Article by Lucien Joppen.
Marty van Tilburg (age 41) has been working for Sitech (see box Sitech Services) for six years. Having studied mechanical engineering, he opted for a job that embodies both mechanical engineering and process control. “When I applied for the job, frankly I didn’t have any experience with valves. Luckily I am a quick learner and there were enough experienced engineers at Sitech who could show me the ropes.”
Sitech’s valve park encompasses more than 15,000 valves, van Tilburg says. These valves are stationed in and around the production facilities of Sitech’s clients – (petro)chemical companies on the Chemelot site.
It is van Tilburg’s job, and of his 15 colleagues, to keep this valve park in tiptop shape. “My coworkers each have a number of factories they serve. Personally, I am not directly involved with the clients; it is my job to intervene, or trouble shoot, when my colleagues need a second opinion.”
When asked about what percentage of the enormous volume is problematic, he says that only 1% is cause for continuous concern. Most of the valve park consists of off-the-shelf valves (mostly control valves) that are overhauled according a set maintenance plan, which can stretch from 1 up to 12 years, or a replacement. Most of these valves function without hesitation in this period. Van Tilburg or one of his colleagues only step in when these valves are breaking down prematurely.
So we’re effectively talking about 250 valves, mostly control and shut-off valves, that are high priority for van Tilburg and his team. “First of all, it is not only about operational issues. A valve type that is difficult to source is also on our to-do list. At the moment we are scanning the market for suppliers of a certain anti-surge valve as the ‘old’ suppliers doesn’t carry this item anymore. Apart from these activities, we are involved in maintenance and services & engineering advice regarding valves that are crucial in the production process.
We experience at first-hand that regular problems are mostly triggered by material breakdowns. Of course, the medium (as in liquids) plays an important role. You’d think that aggressive chemicals would cause the majority of problems. Not for us. Cooling water (coming from the river Maas and the Julianacanal, ed.) poses the biggest challenge, mostly because we don’t know exactly what’s in it. In the past this water has severely corroded seating material in our valves.”
Steam is also very demanding on valves, van Tilburg states. Certain valves are exposed internally to steam clouds which causes springs to rust and, in some cases, total breakdown of the actuator as the aluminium basically dissolves. Finally, process conditions like heat, pressure and flow conditions are putting valves to the test. As van Tilburg says, in normal conditions control valves are set at around 70 percent of their capacity.
“There is a tendency to maximize output, also for ageing plants. This is feasible as we have managed to eliminate certain bottlenecks. For example, we have increased/ enlarged the interior of a control valve, a procedure which changes the flow coefficient. It is possible, provided this procedure doesn’t have over- or under pressure consequences for equipment further downstream.”
According to van Tilburg, the plants that Sitech maintains are in top condition. The facilities might seem old, but these are thoroughly serviced and updated every two to four years, depending on the type of facility.
In between, it is a matter of keeping a close watch on the valves that are critical. This effectively means performing regular checks for control and shut-off valves in order to see whether their performance deviates from the norm.
“With control valves we look, for example, at positioner data regarding the setpoint. In shut-off valves we measure the slip-stick, which tells us whether a valve is sticking or not. Based upon these readings, we discuss our findings with operational management and plan our maintenance activities accordingly.”
As Valve World has written about earlier (see June 2018 issue), Sitech Services is working towards predictive maintenance with its Asset Health Center (see box Vision 2020). Van Tilburg and his colleagues are also involved in this project.
“Ten control valves and fifty shut-off valves are involved. These valves have been selected according to various criteria. First of all, the plants needed to have compatible software in order for our Asset Health Center to read out relevant data. As for the control valves, these were considered performance killers or cost drivers. This was clearly visible after comparing the revision of the valve with the notification and the shift reports.”
The data are collected and analysed in conjunction with the Asset Health Center. The latter has developed predictive models, based upon algorithms, for various pieces of equipment (pumps, valves etc.). These algorithms are designed to predict failures based on processing parameters and additional data (for example weather data, ed.).
Preventing unplanned shutdowns
Van Tilburg says it is all about trends. “We are focussed on data which covers a longer period of time. These data are precursors of potential breakdowns. For example, a certain control valve came to our attention due to hunting: the valve was acting like a shut-off valve in its lower regions and it took too long to move during opening and closing. Based on our observations and the predictive models of the Sitech AHC, we are able to pinpoint failure more accurately.”
Of course, van Tilburg and his colleagues would not want to be proved right in this matter. Ideally, these failures should be prevented by taking measures during planned shutdowns. Van Tilburg says he and his team have prevented at least two unplanned shutdowns on Chemelot.
“In one case, we foresaw problems with a positioner in a control valve. From the outside, one could not detect that the actuator spring was worn out. By replacing this item during a planned shutdown, we were able to prevent possible future problems as the valve most likely would have broken down before the next planned shutdown.”
During the two years that van Tilburg’s team has been working with predictive modelling, they have built a track record which resonates with the plant managers of the facilities that are involved. Van Tilburg admits that it is not easy to convince them to invest in precautionary measures as budgets are tight and the motto ‘if it isn’t broken, don’t fix it’ could supersede preliminary measures like the ones van Tilburg’s team had done by replacing the positioner.
“For a plant manager every euro counts”, van Tilburg says. “However, ideally you want to solve problems when it doesn’t hurt or interfere with the production. By establishing a track record over the last two years, we have been able to demonstrate that we can make a difference. This also makes it easier for us to convince plant managers to use predictive models.”
Finally, when asked if his team uses additional sensors for predictive modelling, van Tilburg answers: “We have discussed the use of vibration sensors that could be employed in the vicinity of (control) valves. For the time being, we will continue this program, bearing in mind that we only have so many hours for this project. Our daily responsibilities and commitments come first.”
Sitech Services was established in 2008 at the Chemelot chemical site in Geleen, in the south of the Netherlands, but has a long track record as it originated from the service departments of former DSM’s divisions. Nowadays Sitech helps companies in the process industry, the chemical industry and the energy sector, to grow and develop by supporting them with their unique services and the latest technologies, using expertise, innovation and extensive digitization as tools.
Chemelot is a unique chemical and materials community that ensures accelerated business growth through the open exchange of ideas. A growing environment for economy and working space, with the goal to reach world class status by 2025 in (more sustainable) chemistry and new materials. At the moment, Sitech Services employs approximately 900 experts for more than 25 production facilities on the Chemelot-site.
Asset Health Center
The seed for Sitech’s Asset Health Center was planted in its document Vision 2020, which was devised by Business Unit Manager Richard Schouten (see image). “The idea behind the vision document”, Schouten explains, “was to formulate a shared vision on future maintenance, incorporating new, exciting technologies such as 3D-printing, data-analytics and so on. Because Sitech is not involved in production, but purely focused on manufacturing and site services, we are able to ‘disconnect’ from the day-to-day routine, take a step back and analyse new ways of conducting maintenance.”
The SAHC was established in 2016. In the years before, the Smart Industry Initiative, a public-private venture, was launched to promote the development of Industry 4.0 concepts in manufacturing. “We recognized that we could fit our SAHC concept into this program and partly fund this centre”, Schouten says.
According to Schouten, the SAHC was set up to make predictive maintenance a reality, not just some theoretical construct. “The term was coined by the US Navy in the 1960’s, but it has been a hollow concept for decades.”