EH-95-1 Averting Water Hammers and Other Steam/Condensate System Incidents
ENVIRONMENT, SAFETY & HEALTH
SAFETY BULLETIN
Assistant Secretary for U. S. Department of Energy
Environment, Safety & Health Washington, D.C. 20585
DOE/EH-0437 Issue No. 95-1 June 1995
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Averting Water Hammers and Other Steam/Condensate System Incidents
Water hammer, the unexpected release and associated shock wave of
high-pressure steam/condensate, can cause death, severe injury, and
extensive property damage. In one such case, a water hammer filled a
confined space with 120 psi steam on June 7, 1993, killing the Hanford
site power operator who opened the valve. Although direct clean-up
costs totalled only $34,000, the costs necessary to upgrade systems
including inspection, component replacement, procedure revision,
labelling, and drawing and to implement adequate conduct of operations,
exceeded $5 million.
Unfortunately, not all employees who work near high-pressure
steam/condensate systems realize the hazards associated with such
systems. In fact, employees who operate and know the dangers involved
with the systems often do not understand the causes of water hammer.
This Bulletin describes the primary and contributing causes leading to
water hammers and other steam/condensate system incidents and provides
recommendations on how to avert similar incidents in the future.
The Department of Energy (DOE) and its contractors are taking
aggressive steps to strengthen programs that protect employees who work
on or near steam systems. These efforts include conducting
lessons-learned workshops and producing at-a-glance employee reference
tools in conjunction with the Hanford and Savannah River sites.
Water Hammer and General Steam/Condensate Incidents
DOE developed improved employee protection measures based on a review
of water hammer and other steam/condensate incidents reported to DOE's
Safety Performance Measurement System (SPMS) and Occurrence Reporting
and Processing System (ORPS). Incidents were reviewed if they resulted
in, or had the potential to cause, employee injury due to a breach in a
steam or condensate system. Many findings listed in the Hanford Type A
Accident Investigation Report (DOE/EH-0335P) parallel those of the
incidents reviewed. While the Hanford report focuses on steam system
operations, the report pointed to other types of systems that have the
potential to affect employees involved with them similarly.
Review of the SPMS and ORPS reports generated a list of primary and
contributing causes that may lead to water hammers and other general
steam/condensate incidents. Both primary and contributing causes are
listed below. Here, the contributing causes are organized into four
categories: design, maintenance, procedures, and management controls.
Primary Causes
* Condensation in lines containing both steam and condensate
* Condensate entrainment in steam-filled lines
* Voiding of normally condensate-filled lines
* Rapid valve action (e.g., check valve closing, relief valve opening,
control valve instability, and personnel error)
Contributing Causes
Design
* Inadequate number and placement of system low-point drains
* Inadequate number of system bypass/equalizing valves
* Inadequate drainage of condensate
* Improper component labelling
Maintenance
* Blocked steam traps (by corrosion products or other defects)
* Age-related problems
- Material strength concerns (e.g., pipes, valves, fittings,
rupture discs, gaskets, boiler tubes)
- Abandoned in-place components/sub-systems and portions of systems
- Corrosion (due to lack of water treatment, wrong materials, etc.)
- Out-of-date equipment
- Inadequate preventive maintenance
* Incomplete preventive maintenance programs
Procedures
* Inadequate system startup procedures
* Inadequate pre-job/task analysis
* Inadequate communications (i.e., supervisor/operator)
* Inadequate lockout/tagout procedures and practices
* Inadequate verification of system status prior to initiating work
* Inadequate protective clothing and equipment
* Inadequate announcements about potentially hazardous operations,
tests, or maintenance in general access areas
* Deficient emergency planning; no specification of "kill" switch
location
Management Controls
* Inadequately trained/qualified system operators
* Inability to verify a worker's knowledge and qualifications
adequately
* Inadequate as-built versus design documentation and drawings
Factors Compromising System Integrity
When water hammer occurs, the system's ability to withstand the
resulting pressure surge(s) is influenced primarily by the strength of
the system's components/materials. Older systems may contain
components/materials incapable of containing pressure surges,
particularly when temperatures and pressures have increased
instantaneously beyond their design tolerance. For example, the valve
that failed at the Hanford incident was constructed of gray cast iron
with less than the expected tensile strength. Cast steel is the
preferred material for such components. Similarly, materials such as
"bondstrand" fiberglass pipes, PVC (polyvinylchloride) unions, and
teflon gaskets which have been used in other steam/condensate systems
are not recommended for today's systems. In addition, some systems are
compromised further by not being subject to water chemistry control
requirements during their early years and by inattention to routine
maintenance.
Working on steam/condensate components usually requires that these
systems be shut down, blown down, or adequately locked out/tagged out.
Several incidents were identified in which employees who were repairing
or replacing valves assumed that the valves were isolated; however, in
fact, a blockage of rust or debris prevented the component from feeling
"hot to the touch." When these blockages broke loose, live steam
flowed from the valve. Although no one was seriously injured in these
incidents, there was potential for serious injury or property damage.
