Life limiting considerations for stainless steel cladding in heavy wall pressure vessels
- Exxon Research and Engineering Co., Florham Park, NJ (United States)
- Exxon Research and Engineering Co., Clinton, NJ (United States)
Heavy wall pressure vessels in refinery service frequently have internal stainless steel (SS) cladding for corrosion resistance. Typically the cladding is 3 mm (0.125 inch) to 6 mm (0.250 inch) thick and is a 300 series austenitic stainless steel. Experience has shown that cladding, especially Type 347 SS weld overlay cladding in reactors over 20 years old, contains cracks. These cracks commonly occur at internal surface discontinuities such as attachment welds and other areas of geometric stress concentration. Cracking of the cladding is the result of low cycle thermal fatigue due to the difference in coefficient of thermal expansion between the austenitic stainless steel cladding and ferritic steel pressure vessel. Yielding of the cladding in compression at high temperature results in a high residual tensile stress in the cladding at ambient temperature, which causes plastic strain accumulation at discontinuities. Finite element analysis of a pressure vessel with cladding shows that a significant level of plastic strain accumulates at internal discontinuities each time the pressure vessel experiences thermal cycles from normal start-up/shut-down, upset conditions and postweld heat treatment. The ability of the cladding to resist cracking depends on the ductility of the cladding. Examination of a Type 347 stainless steel overlay shows it possesses a limited ductility after a PWHT cycle due to the formation of very fine ({le}30 {angstrom}) niobium containing clusters/NbC precipitates. Other grades of weld overlay, hot roll clad or explosively bonded steel are expected to possess a higher ductility and greater resistance to cracking.
- OSTI ID:
- 176085
- Report Number(s):
- CONF-950740--; ISBN 0-7918-1346-0
- Country of Publication:
- United States
- Language:
- English
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