Inspection Procedure for Ultrasonic Thickness Measurement Table of Contents Section 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0
Page No.
Purpose and Scope ....................................................... 2 References .................................................................... 2 Personnel Qualifications ................................................ 2 Ultrasonic Equipment and Materials .............................. 3 Examination Surface ..................................................... 4 Calibration Procedure .................................................... 4 Method of Examination .................................................. 6 Special Technique Consideration .................................. 6 Post Cleaning ................................................................ 8 Examination Report ....................................................... 9 Acceptance Criteria ....................................................... 9 Table 2 ........................................................................ 10 Figure 1 ....................................................................... 11 Table 3 ........................................................................ 11 Figure 2 ....................................................................... 12 Figure 3 ....................................................................... 12 Table 4 ........................................................................ 12 NDE UT Report ........................................................... 13 UT Instrument Verification Report ................................ 14
1.0 PURPOSE AND SCOPE 1.1 This procedure establishes the requirements for Manual Ultrasonic Thickness Measurement of materials and will be applied when Ultrasonic Thickness Measurement is required in accordance with ASME Section V, Article 5 by the referencing Code. This procedure will be used in conjunction with applicable client specifications. 1.2 This procedure will be used whenever manual ultrasonic thickness measurements per the requirements of ASME are specified. 1.3 Ultrasonic examination shall be performed in accordance with a written procedure which shall, as a minimum, contain the requirements found in Table 1.0. Table 1.0 Variables of an Ultrasonic Examination Procedure Requirement Material types and configurations to be examined, including thickness dimensions and product form (casting, forgings, plates, etc.). Personnel qualification requirements. Personnel performance requirements, when required. The surfaces from which the examination shall be performed. Surface condition (examination surface, calibration block). Couplant: brand or type. Technique(s) (straight beam, angle beam, contact, and/or immersion). Angle(s) and mode(s) of wave propagation in the material. Search unit type(s), frequency (ies), and element size(s) shape(s). Special search units, wedges, shoes or saddles, when used. Ultrasonic instrument(s). Calibration [calibration block(s) and technique(s)]. Directions and extent of scanning. Automatic alarm and/or recording equipment, when applicable. Scanning (manual vs. automatic). Computer enhanced data acquisition, when used. Records, including minimum calibration data to be recorded (e.g., instrument settings). Scan overlap (decrease only)
Essential Variable
Nonessential Variable
X X X X X X X X X X X X X X X X X X
1.4 When procedure qualification is specified, a change of a requirement in Table 1.0 identified as an essential variable from the specified value, or range of values, shall require requalification of the written procedure. 1.5 A change of requirement identified as a nonessential variable from the specified value, or range of values, does not does not require requalification of the written procedure.
1.6 All changes of essential or nonessential variables from the value, or range of values, specified by the written procedure shall require revision, or an addendum to, the written procedure.
2.0
REFERENCES
2.1 The latest revision, or revision stated in the contract, of the following referenced documents is applicable to and /or form the basis of this procedure: 2.1.1 ASME Boiler and Pressure Vessel Code, Section V “Non-destructive Examination” (July 2003) 2.1.2 ASTM E-114 “Recommended Practice for Ultrasonic Pulse-Echo Straight-Beam Testing by the Contact Method (2001) 2.1.3 ASTM E-317 “Standard Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Systems without the Use of Electronic Measuring Instruments” (1997). 21.4 ASTM E-797 “Standard Practice for Measuring Thickness by Manual Ultrasonic Pulse-Echo Contact Method” (2001) 2.1.5 AES NDE-QC-1 “Qualification and Certification of Non-destructive Examination Personnel”. 2.1.6 ASNT SNT-TC-1A (2001), CP-189 (2001), and ACCP (Revision3, November 1997).
2.2 This procedure will be superseded only when an equal or more stringent requirement is specified by the customer’s purchase order or contract and is approved by the ATT Corporate Level III.
3.0
PERSONNEL QUALIFICATION
3.1 Personnel performing Ultrasonic Thickness Measurement will be certified to at least Level I Ultrasonic Examination (UT) in accordance with procedure ATT NDE-QC-1 "Qualification and Certification of Non-destructive Examination Personnel".