Any special devices (such as a rupture disc) that release steam inside
a building represent special hazards to those who may be in the
immediate area during system failure. Likewise, pressure tests may
release steam/condensate. These tests should be conducted under
special controls and after all nonessential personnel have left the
area.
Lessons Learned Workshops
DOE's Office of Environment, Safety and Health has conducted two workshops at Hanford
to help prevent additional water hammer incidents from occurring. These workshops
help managers and employees
(1) improve recognition of water hammer risks;
(2) assess the adequacy of system design, operation, and maintenance; and
(3) maximize effectiveness of operator and manager training.
Ongoing reviews and evaluations incorporate new lessons learned
continually, providing attendees with the most up-to-date information
available.
Water Hammer Safety Principle
The workshop focused on the following condensate-induced water hammer
safety principle.
"Steam and water cannot be safely mixed in a piping system without
risking condensate-induced water hammer. Do not mix steam with water
either by injecting water into a steam system or steam into a system
that includes water (condensate). Condensate should be assumed to be
in all low points and dead legs until proven otherwise."
Workshop Recommendations
The following recommendations presented at the workshop are based on
lessons learned from previous water hammer incidents.
1. Review and inspect all steam systems to ensure proper distribution
and sizing of cold traps for startup and operation and to verify
that all low points have steam traps. Give maintenance the
highest priority.
2. Frequently inspect all steam traps to ensure that they operate
properly and that no condensate accumulates. Immediately repair
or replace erratic steam traps. Use thermocouples where feasible
to locate condensate accumulation.
3. Do not "CRACK OPEN" valves to avoid condensation-induced water
hammer. This will not guarantee safe operation. The formation
of a condensation-induced water slug can occur at very low
condensate flow conditions.
4. Valves in pipe lines that lack properly positioned steam traps
should remain open at all times or, preferably, should be removed
from the piping system.
5. Before opening valves in steam lines, check for adequate placement
of steam traps. Verify that the steam traps operate properly and
fully open the bleed valves using reduced system pressure to
remove any remaining condensate.
6. Where feasible, operate the valves remotely using mechanical
extension linkage, reach rods, or adequately controllable
power-operated valves.
7. Inspect the piping system for sagging. Where necessary, install
steam traps or repair the sagging.
8. Check or repair the piping insulation. It will save energy and
reduce accumulation of condensate in the piping system.
9. Activation of cold steam piping should be performed slowly at
reduced pressure and with trap bleed valves continuously open.
10. The above list of recommendations should be followed regardless of
piping size. Do not exclude small pipe sizes without appropriate
analysis.
11. All isolation valves must have bypass systems. However, bypass
operation will not prevent water hammer if condensate is present.
12. Placement of blowdown valves before and after a vertical rise
(such as over-the-road) is required to prevent possible condensate
accumulation.
13. Improperly designed steam/water systems should not have the
incorrect features overcome by operational methods. Systems must have
incorrect features corrected.
Helpful Publications
Occupational Safety and Health Administration standard 29 CFR 1910.147,
"The Control of Hazardous Energy (Lockout/Tagout)," provides excellent
safety guidance for workers maintaining/repairing steam/condensate
systems. However, there is little guidance specific to the safe
operation necessary to minimize the likelihood of water hammer.
Operators are expected to have the expertise required to operate
systems safely. Management can influence operator actions through
required training, job hazard analyses, pre-job briefings, standard
operating procedures, and direct supervision, as required by DOE Order
5480.19, "Conduct of Operations for DOE Facilities."
Steam plant operation and water hammer information can be found in the
McGraw-Hill publication, "Steam-Plant Operation," by E.B. Woodruff and
H.B. Lammers; and in a Nuclear Regulatory Commission (NRC) publication,
"Evaluation of Water Hammer Occurrences in Nuclear Power Plants,"
NUREG-0927. Specifics from these documents should be considered for
inclusion into site/facility procedures and training. The McGraw-Hill
publication can be found in any library. To obtain copies of the NRC
publication, contact the NRC Public Document Room at 202-634-3273 or
the National Technical Information Services at 703-487-4650.
For More Information
For more information on condensate-induced water hammer and other
steam/condensate system incidents, contact Rex Bowser (DOE) at (301)
903-2641. To schedule a water hammer workshop or request a laminated
pocket-sized card printed with the 13 workshop recommendations listed
above, call Herb Debban (ICF Kaiser Hanford Company) at (509)
376-5060.
1. Appendix N, "Description of Water Hammer and Preventive Measures,"
Hanford Type A Accident Investigation Report, DOE EH-0335P
This Safety Bulletin is one in a series of publications issued by EH to
share occupational safety information throughout the DOE complex. To be
added to the Distribution List or to obtain copies of the publication,
call (301) 916-4444. For additional information regarding the publications,
call Barbara Bowers (301) 903-3016.