Thermal and mechanical stress causes cracks in metallic structures. Such cracks have a tendency to grow bigger and the damage can be very disastrous in recovery boilers, which are vital pieces of equipment in the pulp and paper industry. Wall tube leaks of the furnace can lead to substantial boiler damage and unexpected shutdowns.  One way to avoid damage is to use the continuous Savcor CI-system (Cracking Indicator) to detect growing cracks.  "When compared with the conventional method, i.e. periodic visual and audible inspection, the new system can extend the life time of process equipment significantly," says Kaj Lindström of the Finnish company Savcor-Consulting Oy, a specialist in corrosion and preventive maintenance.

In a recovery boiler, bottom tube leaks of the furnace can lead to substantial boiler damage and expensive shut-downs. There is also a risk for a disasterous boiler explosion caused by reactions between the smelt bed and water.
The conventional method of monitoring high pressure steam and water tubes is to carry out periodic visual and audible inspections. In most countries, such inspections are prescribed by legislation as for pressurised vessels.
"However, cracks that are detected this way have already progressed beyond the point at which action should have been taken," says Kaj Lindström.
Early detection of tube leaks in economisers and superheaters is critical in order to minimise the risk of damage in other tubes. The Savcor CI-system is an advanced monitoring system, which is capable of detecting leaks in good time and thereby making it possible to perform a controlled shut-down at the right moment.
Continuous on-line monitoring of a recovery boiler gives immediate information on the origin and growth of structural flaws. The method is especially important for pressurised recovery boilers manufactured of compound materials. By using a CI-system, the entire boiler, including walls, the bottom, economisers and superheaters can be monitored. As a result, orderly and controlled shut-downs for repair can be carried out, and severe equipment failures and extra shutdowns avoided.
More specific information is obtained when using CI-data together with process information. I this case, the user can see in what kind of process situations the cracking occurs and take actions to avoid the consequences.
"On-line monitoring information, together with process information such as bottom temperature, pressure, etc., shows how and in what kind of situations the problems occur and grow. Based on this information, the process can be optimised and stress peaks in the structures thereby minimised," says Kaj Lindström.
"Normally, cracks can be detected only during extensive inspections, but with a Savcor system cracks can be detected immediately they arise and start to grow. Not only can maintenance costs be cut, but also the life time of your process equipment can be prolonged," says Kaj Lindström.
The main benefits of using continuous on-line monitoring are lower maintenance costs, longer intervals between visual inspections and increased safety. With the help of CI-data, it is also possible to avoid process situations causing high stress in the material, and thereby the life time of equipment and structures can be extended.
The system is also generally considered as positive by insurance companies thereby resulting in lower insurance costs.

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For further information, please contact:
Savcor-Consulting Oy, Mr. Kaj Lindström
Insinöörinkatu 8, FIN-50100 MIKKELI, Finland
Tel. +358 15 760 400
Fax +358 15 760 4211
info@savcor.com

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