Temperature imbalance in a superheater header

Superheater outlet header

Final superheater outlet header in a European coal-fired unit, fabricated from P22 and operating at 540°C, 15MPa


  • To determine the remaining life of this component
  • To demonstrate a consistent life assessment route, that might be applied company-wide to plant built to different design codes
  • To compare various temperature measurement and estimation methods


Following the phased-approach:

  • Phase 1: - Initial code-based calculations
  • Phase 2: - Visual inspection, conventional NDE and metallographic examination
  • Phase 3: - Installation of conventional thermocouples and off-line diffusion-couple sensors, application of hardness and oxide-thickness based temperature estimation method.  Recalculation of header life using quantitative inspection results
Schematic cross-section of header showing measured / estimated metal temperatures and inferred steam temperature distribution.


  • Header shown to be life-expired according to inverse-design calculations
  • Comparison of various code formulae and materials standards showed no significant variation in calculated stresses and lives
  • Adequate life demonstrated on the basis of initial inspection results
  • Apparent differences between temperature measurements reconciled through realisation that a temperature imbalance existed between the tube rows


  • Consistent life assessment route established
  • Adequate header life demonstrated for continued operation
  • Thermal imbalance identified, leading to loss of unit efficiency and increased stresses in the header
  • Potential design modifications proposed to reduce this problem
  • Refined FE-based life assessment proposed to address effect of the additional thermal stresses


Jarvis, P., Jones, G.T., Batista, A. and Araujo, C.L.de,
"Life assessment using codes and standard material properties in SP249 Carregado case study"
SPRINT/KBS Dissemination Workshops of MPA Seminar, Stuttgart, Germany, 6-7th October 1994

Plant Integrity