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Condition monitoring of multiphase pumps
34
Feature WORLD PUMPS
April 2010
Condition monitoring
Condition monitoring of multiphase pumps Gerhard Rohlfing discusses the current state of conditioning examination in multiphase twin screw pump systems and how it can increase pump life. He also looks at some examples in the oil and gas industry where, done correctly, it has been found to improve efficiency.
B
esides the ongoing process of control hard and software development, manufacturers of machines and systems have also started using control systems to monitor the equipment’s condition with an aim to increase the machine’s up-time and, as a result, the economic viability of the equipment. This article will look at common methods of accomplishing this and will then define condition monitoring as one tool to increase the availability of systems, considering the advantages of this method and looking at how successful conditioning can be accomplished. The focus will then be on multiphase twin screw pump technology. The fundamental basis for the development of condition monitored multiphase pump systems is the system itself. This article will define a common standard and look at how multiple variants of the system and the application are presented. Finally the article will look at the vital part an IT platform has to play in modern multiphase pump systems as a generator of condition data, and common methods of data communication will be described. The main focus is an outline of existing condition monitoring modules, the benefits of these modules and an outlook on future modules which are part of ongoing research activities.
www.worldpumps.com
Common control methods There are several methods proven to increase system availability using multiphase pump technology. Engineers generally try to choose a product by looking at product availability. High-quality products, proven technology and qualified vendors will be preferred if system availability is of capital importance.
‘Condition monitoring can also be a part of an effective training system, whereby operational experience can be gained.’ To upgrade a system’s reliability, it is also common practice to use fail-proof and highly reliable components for the vital parts of the system. These components in general use multiple redundant functional units, which are accurately tested on performance. The fail-proof programmable logic control system (PLC) of a pump system is one example of this. Another way of minimising the probability of a system breakdown is to reduce the number of sub-components in a system to a minimum. Every additional sub-component is a potential source of defects and can lead to a malfunction of the system – or in the worst case to a system breakdown. An example of a proven integral functional
0262 1762/10 © 2010 Elsevier Ltd. All rights reserved
solution in screw pump systems is the modified motor/pump coupling, which is fitted with fins in order to work like a fan. Without the need for additional components, this coupling can be used to cool pump bearing and gear housings. No additional fan with motor, which can fail, is needed. Another influence on system condition and the duration of system downtime is the technical expertise of operational and maintenance staff. A well trained operator knows the characteristic signals of his or her equipment and will react appropriately, before the system condition changes for the worse. Similarly, a professional maintenance staff member will be able to find the most effective way to repair and restart a plant after a breakdown. So, investing in the qualification of operators and maintenance staff will have a positive influence on the system’s availability. Naturally, routine and preventive maintenance activities also have a direct influence on the availability of machines and systems. Increasing the frequency of maintenance activities and intensifying maintenance activities will reduce breakdowns or repair work. If this does not take place, downtime caused by maintenance work and the relating costs will often increase. Finally, condition monitoring should be mentioned as an intelligent method to increase the availability of technical systems. A condition monitoring system in general uses different sensors to
WORLD PUMPS
Feature April 2010
monitor, on the one hand, the condition of vital system components and, on the other hand, the processes in which they are used. It makes use of an IT system, which processes the data and generates the condition data of the system. Contrary to preventive maintenance, where parts and components of a system are inspected and replaced preventively during periodical maintenance activities, condition monitoring should allow condition-dependent maintenance activities. This should lead to a scenario in which the service life of vital components is utilized at a maximum, being based on detailed information about the component condition. According to this maintenance philosophy, a condition monitoring system, together with an adjusted maintenance logistic, will lead to a highly economical operational concept, resulting in low maintenance costs and high system availability. As well as the increase of system availability, condition monitoring in general allows process optimisation, which positively influences the economic efficiency of the equipment. Condition monitoring can also be a part of an effective training system, whereby operational experience can be gained and used for future product improvement and development.
