Technical Info
Company Info
4313 Nebraska Court
Pomfret, MD 20675
Phone:  (301) 934-5605
Fax: (301) 934-5606
Collecting and Analyzing Deposits
Copyright (c) 2012  Jonas, Inc.  All Rights Reserved
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.
Documentation and Collection of Deposits
Collection and analysis of deposits is an important part of the evaluation of a unit's water and steam chemistry.  It can identify the corrodents which are present in the system and help to determine the sources of impurities.  This analysis can also be used as part of a Blade Path Audit to determine the efficiency and MW losses for each stage of the turbine.
For these reasons, proper techniques and adequate documentation are critical for description, collection, and analysis of deposits.  If not sampled properly, the deposits could be contaminated, there may be insufficient quantity for the required analysis, or inadequately or incorrectly identified.  To avoid these problems, Jonas, Inc. has developed the following procedure for documenting and collecting deposits.
Typical steps:
-  Photograph, video and visually examine the turbine (look at deposit distribution, flow markings, signs of washing, drying, corrosion, erosion, etc.)  
-  Measure the in-situ pH of the deposits
-  Record the deposit thickness and distribution on airfoils and other surfaces  
-  Collect deposits
-  Optical and Scanning Electron (SEM) microscopy to determine deposit morphology
-  Semi-quantitative and quantitative analysis (elements, ions, SiO2, TOC/TIC, etc.)
-  X-ray Diffraction (XRD) (to determine chemical compounds)
-  Loss on Ignition (to determine the amount of organic matter)
-  Infrared Spectroscopy (IR), Gas Chromatography/Mass Spectroscopy (GC/MS) for organics)
The results of the turbine deposit analyses should be recorded and preserved for the service life of the turbine because often, corrosion damage is discovered many years after the chemical upsets which caused it.  These records can help trace the corrosion history of the turbine and of the entire system.  
Identify corrodents in the system, determine sources for impurities, and perform a blade path audit to find efficiency and MW losses in the turbine.
The following analyses can be performed:
-  Visual examination with macro photograph and description of the deposit color and consistency
-  Optical microscopy and Scanning Electron Microscopy (SEM) examination with photographs at low and high magnification. Description of the deposit morphology, color and size of particles
-  Semi-quantitative elemental analysis using Energy Dispersive X-ray Spectroscopy (EDS) (a minimum of 10 mg is required)
-  Quantitative determination of important elements and ions (Na, Cl, SO4, PO4, Ca, Mg, Fe, Cu, SiO2,TOC/TIC, etc.) using ICP, ion chromatography, atomic absorption, spectrophotometry, etc. (each type of analysis requires approx. 100 mg)
-  X-ray Diffraction identification of crystalline species (a minimum of 50 mg is required)
-  Loss on Ignition to determine the amount of organic matter (a minimum of 100 mg is required)
-  If organics are expected to be a part of the deposit, Infrared Spectroscopy (IR) can be used to identify the organic compounds which are present.
If only a wipe sample is available, Items 1 to 3 still provide valuable information. All standard chemical analytical methods are described in ASTM D2186 "Standard Test Methods for Deposit-Forming Impurities in Steam" and Volumes 11.01 and 11.02 of the Annual Book of ASTM Standards.
Analysis of Deposits
Serving the power industry since 1983
Specializing in Sampling and Instrumentation, Corrosion,
Water and Steam Chemistry, and Failure Analysis
Jonas, Inc.