Advanced Corrosion Monitoring
Specifications and
Procedures
The following is a detailed specification
of testing procedures, equipment, and reporting methods used in our advanced
corrosion monitoring program. It is fundamentally based upon the ultrasonic
testing methods established by the American Society of Mechanical Engineers and
the American Petroleum Institute, as well as our own experience. Such testing
and reporting procedures have evolved over many years based upon our response
to the needs and requests of our customers. Changes in our procedures will be
reflected in this specification.
Preliminary Investigation
Prior to the actual testing, East Coast
Industries, Inc. shall conduct a walk through of the subject location, and
review the operation of the piping system(s) in question. Specifics such as
material type, pipe size, pipe construction, operating pressure, and general
physical condition shall be determined. Operating parameters such as previous
mechanical maintenance history, hours of operation, internal fouling,
accumulated deposits, quality of water treatment, etc., shall be noted.
A review of each system layout shall be
made based upon existing piping specifications and blueprints, as well as any
supplemental information available through the engineering department, or
professional engineer. An historical review of any prior leaks, obstructions,
or failures at the subject piping system(s) shall be made with the engineering
department. Areas where a specific concern for the integrity of the piping
exists by building operators and representatives shall be noted as probable
test locations. Visually observed examples of outer pipe corrosion or leakage
shall be also highlighted as probable test locations. Any previous piping
evaluations shall be reviewed to identify possible test sites.
Based upon the number of piping locations
to be tested, a general plan of action shall be proposed, and testing fees
quoted. Locations at the top and bottom extremes of the piping system shall be
considered, as well as at horizontal extremes of the piping layout. Effort
shall be made to evaluate the various size pipes comprising the system,
although minimum pipe size should be limited to 4 in. diameter.
Test Equipment
Field testing shall be performed using a
Panametrics 36DL Plus or equivalent ultrasonic thickness gauging device. The
instrument shall have an on-board waveform display allowing its operator to
instantly evaluate the validity of each and every wall thickness measurement
taken (See below illustration).
All wall thickness measurements which do
not show an acceptable waveform pattern shall be discounted, and further
investigation made to identify the cause of the problem. Measurements showing
an acceptable waveform display and indicating an accurate wall thickness value
shall be saved for later download and analysis. Both the wall thickness value
and the accompanying waveform display shall be saved in the memory of the 36DL
Plus or equivalent device for future reference and re-evaluation, if necessary.
A Panametrics D794 dual crystal element
straight probe transducer, or equivalent, shall be used in order to provide the
highest wall thickness accuracy possible, and to locate interior pitting. This
probe shall have a frequency of 5.0 MHZ and a tip diameter of 7.2 mm, or
suitable equivalent. A coupling agent of glycerine or its acoustic equal shall
be used to facilitate the transmission of the ultrasound signal into the test
surface.
Instrument calibration shall be performed
at the beginning of the test session and at regular time intervals throughout
the investigation. A calibrated test block of the material to be evaluated and
having reference thickness steps above and below the minimum and maximum
anticipated pipe wall thickness to be tested shall be used. The test block and
instrument probe shall be allowed to equalize to the temperature of the test
medium before calibration. Re-calibration shall be performed whenever a change
in temperature of the medium occurs. Re-calibration of the instrument and probe
shall also be performed after each hour of use, at each template location,
whenever the instrument is turned off and on, or when pipe of a different
diameter and wall thickness is measured.
Pipe Surface Preparation
A rubber "template" material
having pre-cut holes of specific size to snugly accept the ultrasonic
measurement probe, and prevent its movement, shall be installed. The rubber
material shall be unaffected by sunlight, chemical attack, paints, solvents,
moderate heat, or any other factor which would otherwise limit its service life
over an extended period of time. It shall be available in various physical
configurations to conform to the needs of each individual test location. The
rubber template shall be permanently bonded to the pipe surface using an
adhesive specifically designed for rubber to steel attachment, and shall
provide an extended service life equal to the rubber itself.
The subject pipe shall be prepared in
order to minimize any surface defects or irregularities which may exist, and to
allow complete bonding between the pipe and rubber "template." This
shall be accomplished by lightly sanding the surface using medium to fine grit
sandpaper. Caution shall be used in order to minimize any metal loss or create
any grooving of the pipe; no grinding of the pipe shall be allowed.
The test location shall be provided an
identification I.D., and be physically marked in order to prevent its removal,
or alteration.
Testing Procedure
A preliminary review of each test
location shall be performed to generalize the condition of that particular
area. A minimum of 12 wall thickness readings shall be taken and saved to
memory for use in the final analysis of the test location. When possible, those
12 measurements shall be taken at 3, 6, 9, and 12 o'clock positions around the
circumference of the pipe, and at three cross sections along the length, each
separated by approximately 3-4 inches (See below diagram). Under conditions
where the entire pipe circumference is not available, measurements shall be
taken at random, but with evenly spaced intervals. The location of the rubber
"templates" may also be determined by the client.
