J-seals are an integral a part of environment friendly steam turbine operation. The failure of a J-seal could cause vital harm to the turbine rotor as materials migrates downstream. For that purpose, plant employees ought to concentrate on the kind of sealing expertise put in of their gear and perceive how greatest to conduct inspections of their steam path programs to determine potential issues throughout usually scheduled outages.
Steam turbine effectivity depends closely on the integrity and efficiency of the steam path stage-to-stage seals. Sealing among the many rotating turbine parts, stationary nozzles, and casing is established by utilizing a labyrinth of high-to-low seal tooth interfaces.
The tight tolerance labyrinth is designed to generate a strain drop throughout every seal tooth, making certain solely a small quantity of steam passes relative to complete turbine steam stream. Replaceable J-seals are a typical inter-stage sealing expertise utilized by steam turbine unique gear producers (OEMs). By changing worn J-seals, the proprietor can re-establish state-to-stage sealing effectivity throughout main steam path overhauls.
J-seals are a two-piece design and manually assembled, which will increase the danger of set up error by the putting in technician. If the seal will not be put in accurately, the caulking wire will distort and hump beneath thermal stresses, and will liberate from the groove. Once the retaining materials loosens, the seal is liable to failure. Liberated seal materials can migrate downstream by a rotating steam path, inflicting vital harm.
It’s necessary to know the kind of sealing expertise used within the steam path previous to any unit inspection. Blade plans for every part of the rotor must be reviewed to confirm the sealing sort used (Figure 1), place of the seal enamel, the path of steam stream, and another particulars.
|1. Inspection planning is vital. J-seals are a typical inter-stage sealing expertise utilized in steam generators, and are designed to be replaceable, so turbine operators can re-establish stage-to-stage sealing effectivity throughout steam path overhauls. Blade plans must be reviewed and technicians ought to know the sealing expertise used within the steam path, making it simpler to identify J-seal issues. Courtesy: HRST|
In order to guard the steam path from liberation- and migration-induced harm, biannual borescope inspections are really helpful to confirm the well being of the seals. The borescope inspector ought to focus efforts on the rotating blade cowl to stationary casing interface on the prime of the blade to find free and liberating J-seals. Any seal suspected of liberation must be inspected 360 levels across the stage to search out any breaks within the materials.
The Case of the Liberated J-seals
A big high-pressure (HP)/intermediate-pressure (IP), dual-flow low-pressure (LP) steam turbine consumer was getting ready for a shutdown to carry out an annual borescope inspection. The unit had abnormally excessive vibrations and load-bearing points at full baseload. An operations evaluation highlighted the chance of inside harm on account of load-bearing points; misalignment was additionally an element, requiring extra info to diagnose harm.
During the deliberate outage, the unit rested shortly after the turning gear failed to interact. The unit cooled whereas stationary because the rotor couldn’t be turned manually. Help was wanted to diagnose turning gear and unit-turning points. Attempts to roll the rotor failed; one thing inside to the steam path was stopping the rotor from performing as designed.
One potential wrongdoer was failed J-seals. The undeniable fact that the rotor wouldn’t flip was a sign that materials might have migrated downstream, and at this level, plans had been made to examine the downstream steam path for harm. In this case, there was concern that damaged J-seal materials might have traveled into the LP system.
Casing drawings of the unit recognized the situation of 4 borescope inspection ports. The first port was opened and offered entry to the final stage IP exhaust to the LP inlet crossover pipe…