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DTMs open the landscape for plant maintenance

Author : Michael Babb, Control Engineering Europe

07 June 2010

While fieldbus is becoming the dominant architecture of process automation, its true value for instrument diagnostics and preventative maintenance can only be realised with powerful software tools like DTM.

The Eemskanaal Plant is one of the twenty ‘clusters’ of gas wells in the NAM project in the Groningen province of The Netherlands.
The Eemskanaal Plant is one of the twenty ‘clusters’ of gas wells in the NAM project in the Groningen province of The Netherlands.

Like most European countries, gas is a critical source of energy for The Netherlands. And most conveniently for the 16 million Dutch people, an abundant annual supply, 35 billion cubic meters, is located in Groningen province, at the far northeastern corner of the country.

PHOTO: This cluster, called ‘OV-Eemskanaal’ includes well heads on the far right and, to the left, processing equipment to dehydrate and remove impurities, and compressors to increase the pressure for transmission. A derrick in the well field is drilling for another gas pocket that is a few kilometres away. Eemskanaal is one of the custody transfer points where gas is piped outside the field for commercial distribution. Operation of all equipment in the cluster is completely automatic, controlled by a central station.

This rich gas area began producing in the 1960s. Since then, the inevitable depletion of resources, aging of equipment, and stricter environmental regulations have required a massive upgrading of the equipment.

NAM, the Dutch Petrol Company (a fifty-fifty joint venture of Shell and Exxon) that oversees the project, began working on the upgrade in 1997. They realised the days of ‘free flow,’ as they say, are gone, and like most other oil and gas companies around the world, a great deal of additional effort is required to continue production. And a lot more capital: a billion euros.

The most urgent need is to boost the gas pressure. Nearly 40 years of production have depleted the source by half, reducing the wellhead pressure to 90 bar. About 30 bar is lost in processing — dehydrating and removing impurities — which leaves 60 left over for transmission. Since this is the threshold value for gas distribution, NAM engineers know that if they are going to be supplying in the year 2040 and beyond,  they will have to do it with gas compression equipment.

Another great need is to stabilise the gas supply for consumers’ varying needs. During the hot summer, the Dutch demand a modest 50 million cubic metres from Groningen. But a few months later, on a cold winter day, they may ask for 250!

Even on a daily basis, the demand may swing at a 3:1 ratio. To handle these wide changes in demand, NAM is planning to reconstruct its huge underground storage facilities, one kilometre below the surface, to act as a buffer for the gas supply.

As one would expect, an engineering project of this scale cannot be handled by a single company, no matter how large it is. A five-company consortium called  Stork GLT was formed in 1997, and after 12 years with all the cluster renovation done, NAM has signed up for another 15 years with the consortium, which is now called ‘GLT-PLUS,’ for the additional renovations and maintenance of the plants.  Yokogawa Europe is the member that  supplies instrumentation and control.

Cluster by cluster
The gas wells are organised into 20 clusters, each consisting of a number of wells plus a treatment plant. The clusters have charming Dutch names such as Tjuchem , Spitsbergen, and Kooipolder.

Each cluster has its own control room, but is normally unmanned and operates automatically, under the supervision of the central control room. The complete field  is controlled by a Yokogawa CentumVP system, the largest Field Wide DCS in the world, claims Ron Schoemaker, representative of Yokogawa within the Consortium.

He says it presently supervises about 800,000 tags, and when the underground storage facilities are connected to the Field Wide DCS, the tag count will be close to a million. The gas field is automated to the degree that, theoretically, one man could run the entire operation. In practice, NAM keeps two men in the control room.

Renovation has proceeded cluster by cluster, with the first two-year project finished in 1998. Since then, it has been a ‘copy-and-paste’ procedure, with the execution time getting shorter, and the learning curve flatter and flatter.

The sequence of clusters is important, because NAM wants to maintain adequate production capacity at all times. The project began with the ‘king size’ clusters in the north, the ones that can produce 25 million cubic metres per day, and ends with to the older and smaller 15 million size clusters in the south.

The latest technology
With the project spanning 25 years, incorporating the latest technology is important, both for NAM and for Yokogawa. But they have to be careful what they choose.

As a NAM project manager says, ‘The suppliers think twice before they recommend specific equipment or solutions in this project, as they are also responsible for keeping it up and running.’ Twenty-five years can be a long time to live with a mistake.

DTMs such as this one collect and organise hundreds of instrument parameters and diagnostics and make them available in comprehensible form for maintenance engineers.
DTMs such as this one collect and organise hundreds of instrument parameters and diagnostics and make them available in comprehensible form for maintenance engineers.

And so back in 1997, Yokogawa was cautious about fieldbus. It wasn’t sufficiently mature at that time, and although the promise was great, the reality wasn’t there.

