Measurement of turbine steam seal clearance
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The upper seal clearance of a turbine can be measured using adhesive tape; how is the lower clearance determined? If a coloring method is used for inspection, determine which color indicates compliance, taking into account the oil film gap during operation.
Just stick tape on the top and bottom, that’s it!
Both the upper and lower air seals can be measured using the adhesive tape method, while the gap at the mid-separation point of the lower air seal can be rechecked to ensure it is within acceptable limits using a feeler gauge. For those equipped with buffer springs on the back side, it is recommended to use wooden wedges to secure them in their free state before carrying out the measurements.
The clearance between the upper and lower steam seals of the turbine, as well as the portion related to the guide vane retainer, can be measured using the adhesive tape method. To determine the clearance, it is determined by counting how many layers of adhesive tape are cut by the serrated teeth of the steam seal; the pressure stage can be checked by using adjustment components in conjunction with a dial indicator. The oil film gap during operation, at around 0.002 MM, can be disregarded.
The common methods for measuring the steam seal gap are: using a feeler gauge to measure the gap at the joint surface, using a lead wire to measure the gaps of the steam seal in different directions above and below it, and using adhesive tape to assess the overall gap of the steam seal. During operation, the position of the rotor in the bearings changes significantly, which imposes certain requirements on the steam seal clearance.