3.2 A subcontractor may use their Qualification and Certification procedures when approved by the ATT Corporate Level III and meeting the requirements of Section 2.1.6. 3.3 UT Level I, II, and lIl personnel may perform all operations necessary in accordance with this procedure to process the objects being examined. Except that Level I personnel shall receive the necessary supervision and guidance from certified UT Level II or Level III personnel. 3.4 Interpretation and evaluation of ultrasonic examination results will only be accomplished by personnel certified as UT Level II or lIl. 4.0
ULTRASONIC EQUIPMENT AND MATERIALS
4.1 The following are the requirements Measurement Examination Equipment.
for
the
Ultrasonic
Thickness
4.1.1 The instrument shall be of the pulse-echo type and must have a CRT or digital and CRT display. 4.1.2 The instrument’s horizontal limit and linearity, Paragraph 8.4, screen height linearity, paragraph 8.5 and amplitude control linearity, paragraph 8.6, shall be verified every 3 months or prior to first use thereafter. 4.1.3 The instrument shall be calibrated at intervals no longer than 12 months to reference standards traceable to the National Institute of Standards and Technologies (NIST) and meet or exceed the manufacturer’s tolerances and specifications. 4.1.4 Any frequency and size search unit may be selected as long as it is capable of resolving the thickness range being measured, provided that it meets the manufacturer’s recommendations and client specifications. 4.1.5 The search unit may be single element, delay line, or dual element contact transducers. 4.1.5.1 Search unit selected shall have sufficient crystal to surface contact to produce stable readings. On smaller diameter pipe, 3.50” and less, a small diameter search unit or curved standoff shoe may be required. 4.2 Couplant may be water, glycerine, cellulose gel (gum), oil, grease or specially formulated commercially available materials. 4.2.1 Inhibitors and/or wetting agents may be used. 4.2.2 The chemical interaction or the corrosive nature of any couplant with the material(s) being examined will be considered when making the choice of couplant.
4.3 The reference standards material from which the block is fabricated shall be of the same product form, material specification or equivalent P- Number grouping, and heat treatment as the material being examined. The finish on the scanning surface of the block shall be representative for the scanning surface on the material to be examined and: 4.3.1 Shall have at least three steps: 4.3.1.1 The thinner step shall have a thickness within +10% of the value stated in the column marked “Lower step” of table 2 for the thickness range to be tested. 4.3.1.2 The thicker step shall have a thickness within +10% of the value stated in the column marked “Upper step” of table 2 for the thickness range to be tested. 4.3.1.3 The third step and the minimum thickness to be tested shall fall within the “Objective Thickness Range” and between the thin and thick calibration steps. The third step shall be machined with a flat bottomed hole in accordance with figure 1 and table 2. 4.3.2 The physical dimensions will be within + 1% of the nominal thickness of the step. 4.3.2.1 The measurement of the steps will be performed with a calibrated mechanical instrument, traceable to NIST. 5.0
EXAMINATION SURFACE
5.1 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. 5.1.1 Tightly adhering paint, scale or coatings do not necessarily need to be removed for testing if they present uniform attenuation characteristics. 5.2 Surfaces may be ground, sanded, wire brushed, scraped, or otherwise prepared for examination purposes when necessary. 5.3 In areas where severe pitting is experienced and where surface preparation is not recommended, readings will be taken on high areas and pit depth will be measured by mechanical depth gauges. As an alternate, an ultrasonic pencil tip probe may be used if the customer desires.
6.0
CALIBRATION PROCEDURE
6.1 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 4.3, at: 6.1.1 The beginning and end of each examination; 6.1.2 When examination personnel are changed; 6.1.3 Anytime that a malfunction or improper operation is suspected (i.e., unusually high or low readings); 6.1.4 When search units are changed; 6.1.5 When new batteries are installed or electrical outlet is changed; 6.1.6 When equipment operating from one power source is changed to another power source or experiences power failure. 6.2 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. 6.3 Calibration shall be accomplished using the same couplant as that to be used when measurements are being taken. 6.3.1 When special form high temperature couplant is being used, a different couplant may be used for calibration. 6.3.2 The temperature of the calibration block shall be within + 25° F of the test specimen. NOTE All ultrasonic measurements shall be made at a threshold setting of 20 %FSH. 6.4
Calibration shall be established with three known thickness.
6.4.1 Determine the objective thickness from table 3 6.4.2 Place the transducer on the thin step and adjust the instrument to read the step within + .001 inch of the actual step thickness. 6.4.3 Place the transducer on the thick step and adjust the instrument to read the step within + .001 inch of the actual step thickness. 6.4.4 Repeat 6.4.2 and 6.4.3 until the instrument reads both steps within the + .001 inch tolerance without further adjustment.
6.4.5 Ultrasonically measure the objective thickness. The thickness shall be within + .001 inch of its actual thickness. 6.5
Gain transfer shall be established in the following manner:
6.5.1 Place the transducer on the reference calibration thickness closest to the corresponding material thickness being examined. Note signal strength and gain control setting. 6.5.2 Place the transducer on the test material in an area with a uniform back-wall reflection free from any indications and representative of sound material. 6.5.3 Observe the signal level and adjust the gain control to produce the same signal height or response as noted from the calibration block. Note the gain control setting. 6.5.4 Subtract the gain control value in 6.5.1 from that in 6.5.3. This number (positive or negative) is the gain transfer. 6.6
Scanning sensitivity.
