Maintenance|Turbine technology


Foam cleaning of steam and gas turbines: well established in the USA, rare in Europe


Deposits on power plant turbine blades lead to deterioration in efficiency and loss of performance. A range of causes may be responsible for the formation of deposits. Such deposits can be removed in various ways. The most common methods are mechanical removal by blasting, water wash, wet steam washing and foam cleaning. Almost unknown in Europe, foam cleaning has been successfully applied in power plants in the United States for over 40 years. This article compares the different methods for scale removal, looking at respective advantages and disadvantages. Being quite “new” to Europe, the foam cleaning method is described in more detail, including examples


Dr-Ing Frank Udo Leidich FULPowerConsulting, Worms, Germany and Wojciech Majka President of the Board, Managing Director at Ecol, Rybnik, Poland


Operating a steam turbine with steam of insufficient quality or purity leads to oversaturation of impurities during expansion, which are then separated from the steam and form deposits on the turbine blades. [1] Depending on the composition, deposits can form on the high-pressure, medium-pressure and/or low-pressure sections of a steam turbine.[2] In a gas turbine, deposits have a similar, if not greater, effect on compressor blades. For gas turbines, in most cases, it is the compressor that suffers from the fouling that can finally result in a reduction of air intake and thereby reduced power output, leading to stall of the compressor that even might destroy the machine. For gas turbines, the deposits are caused by impurities that enter the compressor with the intake air. The water that is injected for cooling or to increase performance (fogging / high fogging) can also lead to the formation of deposits in the compressor or turbine if it is not clean enough. Scale and deposits on blades can be detected by the effects they cause. The consequences are reduced swallowing capacity of the turbine or compressor, increased axial thrust, and higher axial bearing temperatures and, increased vibrations of the rotor shaft due to imbalances. This finally reduces the overall efficiency of the power plant, which sums up to remarkable monetary losses compared to a turbine without such problems.[3]


To remove such deposits or scale, different methods can be applied.[4]


applied in most cases are: mechanical cleaning; water wash;


wet steam washing; and foam cleaning.


These methods will be described and their advantages and disadvantages will be highlighted. As foam cleaning is not very well known in Europe, a few more words will be devoted to it in the article.


Mechanical cleaning by blasting Mechanical removal of deposits requires a relatively long standstill and the opening of the turbine or compressor. Due to the long time and high cost involved, mechanical deposit removal is often only carried out during a major overhaul. As a consequence, efficiency loss in the period between major overhauls is accepted, resulting in a financial loss that is less than the cost of mechanical scale removal with weeks of non- production.


For mechanical cleaning by blasting, a variety of blasting materials is available. This allows selection of the blasting material based on the deposit to be removed and the surface finish to be achieved.


Table 1 gives an overview of blasting materials commonly used for cleaning of turbine blades.


Table 1. Blasting materials typically used for turbine blade cleaning Blasting material Hardness


Used for Steel grid Glass beads


Corundum Nut shells


Silicon carbide Dry ice


480-550 HV1 6 – 7 Mohs 645 HV


8 – 9 Mohs 3.5 Mohs


9.0-9.5 Mohs 2-3 Mohs


Roughening, derusting, decoating, descaling, matting, cleaning and sweeping


Forming, hardening, deburring, decoating, smoothing, polishing, cleaning and structuring


Roughening, derusting, decoating, matting, cleaning and structuring


Gentle cleaning of sensitive surfaces


Cleaning of hardened steel, removal of rust and scale layers Gentle cleaning, removal of rust and scale layers, sweeping


The methods that are


In addition to turbine blade cleaning, as mentioned above, blasting can be used to prepare surfaces for non-destructive testing and to induce compression stresses into the surface of cleaned parts for local structural reinforcement.


Blasting enables all deposits from accessible surfaces to be completely removed, leading to full restoration of turbine performance. However, blasting methods require opening of the turbine casing, as already mentioned, and rotor removal. This makes mechanical cleaning by blasting very time consuming due to pre- and post-blasting work (turbine opening, decoupling, rotor lifting, reinstallation of rotor, rotor realignment, reassembly, closing of turbine casing, balancing, etc).


In a nutshell, mechanical cleaning by blasting: Is very expensive due to high level of workmanship required.


Is the method of choice when major overhaul is anyway due.


Is used in the event of an incident that requires turbine opening.


Will usually not be applied just for scale removal in the case of performance degradation that does not jeopardise turbine operation. Will restore turbine efficiency.


Entails separate cleaning of rotor and casing. The upper part of the split casing can be cleaned easily in a workshop, while the lower part of the casing remains in place and all cleaning activities including removal of the blasting material and the removed deposits need to be collected manually with vacuum cleaners or similar methods.


Water wash


Water wash offers no big advantage compared to mechanical cleaning with respect to the time taken because the turbine casing also needs to be opened.


Washing the turbine internals with demineralised water is effective for water soluble substances that have come into the turbine with the steam.


www.modernpowersystems.com | July/August 2025 | 23


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