TVA Uses Ultrasound to Locate Leaky Valves

Issue 11 and Volume 103.

WHEN THE TENNESSEE Valley Authority needed assistance improving the performance of a fossil plant that was becoming less and less efficient, technicians turned to Colt Atlantic Services Inc. for troubleshooting. Colt, based in Norcross, Ga., is an under-pressure leak-sealing company.

“Using our portable ultrasonic instruments, we checked all start-up valves that were thought to be closed throughout the entire unit,” said Ian Barford, Colt sales manager. “Based on our report, TVA made adjustments on the by-passing valves, replaced critical internal valve components and also replaced valves beyond repair while the unit was shutdown for other reasons.”

During ultrasound inspection, a two-man crew inspects a facility’s valves one at a time, checking for valves that are supposed to be closed but aren’t. An open valve wastes a tremendous amount of steam. On average, a crew diagnoses between 40 and 60 valves per day. The crew checks two points on the inlet side of each valve and two points on the outlet side of each valve. After testing, a detailed report is generated, showing the severity of leakage in all tested valves. The information can be used to set up baselines for re-testing and for tracking any wearing or failed valves. Leaky valves can often be adjusted or repaired while the plant is running, avoiding costly down time.

“Previous to using ultrasonics to diagnose valves, it was nearly impossible to spot internal leaks,” Barford said, “Today we detect internal leaks and know for certain if a valve is not holding or losing efficiency, or if it simply needs an adjustment. This also reduces the chance of taking out a perfectly good valve and replacing it unnecessarily because of preventive maintenance. Now we can move into predictive maintenance, which is much more cost-effective.”

Ultrasonic probes can detect the ultrasonic turbulence produced when fluid moves from the high-pressure side of a valve through the seat to the low-pressure side. The Ultraprobe 2000 translates the ultrasonics into an audible range, heard through an inspector’s headphones and seen as intensity increments on a meter on the back of the instrument. High frequency tuning allows operators to adjust for differences in fluid viscosity and to reduce interference from ambient pipe and machine noises.

TVA found that valve testing and repair improved the unit’s rating by 25 to 30 MW, the most efficient the unit had been in more than three years. “This improvement translated into approximately $50,000 to $60,000 per hour in savings, well over $1.3 million a day,” Barford said.

The Ultraprobe 2000 can detect leaks in start-up valves, steam traps and other mechanical apparatus.