UT Procedure

1.0 PURPOSEThis procedure establishes the requirements for Ultrasonic Thickness Measurement of materials using pulse-echo, A-scan, and digital thickness gauges.

2.0 SCOPEABC Inspection and Consultants will follow this procedure when a customer requests Ultrasonic Thickness Examination to be performed in accordance with ASME Section V Article 4.

3.0 RESPONSIBILITIES3.1. Personnel performing Ultrasonic Thickness Measurement will be certified to at least Level I in accordance with ABC Inspection and Consultants Written Practice for Qualification and Certification of Inspection Personnel.3.2. UT Level I, II, and III personnel may perform all operations necessary in accordance with this procedure to process the objects being examined.3.3. Interpretation and evaluation of ultrasonic examination results will be accomplished by personnel certified as UT Level II or III.

4.0 DEFINITIONSA-scan - a method of data presentation utilizing a horizontal baseline that indicates distance, or time, and a vertical deflection from the baseline, which indicates amplitude.Attenuation - a factor that describes the decrease in ultrasound intensity with distance. Normally expressed in decibel per unit length. Couplant - a substance used between the search unit and test surface to permit or improve transmission of ultrasonic energy.Indication - that which marks or denotes the presence of a reflector.Probe - see search unit Pulse echo method - an inspection method in which the presence and position of a reflector are indicated by the echo amplitude and time.Search unit - an electro-acoustic device used to transmit or receive ultrasonic energy, or both. The device generally consists of a nameplate, connector, case, backing, piezo-electric element, wearface, or lens, or wedge. Transducer - an electroacoustical device for converting electrical energy into acoustical energy and vice versa. See also crystal. Ultrasonic - pertaining to mechanical vibrations having a frequency greater than approximately 20,000 Hz.

5.0 EQUIPMENT AND MATERIALS5.1 The following are the requirements for the Ultrasonic Thickness Measurement Examination Equipment:5.1.1 The instrument will be of the pulse-echo type and may have a digital or CRT display.5.1.2 The instrument shall be calibrated at intervals no longer than 3 months to reference standards traceable to the National Bureau of Standards.5.1.3 Any frequency and size search unit may be selected as long as it is capable of resolving the thickness range being measured.5.1.4 The search unit may be either a single element, delay line, or dual element contact transducers.5.2 Couplants may be water, glycerin, cellulose gel (gum), oil, grease, or specially formulated commercially available materials.5.2.1 Inhibitors and/or wetting agents may be used.5.2.2 The chemical interaction or the corrosive nature of any couplant with the material(s) being examined will be considered when making the choice of

couplants.5.3 The reference standards will be of similar acoustic velocity, attenuation, surface, shape and finish to that of the material being examined and:5.3.1 will have at least two stepsa) the thinner step will have a thickness less than or equal to the minimum thickness, and;b) the thicker step will have a thickness greater than or equal to the maximum thickness to be tested.5.3.2 The physical dimensions will be within +1 % of the nominal thickness of the step.a) The measurement of the steps will be performed with a calibrated instrument, traceable to the National Bureau of Standards.

6.0 TESTING SURFACE6.1 Surfaces will be uniform and free of loose scale and paint, discontinuities such as pits or gouges, weld spatter, dirt, or other foreign matter, which may adversely affect test results.6.1.1 Tightly adhering paint, scale, or coatings do not necessarily need to be removed for testing if they present uniform attenuation characteristics.6.2 Surfaces may be ground, sanded, wire brushed, scrapped, or otherwise prepared for examination purposes when necessary.6.3 In areas where severe pitting is experienced and surface preparation is not recommended, readings will be taken on high, areas and pit depth will be measured with mechanical depth gauges.

7.0 CALIBRATION PROCEDURE7.1 The proper functioning of the examination equipment will be checked and the equipment will be calibrated by use of the reference standard, as described in paragraph 5.3, at:a) Once every two hours of inspection work;b) When examination personnel are changed;c) At any time that a malfunction or improper operation is suspected (i.e., unusually high or low readings);d) When search units are changed;e) When new batteries are installed or electrical outlet is changed;f) When equipment operating from one power source is changed to another power source or power failure.7.2 If during a calibration, it is determined that the examination equipment is not functioning properly or it is found to be out of calibration all of the measurements since the last valid equipment calibration will be retaken.7.3 Calibration will be accomplished using the same couplant as that to be used when measurements are being taken.7.3.1 When special form high temperature couplants are being used, a different couplant may be used for calibration.7.4 The equipment will be calibrated in accordance with the instrument manufacturers operating instructions, on the appropriate reference standard using a minimum of two thickness steps.7.4.1 The temperature of the calibration block will be 5Oo F of the test specimen.within 7.4.2 Place the search unit on the thinner step (which is less than or equal to the minimum thickness being examined) and adjustment the instrument to read the same as the thickness of the step.7.4.3 Place the search unit on the thicker step (which is greater than or equal to the maximum thickness being examined) and, if adjustment is needed to get the instrument to read the same as the thickness of the step, go back to the thinner step and readjust if needed.7.4.4 Repeat the operations described in paragraphs 5.3.1 and 5.3.2 until both the thin and thick steps read correctly without further adjustment.

7.4.5 A third step with a thickness between the thin and thick step will be used, when available, to verify calibration.a) If the third step reading and the instrument reading differ 1%, then the instrument will be recalibrated.by more than

8.0 METHOD OF EXAMINATION8.1 Couplant may be applied to the search unit or directly on the component being examined.8.2 The extent of the examination and the location of the readings will comply with the referencing code and the customer requirements8.1.1 Readings may be taken at randomly selected locations or taken in specified grid patterns as required.

9.0 SPECIAL TECHNIQUE CONSIDERATIONS9.1 Dual transducer element search units are inherently nonlinear for thickness measurements less than 0.125”.9.2 If measurements below 0.125” must be made with dual transducer element search units, calibration must be accomplished with at least 3 thickness steps below 0.125” within the range of the expected readings9.3 When testing steel at elevated temperatures above 200o F up specially designed search units and couplants will be used.9.3.1 A rule of thumb that may be used to compensate for reading errors due to elevated temperatures is as follows:a) The apparent thickness reading obtained from steel walls having elevated temperatures is high (too thick) by a factor of about 1% per 100o F. Thus, if the instrument was calibrated on a piece of similar materials at 68o F, and if the reading was obtained with a surface temperature of 860o F, the apparent reading should be reduced by 8%.

10.0 POST CLEANING10.1 Immediately upon completion of the examination, the couplant will be removed by a suitable cleaning method.10.1.1 The considerations of paragraph 5.2.2 will also apply for the cleaning agents.

11.0 EXAMINATION REPORT11.1 A ultrasonic examination report, Attachment A, shall be prepared by the certified UT Level II Inspector. A copy of the UT report must be submitted to the client at the end of the shift. (See attached form for typical UT report).

12.0 REFERENCES12.1 American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section V, Article 5, current edition.