This paper is inspired by a series of failures that occurred in steam drums and deareators in power generation and chemical/petrochemical plants. In each case the failure occurred in non-Post Weld Heat Treated (PWHT) carbon steel (CS) and low alloy steel (LAS) welded joints and was related to the synergic action of the mechanical stresses and the chemical environment (boiler and feed water). Although technical literature has already covered and discussed the topic and the Users have experienced such damage for a long time, the primary mechanism and root causes of the failure events are still unclear.

This paper shows an overview of different case histories and failure investigations related to in-service cracking of non-PWHT CS welded joints in deaerators and steam drums in some Italian power plants. The damage was associated to a sort of Environmental Assisted Cracking (EAC) related to static and/or slow rate dynamic stresses and corrosive potential of water (mainly dissolved oxygen and pH).

The feedback of the failure investigations has been a starting point for a detailed design and fabrication review involving design, material selection, welding process selection, Post Weld Heat Treatments (PWHT) and Non Destructive Testing (NDT).

Subject
Environmental cracking, Water, Materials, Crack propagation, Corrosion cracking, Stress cracking, Thermal stress, Welded joints, Boilers, Deaerators, Cracks, Damage, Residual stress
Keywords:
Environmentally Assisted Cracking, Strain Induced Corrosion Cracking, boiler water, carbon and low alloy steels, fabrication, post weld heat treatment, inspection
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2015
GOV
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