Life Time Estimation
Normally, the ageing process of pressure-bearing materials is relatively
slow and it affects the respective component rather evenly (creep
In contrast to this, the effects of corrosion and erosion may occur within much shorter periods and are locally controlled by completely differing dynamics (degradation rate). Not only pressure-bearing materials are concerned, but also their protective coatings (metallic, ceramic).
Thus, as a result of corrosion and/or erosion, the lifetime of a component often ends unexpectedly and abruptly (cracked tube), leading to reduced availability and highly increased – and unplanned – repair costs.
An essential part of foresighted maintenance is therefore to monitor the spatiotemporal effects of corrosion and erosion in a way that ensures informative and detailed data on the current state.
CheMin supervises maintenance works by inspections, in the soiled as well as in the cleaned state. If possible, the entire flue gas passage and all accessible components are inspected.
In a soiled state, local anomalies in the properties of fouling (form, thickness, colour, hardness) provide important indications of specific local conditions. From this information on the current state, potential boiler risk areas vulnerable to corrosion and erosion can be deduced.
In a cleaned state, all relevant heat transfer surfaces will be investigated and previously identified risk areas reinforced. This „investigation“ is not based on grid measurements of the remaining wall thickness, but visually through the experienced eyes of the CheMin staff, and is supported by oblique lighting of the heat transfer surfaces. So the spots are identified which are worst hit by corrosion and/or erosion in the accessible areas, from random testing to 100% inspection of a component. These spots are marked and assessed by measuring the remaining wall thickness (for protective layers: measuring protective layer thickness).
Obtained data are filed and recorded in a special CheMin data base so that, in the course of several maintenance cycles, the development of certain components and their remaining lifetime is displayed in a clear, transparent – and foreseeable (!) – way for the operator.
This method can be used for pressure-bearing materials as well as for protective layers such as cladding, thermal coatings etc., which are applied on them.
Our CheMin experience clearly demonstrates that grid measurements of the remaining wall thickness (or the remaining thickness of protective layers) only give a rough idea, and that local anomalies are not detected, and that, given the case of degradation at tube flanks, an apex measurement may convey an absolutely wrong idea, etc.