the recommended practice and to the ISO TC153 standard, whilst the people behind CONVAL are already working hard to develop an RP / ISO compliant module.
“And finally, we are in continuous dialog to realize an AV Assembly certification process, which is highly needed,” notes Mr. Meliefste.
And last but by no means least, the value of the WIB’s recommended practice is also evidenced by a communication from the ISO. Mr. Meliefste: “with the help of people such as Metso’s David Bayreuther, the WIB’s recommended practice has been accepted as an ISO TC153 WG 16 project to become an international standard. It is my sincere hope that the WIB’s recommended practice will make a major contribution to safety and reliability in when it comes to actuated valves in process facilities.”
About the WIB
The WIB is an international Instrument Users’ Association (WIB actually stands for Working party on Instrument Behaviour). This end-user organization was established in the mid 1960s and currently has an international membership of 41 companies. Organized into Working Groups (currently eleven) the role of the WIB is to promote the exchange of experience, provide selection guidance, conduct laboratory testing, set minimum requirements, promote standardisation. It also seeks co-operation on a European level.