‘When we started, fieldbus was too new for us to consider using it,’ says Mr. Schoemaker. But the concept of predictive maintenance appealed to his team, and so the first 13 clusters were done with standard HART instruments, in a ‘quasi fieldbus’ of sorts. Yokogawa’s field controllers are connected to the central control system by using a dedicated fibreoptic network.

Robin de Vries, Plant Asset Expert for Yokogawa, says his company stuck its toe in the water at the Leermens cluster in 2004. It was the first one equipped with Fieldbus Foundation technology on a pilot basis, and has 25 FF devices in four segments. The next, Spitsbergen got the full fieldbus treatment. Since that time, it’s been full speed ahead with fieldbus technology.

Mr. de Vries estimates there are now 2,500 ‘intelligent’ instruments connected with Foundation Fieldbus and 8,000 with HART. Most of them are Yokogawa instruments for pressure, mass flow, temperature, and conductivity.

But standardised instrumentation buses make it easy to connect other manufacturers’ devices, and so there is a scattering of Magnetrol and Endress+Hauser level instrumentation and Emerson valve positioners.

DTMs for configuration
The first installations of fieldbus technology, which began in 2004, were before the FDT/DTM was generally available. ABB, Endress+Hauser, Invensys, Metso, and Siemens had begun the discussions of the technology and had an informal association dating back to the early 2000s. The growing number of members and interest led to the formation of the ‘FDT Group’ in September 2005.

By the time the first DTMs arrived at the project, several FF installations were already in operation, so there wasn’t much opportunity to use them to configure the instruments. That is in the process of changing, of course.

One area of DTM application that has been especially useful has been the configuring the physical layer of the fieldbus. The task of setting up a fieldbus has proven to be more difficult than anticipated, not only for Yokogawa but other process control equipment manufacturers and systems integrators working with FF.

But, DTMs have come to the ‘rescue’ says Mr. de Vries. Pepperl+Fuchs’s fieldbus physical layer equipment is used in the project, and the company has prepared a DTM to help configure the network. It has proved to be most helpful for engineers who are tasked with setting up the network and configuring it for operation, simplifying many aspects of the work.

DTMs for diagnostics
But the real power of the DTMs is already visible in the diagnostic and proactive maintenance sections of the project. One of the great strengths of Fieldbus Foundation is that it allows for an extensive set of instrument diagnostics to be transmitted back to the central control system, where the data can be recorded in the asset management system.

The emphasis has now shifted to the immediate problem this poses: with so much data — hundreds of parameters from thousands of instruments — how do you bring it all together to make useful information?

Even though this communications technology is very powerful, it is difficult for maintenance engineers to use data coming from it, admits Mr. de Vries. To make his point, he shows a screen that displays FF diagnostics; it’s a long list of variables, many with cryptic acronyms.

He shows an example, one that would be difficult for a ‘traditional’ maintenance engineer to understand: The fieldbus parameter is called ‘LIN_TYPE.’

‘This is actually the linearisation characteristic of the measured signal that will be used in control loops — direct, indirect, indirect with square root function. In the DTM this parameter is clearly described as ‘Linearisation Type’ in the ‘easy setup’ menu.

Ron Schoemaker and Robin de Vries, Yokogawa Europe
Ron Schoemaker and Robin de Vries, Yokogawa Europe

‘For a maintenance engineer to use the Fieldbus Foundation diagnostic list, he would have to have a printed manual to consult, to tell him what all these variable are, and which ones are the most important to look at. The DTM organises this for him, and makes it quite plain what he is supposed to do, what action he should take.’

For sure, maintenance has become an important part of the project. Outside the central control room, maintained by two operators, is the maintenance area, where a dozen engineers sit. They keep a constant eye on the health of the various clusters. Each has three computer screens to look at.

Yokogawa’s Plant Resource Management (PRM) software is the backbone for all maintenance operations. The combination of FF networking technology, combined with the use of DTMs and the PRM software make it possible for the engineers to keep track of thousands of valves and instruments. In many cases, when problems arise, the maintenance engineers can use DTMs to get a quick picture of what is happening with the equipment.

Work orders are prepared each day, and the next morning a gathering of representative maintenance engineers meet with operations personnel to discuss needs and priorities. The close collaboration means there are few, if any, ‘surprises’ to the departments involved.

And so, the maintenance department, thanks to powerful tools like DTMs, are beginning to change from ‘corrective’ mode to ‘proactive’ mode. The intelligent instruments and the database infrastructure has now been put into operation to make this happen. There is still a learning curve, but the engineers are starting to make their way through it.

For an introductory article on FDT technology, "FDT: The ‘Right Technology at the Right Time'" go here.

To read two more application articles in our FDT series, click on the links below.

Commissioning Like a Pro

Technology With Added Value

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