6.6.1 Place the transducer on the object step and maximize the response from the flat bottom hole. Observe the signal level and adjust the gain control to produce a signal that is 80% FSH. 6.6.2 Repeat the steps in paragraph 6.4 and verify the system meets the required tolerance. 6.6.3 Add the gain transfer amount (6.5.4) to the reference setting (6.6.1). This is the gain control sensitivity setting for scanning. 6.7 All calibrations shall be recorded. The setup parameters used, including gain, percent screen height setting, time of calibration and the identification of the operator performing the calibration. 7.0 METHOD OF EXAMINATION 7.1 Couplant may be applied to the search unit or directly on the component being examined. 7.2 The extent of the examination and the location of the readings will comply with the referencing code and the customer requirements. 7.2.1 Readings may be taken at randomly selected locations or taken in specified grid patterns as required. 7.3
Scanning speeds will not exceed a rate of 6 in./ sec.
8.0
SPECIAL TECHNIQUE CONSIDERATIONS
8.1 Dual transducer element search units are inherently nonlinear for thickness measurements less than 0.125". 8.1.1 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 readings. Additionally the proposed technique shall be in accordance with manufacturer’s recommendations and applicable client specifications. 8.2 When testing steel at elevated temperatures, above 200°F and up to 1000°F, specially designed search units and couplant shall be used. NOTE To compensate for reading errors due to elevated temperatures the following shall be used. The apparent thickness reading obtained from steel walls having elevated temperatures is high (too thick) by a factor of about 1% per 100°F. Thus, if the instrument was calibrated on a piece of similar materials at 68° F, and if the reading was obtained with a surface temperature of 860° F, the apparent reading should be reduced by 8%. 8.3
Consideration must be given to the back-wall echo during testing.
8.3.1 When encountering wall thinning due to corrosion, the roughening of the back surface can affect the amplitude and shape of the back- wall echo. Such a change in the back-wall echo should be noted. 8.3.2 When encountering wall thinning caused by erosion, the back wall echo might disappear as the sharply-angled far surface reflects the incident wave away from the transducer. If the back wall echo disappears for this or any other reason, such as abrupt thinning into the near surface region, the cause will be investigated with shear wave transducers or other inspection technique, as appropriate. Such a disappearance of the back-wall echo can indicate a critical degree of thinning and must be explored until the reason for such a loss of signal is defined. 8.3.3 Indications being displayed at or near the back-wall may be absorbed into the back-wall signal and initially appear to be the inner diameter (ID) connected. Interpretation shall be performed at lower gain settings to determine if two separate signals exist. A lower amplitude signal in front of a higher amplitude back-wall signal may indicate a near ID inclusion. If any question exists, the area shall be investigated with a shear wave search unit to determine if an ID corner trap exists between the indication and the backwall.
8.4
Horizontal limit and linearity
8.4.1 Couple a longitudinal transducer, 2.25 to 5.0 MHz, to an IIW block (or equivalent thickness) as not to intercept any test holes (figure 2). The couplant used must provide stable indications during the measurements. NOTE All multiple positioning and position measurements shall be made with the respective back-reflection set at 50% of full screen height. 8.4.2 Adjust the instrument gain, sweep-delay, and sweep-length controls to display eleven non-interfering back reflections. Further adjust the sweep controls to position the leading edge of the third and ninth back reflections at 20% and 80% horizontal screen divisions respectively. 8.4.3 Read and record each scale position on a UT Instrument Verification Report form (attached) and plot. Record greatest linearity error in % of full horizontal scale. 8.4.4 Horizontal limit is given by the maximum available trace length falling within the CRT gradticule lines expressed in linear units (inches or millimetres). Unless otherwise noted this is also assumed to represent 100% full screen. Failure to obtain full-scale deflection may indicate an equipment malfunction. 8.4.5 Record all data and conformance on a UT Instrument Verification Report form (attached). 8.5
Screen height linearity
8.5.1 Couple a longitudinal transducer, 2.25 to 5.0 MHz, to a distance sensitivity (DS) block (or equivalent) so that indications from the 2 inch and 4 inch back-reflection can be observed (figure 3 position A). 8.5.2 Adjust the search unit position to give a 2:1 ratio of amplitude between the two indications. 8.5.3 With the larger set at 80% of full screen height (FSH), and without moving the search unit, adjust gain to successively set the larger indication from 100% to 20% of full screen height in 10% increments. 8.5.4 Read the smaller indication at each setting. The smaller reading must be 50% of the larger reading amplitude, within 5% of FSH. The settings and readings must be estimated to the nearest 1% of FSH. 8.5.5 Record all data and conformance on a UT Instrument Verification Report form (attached)
8.6
Amplitude control linearity
8.6.1 Couple a longitudinal transducer, 2.25 to 5.0 MHz, to a DS block (or equivalent) so that the 4 inch back-reflection is peaked on the screen (figure 3 position B). 8.6.2 With an increase and decrease in gain, as shown in table 3, the indication must fall within the specified limits. 8.6.3 Record conformance on a UT Instrument Verification Report form (attached 1). 9.0 POST CLEANING 9.1 Immediately upon completion of the examination, the couplant shall be removed by a suitable cleaning method. 9.1.1 The considerations of paragraph 4.2.2 shall also apply for the cleaning agents.
