Conference on developments in desalination technology
For a steam power plant in Finland, operated by „Porvoon Energia“, a solution had to be found to replace the extremely corroded steel pipes for the transport of cooling water efficiently and quickly. The medium to be transported is sea water. It is known for its high corrosion potential of metals and has impressively demonstrated this with the existing steel pipeline after only 4 years in operation.
Corrosion is an electrochemical reaction of a material with its environment, which leads to a change in the material. The type of corrosion can be chemical, electrochemical or metal-physical.
The following factors are decisive for the corrosion rate and influence it immediately:
• The more reactivity of a metal, the higher the probability of corrosion.
• Any impurities accelerate the rate of corrosion.
• Water and electrolytes (e.g. salt) contained in it, as well as higher temperatures increase the corrosion rate.
• Coatings of the metallic surface with materials that are more active than the metal itself can delay the corrosion rate (e.g. zinc).
The effects and degree of corrosion in a piping system vary according to the application and material quality, and depend heavily on the factors mentioned above. In most cases, corroded piping systems are subject to the following problems:
• In some cases the cross-section and thus the flow rate can be reduced by incrustations, in which case more pump capacity is required and operating costs increase.
• Contamination of the liquid to be transported by particles that are detached.
• The pipe walls corrode and become thinner. The pressure resistance decreases as a result.
• Leakages are the further consequence. High costs due to water damage.
A large part of the pipelines currently in operation for seawater or saltwater applications are generally made of high-quality stainless steel, galvanised steel or cast iron. These materials are widely referred to as „saltwater resistant“, but are subject to corrosion over time, which inevitably leads to high maintenance costs and even plant failure/downtime.
For some years now, however, the trend has been towards plastics. Especially under seawater conditions, the service life of thermoplastic materials, which offer excellent corrosion resistance, is many times longer. Due to the very smooth surface of e.g. PE 100-RC pipes, particles find it very difficult to adhere and therefore hardly any deposits are formed.
After detailed consideration and planning, it was decided to replace the corroded steel pipelines with PE 100-RC pipes and fittings. The requirements regarding temperature and pressure, including the calculated safety margins, are met with an SDR 11 (PN 16) system. In addition, easy installation and low material costs were factors that ultimately influenced the decision.
Below are just some of the advantages of PE100-RC pipe systems:
• High flexibility, low weight
• Homogeneously weldable, UV resistant
• Very good chemical resistance
• Resistant to weathering, long service life
• Perfect abrasion resistance and resistance to pressure shocks
(up to 200 % of the nominal operating pressure)
• Use also at very low temperatures (application range -40 °C to + 60 °C)
• Physiological harmlessness
The planning and laying of the new AGRU PE 100-RC pipeline was carried out by the experienced Finnish company Atolli. AGRU PE 100-RC heating coil fittings were used for welding the pipeline sections.
The installation was carried out on schedule within a few working days and the power plant was put back into operation.
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