Specifications and Procedures - Tanks

     The following is a detailed specification of testing procedures, diagnostic equipment, and reporting methods used in our ultrasonic tank testing investigations. It is fundamentally based upon the testing methods established by the American Society of Mechanical Engineers for Boiler and Pressure Vessels, and the American Petroleum Institute Standard 650 and 653, as well as our own testing experience. Such test procedures and reporting of the data have evolved over many years based upon our response to the needs and requests of our customers. Changes in any testing or reporting procedures will be reflected in this specification.





Preliminary Investigation

     Prior to the actual testing, East Coast Industries, Inc. shall conduct a full walk through of the subject location, and review the function and operation of the tank(s) in question. Specifics such as material type, service provided, accessibility, physical size, shape, construction, operating pressure, and general physical condition shall be determined. Operating parameters and deficiencies such as previous leaks, repairs or failures, mechanical maintenance history, internal fouling, accumulated deposits, quality of the water treatment (if applicable), internal and external coatings, etc., shall be noted.

     Construction specifications and blueprints, as well as any supplemental information available through the engineering or building department, shall be provided in order to gain any additional and relevant information useful to the survey. In addition, an historical review of any prior leaks, repairs, or failures at any associated piping system(s) shall be made with the engineering department. Areas where a specific concern for the integrity of any tank has been raised by building operators and representatives shall be noted as probable test locations. Visually observed examples of outer tank corrosion or leakage shall be also highlighted as high priority test locations.

     Based upon the size and geometry of the tank, a general outline of investigation shall be proposed, and testing fees quoted. Testing shall be proposed to take one ultrasonic wall thickness measurement approximately every 6 in. to 12 in. vertically and horizontally along the shell and heads for a cylindrical tank, and along the walls, top, and bottom of a square or rectangular tank. Fewer or greater wall thickness measurements shall be performed depending upon the interests of the client, the geometry of the tank, physical accessibility, the assumed condition of the tank, and/or other criteria.

     A written procedure or outline for tank or pressure vessel testing established by the client or the client's engineering representative shall be reviewed for suitability in gaining the desired diagnostic information. In such cases, and where the proposed testing procedure is acceptable, testing will proceed according to the clients specifications, and the results noted as based upon an alternate procedure.

     Sufficient testing shall be performed in all tank testing investigations as to be judged acceptable by East Coast Industries, Inc. - the high volume of data sought being critically necessary in order to produce an accurate general assessment of the interior tank surface in a graphical 3D format, and to maximize the probability of identifying any pitting or low wall thickness conditions which may exist. The volume of data necessary will vary with tank size, location, accessibility, and service application.

     As a general guideline, we recommend the following levels of testing:


Testing Equipment

     Field testing shall be performed using a Panametrics 36DL Plus ultrasonic thickness gauging device, or its diagnostic equal. 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 for 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 for future reference and re-evaluation, if necessary.

     The instrument shall feature "echo to echo" technology allowing the measurement of coated or painted surfaces without scraping, sanding, grinding, or otherwise potentially removing any outer metal from the test surface, and to eliminate the time and expense necessary to remove and replace such coatings. Tanks with insulation, or disbonded paints or heavy "black tar or mastic" like outer coatings will likely require its removal - with the removal and replacement of such coatings or insulation being the sole responsibility of the client.

     A Panametrics D794 or equal dual crystal element straight probe transducer shall be used in order to provide the highest wall thickness accuracy possible, and to provide the greatest success in locating any interior pitting. This probe shall have a frequency of 5.0 MHz and a tip diameter of 7.2 mm. A coupling agent of glycerine or its acoustic equal shall be used to facilitate the transmission of the ultrasound signal into the test surface. The appropriate high temperature couplant (based upon operating temperature) shall be used for hot water, steam, steam condensate, and flash steam tanks.

     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 same material to be evaluated, and having reference thickness steps above and below the minimum and maximum anticipated tank or vessel wall thickness to be tested, shall be used. The test block and instrument probe shall always 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, whenever the instrument is turned off and on, or when a significantly different wall thickness is encountered.


Testing Procedure

     A preliminary ultrasonic spot check inspection of the tank shall be performed in order to assess the general condition of each tank. Where paint or other coating exists, and where "echo to echo" technique is used, a test shall first be performed to verify the reliability and accuracy of "echo to echo" measurement through the coating.

     The physical dimensions and operating conditions of each tank shall be determined. For cylindrical tanks and vessels, a uniform grid or layout along each horizontal (X) and vertical (Y) axis shall be determined at both the shell and heads. For square and rectangular tanks, a similar grid or layout of X and Y axis shall be made for each side, the bottom and the top.