The path to successful monitoring For successful condition monitoring, general know-how about the vital system components and about the operational process is essential. Only a combination of component condition data and process data, however, will make it possible to successfully evaluate a system’s condition. One example is the condition monitoring of a wind engine’s drive and gear system. After several years of development, including thousands of hours’ operational experience, the condition monitoring of wind engines is, today, a proven and effective tool and is now requested for wind engines by insurance companies. This combination of evaluated load characteristic of the rotor system and sensor data of the gear system makes it possible to make accurate statements about the remaining gear system’s service life. The same requirements have to be fulfilled with the condition monitoring of multiphase twin-screw pump systems. An adequate amount of operating hours and field experience in different installations can lead to a deep understanding of the unsteady multiphase transport process. However, it is also necessary to possess basic theory in order to describe the
Figure 1. The components making up the multiphase pump (MPP) system. ©Bornemann GmbH 2009.
effective static and dynamic loads, and the corresponding load capacity of vital system components should be known and describable in detail. Without this, the background condition monitoring of multiphase twin-screw pump systems will not meet expectations. The major properties of a condition monitoring system include the ability to collect, analyse and store process and condition data of current and previous operation in order to predict system’s future service life. In order to carry out maintenance planning and future product improvement and development, a local monitoring system needs data exchange in a higher-level control centre, as well as the application of expert knowledge on a condition monitoring system and collected field experience. This data exchange can be put into place by setting up personal data transport or remote access in different layouts. In this case, the security and integrity of the data thereby should have the highest priority.
Multiphase twin-screw pump system For successful condition monitoring, we need not only an infrastructure (described later in this article), but also system monitoring know-how and an understanding of the process in which the system works. When we consider a modern and basic multiphase screw pump system, the configuration as seen in Figure 1 has to be examined. The main component of Bornemann’s MPP (Multiphase Pump) system is the multiphase screw pump with its seal
system and the main drive. The MPP is controlled by a PLC with a human machine interface (HMI). The PLC gets its signals from different sensors and switches (such as pressure, temperature, vibration, level, speed and power) and controls different actuators (such as main drive, valve actuators and actuators of seal system) to keep the MPP system on-line. The company’s MPP system can be customized to its location, to the multiphase medium, to the operating conditions and to individual customer specifications. Currently, a Bornemann MPP system is operating in a variety of conditions, such as desert, permafrost, tropes, offshore top side and even sub-sea. The pumps are used to transport heavy crude oil as well as conventional multiphase mixtures of oil, water, parts of solids and natural gas from zero to 98% gas void fraction (GVF). Wet gas (98% to 100% GVF) and thermal operation at steaminjected fields can also be handled. These kinds of media can be corrosive and abrasive, as well as explosive and mostly toxic. Multiphase screw pumps can also be used to reduce wellhead pressure to nearly atmospheric pressure, to increase discharge of the formation and to boost pipeline pressure if needed to above 100 bar. They can be used to transport only a few m3 of oil per hour from marginal fields or more than 2,000 m3 per hour to a central processing unit (transfer pump). Operation often happens under permanently unsteady conditions. Due to this wide range of applications, MPP systems have to fulfil a wide range of
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Feature WORLD PUMPS
requirements. Therefore, specialized variants of the system are available.
The scope of an MPP An MPP system can include a circuitbreaker, a transformer, switchboards, grounding and uninterrupted power supply. As the main drive, an electrical motor and a variable frequency converter (VFD) is a often used. Diesel or gas engines are an alternative. Beside the seal system (which is used to flush the seals, handle barrier fluid or recover leakage), other auxiliary systems can be a part of the MPP system, such as compressor units for pneumatic valve actuators, hydraulic systems for hydraulic valve actuators, lube oil circulation systems, cooling systems, fire and gas detection systems, air conditioning, fire-fighting system, fluid injection systems and different kinds of control systems. Despite the necessary variation in conditions such as location, process and equipment, a modern multiphase screw pump system will generally implement a condition monitoring system, which generally forms a perfect match with a MPP system. Usually the control system consists of a PLC on a skid, which communicates to a humanmachine interface (HMI) via an Ethernet connection and receives all necessary sensor signals. Most modern MPP systems also feature a storage unit for process data.
These days it is possible to upgrade an MPP system to allow it to perform condition monitoring. The only equipment to be added is an intelligent condition monitoring system, suitable modules and a remote access system (RAS) (See Figure 2). Retrofitting a modern multiphase screw pump system should be possible in most cases. To connect the MPP system at all mentioned locations over the world, different RAS systems are also available. Depending on the local technical conditions, the MPP system can be connected via analogue or digital telephone line, broadband data communication, GSM/ UMTS mobile radio service, directional radio or satellite transmission. These can also be used to connect the customer’s control room. The oil and gas industry has to ensure that it has effective data integrity and data security in order to avoid hostile network access. As a result, it tends to favour data communication via a separated world-wide network. This kind of network combines the advantages of the internet, such as worldwide availability, with the security of a separated network, with known and identified users. The operator of an MPP system also needs to be able to decide what system access third parties have, including any control of the Remote Access Server hardware contact, and should have clear insight into data storage procedures.