10.0 EXAMINATION REPORT
10.1 The following data will be recorded as a minimum for future reference at the time of each examination and included in the report: 10.1.1 Part number identification; 10.1.2 Operator's name and certification level: 10.1.3 Instrument description, make, model, serial number; and NIST Traceable calibration due date; 10.1.4 Setup - couplant, cable type and length; 10.1.5 Search unit description - type, size, frequency, special shoes; 10.1.6 Reference standards, size, and material types; 10.1.7 Record required instrument settings; 10.1.8 Scanning method and any limitations; 10.1.9 Each thickness measurement and its location; 10.1.10 Reference to this procedure.
11.0 ACCEPTANCE STANDARDS 11.1 Acceptance or rejection of a component will be based on customer requirements, and/or the minimum design thickness allowed by the referencing code.
Maximum
Thickness
Minimum
lower Step
Target
Upper Step
.03”
Up to .125” incl.
.20”
.10” .10” .25” .50” .50” .75” 1.00” 1.00” 1.00” 1.50” 1.50” 2.00” 2.00” 2.00” 2.00” 2.00” 2.00”
over .125” through .375” over .375” through .50” over .50” through .750” over .750” through 1.00” over 1.00” through 1.25” over 1.25” through 1.50” over 1.50” through 1.75” over 1.75” through 2.00” over 2.00” through 2.25” over 2.25” through 2.50” over 2.50” through 2.75” over 2.75” through 3.00” over 3.00” through 3.25” over 3.25” through 3.50” over 3.50” through 3.75” over 3.75” through 4.00” over 4.00” through 4.25”
.50” .625” .90” 1.30” 1.60” 1.90” 2.15” 2.50” 2.80” 2.90” 3.00” 3.50” 3.75” 4.00” 4.25” 4.50” 4.75”
Table 3 Thickness Testing Reference Table for Lower, Target, and Upper Bracket Ranges.
Figure 1 Calibration Standard
Material Thickness
Flat Bottom Hole Dia. +1/32 in.
Up to 1 in. Over 1 to 2 in. Over 2 to 3 in. Over 3 to 4 in. Over 4 in. GENERAL NOTE: Flat bottom holes machined to a minimum depth of 1/8 inch parallel to the transducer contact surface.
Table 2 Flat Bottom Hole Requirements
1/16 in. 1/8 in. 3/16 in. 5/16 in. 3/8 in.
Figure 2
Figure 3
Indication Set at
dB Control
Indication Limits
% of Full Screen
Change
% of Full Screen
80%
-6 dB
32 % to 48%
80% 40% 20%
-12 dB +6 dB +12 dB
16% to 24% 64% to 96% 64% to 96%
Table 4
Date: INSTRUMENT MAKE:
INSTRUMENT MODEL
INSTRUMENT SERICAL #:
CAL DUE DATE:
ULTRASONIC INSTRUMENT VERIFICATION REPORT COUPLANT and BATCH #:
CABLE TYPE:
CABLE LENGTH:
REFERENCE BLOCK:
TRANSDUCER TYPE:
TRANSDUCER SIZE:
TRANSDUCER FREQUENCY:
TRANSDUCER SERIAL #:
HORIZONTAL LIMIT AND LINEARITY 11
Ideal Linearity Line
10 9
BACK REFLECTION #
8
GREATES ERROR (% FULL HORIZONTAL SCALE)
7 6 5 4 3 2
1 0 10 20 30 40 50 60 70 80 90 100 POSITION OF SIGNAL ON SWEEP TRACE - % FULL SCALE
SCREEN HEIGHT LINEARITY 2” Response 4” Response % Error
100 90 80 70 60 50 40 30 20
AMPLITUDE CONTROL LINEARITY INDICATION SET AT % FULL SCREEN
dB CONTROL CHANGE
INDICATION LIMITS % FULL SCREEN
INDICATION SET AT % FULL SCREEN
80
-6 dB
32 – 48%
80 40 20
-12 dB +6 dB +12 dB
16 – 24% 64 – 96% 64 – 96%
This system meets the requirements for Horizontal Limit and linearity, screen height linearity and Amplitude Control Linearity as stated in ASME Section V Article 4. Technician:
Level:
