“The sizing of actuators for on/off valves is an issue which needs more attention in the industry. One of the problems is that there is no international standard for testing and validation of torque data by valve manufacturers. These ‘paper’ data need to be supported by documentation that proves how these data are generated.”
Kees Meliefste, senior instrumentation specialist for Dow Chemicals, is a seasoned veteran in the valves and actuation business. He has been working for the multinational for more than 28 years. Originally trained in civil engineering, he opted to retrain himself in control systems engineering. “The labour market in the early eighties was dire”, Meliefste states in his office at the site in Terneuzen (see box). “However, there were still possibilities in the above domain.”
Momentarily, Meliefste is the Technology Leader of the so-called Global Technology Team that is focused on automated valves (control and on/off). “Our responsibilities encompass both the technology and the supply chain pertaining to valves, actuators and related equipment (solenoids, switchboxes, positioners, boosters etc.). As such we are also involved in the procurement process.”
Meliefste states that Dow’s internal organisation is far from fragmented when it comes to valves and actuation. “All relevant disciplines – valve specialists, operations, maintenance, procurement – are involved, which is a process that started 25 years ago. As a result, we have established a tight working unit with a strong front-end loading capacity. If we do our job well at the front end, we can eliminate most of the complications at the operational level.”
Meliefste adds that the Global Technology Team members have their respective responsibilities for the production sites they are assigned to. “My direct colleagues and I are involved in plant and project support, standardization, quality management and functional safety (partly SIS, ed.)”
Although Dow has managed to create an effective management system for its global valve and actuation park, there are and will always be issues that need to be addressed. Not only by Dow, but also by its peers in the (petro) chemical industry. Meliefste also mentions the WIB-initiative, the Process Automation Users Association for the Dutch and Belgian industry. WIB is working closely with its sister organisation in the UK (Evaluation International) and its German counterpart (NAMUR).
“One of the issues the WIB-working group for valves/actuation is working on is the proper sizing of actuators for automated on/off valves”, Meliefste says. “This issue has arisen over the last decades; more and more on/off valves are automated and its role has become more prominent in the process configuration. However, as a rule of thumb, automated on/off valves are treated as ‘off-the-shelf’ products and not as an engineered product such as control valves.”
Final Elements in SIS-loop
According to Meliefste, automated on/off valves have evolved in their role as final elements in SIS-loops. Therefore these valves are critical and shouldn’t be off-the-shelf but rather more tailored to the needs of the application.
“On/off valves are not always used at the same frequency and intensity. For example, in our batch plants, on/off valves are used intensively, while in our continuous operating plants the on/off valves only switches once per so many years. This highly impacts the required actuator torque to operate the valve. As I have mentioned before, automated on/off valves are increasingly part of our safety systems. This is one of the reasons why this torque has become more important.”
Torque Data Not Accurate
Meliefste says that a lot of the torque data that are provided by manufacturers regarding on/off valves which are used for automation is not accurate and consistent. Actually there is a lack of quality valve torque data, including application related correction factors.
“For end users it is unclear how these torque data were generated. Therefore, at WIB we are working on a recommended practice as how manufacturers should generate and validate these data. As end users we need accurate data to properly size the actuator to the on/off valve. In general, the sizing aspect is well covered by the ISO 12490 guideline but specific aspects, such as the quality of torque data and actuator sizing data sheet, need to be addressed, hence the WIB-initiative.”
Data: No Black Box Scenario
When asked about the role of (process) data in his daily work, Meliefste mentions that Dow has embraced Industry 4.0, which entails the use of (big) data for various purposes, for example predictive maintenance. Meliefste acknowledges that Industry 4.0 definitely has potential. However, it will take some time to implement these concepts.
“It will require more effort to actually use big data in our operations. Of course we use process related data in our company but there is still a lot of ground to be won. For example, for 15 years we have been generating data from our control valves but we haven’t got the capacity to analyse these (historical) data and translate these findings into management insights. For now, the challenge is to establish a business case within the company that would allocate budget and manpower to get into a learning curve. Whatever the Industry 4.0 will be, I do think that we need to know how these systems are working. It shouldn’t be a black box scenario.”
As mentioned before, Meliefste and his colleagues in the Global Technology team are also involved in procurement. He does not engage in the actual buying process but he has an important say as to which suppliers are included in the Approved Vendor List. When asked whether Dow has rationalized this list, for example by decreasing the total number of suppliers, his answer is “yes, to a certain extent, but never single source”.
“We have managed to stabilize our supply base. Over the years we have standardized our portfolio according to brand/supplier and model configurations. In this matrix, we apply the 90/10 rule as we are not be able to cover all our applications. As our installed base is gigantic – we are talking tens of thousands of valves on a global base – there are still valves in operation that are not on our list. If these are working well, there would not be a need to replace these. Having said this, during one of our next overhauls we will replace a significant number because these valves are at the end of their life.”