Figure 2. The control system of a MPP unit incorporating additional CM hardware. ©Bornemann GmbH 2009.
www.worldpumps.com
April 2010
More than pure maintenance The real benefits of a condition monitoring system are generated by the various available modules. A basic module is the system online view, which can be set up through remote access to the PLC. This online view allows every authorized user to have individual access to the process and component condition data. If needed, he or she can get full access to the control system. In the lifetime of an MPP system, the first significant benefit of using a condition monitoring system occurs during commissioning and start-up. With an online view of the pump system available to third parties, these parties can offer different support during start-up and commissioning. Pump, control or drive experts can be involved during the start-up phase on short demand. This access extends the available know-how to a maximum, with minimum costs and maximum flexibility. Using remote access, it is proven practice to adjust system parameters according to the operating conditions needed. Sensor set points, drive parameters, parameters of further sub-systems such as cooling systems, lube oil systems or air conditioning can all be adjusted in order to optimize the pump system’s operation during the adjustment process of the start up phase. Troubleshooting or adding complete software updates for the HMI, PLC or the condition monitoring software itself can also be handled via remote access.
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Feature WORLD PUMPS
April 2010
Figure 3. The remote access system (RAS) can make use of a variety of remote connections to transmit information . ©Bornemann GmbH 2009.
Of course, expert online viewing via remote access is also an effective way to reduce the need for troubleshooting and, as a consequence, system downtime. Moreover, the process of contacting system experts at short notice creates additional experience for the operating crew. Beside troubleshooting and training support, condition monitoring via remote access can also be used to improve the performance of the multiphase transport process. Supported by the MPP system expert, operators can adjust the system’s operation data, examining the interaction with connected wells upstream or, for example, a central separator plant downstream. So, besides the many benefits that result from an online view on the control system, the condition monitoring modules are also useful in automatically generating condition data of the vital components in a multiphase pump system. First of all, the vital components have to be analyzed and selected. It is vitally important to select a component with regard to system function and its failure probability. As a result of this analysis, four main subject areas can be distinguished: the drive system, the multiphase pump, the subsystems in general and operation supplies. www.worldpumps.com
In a drive system, such as an electric motor, the windings, bearings and the variable frequency drive (VFD) with its sub-control system are vital components. With multiphase pumps, the coupling, conveying elements, bearings, gear wheels and mechanical seals are of major importance. Attention should be paid to all subsystems. As well as this, the operation of hydraulic pumps, compressors or valve operating mechanisms has to be taken into consideration. Finally, operation supplies of a MPP system, such as lube oil, liquid filling, barrier fluid or flushing of mechanical seals, batteries and filter cartridges can affect the system’s service life and possible bring about system breakdown.
The drive system In the drive system, the condition of windings can be monitored by winding temperature (adjusted by local ambient temperature) in relation to the required hydraulic power of the pump (depending on speed and differential pressure). The condition of the motor and also of the pump bearings is monitored by the bearing temperature, with regard to speed, the pump’s differential pressure, medium temperature and the local ambient
temperature. Of course, vibration control is an effective tool to monitor occurring bearing failures. Depending on the brand, the frequency converter’s internal control system generates condition data, which can be transmitted to the main control unit of the MPP system.
The pumps Vibration analysis is an effective conditional monitoring tool for calculating the condition data of the screw pump’s vital components. With regard to characteristic process data, such as engine power, speed, differential pressure, pressure ratio or component and medium temperature, vibration monitoring is able to analyse coupling misalignment, failures of the outer and inner ring of bearings or damage of roller elements and the beginning of damage of gear wheels, conveyor screws or shafts. The condition of mechanical seals can be analysed by monitoring leakage rate with regard to seal differential pressure, temperature and speed. Shaft seals with an integrated condition monitoring sensor [2] are not cost-effective for every application. An optical sensor detects leaking liquid (oil or water) on the surface of a special fabric and informs the operator about possible seal failure before it gets worse.
WORLD PUMPS
Feature April 2010
Other subsystems Common MPP subsystems include hydraulic systems for double acting mechanical seals and hydraulically driven valves or compressors for pneumatic actuators. If the operating time of the actuators is abnormal when compared to characteristic process data such as engine power, pump speed, differential pressure or pressure ratio of the multiphase pump, indications such as the process medium temperature, component temperatures or vibration level of the system can give preventive information about any sub-system malfunctions.
