Ecol case study: Over 323 kg of deposits removed from two Siemens SST-700 steam turbines

condition of the turbine prior to cleaning

Even a small amount of deposits in the turbine’s flow path can, over time, reduce its efficiency and impair its performance. At a power station in Turkey, it was decided to carry out chemical cleaning using foam to effectively remove contaminants without the need for time-consuming dismantling of the casing and components. The results of the process showed that, when carried out correctly, cleaning can not only remove deposits but also lead to a marked improvement in the turbine’s efficiency.

In this case study, we show what problem the power station faced, how the cleaning was carried out, and what specific results were achieved following the process.

How foam cleaning improved the operating performance of the turbines at the Tufanbeyli power station in Turkey

Ecol carried out chemical foam cleaning of the high-pressure (HP) sections of two Siemens SST-700 steam turbines, each with a rated capacity of 150 MW, at the thermal power station. The aim was to remove deposits that had accumulated in the flow system and to restore the turbines to normal operating conditions.

The project was carried out during scheduled maintenance shutdowns in April 2026.

Key project results

• Over 323 kg of deposits removed from both turbines.
• 35–40°C – the reduction in the temperature of the WP thrust bearing following cleaning.
• 20–30 per cent – the reduction in the axial displacement of the WP shaft.
• 5 days – the duration of the work on Unit 1. 6 days – the duration of the work on Unit 2.

Both turbines were cleaned by an 11-person team working in a two-shift system.

Problem: deposits in the high-pressure section

The main objective of the work was to remove unwanted deposits from the high-pressure section of both Siemens SST-700 turbines. Contaminants present in the flow path affected not only the thermodynamic efficiency and performance of the units, but also other turbine operating parameters, including thrust bearing temperature, axial shaft displacement, rotor stability and the smoothness of the machine’s operation.

Deposits alter the aerodynamic profile of the blades and guide vanes, increase the roughness of their surfaces and impair steam flow conditions. Consequently, they can lead to efficiency losses and a reduction in power output, as well as altering the axial forces acting on the rotor and increasing the thermal and mechanical loads on the thrust bearing.

Therefore, in this project, it was crucial not only to confirm the effectiveness of deposit removal, but above all to confirm the impact of cleaning on the turbine’s performance parameters.

what was found on the blades?

Analyses of deposits collected from individual rows of WP blades revealed a similar nature of contamination in both units. This indicated common sources of origin, primarily linked to the chemistry of the water-steam cycle and the transport of corrosion products.
The analysed deposits primarily contained compounds of aluminium, phosphorus and sodium, with a relatively low iron content. The proportion of aluminium was 26–37 per cent, phosphorus 24–32 per cent, sodium 19–32 per cent, iron 4–9 per cent and copper 6–10 per cent by mass.

An analysis of the mechanism underlying the formation of the deposits indicated that these were not typical corrosion products. The predominant contaminants were associated, amongst other things, with the carry-over of impurities from the boiler, the incomplete removal of reagents used in water treatment, and the concentration of dissolved salts during steam expansion.

The analysis also revealed an increase in the proportion of sodium and phosphorus in the successive stages of the turbine as the pressure fell from approximately 115 to 46 bar and the temperature from approximately 460 to 345°C. This indicates the condensation and deposition of some of these compounds in the middle and final parts of the steam turbine section.

Silica (SiO₂) was also a significant component of the deposits. Under conditions of high pressure and temperature, some of the silica may be carried along with the steam and, during its expansion, precipitate onto the surfaces of the blades, forming very hard deposits that are difficult to remove.

laboratory tests first, then cleaning

Before work commenced, Ecol carried out tests to confirm the impact of the technology on the corrosion susceptibility of the blade material. The tests were performed on material supplied by the customer – fragments of blades from Siemens SST-700 turbine components – made of martensitic steel 1.4121 (X20Cr13 / AISI 420). The aim was to confirm that the chemical process used does not cause accelerated degradation of the material.

The samples were subjected to four-hour tests in solutions containing acid, a corrosion inhibitor and – in one of the variants – an activator. After the tests were completed, the samples were neutralised with ammonia water at a concentration of less than 1 per cent and dried.

The calculated corrosion rates were 0.002016 mm/year for the first sample and 0.001558 mm/year for the second. Both results were classified as Group II – materials with high corrosion resistance.

Visual and microscopic examinations following the tests revealed no pitting, intergranular corrosion or other forms of localised material degradation. Only very minor, localised surface changes were observed.
The results confirmed that the presence of the chemicals used did not cause an increase in the corrosion rate, and that the foam cleaning process did not lead to accelerated degradation of 1.4121 steel.

cleaning without opening the turbine casing

Ecol employed a chemical cleaning process for the WP section without opening the turbine casing. Active chemical agents were incorporated into foam, which was then introduced into the turbine’s flow path.

The foam acted as a carrier for the chemical reagents, ensuring extended contact time with contaminated surfaces and enabling access to hard-to-reach areas of the flow path. This made it possible to dissolve, loosen and remove deposits without the need for extensive dismantling of the turbine.

Preparation of the installation included, amongst other things, isolating the section to be cleaned from the rest of the system, dismantling specified components of the steam and drainage systems, and installing temporary tanks, pumps, heat exchangers, circulation systems, pipework, measuring equipment and chemical dosing systems.

