Measurement And Analysis Of The Stress And Safety Assessment For A High Pressure Heater In A Power Plant At Different Cases

High pressure heater is one of the key equipments in generating set of thermalpower plant. A high pressure heater in a thermal power plant leaked several times since2001 in the lower half part of the circumferential weld of the cylinder. Similar leakagefailures are reported other plants, so it is necessary for safety of the equipment toanalyze the reason of the leakage of the high pressure heater cylinder and to propose thepreventing means. In this paper, investigation of the temperature and stress field in thewall of the high pressure heater were carried out by measurement and FE analysis indifferent cases. The fatigue life and safety of the high pressure heater are assessed. Themain research results are as followings:(1) The temperature distributions of the heater near the water-steam interfacelevel were measured and analyzed by thermal couples and FEA method. Differenttemperature distributions and obvious temperature gradient are observed in the localarea near the water-steam interface level. Internal leakage of steam existing in thecontainment shell of the heater results in steam temperature being higher thancondensed water at condensate zone, so the wall temperature of the heater near thewater-steam interface level fluctuates obviously with water-steam interface levelchange.(2) The stress distributions of the heater near the water-steam interface levelwere measured by high temperature strain gages. The stress fields at different cases,including with and without internal leakages of steam, were analyzed by FEA method. The results from measurement and FE analysis show that the maximum axial alternatingstress takes place at the point of 7 o'clock. The maximum stress fluctuation reaches34MPa and 35MPa by measurement and FEA, respectively. When the internal leakageof steam increases and the steam temperature at condensate zone is 300℃, themaximum stress fluctuation reaches 52MPa.(3) Based on the measurement and the numerical simulation of the temperatureand the stress fields, measured material properties for the weld and HAZ, the leakagereason and fatigue life assessment are carried out. Internal leakage of steam, uneventemperature distribution and stress fluctuating result in fatigue crack growth. Thefatigue lives are assessed with Chinese standards JB4732 and GB/T19624. The fatiguelife of the cylinder without defect is much higher than 10~6 cycles. The fatigue lives withinner surface defects, whose depth and length are (1mm, 4mm) and (2mm, 8mm),are1.37×10~6 and 0.69×10~6 cycles, respectively.