Operation supplies Operation supplies can generally be controlled by recording the tank levels and analysing the oil consumption during a defined time span. The condition of the battery charging can be analysed continuously, while the contamination of filter cartridges in general is monitored by a differential pressure transmitter. One aspect of ongoing research is finding ways to theoretically calculate remaining component service life. Focal points for this include the conveyor elements, bearings and mechanical seals of the multiphase pump. A German manufacturer is working on a CM-Module to calculate mechanical seals’ remaining service life, and has the positive results for applications with pure water [3].
Practical examples Here are three practical examples for the successful application of condition monitoring and remote access to pump systems operating in the oil and gas industry. The first example involved troubleshooting a multiphase pump system on a North Sea platform. The operator informed pump system experts via telephone that it was not possible to close the air inlet shutter of the system. As a consequence, operation was limited. After receiving an individual, temporary password, the system experts contacted the MPP system’s control system via remote access. A private security network from the experts to the onshore base was used as communication line. The signals were transferred by submarine cable from the onshore base to a central processing platform, while from the processing platform to the satellite platform with the MPP system a radio link system was used. Together, the MPP system expert and the software specialist accurately checked the PLC and
HMI signals to the inlet shutter and no failure could be identified. In order to check the mechanical function of the closed inlet shutter, the expert cut off the electrical power by remote access and the operator at site could see the inlet shutter moving correctly in the close position. This test made it clear that the malfunction was not due to a failure of the inlet shutter drive (nearly unrealistic, as a protected electrical motor is used). A visual inspection of the control relay of the drive indicated heavy wear at, which was identified as causing the malfunction. After identifying the type of relay, a new part was ordered, sent to the platform and was substituted by the platform electrician. Altogether, only four to five hours’ work for one operator on-site, for the pump system expert and for the software specialist were necessary to analyse and solve the whole problem. In contrast to this remote access supported solution, the conventional requirement of a field service trip, which is usually performed by a software expert and the technician for the MPP system, can take four to six days, depending on the flight schedule. The estimated costs would include by factor ten.
‘Only four to five hours’ work for one operator on-site, for the pump system expert and for the software specialist were necessary.’ In a second practical example, the online view via remote access was also used to quickly solve a quite common problem. After some months of MPP system operation, the process parameters had changed and the median temperature in the pump casing and discharge piping had increased to an unexpectedly high level. The fixed set points for the temperatures had been exceeded several times and continuous operation had stopped. After technical clarification of the pump system’s design limits and a detailed check of the changed process data via condition monitoring, the manufacturer of pump system and operator decided to adjust the temperature set points via remote access. In a similar way to the first example, the operator enabled external experts to enter the system by remote access by connecting a hard-wired communication line on-site to which the expert could log in via an individual password. These two procedures gave the operator full access control. Due to safety issues, the system’s operation had to be stopped, before logging in via remote access in order to modify the PLC-software code. The
new maximum set point had been adjusted and the alarm set point had been modified on the human machine interface (HMI), by using a special password level. Three hours later, the system could be restarted again and operation could be continued without further interruption caused by a high temperature shut-down. No software specialist had been at site, and no flight had to be taken. A third example involved a condition monitoring system incorporating vibration monitoring. The system is incorporated in several high pressure crude oil pumps, which are driven by a diesel engine. The system is fully equipped with suction and discharge pressure sensors, temperature sensors, speed sensors, displacement sensors for crank shaft and vibration monitoring systems, with vibration sensors positioned at the motor and at the pump. As well as this, all sensor data can be compared and correlated. There is frequent and automatic analysis of the pump system’s dynamic characteristics, including important components like bearings, coupling and gear wheels. The vibration monitoring system is combined with the other process data. The system also makes it possible to supply frequent protocols from a team of experienced pump and vibration monitoring experts. In these protocols, the condition of the monitored component is described, from the start-up of the system, when a fingerprint of the dynamic characteristic is taken. Critical developments are directly transmitted to the system’s control panel. An important part of this permanent analysis is checking bearing frequencies, which can help predict, and therefore prevent, a potential breakdown. These types of adjusted maintenance activities prevent avoidable costs and downtime. ■
References [1] MPA-Joint Research Project, 1997 to 2006, German Federal Ministry of Education and Research. [2] Freudenberg Simrit GmbH Co. KG; 17.04.07 Technical Information “Shaft seals with bidirectional Condition-Monitoring”. [3] Product news EagleBurgmann, Wolfratshausen, Germany.
