Steam Trap Case Studies
The following three examples illustrate the importance of using extreme care in steam trap operation and maintenance.
Safety Precautions Could Have Averted Deaths and Injuries at a Major Government Research Facility
On October 10, 1986, a condensate-induced water hammer at a major research government facility injured four steamfitters—two of them fatally. One of the steamfitters attempted to activate an 8-inch steam line located in a manhole. He noticed that there was no steam in either the steam line or the steam trap assembly and concluded that the steam trap had failed. Steam traps are devices designed to automatically remove condensate (liquid) from steam piping while the steam system is operating in a steady state. Without shutting off the steam supply, he and another steamfitter replaced the trap and left.
Later the first steamfitter, his supervisor, and two other steamfitters returned and found the line held a large amount of condensate. They cracked open a gate valve to drain the condensate into an 8-inch main. They cracked the valve open enough to allow water to pass, but this was too far open to control the sudden movement of steam into the main after all the condensate had been removed. A series of powerful water hammer surges caused the gaskets on two blind flanges in the manhole to fail, releasing hot condensate and steam into the manhole. All four steamfitters suffered external burns and steam inhalation. Two of them died as a result.
A Type A Accident Investigation Board determined that the probable cause of the event was a lack of procedures and training, resulting in operational error. Operators had used an in-line gate valve to remove condensate from a steam line under pressure instead of drains installed for that purpose.
The board also cited several management problems. There had been no Operational Readiness Review prior to system activation. Laboratory personnel had not witnessed all the hydrostatic and pressure testing, nor had all test results been submitted, as required by the contract. Documentation for design changes was inadequate. The board also determined that management had not been significantly involved in the activities of the steam shop.
One Hospital's Ordeal: Proper Safety Procedures Could Have Saved a Person's Life
In June 1991, a valve gasket blew out in a steam system at a Georgia hospital. Operators isolated that section of the line and replaced the gasket. The section was closed for 2 weeks, allowing condensate to accumulate in the line. After the repair was completed, an operator opened the steam valve at the upstream end of the section. He drove to the other end and started to open the downstream steam valve. He did not open the blow-off valve to remove condensate before he opened the steam valve. Water hammer ruptured the valve before it was 20% open, releasing steam and condensate and killing the operator.
Investigators determined that about 1,900 pounds of water had accumulated at the low point in the line adjacent to the repaired valve, where a steam trap had been disconnected. Because the line was cold, the incoming steam condensed quickly, lowering the system pressure and accelerating the steam flow into the section. This swept the accumulated water toward the downstream valve and may have produced a relatively small steam-propelled water slug impact before the operator arrived. About 600 pounds of steam condensed in the cold section of the pipe before equilibrium was reached.
When the downstream valve was opened, the steam on the downstream side rapidly condensed into water on the upstream side. This flow picked up a 75 cubic foot slug of water about 400 feet downstream of the valve. The slug sealed off a steam pocket and accelerated until it hit the valve, causing it to rupture.
Investigators concluded that the accident could have been prevented if the operator had allowed the pipe to warm up first and if he had used the blow-off valve to remove condensate before opening the downstream valve.
Steam Trap Maintenance Results in Savings of More Than $100,000!
A steam trap assessment of three VA hospitals located in Providence, RI, Brockton, MA, and West Roxbury, MA was conducted with help of FEMP's SAVEnergy Program. The facilities are served by 15, 40, and 80 psig steam lines. The Providence system alone includes approximately 1,100 steam traps.
The assessment targeted steam trap performance and the value of steam losses from malfunctioning traps. The malfunctioning traps were designated for either repair or replacement. Included in this assessment was a training program on steam trap testing.
The cost of the initial steam trap audit was $25,000 for the three facilities. Estimated energy savings totaled $104,000. The cost of repair and replacement traps was about $10,000. Thus, the cost savings of $104,000 would pay for the implementation costs of $35,000 in about 4 months.