Report: An in-depth look into monitoring for steam applications
Steam … not just for railway enthusiasts. Steam's ability to transfer energy between source and consumer means it continues to be widely used. Industries such as food and drink production, chemical processing, extractive industries, space heating and hot water to specialist applications in pharmaceutical and healthcare. Across all these industries steam systems are usually energy intensive and business critical but are hard to monitor regularly and consistently.
This report examines common monitoring techniques for commercial and industrial steam users and reviews the issues with those traditional methods. We then explore an alternative strategy, combining those established methods with technology available through the Industrial Internet of Things (IIoT) and facilitated by easily deployable, cost-effective sensing devices.
Steam has been utilised for well over two hundred years because of the effectiveness with which it can store and transport energy. While it takes around 400kJ (or 0.1 kWh) of energy to heat 1 kg up water to 100°C, it takes over 2,700kJ (750 kWh) to turn that into steam at 180°C. Steam naturally flows between the point of generation and consumption, transferring that energy as it does so. The steam then returns to liquid (condensate) as its energy is transferred to other locations and processes on site.
While steam functions well as an energy transfer mechanism, it needs careful management and monitoring to ensure efficiency, minimise costs and keep installations safe.
Efficiency, carbon, and cost
Generating steam is energy intensive. Efficiency needs to be maximised and losses minimised. The costs of energy in many countries has risen significantly over time while reduction of carbon emissions from fossil fuel use (oil and gas being common fuels for steam boilers) is a priority. Most countries now mandate measures and standards to improve energy efficiency, reduce carbon emissions and reduce water consumption.
Maintenance and monitoring considers five main operational areas:
Losses: Wherever energy is lost without having done useful work, losses are occurring. Monitoring aims to identify those losses so that they can be reduced or eliminated.
Disruption: Whenever equipment fails it has the potential to disruption production and operational processes that depend on it. Monitoring must identify impending failure and non-performance before it affects processes.
Maintenance: Periodic maintenance is essential to keep equipment operating in optimum condition. However, maintenance downtime is disruptive and costly. Monitoring must ensure maintenance happens at the right point.
Ensuring safety: Steam systems are high-energy systems with corresponding hazards and risks. Leaking steam carries significant risk for burns and injuries to personnel, liquid leaks cause water damage and slip risks.
Impact: Most organisations monitor their environmental impact through sustainability appraisals and similar reporting metrics. The energy intensity of steam operations causes it to account for significant environmental costs and emissions in those organisations. Monitoring needs to help quantify and optimise emissions and resource usage.
Steam system monitoring
Each steam system is unique but the physical rules under which they operate are consistent and universal, which leads to installations with common features and much standardised equipment.
Steam and condensate pipework
No pumps are necessary to move steam from the point of generation to the point of use, it will flow naturally between those points. Pipework is necessary to contain and channel the steam between those points. It should typically have a low rate of wear but where the steam is not of a good quality, e.g. significant amounts of condensate within the steam, or chemically contaminated, then wear can be accelerated.
Pipework is typically checked visually for issues. It can also be checked with thermal imaging systems for variations and discrepancies in temperature.
Steam trap monitoring
The significant energy in each kilogram of steam means that all installations prioritise reducing the loss of steam. However, this must be balanced against the need to remove “used” steam (condensate, i.e. steam returned to liquid water) from the system. Liquid water travelling with steam significantly reduces system efficiency and can cause damage when driven onto internal surfaces by fast moving steam (“water hammer”).
Many of the technology developments since the industrial revolution have focused on removing this condensate while avoiding the loss of steam – the “steam trap” has become one of the most common pieces of equipment in use to enable this separation to take place efficiently.
Steam traps serve a critical function separating condensate and noncondensable gases from live steam. They are essential to both operational efficiency and safe operation of the system. Around 3 million steam traps are sold around the world each year, the vast majority being mechanical. Like all equipment with moving parts they wear, leading to reduced performance over time and likely their failure. Even those types with no moving parts are not immune to problems caused by contamination (e.g. blockage) or damage induced by faults in other parts of the system (such as water hammer).
