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The Office of Environment, Safety and Health, through its Office of Nuclear and Facility Safety, publishes the Operating Experience (OE) Summary approximately twice per month. The OE Summary promotes safety throughout the Department of Energy complex by encouraging feedback of operating experience and information exchange among DOE facilities. For DOE facilities, the OE Summary should be processed as a DOE-Wide information source as described in DOE-STD-7501- 99, The DOE Corporate Lessons Learned Program. Note: In response to the need to better involve the field management and the operating contractors in the process of disseminating important lessons and in analyzing these lessons the Department has discontinued the publication of the OE weekly in its current form. The concept and intent however, will not be discontinued. The Department is currently working with EFCOG to develop an integrated Lessons Learned program which will provide for the appropriate reporting, analysis and dissemination of information. |
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The following is part of the DOE OE Summary located at: http://tis.eh.doe.gov/web/oeaf/oe_weekly/oe_weekly_97/oe97-42.html. “The engineers reviewed the steam trap design and decided to replace the existing "bucket" style steam traps with newer, more effective "orifice" traps. The new style trap is designed to drain condensate continuously and completely. These traps have no internal moving parts, which will greatly reduce trap maintenance.” SEE BELOW: |
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Operating
Experience Weekly Summary 97-42
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Operating Experience Weekly Summary 97-42October 10 through October 16, 1997
(Partial SUMMARY) FINAL REPORTFINAL REPORT1. WATER HAMMER PROBLEMS AT ROCKY FLATSThis week OEAF engineers reviewed a final occurrence report on water hammer problems at the Rocky Flats Environmental Technology Site. On May 7, 1997, technical support and utilities personnel notified a building manager that water hammers were continuing to occur in the steam system at two locations within the facility, as well as outside. The building manager cordoned off the affected areas and restricted access until a fact-finding team identified the cause of the water hammers and developed corrective actions. Water hammer events are significant because they can cause fatalities, personnel injury, and equipment damage. (ORPS Report RFO--KHLL-SOLIDWST-1997-0014) The building manager conducted a fact-finding meeting and formed a team to coordinate efforts between the integrating contractor and the subcontractors involved in the operation of the site steam system. They determined that water hammers primarily occurred in one building, but were impacting six others. They also determined the direct and root cause of these events was an equipment/material problem (defective or failed part) because valves and steam traps were not operating as designed. Steam traps drain and remove condensate automatically from the steam lines, and the valves regulate the flow of steam within the system. As the steam gives up heat, it converts to condensate. The traps were not removing condensate from the lines and were allowing backflow of steam and condensate. Engineers determined that six traps in a valve station were not functioning properly. They also determined that condensate accumulated in the steam lines during off-peak hours. When steam demand increased, the condensate mixed with the steam, causing a "flash" condensate-induced water hammer. Steam and water cannot mix safely in a piping system without risking condensate-induced water hammer. The engineers reviewed the steam trap design and decided to replace the existing "bucket" style steam traps with newer, more effective "orifice" traps. The new style trap is designed to drain condensate continuously and completely. These traps have no internal moving parts, which will greatly reduce trap maintenance. The new traps were installed with a special 40-mesh stainless steel strainer insert to trap any particles or contaminants before they reach the drain nozzle. The condensate that drains from piping system traps collects in a condensate tank. The temperature of the tank was 200 degrees Fahrenheit. Engineers believe this temperature contributed to the hammer problems while the piping systems heated up. As a corrective action, mechanics repaired condensate line leaks, repacked a condensate pump, and removed the insulation around the condensate tank. Condensate tank temperature dropped to 180 degrees Fahrenheit, which was within the parameters for efficient warming of the pipes with no discernable hammer. Between June 17 and 19, 1997, utilities operators successfully reintroduced steam to the system for all affected buildings with no discernable "hammer." Before reintroduction of steam, operators emptied condensate from the steam and condensate lines, then manipulated valves to slowly introduce steam and isolate any potential hammering. This event illustrates that facility personnel were aware of, and sensitive to, water hammer issues. Facility management took appropriate steps to isolate the steam system to prevent injury to personnel and equipment damage. Engineering personnel determined that the water hammers were caused by several valves and traps that were not operating as designed and by a condensate collection tank with system leaks and inefficient valves. Engineers corrected the steam system deficiencies and design problems by replacing older-design steam traps with newer, more effective equipment. NFS has reported other water hammer events in the Weekly Summary. The following are examples. · Weekly Summary 96-40 reported that seven workers at a commercial nuclear power plant were injured when an 18-inch diameter reheater drain line ruptured because of a water hammer. All seven workers suffered serious steam burns and steam inhallation injuries. (NRC Event No. 31053) · Weekly Summary 96-39 reported that two power operators caused a condensate-induced water hammer event at the Hanford Plutonium Finishing Plant when they opened a bypass valve instead of a diaphragm-operated valve as directed in a work package. Investigators determined that the potential for water hammer was not discussed during the pre-job briefing. (ORPS Report RL--WHC-PFP-1996-0038) Serious water hammer events at DOE facilities have resulted in Type A accident investigations. On June 7, 1993, a water hammer event at Hanford resulted in a valve rupture and fatal injury (ORPS Reports RL--WHC-WHC300EM-1993-0022). The Type A Accident Investigation Board Report, June 7, 1993, U-3 Pit Valve Failure Resulting in a Fatality at the Department of Energy Hanford Site, identified probable causes of the event to be inadequacies in operating practices, lessons learned, training, operating procedures, policy, guidance, safety implementation, design, and oversight. On October 10, 1986, a condensate-induced water hammer at the Broohaven National Laboratory resulted in two fatalities and two severe injuries. The Type A Accident Investigation Board determined the direct cause was the use of an in-line gate valve to remove condensate instead of drains that had been installed for that purpose. There were no written instructions for warming and activating the steam lines, and there was no formal training program to familiarize steamfitters with specific systems at Brookhaven. (Type A Investigation Report, November 14,1986) Water hammers can cause serious piping and equipment damage. They can also cause uncontrolled releases of radioactive or hazardous materials and serious injury or death. These events can be prevented with planning, procedures, equipment design and condition, and cognizance of steam and water conditions. Appropriate training and procedures provide a measure of protection against water hammers. Managers at DOE facilities should review their procedures and training to determine if their controls will prevent water-hammer damage. In June 1995, the Office of Environment, Safety and Health issued Safety & Health Bulletin 95-01, "Averting Water Hammers and Other Steam/Condensate System Incidents." This bulletin provides lessons-learned information and recommendations from DOE-sponsored workshops on water hammers and water hammer prevention. To obtain copies of this publication, call (301) 903-2641. The April 1994 article, Steam Line Water Hammer: Cause and Prevention, published in the Occupational Safety Observer, discusses (1) causes of water hammer, (2) methods to control condensate accumulation, (3) heat-up practices, and (4) proper system design. Mark Gintner of the Westinghouse Hanford Company has video training tapes on condensate-induced water hammer. Information on how to obtain these tapes and other training materials on condensate-induced water hammer may be obtained by contacting him at (509)-373-9145, or electronically, mark_a_gintner@rl.gov. KEYWORDS: water hammer, condensate, steam trap FUNCTIONAL AREAS: Operations, Startup, Design |
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http://tis.eh.doe.gov/web/oeaf/oe_weekly/oe_weekly_97/oe97-42.html |
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Last modified: Tuesday, 04-Nov-97 11:59:00 |