BOILERS COMBINED CYCLE CORROSION FLOW-ASSISTED CORROSION MONITORING OPERATIONS POWER STEAM FLUOR ENTERPRISES

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Abstract

The aim of this article is help improve an understanding of flow-accelerated corrosion (FAC) in a way that is useful for engineers and operators of steam generation power stations.

FAC is a process by which the protective magnetite film (Fe₃O₄) on the internal pipe/tube wall of a boiler tube is chemically dissolved and removed by the flowing fluid. The cyclical formation of oxide and subsequent dissolution of this may lead to catastrophic failures in steam generation power plants. Some FAC failures have resulted in fatalities. 

Despite extensive research in the last 45 years to prevent catastrophic failures, such as a result from FAC, these failures still occur, indicating that our knowledge and understanding of FAC can be further developed and expanded. FAC is caused by the environment to which the pipe/tube material, typically carbon steel, is exposed such as pH, flow velocity and turbulence, pipe geometry, oxygen content, and water chemistry.

While there are other processes that cause pipe/tube degradation and catastrophic failures (e.g., erosion-corrosion, cavitation erosion, flashing-induced erosion, and shear stress erosion), this article will focus on FAC and its impact on the internal pipe/tube walls in steam generation power plants.

The article aims to provide a brief overview and summary of the major research, lessons learned, and past experiences with FAC. The article will then quantify the chemical reactions, flow conditions, water chemistry, and various process conditions to provide an understanding of the theoretical limitations for the operating environment that is conducive for FAC. These theoretical limits will help engineers and operators design and operate a steam generation power plant that minimizes FAC and prolongs plant life. 

Introduction

Flow-accelerated corrosion (FAC) has been an ongoing issue for the past 45 years in steam generated electric power plants, including coal-fired power plants, combined cycle plants, cogeneration plants, and nuclear power plants. Extensive research has been done on FAC and case studies for lessons learned have been documented in order to mitigate this issue.

FAC is a process by which the protective magnetite film on the internal pipe/tube wall is chemically dissolved and removed by the flowing fluid. This typically occurs on the tube walls in the economizer sections of the steam generator units. The cyclical formation of the oxide and dissolution of this may lead to catastrophic failures in the steam generation power plants, and some of these failures have resulted in fatalities. Despite the extensive research during the last 45 years to prevent these failures, they still occur, which indicates our knowledge and understanding of FAC can be further developed and expanded.

FAC is caused by the environment to which the pipe/tube metallurgy, typically carbon steel, is exposed such as pH, flow velocity and turbulence, pipe geometry, oxygen content, and water chemistry. While many of the parameters listed here can lead to other types of failures such as erosion corrosion, cavitation erosion, and shear stress erosion, this article will focus mainly on single-phase (liquid) FAC and its impact on the internal pipe/tube walls in steam generation power plants. It will provide a brief overview and summary of the major research, lessons learned, and past experiences with FAC. The article will then quantify the chemical reactions, flow conditions, water chemistry, and various process conditions to provide an understanding of the theoretical limitations for the operating environment that is conducive for FAC.

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