There are two main failure modes that need to be considered in steam traps:
Open Trap: The trap lets condensate out but no longer keeps steam in effectively while doing so. A single persistent steam leak wastes a significant amount of steam – representing wasted energy, costs, and carbon emissions. Many sites treat identification of this failure mode as a priority since it leads to significant loss of steam – even a small trap failed open can leak up to 5 kg per hour of steam (3,750 kWh of energy).
Closed (Cold) Trap: Steam traps that have failed closed prevent effective condensate removal, that can lead to water hammer and reduction in system efficiency.
With up to 10% of mechanical traps failing in a site each year the costs and performance issues caused by failed traps can quickly mount up.
Traps are typically found in two installation main scenarios:
Drip Trap: A trap installed in pipework to remove condensate that builds up in runs of steam supply pipework. Usually smaller traps as the condensate loads are relatively low. Commonly found distributed along runs of pipework – e.g. a drip trap every 30-50 metres of steam supply pipe.
Process Trap: A trap installed adjacent to equipment that uses steam, e.g. a heat exchanger. Energy transferred out of the steam by the equipment using it will return to condensate and the process trap ensures that is removed. Process traps can vary from very small to very large depending on how much steam is required by the associated equipment. Process traps typically handle high loads and those loads may be varying or intermittent depending on the process equipment in use.
Charaterising trap failures
Most mechanical trap faults are diagnosed through a combination of temperature and ultrasound analysis. Temperature analysis on its own, when readings are frequent and accurate, can be used to diagnose many operational conditions but the combination of temperature and ultrasound introduces maximum certainty and reliability to automated diagnosis. Most issues with steam trap are readily diagnosed using a combination of these monitoring techniques and a wide range of devices and equipment is available for manual inspections using these techniques.
Spotting cold traps
Failed closed traps are more easily missed in manual monitoring due to the long intervals between measurements and the possibility that assessment may not always align with the operational period of the trap. Drip leg traps are particularly prone to be being missed as they are often small and hidden away or hard to access than larger, more visible, process traps.
Traps that are leaking steam tend to attract more attention, but closed traps are a more significant source of safety and reliability issues. They prevent the effective removal of condensate from a system and can allow it to build-up to levels that lead to water hammer; with a very detrimental impact on equipment reliability and risk of serious failure.
The “used” steam, condensate, is still at a high temperature after use. To maximise efficiency, and reduce water consumption, the condensate is normally returned to the boiler to be turned into steam again. Condensate is usually pumped back to the boiler, but systems may use various combinations of pump, pressure and gravity return to move condensate. Where condensate is not returned to the boiler effectively or reliability it causes significant energy losses and can hugely increase process water consumption.
Multiple challenges exist for monitoring in real-world steam installations, particularly the management of inspection schedules, site access and staff availability.
Point in time monitoring
A manual monitoring approach is naturally limited to providing a snapshot view of performance at a moment in time. Surveys are often regularly scheduled but engineering staff cannot monitor every steam trap 24/7. The maintenance schedules at many sites means that in practice many traps may only be inspected every 6 months.
Point in time inspections limit the amount of data available – frequent, repetitive measurement is required to understand the performance of a trap under varying environmental and process conditions. This is particularly true for problems that lead to gradual but detectable trends in performance – these can be difficult to spot without sufficient data to allow a trend to be determined amongst environmental and process related fluctuations.
Many manual schedules reduce the frequency of inspections for equipment perceived as being of lower importance – notably units such as “drip-line” steam-traps. The potential for condensate build-up in a system can cause that to be a significant hazard for equipment reliability and safety.
Periodic inspection is also less likely to pick up issues with equipment that exhibits intermittent symptoms. A section of pipework suffering from intermittent water hammer may not do so during an inspection; an undersized condensate recovery loop will only exhibit a problem when operating above its capacity which may, or may not, occur during an inspection.