Contact Joh. Heinr. Bornemann GmbH Industriestrasse 2 31683 Obernkirchen Tel.: +49 5724 390 - 0 Fax: +49 5724 390 - 290 E-mail: [email protected] www.bornemann.com
www.worldpumps.com
39
Feature WORLD PUMPS
April 2010
Condition monitoring
Condition monitoring of multiphase pumps Gerhard Rohlfing discusses the current state of conditioning examination in multiphase twin screw pump systems and how it can increase pump life. He also looks at some examples in the oil and gas industry where, done correctly, it has been found to improve efficiency.
B
esides the ongoing process of control hard and software development, manufacturers of machines and systems have also started using control systems to monitor the equipment’s condition with an aim to increase the machine’s up-time and, as a result, the economic viability of the equipment. This article will look at common methods of accomplishing this and will then define condition monitoring as one tool to increase the availability of systems, considering the advantages of this method and looking at how successful conditioning can be accomplished. The focus will then be on multiphase twin screw pump technology. The fundamental basis for the development of condition monitored multiphase pump systems is the system itself. This article will define a common standard and look at how multiple variants of the system and the application are presented. Finally the article will look at the vital part an IT platform has to play in modern multiphase pump systems as a generator of condition data, and common methods of data communication will be described. The main focus is an outline of existing condition monitoring modules, the benefits of these modules and an outlook on future modules which are part of ongoing research activities.
www.worldpumps.com
Common control methods There are several methods proven to increase system availability using multiphase pump technology. Engineers generally try to choose a product by looking at product availability. High-quality products, proven technology and qualified vendors will be preferred if system availability is of capital importance.
‘Condition monitoring can also be a part of an effective training system, whereby operational experience can be gained.’ To upgrade a system’s reliability, it is also common practice to use fail-proof and highly reliable components for the vital parts of the system. These components in general use multiple redundant functional units, which are accurately tested on performance. The fail-proof programmable logic control system (PLC) of a pump system is one example of this. Another way of minimising the probability of a system breakdown is to reduce the number of sub-components in a system to a minimum. Every additional sub-component is a potential source of defects and can lead to a malfunction of the system – or in the worst case to a system breakdown. An example of a proven integral functional
0262 1762/10 © 2010 Elsevier Ltd. All rights reserved
solution in screw pump systems is the modified motor/pump coupling, which is fitted with fins in order to work like a fan. Without the need for additional components, this coupling can be used to cool pump bearing and gear housings. No additional fan with motor, which can fail, is needed. Another influence on system condition and the duration of system downtime is the technical expertise of operational and maintenance staff. A well trained operator knows the characteristic signals of his or her equipment and will react appropriately, before the system condition changes for the worse. Similarly, a professional maintenance staff member will be able to find the most effective way to repair and restart a plant after a breakdown. So, investing in the qualification of operators and maintenance staff will have a positive influence on the system’s availability. Naturally, routine and preventive maintenance activities also have a direct influence on the availability of machines and systems. Increasing the frequency of maintenance activities and intensifying maintenance activities will reduce breakdowns or repair work. If this does not take place, downtime caused by maintenance work and the relating costs will often increase. Finally, condition monitoring should be mentioned as an intelligent method to increase the availability of technical systems. A condition monitoring system in general uses different sensors to
WORLD PUMPS
Feature April 2010
monitor, on the one hand, the condition of vital system components and, on the other hand, the processes in which they are used. It makes use of an IT system, which processes the data and generates the condition data of the system. Contrary to preventive maintenance, where parts and components of a system are inspected and replaced preventively during periodical maintenance activities, condition monitoring should allow condition-dependent maintenance activities. This should lead to a scenario in which the service life of vital components is utilized at a maximum, being based on detailed information about the component condition. According to this maintenance philosophy, a condition monitoring system, together with an adjusted maintenance logistic, will lead to a highly economical operational concept, resulting in low maintenance costs and high system availability. As well as the increase of system availability, condition monitoring in general allows process optimisation, which positively influences the economic efficiency of the equipment. Condition monitoring can also be a part of an effective training system, whereby operational experience can be gained and used for future product improvement and development.
