EN 12953 Standard Directives for the Fire-Tube Boilers Design

EN 12953 Standard Directives for the Design, Construction and Safety of Fire-Tube Boilers

EN 12953 Standard Directives for the Design, Construction and Safety of Fire-Tube Boilers

The EN 12953 standard provides a comprehensive framework for the design, construction, and safe operation of fire-tube boilers. It is divided into several parts that address specific aspects. The main directives are summarized below:

• Construction Materials (EN 12953-2)

  • Specifies requirements for materials used in pressure parts, including plate products, tubes, valves, bolts, and welding consumables.
  • Material selection must comply with harmonized European standards, European Approvals for Materials (EAM), or Particular Material Appraisals (PMA). The standard emphasizes using materials with compatible electrochemical potentials to prevent corrosion.
  • Example: grey cast iron is permitted for specific components such as steam stop valves and blowdown valves in steam boilers, and for all valves larger than DN 50 in hot-water boilers. Care is required for downstream piping in steam systems to avoid water hammer and to respect cast iron’s lower operating temperature limits.

• Design and Calculation of Pressure Parts (EN 12953-3)

  • General design: covers steam and hot-water boilers, with attention to main weld types, weld factors, and thermal design of furnace tubes. The standard highlights the need for adequate reinforcement of shell openings with detailed calculation rules.
  • Specific components: guidance for calculating cylindrical shell thickness considering internal pressure, material tolerances, and forming processes. Includes design of boiler supports, lifting lugs, and integration of openings in shells.
  • End plates: specifications for different end-plate configurations.
  • Other components: although focused on fire-tube boilers, EN 12953-3 refers to EN 12952 for the design of economizers, superheaters, membrane walls, and drums.

• Manufacturing and Construction Techniques (EN 12953-4)

  • General fabrication: forming tolerances for shells, dished ends, and furnace tubes; requirements for tube-to-tube-plate connections.
  • Connections and openings: guidance for incorporating connections and openings, including those for safety devices and access; requirements for mounting nozzles and fittings.
  • Welding: full-penetration welds where required; preheating based on composition and thickness; approval of welding procedures (e.g., per EN 288-3 / ISO 15614).
  • Furnace tubes: detailed construction requirements to ensure proper installation and welding for strength and integrity.

• Inspection Procedures During and After Construction (EN 12953-5)

  • Production control, documentation, and boiler marking requirements.
  • Manufacturers must document procedures for control, calibration, and adjustment of measuring equipment used during fabrication.
  • Inspection activities include:
    • Design & documentation: verification of design data, calculations, manufacturing drawings, material specs, and subcontracting for compliance.
    • Materials: checking certificates and test reports; ensuring traceability.
    • Welding: visual inspection, verification of consumables, equipment calibration, and NDT of welds in accordance with approved WPS.
    • Dimensional checks: verifying conformity of construction to approved drawings.

• Requirements for Boiler Equipment, Combustion Systems, and Safety Devices (EN 12953-6 / -7 / -8 / -9 / -12)

  • EN 12953-6 (Boiler equipment):
    • Safety valves: at least one safety valve sized for the boiler’s capacity.
    • Valves, fittings, flanges: materials selected per EN 12953-2.
    • Protection systems: protective devices compliant with EN 12953-9.
    • Water-level indication: adequate means to indicate water level in steam boilers.
  • EN 12953-7 (Combustion systems for liquid and gaseous fuels):
    • Requirements for single- and multi-fuel burners.
    • Fuel-supply system design: piping must withstand mechanical, chemical, and thermal stresses.
    • Safety devices: automatic shutdown upon flame failure or abnormal conditions.
  • EN 12953-8 (Overpressure protection): protection against overpressure in fire-tube boilers.
  • EN 12953-9 (Limiting devices): requirements for limiters such as pressure switches, level indicators, and temperature limiters.
  • EN 12953-12 (Grate firing systems for solid fuels): requirements for grate combustion systems, including fuel bunkers, handling, combustion airflows, and operational safety.

The EN 12953 series therefore provides exhaustive directives for fire-tube boilers, covering material selection, design calculations, construction techniques, inspections, and requirements for essential equipment such as combustion systems and safety devices. Compliance with these directives ensures safe and reliable boiler operation.