Site access and infrastructure
Plant rooms, boiler rooms, access ducts, walkways and high-temperature equipment present unique access and working challenges to anyone undertaking manual inspections.
Even well insulated steam pipework and equipment generates significant escaped heat. That heat, and the common escape of steam due to leaks or normal operations (e.g. plate heat exchangers warming and cooling) can make enclosed plant rooms and sites a difficult environment to work in. With well insulated pipework and no significant leakage it is not uncommon to find temperatures of 40°C (104°F) in plant rooms and poorly ventilated areas. Temperatures up to 50°C (122°F) are not uncommon in tunnels, and narrow access areas, carrying steam and condensate pipework. Working for an extended time in such conditions is hazardous and tiring for staff.
In larger sites buildings may be spread over complex terrain, with networks of tunnels to route energy and services between buildings. In most countries working in hazardous confined spaces such as these imposes new restrictions and regulatory requirements that generate additional access constraints and costs. In many geographies such tunnel systems and steam networks were installed several decades ago, and present additional challenges due to the presence hazardous materials – particularly asbestos in old insulation materials and fittings. The difficulty of accessing such locations means that inspection schedules are likely to be less frequent than is optimal.
Engineering and staff availability
Manual inspection needs to be undertaken by on-site maintenance teams, external contractors, or engineering support staff. Many sites are heavily automated and the number of staff available to undertake such repetitive work is often limited, external contractors can be expensive and using qualified engineers for “point and shoot” temperature measurements is not an effective use of their time and expertise.
Sites that are complex or hazardous also need staff to be trained and qualified to work in those environments. In many cases this leads to additional requirements for training additional personal protective equipment (such as breathing apparatus).
An alternative monitoring approach
The traditional approach to assessing steam trap performance is well established but labour intensive, difficult to schedule and unable to deliver data constantly and immediately. An alternative approach would take the monitoring techniques widely utilised by already and make them automatic, persistent, and easily deployed.
Our whole system approach maximises the number of components that can be monitored, reduces manual testing and spots intermittent faults that manual testing misses. Automated monitoring is there non-stop for every event and frees valuable engineer time for non-routine tasks. Pinpointing and detecting problems in real time, steam system monitoring also helps identify areas of improvement for carbon reduction, process efficiency and cost savings.
DCO has introduced its steam trap monitors to provide a remotely accessible, self-contained solution that ensures trap performance data is collected around the clock.
Trap monitoring technique
Diagnosing the performance of steam traps is most frequently undertaken with temperature and ultrasound measurements. Temperature through contact measurement, infrared thermometers, or thermal imaging equipment. Ultrasound through detection probes and acoustic sensing equipment.
The DCO steam trap monitor includes contact temperature measurement probes that are installed upstream and downstream of the trap to collect these temperature measurements.
The steam trap monitoring assesses the temperature on the steam side of the trap and on the condensate side of the trap. Independently, these two measurements provide a useful measure of the performance of the trap but combined with a calculation of the temperature delta between them they provide a simple but effective means to determine instantaneous performance and changes in performance over short, medium and long intervals of time.
Each trap monitor can be configured to understand what type of trap it is monitoring or, in most cases, can determine the trap type itself. This allows the monitor to make intelligent analysis decisions on the use of temperature and ultrasound measurements to determine the performance of the trap. Each type of trap has highly characteristic acoustic signals that can be analysed to understand what that trap is doing in real time.
For a given set of design parameters – steam inlet temperature (and pressure), condensate outlet temperature (and pressure) – the expected
temperature profile for the pipework and trap is already calculated by the installer (or manufacturer). Additional configuration in the trap’s analysis dashboard allows this information to be used to generate cost, loss and efficiency models for the trap and associated equipment.
The monitoring sensors provided by DCO also include environmental monitoring as well as vibration, orientation, and sound sensing capabilities.