The path to successful monitoring For successful condition monitoring, general know-how about the vital system components and about the operational process is essential. Only a combination of component condition data and process data, however, will make it possible to successfully evaluate a system’s condition. One example is the condition monitoring of a wind engine’s drive and gear system. After several years of development, including thousands of hours’ operational experience, the condition monitoring of wind engines is, today, a proven and effective tool and is now requested for wind engines by insurance companies. This combination of evaluated load characteristic of the rotor system and sensor data of the gear system makes it possible to make accurate statements about the remaining gear system’s service life. The same requirements have to be fulfilled with the condition monitoring of multiphase twin-screw pump systems. An adequate amount of operating hours and field experience in different installations can lead to a deep understanding of the unsteady multiphase transport process. However, it is also necessary to possess basic theory in order to describe the
Figure 1. The components making up the multiphase pump (MPP) system. ©Bornemann GmbH 2009.
effective static and dynamic loads, and the corresponding load capacity of vital system components should be known and describable in detail. Without this, the background condition monitoring of multiphase twin-screw pump systems will not meet expectations. The major properties of a condition monitoring system include the ability to collect, analyse and store process and condition data of current and previous operation in order to predict system’s future service life. In order to carry out maintenance planning and future product improvement and development, a local monitoring system needs data exchange in a higher-level control centre, as well as the application of expert knowledge on a condition monitoring system and collected field experience. This data exchange can be put into place by setting up personal data transport or remote access in different layouts. In this case, the security and integrity of the data thereby should have the highest priority.
Multiphase twin-screw pump system For successful condition monitoring, we need not only an infrastructure (described later in this article), but also system monitoring know-how and an understanding of the process in which the system works. When we consider a modern and basic multiphase screw pump system, the configuration as seen in Figure 1 has to be examined. The main component of Bornemann’s MPP (Multiphase Pump) system is the multiphase screw pump with its seal
system and the main drive. The MPP is controlled by a PLC with a human machine interface (HMI). The PLC gets its signals from different sensors and switches (such as pressure, temperature, vibration, level, speed and power) and controls different actuators (such as main drive, valve actuators and actuators of seal system) to keep the MPP system on-line. The company’s MPP system can be customized to its location, to the multiphase medium, to the operating conditions and to individual customer specifications. Currently, a Bornemann MPP system is operating in a variety of conditions, such as desert, permafrost, tropes, offshore top side and even sub-sea. The pumps are used to transport heavy crude oil as well as conventional multiphase mixtures of oil, water, parts of solids and natural gas from zero to 98% gas void fraction (GVF). Wet gas (98% to 100% GVF) and thermal operation at steaminjected fields can also be handled. These kinds of media can be corrosive and abrasive, as well as explosive and mostly toxic. Multiphase screw pumps can also be used to reduce wellhead pressure to nearly atmospheric pressure, to increase discharge of the formation and to boost pipeline pressure if needed to above 100 bar. They can be used to transport only a few m3 of oil per hour from marginal fields or more than 2,000 m3 per hour to a central processing unit (transfer pump). Operation often happens under permanently unsteady conditions. Due to this wide range of applications, MPP systems have to fulfil a wide range of
www.worldpumps.com
35
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Feature WORLD PUMPS
requirements. Therefore, specialized variants of the system are available.
The scope of an MPP An MPP system can include a circuitbreaker, a transformer, switchboards, grounding and uninterrupted power supply. As the main drive, an electrical motor and a variable frequency converter (VFD) is a often used. Diesel or gas engines are an alternative. Beside the seal system (which is used to flush the seals, handle barrier fluid or recover leakage), other auxiliary systems can be a part of the MPP system, such as compressor units for pneumatic valve actuators, hydraulic systems for hydraulic valve actuators, lube oil circulation systems, cooling systems, fire and gas detection systems, air conditioning, fire-fighting system, fluid injection systems and different kinds of control systems. Despite the necessary variation in conditions such as location, process and equipment, a modern multiphase screw pump system will generally implement a condition monitoring system, which generally forms a perfect match with a MPP system. Usually the control system consists of a PLC on a skid, which communicates to a humanmachine interface (HMI) via an Ethernet connection and receives all necessary sensor signals. Most modern MPP systems also feature a storage unit for process data.
These days it is possible to upgrade an MPP system to allow it to perform condition monitoring. The only equipment to be added is an intelligent condition monitoring system, suitable modules and a remote access system (RAS) (See Figure 2). Retrofitting a modern multiphase screw pump system should be possible in most cases. To connect the MPP system at all mentioned locations over the world, different RAS systems are also available. Depending on the local technical conditions, the MPP system can be connected via analogue or digital telephone line, broadband data communication, GSM/ UMTS mobile radio service, directional radio or satellite transmission. These can also be used to connect the customer’s control room. The oil and gas industry has to ensure that it has effective data integrity and data security in order to avoid hostile network access. As a result, it tends to favour data communication via a separated world-wide network. This kind of network combines the advantages of the internet, such as worldwide availability, with the security of a separated network, with known and identified users. The operator of an MPP system also needs to be able to decide what system access third parties have, including any control of the Remote Access Server hardware contact, and should have clear insight into data storage procedures.
