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The negative effects of flue-gas side corrosion on boiler materials (pressure-bearing or as protective layers / retaining parts / sheet metals) or in flue gas cleaning usually trigger off the search, testing and, finally, the application of more resistant materials.
The selection of materials is limited by environmental conditions at the application site (temperature of the medium, flue gas temperature, flue gas chemistry, the chemistry of the fouling, erosion, etc.) and by the expected performance features (lifetime, reparability, function within composite materials etc.).
Our practical experiences with view to boiler corrosion and the functional failure of boilers and flue gas cleaning demonstrate that relevant environmental conditions can be highly varying and inconsistent, thus complicating the forecast of the performance features of the material in question.
Consequently, the testing of materials under “unreal” environmental conditions does not suffice as a decision aid for operators. Relevant publications on laboratory tests confirm this.
So the trend towards “online” material tests has emerged during recent years, i.e. probes are inserted in the respective boiler at the projected application site in order to record the material’s performance features. The retrieval of data has been accelerated, in contrast to permanently installed test areas.
Based on CheMin’s experience relating to corrosion damage and the functional failure of protective layers, we developed our own material probes and filed a patent application for them. The following properties determine the special performance features of our probes:
- The probe’s body is a real component in terms of size (boiler tube, solid material), with corresponding applications (e.g. protective layers) as appropriate.
- Temperatures for the front part of the probe body (e.g. 70 cm long) are set within a freely selectable, constant temperature range (e.g. from 250 to 500°C), i.e. the “material temperature” - the parameter relevant for corrosion and functional features – is recorded simultaneously over a broad temperature range. Critical temperature threshold values are thus detected.
- The probe body can be used for a time period which is, for the most part, freely selectable, from hours to months. This means that either specific operational states or several varying states can be investigated as desired. The probe body can be inserted or removed at any time.
- Following its on-site application - and similar to damage investigations – the probe’s body is disassembled in the lab and undergoes microanalytical testing to record the causes, type and intensity of corrosion (degradation rate), or the adverse effects on its functionality. Within this temperature range “all” temperatures of relevance can be examined equivalently (e.g. ranging from 250°-300°C for evaporators, from 400°C - 500°C for superheaters, or from 80°C - 200°C for ECO, LUVO, and with regard to flue gas cleaning).
CheMin: Practice-oriented and flexible optimisation of hot and cold material applications.