OSHA Hazard Information Bulletins
October 31, 1996
| MEMORANDUM FOR: |
REGIONAL ADMINISTRATORS |
| FROM: |
STEPHEN J. MALLINGER
Acting Director
Directorate of Technical Support |
| SUBJECT: |
Hazard Information Bulletin(1): Potential for
Feed Water Pipes in Electrical Power Generation
Facilities to Rupture Causing Hazardous Release of
Steam and Hot Water |
________
FOOTNOTE(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.
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:
(1) ANSI B31.1-1995, American National Standards for Power
Piping.
(2) Recommendations for an Effective Flow-Accelerated Corrosion
Program, Electrical Power Research Institute, NSAC/202L.
(3) 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.
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