Water quality requirements industrial boiler EN12953-10
EN 12953-10: Water Quality Requirements in Industrial Shell Boilers | BOIXAC Technical blog › Standards & operations EN 12953-10: Water Quality Requirements in Industrial Shell Boilers Technical analysis of the parameters the standard defines for feedwater and boiler water, and their significance for the integrity and safety of steam generation systems. BOIXAC Tech SL Updated: 2026 Reading time: ~10 min Note on the scope of this article This text is intended solely for informational and educational purposes. It does not constitute technical, engineering or water treatment advice, and cannot under any circumstances replace the specific analysis carried out by a qualified specialist on a given installation. The values and parameters mentioned are drawn from EN 12953-10 and the specialist technical literature; they must always be interpreted in the context of the current version of the standard, the boiler manufacturer’s instructions and the requirements of the authorised inspection body. BOIXAC assumes no liability for decisions taken on the basis of the content of this article. Water quality is, alongside design and manufacturing conditions, the single factor that most influences the long-term integrity of a shell boiler. The European standard EN 12953-10 establishes minimum water quality requirements for feedwater and boiler water in this type of equipment, with the fundamental aim of minimising risk to personnel and surrounding installations. For process engineers, maintenance managers and plant operators running steam generation systems, understanding the framework this standard defines — which parameters it controls, why, and according to what criteria — is an essential element of plant technical management. 1. Normative framework and scope The standard EN 12953-10:2003 forms part of the EN 12953 series, which collectively regulates the design, manufacture, documentation and operation of shell boilers (also referred to as firetube boilers). Part 10 deals specifically with the quality requirements for feedwater and boiler water. Its scope covers all shell boilers heated by combustion of one or more fuels or by hot gases, intended for the generation of steam and/or hot water. The standard applies to components between the feedwater inlet and the steam outlet of the generator. The quality of the steam produced is expressly excluded from scope; where specific steam purity requirements apply, additional normative documents are required. Relationship with Spanish operating regulations Spanish Royal Decree 2060/2008 of 12 December, approving the Pressure Equipment Regulations, requires operators of steam or hot water boilers to maintain water within the specifications of UNE-EN 12953-10 (shell boilers) or UNE-EN 12952-12 (water-tube boilers). Compliance is therefore a legal obligation for the installation operator. 2. Technical purpose of the standard: damage mechanisms to be prevented Scale and deposits The precipitation of calcium, magnesium and silicate salts onto heat transfer surfaces creates layers of low thermal conductivity. A deposit as thin as 1 mm can increase fuel consumption by around 5–8 % and locally raise the metal wall temperature to values that compromise its integrity. Corrosion Dissolved oxygen and free carbon dioxide are the primary corrosive agents. Oxygen corrosion produces localised pitting that can progress until the tube wall is perforated. Inadequate pH promotes various forms of chemical attack on carbon steel. Foaming and carry-over The presence of total dissolved solids (TDS) at elevated concentrations, or of certain organic substances, can cause foam formation at the water surface. This leads to carry-over of boiler water droplets into the steam (priming), contaminating the steam with salts. Sludge and blockages Suspended impurities and precipitates not removed by blowdown can accumulate as sludge in low-velocity water zones, impeding circulation and heat transfer, and promoting under-deposit corrosion. 3. Fundamental distinction: feedwater and boiler water The standard precisely distinguishes two types of water that have different requirements and are controlled independently. Feedwater is the water entering the boiler to replace the evaporated volume. It is typically a mixture of recovered condensate and make-up water, having undergone the necessary external pre-treatment processes. Boiler water is the water present inside the boiler drum during operation. Because feedwater is a continuous source of impurities, boiler water undergoes progressive concentration of these substances. Its admissible parameters are managed through system blowdown. 4. Quality parameters: technical description pHat 25 °C Determines the acidic or alkaline character of the water. Moderately alkaline feedwater pH inhibits oxygen corrosion; in boiler water, alkalinity is required to maintain steel passivation. Total hardnessCa + Mg, mmol/l Expresses the concentration of calcium and magnesium ions, the main scale-forming species. The standard requires extremely low levels in feedwater, which in practice necessitate softening or demineralisation treatment. Dissolved oxygenO₂, mg/l Primary corrosive agent. Must be eliminated by combining thermal deaeration with oxygen scavenger dosing. The standard distinguishes limits according to the design pressure of the boiler. Direct conductivityµS/cm at 25 °C Indirect indicator of total dissolved solids (TDS) concentration. The standard classifies the operating regime according to whether feedwater direct conductivity is above or below 30 µS/cm. Acid conductivityµS/cm, after cation exchanger Determined by passing the sample through a strongly acidic cation exchanger. Particularly sensitive to CO₂, chlorides and sulphates, providing a more reliable measure of aggressive anions. Total ironFe, mg/l Originates primarily from corrosion of steel pipework in the condensate circuit. Forms deposits on heating surfaces that degrade heat transfer performance. Total copperCu, mg/l Originates from corrosion of copper-alloy equipment and pipework in the circuit. Its deposition on steel surfaces can accelerate galvanic corrosion. SilicaSiO₂, mg/l Forms calcium and magnesium silicate scale with very low thermal conductivity and high mechanical hardness, difficult to remove without chemical cleaning. Its limit in boiler water varies with operating pressure. Oils and greasesmg/l Their presence causes intense foaming and water carry-over with steam. Can promote corrosion by forming films on metal surfaces that alter heat transfer conditions. Total organic carbon (TOC)mg/l C Organic substances can thermally decompose under boiler operating conditions, generating carbonic acid and other acidic products that raise acid conductivity and cause corrosion. 5. Boiler water parameters: the role of blowdown Because boiler water concentrates progressively, quality management requires an active strategy for impurity removal. The fundamental tool for this is blowdown. The standard provides for the dosing of chemical conditioning agents into boiler water … Read more