Figure 2. The control system of a MPP unit incorporating additional CM hardware. ©Bornemann GmbH 2009.
www.worldpumps.com
April 2010
More than pure maintenance The real benefits of a condition monitoring system are generated by the various available modules. A basic module is the system online view, which can be set up through remote access to the PLC. This online view allows every authorized user to have individual access to the process and component condition data. If needed, he or she can get full access to the control system. In the lifetime of an MPP system, the first significant benefit of using a condition monitoring system occurs during commissioning and start-up. With an online view of the pump system available to third parties, these parties can offer different support during start-up and commissioning. Pump, control or drive experts can be involved during the start-up phase on short demand. This access extends the available know-how to a maximum, with minimum costs and maximum flexibility. Using remote access, it is proven practice to adjust system parameters according to the operating conditions needed. Sensor set points, drive parameters, parameters of further sub-systems such as cooling systems, lube oil systems or air conditioning can all be adjusted in order to optimize the pump system’s operation during the adjustment process of the start up phase. Troubleshooting or adding complete software updates for the HMI, PLC or the condition monitoring software itself can also be handled via remote access.
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Feature WORLD PUMPS
April 2010
Figure 3. The remote access system (RAS) can make use of a variety of remote connections to transmit information . ©Bornemann GmbH 2009.
Of course, expert online viewing via remote access is also an effective way to reduce the need for troubleshooting and, as a consequence, system downtime. Moreover, the process of contacting system experts at short notice creates additional experience for the operating crew. Beside troubleshooting and training support, condition monitoring via remote access can also be used to improve the performance of the multiphase transport process. Supported by the MPP system expert, operators can adjust the system’s operation data, examining the interaction with connected wells upstream or, for example, a central separator plant downstream. So, besides the many benefits that result from an online view on the control system, the condition monitoring modules are also useful in automatically generating condition data of the vital components in a multiphase pump system. First of all, the vital components have to be analyzed and selected. It is vitally important to select a component with regard to system function and its failure probability. As a result of this analysis, four main subject areas can be distinguished: the drive system, the multiphase pump, the subsystems in general and operation supplies. www.worldpumps.com
In a drive system, such as an electric motor, the windings, bearings and the variable frequency drive (VFD) with its sub-control system are vital components. With multiphase pumps, the coupling, conveying elements, bearings, gear wheels and mechanical seals are of major importance. Attention should be paid to all subsystems. As well as this, the operation of hydraulic pumps, compressors or valve operating mechanisms has to be taken into consideration. Finally, operation supplies of a MPP system, such as lube oil, liquid filling, barrier fluid or flushing of mechanical seals, batteries and filter cartridges can affect the system’s service life and possible bring about system breakdown.
The drive system In the drive system, the condition of windings can be monitored by winding temperature (adjusted by local ambient temperature) in relation to the required hydraulic power of the pump (depending on speed and differential pressure). The condition of the motor and also of the pump bearings is monitored by the bearing temperature, with regard to speed, the pump’s differential pressure, medium temperature and the local ambient
temperature. Of course, vibration control is an effective tool to monitor occurring bearing failures. Depending on the brand, the frequency converter’s internal control system generates condition data, which can be transmitted to the main control unit of the MPP system.
The pumps Vibration analysis is an effective conditional monitoring tool for calculating the condition data of the screw pump’s vital components. With regard to characteristic process data, such as engine power, speed, differential pressure, pressure ratio or component and medium temperature, vibration monitoring is able to analyse coupling misalignment, failures of the outer and inner ring of bearings or damage of roller elements and the beginning of damage of gear wheels, conveyor screws or shafts. The condition of mechanical seals can be analysed by monitoring leakage rate with regard to seal differential pressure, temperature and speed. Shaft seals with an integrated condition monitoring sensor [2] are not cost-effective for every application. An optical sensor detects leaking liquid (oil or water) on the surface of a special fabric and informs the operator about possible seal failure before it gets worse.
WORLD PUMPS
Feature April 2010
Other subsystems Common MPP subsystems include hydraulic systems for double acting mechanical seals and hydraulically driven valves or compressors for pneumatic actuators. If the operating time of the actuators is abnormal when compared to characteristic process data such as engine power, pump speed, differential pressure or pressure ratio of the multiphase pump, indications such as the process medium temperature, component temperatures or vibration level of the system can give preventive information about any sub-system malfunctions.
