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Steam is an essential component in the generation of electricity
in any power plant. The loss of steam or a failure in a steam
system can create serious operational problems, resulting in
reduced production of electricity, or at the worst, a major
shutdown.
A Midwestern nuclear power plant needed to replace a 2-inch
control valve in a steam-return line. The valve, stuck in the
open position, was discovered after the plant was brought back
on line after a maintenance outage. The defective valve
prevented isolation of a section of the plant scheduled for
routine work. Replacing the valve would prevent an unplanned
shutdown at the plant.
STOPPLE® Plugging System
After carefully considering capabilities and experience, the plant operator chose TDW Services, Inc., to tap the 2-inch line and use its STOPPLE® Plugging System to isolate the faulty valve. Developed and patented in the 1960s, TDW has employed this high temperature plugging system in many steam applications and has perfected the capability for use up to 650°F at 600 psi. TDW Services is no stranger to the nuclear power industry, having applied the STOPPLE® Plugging method to isolate "Section III and safety related" cooling water lines up to 60 inches in diameter while maintenance work was being performed. This plugging capability includes the ability to isolate and bypass a trouble spot while work is being done, keeping the line in full service.
In this case, a plugging fitting was welded to the carbon steel line upstream of the faulty valve and tapped through, using a T-101 Drilling Machine. A mechanical jackscrew actuator was used to insert the STOPPLE® Plugging Head into the line against 250 pounds of pressure to stop flow, isolating the faulty valve.
During the next eight hours, the valve was cut out and replaced. The portion of the steam system upstream from the plugging head remained in service while the valve was replaced.
Had it been necessary, a second plugging machine could have been used downstream of the valve, and flow directed around the valve, keeping the entire system in operation. The process is simple and cost effective, even on a steam system.
Boiler Repair Success
In another recent high temperature job TDW Services isolated a section of 24-inch line between two boilers operating at 650°F at 450 psi while a faulty isolation valve was being replaced. The faulty valve prevented routine maintenance on one of the boilers. The line was plugged, isolating the defective valve and one boiler. The valve was replaced and boiler maintenance performed while the other boiler remained on line.
TDW Services has hot tapping and plugging capabilities in sizes from ½ inch up to and including 102 inches in diameter. The process will work on steel, cast iron, ductile iron, plastic, copper and concrete pipe. TDW Services has successfully applied these procedures in systems operating up to 2,200 psi.
TDW Services' Capabilities
When confronted with the need to replace a valve, make a tie-in, add instrumentation or when a section of your system needs to be isolated for maintenance, contact TDW Services. They will assist in developing specifications, engineering cost-effective solutions, and ensuring that every detail of your hot tap, line stop, and bypass is planned and executed precisely. TDW has a long history in the nuclear industry. Experienced, certified technicians, a staff of professional engineers, service centers located strategically worldwide, the largest equipment inventory and response time unmatched in the industry are what make TDW your solution specialists.
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