HOW TO QUANTIFY FLOW INTENSITIES PROPERLY? A NEW APPROACH FOR THE KEY ISSUE IN EROSION CORROSION AND ITS PREVENTION

摘要

It is well known that critical flow intensities exist beyond which flow induced localized corrosion (FILC), i.e. erosion corrosion, initiate and propargate in given systems. Quantification of such critical flow intensities is tried in terms of ,,critical flow velocities" given in m/s), ,,critical Reynolds Number (dimensionless)", and/or ,,critical wall shear stresses" given in Pa. However, none of these terms represent the real hydrodynamic force, which is responsible for the mechanical destruction of protective scales. This holds even for the wall shear stress, which is several orders of magnitudes to small. A new approach is presented which allows for the first time to quantify the maximum interaction forces between flowing media and the wall, which come out to be well in the order of fracture stresses of protective scales. Now the boundary conditions can be defined more properly and more straightforward under which certain additives (e.g. flow improvers / drag reducers) can really inhibit the onset of FILC. Examples are given for different flow regimes.