Deposits should be collected during every opening or disassembly of the turbine. Care should be taken to preserve turbine blade deposits
without contaminating them with dirt, cleaning fluids, lubricants, etc. Deposits should be collected as soon as possible after
each section of the turbine is opened. This will reduce the possibility of contamination.
Both overall and closeup photographs and
deposit samples should be obtained from every unique surface that is available (individual turbine blade rows, boiler drum above and
below the water line, etc.). On turbines, ideally, samples would be obtained for each stationary and rotating stage of the HP,
IP and LP turbine sections. Since this is not always practical, as a minimum, four locations should be sampled. They are:
-
high pressure turbine control stage
- intermediate pressure section
- low pressure turbine blades
- the blade row
before the saturation line (L-1 rotating blade in fossil utility turbines)
Deposit samples should be scraped off with a clean stainless
steel knife or spatula onto a piece of clean hard paper. The entire deposit should then be placed in its own clean plastic bag
or vial. If there is insufficient deposit to scrape off, a wipe sample can be obtained using a piece of clean filter paper while
wearing clean plastic gloves. The filter paper containing the wipe sample should then be placed in a clean plastic bag or vial.
The quantity of deposit required for analysis is specified in the following section.
The sample container should be labeled with the
Plant and Unit number, identification and location where the sample was taken, and the date and time it was sampled.
In order
to ensure there is enough sample for all the analyses which will be performed, a minimum of 1 gram (~1 cm^3) should be obtained from
each location sampled. Sometimes this requires combining samples from several similar locations, such as on turbine blades
on the same stage.
In-situ pH of the deposit should be measured using a fine division pH paper. The pH paper is placed on the
deposit and wetted with an eye dropper using the best available laboratory water (ASTM Grade 3). The resulting color on the
pH paper is then compared with the color scale on the pH paper dispenser and the pH is recorded.
The deposit thickness should be measured,
if possible, using a micrometer, calipers, or by comparison to a filler gage. If any pitting is present, the location and average
depth of the pits should be recorded, along with a photograph of the pitted areas, cracking, erosion, foreign object damage (FOD),
etc.