Operation supplies Operation supplies can generally be controlled by recording the tank levels and analysing the oil consumption during a defined time span. The condition of the battery charging can be analysed continuously, while the contamination of filter cartridges in general is monitored by a differential pressure transmitter. One aspect of ongoing research is finding ways to theoretically calculate remaining component service life. Focal points for this include the conveyor elements, bearings and mechanical seals of the multiphase pump. A German manufacturer is working on a CM-Module to calculate mechanical seals’ remaining service life, and has the positive results for applications with pure water [3].
Practical examples Here are three practical examples for the successful application of condition monitoring and remote access to pump systems operating in the oil and gas industry. The first example involved troubleshooting a multiphase pump system on a North Sea platform. The operator informed pump system experts via telephone that it was not possible to close the air inlet shutter of the system. As a consequence, operation was limited. After receiving an individual, temporary password, the system experts contacted the MPP system’s control system via remote access. A private security network from the experts to the onshore base was used as communication line. The signals were transferred by submarine cable from the onshore base to a central processing platform, while from the processing platform to the satellite platform with the MPP system a radio link system was used. Together, the MPP system expert and the software specialist accurately checked the PLC and
HMI signals to the inlet shutter and no failure could be identified. In order to check the mechanical function of the closed inlet shutter, the expert cut off the electrical power by remote access and the operator at site could see the inlet shutter moving correctly in the close position. This test made it clear that the malfunction was not due to a failure of the inlet shutter drive (nearly unrealistic, as a protected electrical motor is used). A visual inspection of the control relay of the drive indicated heavy wear at, which was identified as causing the malfunction. After identifying the type of relay, a new part was ordered, sent to the platform and was substituted by the platform electrician. Altogether, only four to five hours’ work for one operator on-site, for the pump system expert and for the software specialist were necessary to analyse and solve the whole problem. In contrast to this remote access supported solution, the conventional requirement of a field service trip, which is usually performed by a software expert and the technician for the MPP system, can take four to six days, depending on the flight schedule. The estimated costs would include by factor ten.
‘Only four to five hours’ work for one operator on-site, for the pump system expert and for the software specialist were necessary.’ In a second practical example, the online view via remote access was also used to quickly solve a quite common problem. After some months of MPP system operation, the process parameters had changed and the median temperature in the pump casing and discharge piping had increased to an unexpectedly high level. The fixed set points for the temperatures had been exceeded several times and continuous operation had stopped. After technical clarification of the pump system’s design limits and a detailed check of the changed process data via condition monitoring, the manufacturer of pump system and operator decided to adjust the temperature set points via remote access. In a similar way to the first example, the operator enabled external experts to enter the system by remote access by connecting a hard-wired communication line on-site to which the expert could log in via an individual password. These two procedures gave the operator full access control. Due to safety issues, the system’s operation had to be stopped, before logging in via remote access in order to modify the PLC-software code. The
new maximum set point had been adjusted and the alarm set point had been modified on the human machine interface (HMI), by using a special password level. Three hours later, the system could be restarted again and operation could be continued without further interruption caused by a high temperature shut-down. No software specialist had been at site, and no flight had to be taken. A third example involved a condition monitoring system incorporating vibration monitoring. The system is incorporated in several high pressure crude oil pumps, which are driven by a diesel engine. The system is fully equipped with suction and discharge pressure sensors, temperature sensors, speed sensors, displacement sensors for crank shaft and vibration monitoring systems, with vibration sensors positioned at the motor and at the pump. As well as this, all sensor data can be compared and correlated. There is frequent and automatic analysis of the pump system’s dynamic characteristics, including important components like bearings, coupling and gear wheels. The vibration monitoring system is combined with the other process data. The system also makes it possible to supply frequent protocols from a team of experienced pump and vibration monitoring experts. In these protocols, the condition of the monitored component is described, from the start-up of the system, when a fingerprint of the dynamic characteristic is taken. Critical developments are directly transmitted to the system’s control panel. An important part of this permanent analysis is checking bearing frequencies, which can help predict, and therefore prevent, a potential breakdown. These types of adjusted maintenance activities prevent avoidable costs and downtime. ■
References [1] MPA-Joint Research Project, 1997 to 2006, German Federal Ministry of Education and Research. [2] Freudenberg Simrit GmbH Co. KG; 17.04.07 Technical Information “Shaft seals with bidirectional Condition-Monitoring”. [3] Product news EagleBurgmann, Wolfratshausen, Germany.
Contact Joh. Heinr. Bornemann GmbH Industriestrasse 2 31683 Obernkirchen Tel.: +49 5724 390 - 0 Fax: +49 5724 390 - 290 E-mail: [email protected] www.bornemann.com
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