A photograph of each test location shall
be taken in order to illustrate the general test area location and supplement
the written description. All relevant information regarding the location,
operating conditions, observed problems, etc. shall be incorporated into the
final report. All observed piping related problems such as thread leakage,
outer surface corrosion, weld failure, and insulation failure, etc. shall be
noted for incorporation into the final report. A photograph shall be taken to
document the location and specific piping condition, or to document a failure
event or condition.
Small 8 in. to 12 in. sections of
insulated or covered pipe surfaces shall be removed in order to provide access,
if necessary. The removal, replacement, and re-painting of the insulation or
pipe covering shall be the responsibility of the engineering or property
management. Asbestos covered pipe will not be tested until properly
abated.
Reporting Procedure
A final written report shall be produced
following the completion of the field testing, and incorporate all compiled
data. No measured data derived from the field testing shall be discounted,
amended, or falsified. Excepting clear examples where error on the part of the
ultrasound technician has produced a false wall thickness measurement, as
verified by a review of the saved waveform, all test data shall be incorporated
into the final report. An attempt shall be made to explain all data anomalies.
The report shall be available within 14 days following completion of the actual
field testing.
The report shall be separated into
sections of summary and detailed information in order to suit the information
needs of various potential readers. The final report shall be written in a
clear and easily understandable format, shall be arranged in a logical
progression, and provide a full explanation of all accumulated data and derived
statistics. Specifically requested information from the client falling outside
the general scope of the report shall be incorporated into the final
report.
An introductory report section shall be
provided detailing the testing procedure and instrumentation used. It shall
also include a listing and explanation of any assumptions made during the
testing and reporting procedure, as well as any investigative limitations
created by either the testing procedure, pipe medium, physical access,
availability of physical data relative to the pipe, or actions of the client.
Definitions of any technical terms and labels used in the report shall be
provided.
A detailed section for each individual
test location shall be compiled providing all measured and calculated data.
Full physical identification of the pipe and piping service shall be provided.
A photograph of the location shall be included with highlighted indication of
the general test area. All 12 measured ultrasonic test values shall be graphed
to provide a visual representation of the variation at the interior pipe
surface. The report shall be printed in color in order to best display the
subject location, and to illustrate the wall thickness measurement data.
The original wall thickness of the pipe
shall be determined, and estimated to be at industry specification, or above or
below industry specification. It shall be noted as such in the report. The
minimum allowable wall thickness for each individual location shall be
calculated based upon the particular pipe diameter, operating pressure,
construction (E value), material (S value), schedule, and pipe service
provided.
Two alternate corrosion rate and
remaining life prediction scenarios shall be calculated for each test location.
An "Average Case" scenario shall be presented based upon the average of
all measured wall thickness values, and provide estimates for the following
parameters:
- Wall Thickness
- Remaining Pipe Life
- Corrosion Rate
- Percentage Of Allowable
Loss
- Remaining Pipe Life
- Retirement Date
- Overall Pipe Condition
An alternate "Worst Case" scenario
shall also be presented based upon the single lowest measured wall thickness
value found within the 12 measured values, and shall provide minimum estimates
for the same parameters as highlighted above. Calculations shall be provided
based upon estimates over the entire building history, and over the most recent
test period only. A comments section offering any additional information,
details, or explanation about the test location or results shall also be
provided.
Summary graphs shall be produced showing
the following trends and relationships:
- Average And Minimum Wall
Thickness
- Average And Maximum Corrosion
Rates
- Average And Maximum Pipe
Loss
- Average And Minimum Pipe
Life
- Pitting Index
- Comments
A written summary section shall be
provided to review the entire report and consolidate its contents into its
major generalizations. The most significant findings of the investigation will
be highlighted. Recommendations specific to the findings in the report shall be
provided.
An explanation of all mathematical
calculations used in the preparation of the report shall be provided in order
that interested individuals can verify and reproduce the calculations of
corrosion rate and retirement date predictions used throughout the report. An
appendix section shall provide all supplemental information relative to the
accumulation of data, and preparation of the report. Observed problems or other
information noted during the course of the ultrasonic testing investigation
shall be documented.
The report shall be clearly written and
presented in a bound format with the primary objective of providing the
greatest amount of useful information about the subject system(s) to the
client. The initial test report shall provide a base line of information about
each test location; with more detailed and useful information provided after
each successive test. Follow-up tests shall be based upon the above format, and
included into the original report.
The test report shall be archived in its
original computer format for a minimum period of five years, or longer if
requested. Additional copies of the report shall be available for as long as
the data is on archive.
This fixed point monitoring or
"template testing" procedure is applicable to most piping systems,
cooling tower pans, tanks, and pressure vessels using substantially similar
preparation and measurement techniques. Additional proprietary procedures and
techniques regarding this program exist, but have not been detailed in this
specification.
Testing
Services