OSHA Hazard Information Bulletins1
Potential for Feed Water Pipes in Electrical Power Generation Facilities to Rupture Causing
Hazardous Release of Steam and Hot Water
October 31, 1996
- STEPHEN J. MALLINGER
- Acting Director
- Directorate of Technical Support
- Hazard Information Bulletin1: Potential for Feed Water Pipes in Electrical Power Generation Facilities to Rupture Causing Hazardous Release of Steam and Hot Water
The Chicago Regional Office has brought to our attention the potential for feed water pipes in electrical power generation facilities to rupture causing hazardous release of steam and hot water. During an investigation of a multiple fatality accident at an electrical power generation facility in an industrial plant, the Appleton Area Office uncovered at least three other feed water pipe failure incidents in other power plants. In two of the three incidents, six additional fatalities had occurred. In all cases, the feed water pipe failures were attributed to wall thinning as a result of single-phase erosion/corrosion, leading to rupture of the pipes under high working pressures.
The rupture of feed water pipes due to wall thinning creates the potential for serious burns, massive property damage, and power outages in electrical power generation plants. These feed water pipe failures could not be linked to any specific aspect of system designs, materials, or operating histories to support a conclusion that single-phase erosion/corrosion was distinctive to these particular power plants. This suggests that these may not be isolated incidents but a problem that may be widespread in the industry.
Several factors affect the rate of erosion/corrosion in piping. These factors include material composition of carbon steel piping, temperature, low water pH, low dissolved oxygen content, pipe geometry, and fluid velocity. The flow path through elbows, bends, tees, orifices, welds, valves, and backing rings creates turbulence in flow which, with fluid velocity, has the potential to react with the protective oxide layer of carbon steel piping, contributing to the erosion/corrosion process.
Feed water pipes are addressed in the standard boiler inspection. Generally only a visual inspection with the pipe insulation in place is done or required. Since this will not reveal pipe thinning, employers may not have actual knowledge of the pipe wall thinning that could be occurring.
To minimize the potential for personal injury or loss of life, property damage, and power interruptions resulting from feed water pipe failure, it is recommended that employers of electrical power generation facilities establish a flow-assisted corrosion (FAC) program:
- to identify the most susceptible piping components/areas and establish a sampling protocol consistent with engineering principles and practices;
- use appropriate nondestructive testing (usually ultrasound) to determine the extent of pipe thinning (if any); and,
- where thinning is identified, establish a preventative maintenance program and replace piping in accordance with ASME recommendations.
For additional information on FAC, the following documents are suggested:
- ANSI B31.1-1995, American National Standards for Power Piping.
- Recommendations for an Effective Flow-Accelerated Corrosion Program, Electrical Power Research Institute, NSAC/202L.
- Yukawa, S, Guidelines for Pressure Vessel Safety Assessment, NIST Special Publication 780.
Please distribute this bulletin to all Area Offices, State Plan States, Consultation Project Offices, and appropriate labor and industry groups.
1 The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood health hazards, inadequacies of materials, devices, techniques, and safety engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports, and concerns expressed by safety and health professionals, employers, and the public. Bulletins are developed based on a thorough evaluation of available facts in coordination with appropriate parties.