Measurement of the environment, particularly temperature and humidity at sufficient accuracy, enables anomaly detection. Differences in the local environment of each sensing unit, particularly in enclosed environments, can be used to determine the presence of leaks. Variations in measurements between units can be used to localise the probable location of those leaks.
Vibration and ultrasound sensing can be used in conjunction with the other measured data to gain greater insight into trap operation. The use of ultrasound to assess the performance and functioning of mechanical traps is a well understood technique, and DCO’s use of it in remote monitoring is explored further in our technology explainers and other case studies.
Constant monitoring of the physical parameters of the trap is key to understanding its performance – both on short and long timescales. Every
trap will have a specified (as designed) model of behaviour and detailed monitoring permits that to be compared to a picture of real-world device performance. Synthesising multiple physical measurements – temperatures, acoustics, environmental conditions – creates valuable information about the trap and a wealth of performance data. A rich data set allows rapid changes in performance to be seen, indicating localised or remote failures. Furthermore, the same data set, viewed over longer timescales, allows gradual reductions in performance to be identified and maintenance planned.
Combining data for accuracy
To provide the most accurate, reliable, and repeatable information steam trap monitors will use multiple data points to determine current states. In-built monitoring intelligence allows anomalies in one area to trigger further monitoring and analysis by different types of physical sensing.
Time is data
A key advantage of automated monitoring with many data points is that time itself becomes a usable data point. Identification of patterns over periods of time not possible with manual measurement, aids delivering accurate notifications and alerts. Knowing system status over time helps prevent false warnings during transient events such as system start-up and shutdown. Patterns of behaviour over time become an aid to diagnosis – a significant benefit of automated monitoring is collecting data all the time. There is no possibility of missing a data point just because no manual monitoring was in place at that point in time.
Better and more timely monitoring improves safety. Reducing persistent leaks improves the safety of the operating environment for staff. Eliminating water hammer greatly lowers the risks of serious operational failures. Limiting condensate leakage removes pools of standing water and makes improves working conditions through reduced damp and humidity.
Improved cold trap recognition
Since closed traps are more easily missed in manual monitoring automated temperature measurement is a particularly effective and rapid way of
diagnosing such traps. Measurements from around the trap are combined with measurements from other parts of the system to ensure that alerts and notifications accurately reflect trap status – upstream monitoring is used to determine steam mainline temperatures while monitoring adjacent to valves and control units provides indications of whether a trap is active or not.
Through the use of multiple temperature measurements automated monitoring can accurately determine whether a trap should be operational
and raise a warning if it not performing, or operating, as expected.
The need to supply power and communications wires to sensors is a common barrier to retrofit installations. The wireless devices that already exist generally need frequent battery changes or have very infrequent reporting intervals to achieve their stated battery lives.
The need to either install new cabling or to make frequent battery changes has been a barrier to deployment of monitoring in many instances. Particularly where installation locations are difficult to access the installed sensor needs to be operational on a long lifetime without further manual intervention.
A combination of wireless communications and local energy harvesting is implemented to simplify installation.
Each installed monitoring unit has a power harvesting module included that provides a local source of energy derived from pipework at elevated temperatures (steam, condensate, or other process sources). Local energy harvesting ensures that the unit needs electrical installation and access to the unit to update and maintain batteries is not required.
Fully automated, remote monitoring greatly reduces manual on-site monitoring and eliminates the need for personnel to routinely check traps in
inaccessible and hazardous locations. It collects real-time performance data that is analysed in real-time to generate operational information. It can identify current and historical issues in a timely way and deliver analysis that can be used to schedule maintenance and repair activity in a targeted resource-efficient manner. Rapid diagnosis of issues improves operational efficiency and provides engineering teams with the data they need to concentrate their workload and maximise their effectiveness.
Our integration of common diagnostic techniques, remote monitoring and intelligent sensing and energy harvesting finds a natural home in steam systems. A perfect location for our maintenance free equipment sensors, harnessing energy from their surroundings for maintenance free and always on operation.
With DCO Systems, our steam monitoring solutions can give you new insight into your systems.