For more than a century, the stainless steel tube has been a hardware mainstay in a large variety of different industries. Sandvik Materials Technology manufactures tubes from high-performance stainless steel alloys, with applications including chemical processing, industrial heating, power generation and petrochemical plants. In such facilities, tubes are the building blocks for the vast systems of piping that not only conduct materials, but often also play host to crucial chemical processes.
Surprisingly, the ability to closely monitor conditions inside the tube has been very limited. This was especially true in the case of harsh processes involving very high temperatures or corrosive substances. But these are the very processes where technicians need to have optimal insight in order to act, rather than relying on a combination of deduction, intuition and post-failure troubleshooting.
What you don’t know can hurt you
Stainless steel tubes are selected largely for their material properties, with different grades exhibiting varying degrees of hardness, corrosion resistance, yield strength and tensility. These properties are conferred by the precise combination of elements in each grade; differing proportions of nickel, chromium, molybdenum and manganese determine the material’s microstructure and performance under different environmental conditions.
Once in place, the hardware experiences stresses including temperature fluctuations, physical strain, corrosion and vibrations. These are often dynamic, varying in rate and intensity over time, which makes it difficult to accurately predict damage and eventual failure. The classic approach has been a combination of regular assessments and reacting to problems as they arise. From a commercial point of view, this results in costly downtime and maintenance or repair costs.
What technicians really needed was a way to monitor conditions with accuracy and in real time, enabling a shift from a routine and reactive approach to an intelligent and proactive one. This is what Sandvik set out to achieve when developing Sentusys. The new intelligent tube system connects integrated sensors with cloud computing and data analytics to deliver detailed and actionable insights.
The system explained
Each intelligent tube contains highly sensitive sensors embedded within the metal wall, thus avoiding direct contact between the sensor and the internal chemical processes taking place in often harsh conditions within the tubal cavity. However, their proximity is such that the sensors are able to collect accurate readings of the tube’s internal environment, including temperature fluctuations, vibration and physical strain.
This data is collected and sent continuously via cables to the signal conditioning equipment, where a gateway employs 4G technology and local output for real-time production process control. Technicians can closely monitor conditions and respond to potential issues before they become limiting, avoiding downtime and maintaining operational efficiency.
In addition to this local processing, the system is connected via 4Gto a cloud-based Microsoft Azure data platform, where the readings are transmitted and stored for deeper analysis yielding, for example, longer term insights into trends and patterns.
Sandvik’s research and development team were faced with considerable challenges in developing the new technology. The intelligent tubes had to combine the accuracy and sensitivity of a digital system with the hard-wearing quality required of physical equipment exposed to harsh industrial processes. They therefore had to be fully load-carrying and tough enough to withstand the thermal, chemical and physical stresses being monitored.
The system also had to be versatile and adaptable for use with a variety of stainless steel grades, given the breadth of tube applications, each calling for different material properties to deliver optimal performance. Sentusys intelligent tube can indeed be made from the majority of stainless steel alloys, and in a range of sizes from 15-110mm in diameter, and up to 15m in length. Crucially, the inclusion of the sensor system does not affect the material certification of the metal: it simply requires an additional 2mm thickness to the tube wall.
Intelligent tubes in action
Industrial boilers are one of the key applications of intelligent tubing. Such systems are highly sensitive to temperature fluctuations, and typically use cooling water to limit thermal damage. If a technician discovers a boiler has been operating without sufficient cooling water, the potential risk of damage and failure, combined with a lack of insight into exactly what temperatures the system has been exposed to, might lead to a precautionary shutdown and costly investigation. But with the data monitoring system in place, it’s easy to track the condition history and make an intelligent assessment of likely consequences before taking the appropriate action.
One user of the intelligent tube system is Swedish power plant Bomhus Energi AB, where intelligent tubes are monitoring 
the inner workings of a 150 MW bubbling fluid bed boiler. The primary aim is to proactively work against corrosion, a constant risk in the low pressure, high humidity and high temperature environment. Technicians keep a close eye on the thermal fluctuations in real-time, taking action when necessary to maintain temperatures above the dewpoint, thus avoiding corrosive damage to the pipes and resultant costs.
This level of monitoring represents the first fruits yielded by the new technology. As the stored data builds over time, it is anticipated that machine learning, data mining and artificial intelligence will be brought into play to deliver even more insight-driven process optimisation. The humble steel tube now has a brain.
About the author:
Erika Hedblom is manager, intelligent tube systems at Sandvik Materials Technology