     In all cases, the primary objective shall be to provide the most uniform test coverage of the tank wall surface, and to acquire sufficient thickness measurements to provide a full service life analysis as per the above general testing guidelines. Under conditions where the entire tank surface is not available, measurements shall be taken at random, but with evenly spaced intervals. Measurements shall be identified as being taken at random, or based upon the above referenced standard grid in the final report.

     The shell and heads, or walls and bottom surfaces of the tank shall be each temporarily marked with an established grid or layout of test locations, and addressed separately. A final determination of measurement points shall be made which will provide sufficient data information. Testing shall logically proceed beginning either at the vertical (Y) or horizontal (X) axis and continue until complete; the same procedure then duplicated at each additional tank or pressure vessel surface.

     A photograph of each test location shall be taken in order to illustrate the tank under evaluation, and its outward appearance. All relevant information regarding the location, operating conditions, observed problems, etc. shall be noted on a formal worksheet for incorporation into the final report. All observed piping related problems such as thread leakage, outer surface corrosion, weld failure, and insulation failure, etc. shall also be noted for incorporation into the final report.

     Unless specifically agreed to otherwise, the removal, replacement, and re-painting of any insulation or covering shall be the responsibility of the engineering or property management. Asbestos covered tanks or pressure vessels will not be tested until properly abated.


Reporting Procedure

     A final written report shall be produced following the completion of the field testing, and shall incorporate all compiled data and calculations. The report shall be in the form of a hard cover binder.

     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 individual sections specific to each tank under evaluation, and offer both 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, 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 executive summary for each tank or pressure vessel shall be produced; condensing the most important findings of the report, as well as any specific highlights of the investigation. 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 anomalies or limitations created by either the testing procedure used, tank or vessel materials, accessibility, insulation, or actions of the client. Definitions of any technical terms and labels used in the report shall be provided.

     Full physical identification of the tank and tank service shall be provided, followed by a detailed section for each individual test location providing all measured and calculated data. The report shall be printed in color in order to best display the subject location, and to illustrate the calculations and predictions of the thickness measurement data.

     The original wall thickness of the tank or vessel shall be determined. The minimum allowable wall thickness for each tank or vessel shall be calculated based upon the overall shape, diameter, head shape, base supports, ASME or API code, operating pressure, construction, material strength, thickness schedule, service provided, and other relevant physical parameters.

     Three alternate corrosion rate and remaining life prediction scenarios shall be calculated for each test location; broken down according to common tank or vessel components. For round tanks - shell and heads shall be evaluated individually and according to their individual characteristics. For square and rectangular tanks - separate corrosion rate and retirement date scenarios shall be calculated for the sides, top and bottom independently. An average case scenario shall be presented based upon the average of all measured wall thickness values for each common component, and shall provide estimates for the following parameters:

     An alternate worst case scenario shall be presented based upon the single lowest measured wall thickness value found within all measurements, and shall provide minimum thickness based estimates for the same parameters as highlighted above.

     Considering that one single low wall thickness value among thousands may not necessarily represent a true overall service life of a tank or pressure vessel, a third alternate corrosion scenario shall be presented based upon the lowest five measured wall thickness values found within all measurements, and shall provide intermediate thickness based estimates for the same parameters as highlighted above.

     A block graph showing the relationship between the original wall thickness, the minimum allowable wall thickness, and minimum, average and maximum wall thickness values shall be provided for a round vessel's shell and heads, or for a square or rectangular tank's sides, bottom, and top. A comments section offering any additional information, details, or explanation about the test location, conditions, or results shall also be provided.

     All individual wall thickness values and the respective locations along the tank or vessel surface shall be presented in spreadsheet or some other logical format.

     A series of graphs shall be produced to illustrate the interior condition of the tank or pressure vessel, and shall be rendered in three dimensions, or 3D, for best illustration. Separate graphs shall be produced for the shell and heads in the case of round tanks, and sides, bottom and top where square or rectangular tanks are involved. Various perspectives of the data, such as cross section or above or below views shall also be provided should they offer a better understanding of the interior wall surface conditions.

     Final recommendations specific to all the findings of the report shall be provided in a summary section of the report. Overall, and fundamental to the purpose of any investigation, 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 tank or pressure vessel to the client.

     An appendix section shall provide all supplemental information relative to the accumulation of data, and preparation of the report. Observed problems, leaks, anomalies, or other information noted during the course of the testing process shall be photo documented.

     The final report shall be archived in its original computer format for a period of ten years, or longer if requested. Additional copies of the report shall be available for as long as the data is on archive. Follow-up investigations at the same locations shall include test data from the most previous report; with a series of calculations performed showing average differences in wall thickness and corrosion rate.


Click Here to Request Further Information


Turn Back One Page




Main Page        Testing Services        Technical Bulletins        Case Histories
Business Opportunities        Specialty Products        Recommended Links
Request Information        Mailing List        About ECI        Contact Us

© Copyright 2000