On site, Ecol utilised a foam generator, a foam collection system, temporary chemical tanks, a system for discharging used foam and a mobile laboratory.

controlled process from rinsing to passivation

The process for Unit 1 and Unit 2 comprised pre-rinsing, two stages of acid cleaning, inter-operational rinsing, neutralisation and passivation, and final rinsing. The progress of the work was monitored on an ongoing basis based on changes in pH and conductivity.

Following completion of neutralisation and passivation, a final rinse was carried out, during which conductivity and the parameters of the condensate discharged from the turbine drains were monitored.

Prior to the commissioning of both units, the pH and conductivity were adjusted to the values required in accordance with the technical specification.

the effect is visible not only on the blades

A comparison of the Unit 1 and Unit 2 blades before and after the process shows that the accumulated deposits have been removed from the surfaces of the WP section components.

Under maximum load, the axial displacement of the WP shaft decreased from 0.90 to 0.63 mm in STG1 and from 0.846 to 0.670 mm in STG2. The temperature of the WP bearing fell from 107.1 to 67.4°C and from 109.3 to 73.0°C respectively.

A reduction in vibration levels was also recorded at most measurement points. For the generator bearings on the excited side, the reduction was approximately 19 per cent for STG1 and 31 per cent for STG2, whilst on the non-excited side it was approximately 23 per cent and 22 per cent respectively. In the IP section, the reductions were approximately 25–28 per cent at the inlet and approximately 10–26 per cent at the outlet.

However, the document indicates that the parameters considered by the operator to be critical for reliability – the temperature of the thrust bearing and the axial position of the shaft – improved simultaneously.

over 323 kg of deposits removed

Foam cleaning of the WP sections resulted in the removal of approximately 156.13 kg of deposits from Unit 1 and approximately 167.19 kg from Unit 2. In total, over 323 kg of deposits were removed from both turbines.
Silica (SiO₂) accounted for the largest proportion of the removed material: 115.40 kg from Unit 1 and 89.33 kg from Unit 2. Sodium ions also accounted for a significant proportion – 15.08 and 51.96 kg respectively – as did iron – 23.73 and 24.25 kg.

results confirmed on two independent units

A comparison of the performance of both turbines before and after cleaning confirmed the reproducibility of the results achieved using active foam cleaning technology. Regardless of differences in the initial condition of the units, a reduction in thrust bearing temperature of 35–40°C was achieved, along with a 20–30% reduction in the axial displacement of the WP shaft, a reduction in vibration levels at most measurement points, and the maintenance of operating parameters under full load.

The results indicate that the removal of deposits from the high-pressure section affected not only the steam flow conditions but also the mechanical operating conditions of the rotor. The document highlights the simultaneous reduction in thrust bearing temperature and axial forces as confirmation of the improvement in the operating conditions of both units.

customer review

Following the completion of the cleaning of Units 1 and 2, the client confirmed the high effectiveness of the process
In their feedback, the client emphasised the importance of reducing the temperature of the thrust bearing and the axial position of the shaft for the stability, safety and reliability of the turbine’s operation. They also highlighted the professional approach of the Ecol team, the efficient organisation of the work and the technical support provided during the subsequent stages of the project.

The client also stated their intention to continue working with Ecol on future projects of this type

– The effects of the process were evident not only in the amount of contaminants removed, but above all in the improvement in the machine’s mechanical performance parameters, as confirmed by operational monitoring following the units’ commissioning.

Michał Iwanecki – Chief Technologist

– The greatest value of the project was the reproducibility of the results achieved on two independent units and the confirmation that active foam cleaning can significantly improve not only energy efficiency but also the mechanical reliability of the turbine.

Robert Prenzel – Project Manager

– Throughout the entire process, we cannot afford even the slightest error. The client’s biggest problem was axial shaft misalignment, which affected the operating temperature of the bearings and, as a result, led to reduced performance or an increased risk of failure. The effects of deposits in the water-steam system have been eliminated.

Marcin Wojtasik – Chief Engineer

summary

A project at a power station in Turkey demonstrated that active foam cleaning can be used to remove deposits from the high-pressure sections of Siemens SST-700 turbines without opening the turbine casing. In the case of two units, a total of over 323 kg of deposits was removed, and an improvement in key mechanical parameters was observed following restart.

The most pronounced effects were observed in the temperature of the WP thrust bearing and the axial displacement of the shaft. The bearing temperature fell by 35–40°C, whilst the axial displacement of the WP shaft decreased by 20–30 per cent. At the same time, a reduction in vibration levels was recorded at most measurement points.

The project was carried out on two independent units, and the similar results obtained in both cases confirmed the reproducibility of the foam cleaning technology used.

The project in figures:

• 2 – Siemens SST-700 turbines cleaned.
• 150 MW – rated power of each turbine.
• >323 kg – total mass of deposits removed.
• 35–40°C – drop in temperature of the WP thrust bearing.
• 20–30% – reduction in axial displacement of the WP shaft.
• 11 people – the size of the team working on each unit.
• 18 hours – the time taken to clean and passivate each unit.
• 24 hours – the time taken for steam blowing of each unit.