ULTRASONIC TESTING PROCEDURE
1.0 Scope:
1.0
This procedure explains the requirements for manual pulse echo contact method of ultrasonic examination of butt joints in steel
2.0 Reference:
ASME SEC. V ARTICLE 4,5 & 23 – Boiler and Pressure Vessel Code.
ASME/ANSI B31.3 - Process Piping
ASME/ANSI B31.1 - Power Piping
API – 1104
ASME Sec. VIII, Div.1 & 2 – Pressure Vessel
AWS D1.1
3.0 Personnel Qualification:
4.0 The personnel performing examination shall be certified in accordance for qualification and certification of NDT personnel. SNA-TC-1A 2020
5.0 Equipment:
5.1 The examination shall be conducted with pulse echo ultrasonic equipment that generates frequencies over the range of 1MHz to 5MHz. The equipment model microscan EX–10, make EEC, Modsonic Einstein-I or equivalent satisfying the above requirements shall be used.
5.2 The equipment shall have valid calibration and stickered mentioning the date of expiry.
6.0 Probes:
6.1 Search units shall contain single crystal transducers.
6.2 For straight beam examination longitudinal wave probes (0°) shall be used. For angle beam examination shear wave probes of 45° shall generally be used and atleast one probe of other angles up to 70° shall be used appropriate to the configuration being examined. Groove angle and thickness shall be considered in selecting the probe angle other than 45°
6.3 For straight beam examination, the crystal dimensions shall be selected in the range of 10 mm to 25 mm. For angle beam examination, the crystal dimensions shall be selected appropriate to the contact available with examination surface and will generally be 8x9 mm or 20x22 mm.
6.4 Probes of frequencies between 2 MHz and 4 MHz shall be used for both straight beam and angle beam examination.
7.0 Surface Condition:
7.1 The finished contact surface shall be free from weld spatter and surface irregularities which will impair the free movement of the search unit.
7.2 The weld reinforcement shall be ground flush smooth with adjacent base material, if required.
8.0 Couplant:
Grease-oil mix shall be used as couplant. The couplant used for the examination shall be the same as that used for calibration.
Couplant used on nickel base alloys shall not contain more than 250 ppm of sulphur.
Couplants used on austenitic stainless steel or titanium shall not contain more than 250 ppm of halides (Chlorides plus fluorides).
9.0 Calibration of Equipment:
9.1 Basic Reference Block:
The basic reference reflectors shall be used to establish a primary reference response of the equipment. The material from which the block is fabricated shall be of the same product form and material specifications or equivalent P - Number grouping (P. Nos. 1, 3, 4 and 5 are considered equivalent) as one of the material being examined.
Reference blocks for dissimilar metal welds, the material selection shall be based on the material on the side of the weld from which the examination will be conducted. If the examination will be conducted from both sides, calibration reflectors shall be provided in both materials.
Reference blocks shall receive at least the minimum tempering treatment required by the material specification for the type and grade.
9.2 When two or more base material thicknesses are involved, the reference block thickness shall be determined by the average thickness of the weld.
9.3 The thickness and the location and size of holes in the basic reference block to be used shall be as indicated in the Figure - 1. Notched reference blocks shall only be used for thickness less than 12.7 mm.
9.4 The finish on the surface of the reference block shall be representative of the surface finish on the component. Variation in component configuration and surface finish, require transfer correction to be calculated.
9.5 The reference block material shall be completely examined with a straight beam search unit. Areas that contain an indication exceeding the remaining back reflection shall not be used as block material.
9.6 When the component has flat surfaces or curved surface with a diameter greater than 20 inches, a flat basic reference block shall be used. (Figure - 1).
9.7 When the component is curved and has a diameter less than 20 inches, a curved basic reference block shall be used. The components to be tested can have a curvature between 0.9 to 1.5 times of basic reference block diameter.
9.8 The reference blocks manufactured in house, shall be inspected and certified by NDT Level III.
10.0 Calibration Techniques:
10.1 Technique for Straight Beam Calibration:
The sweep range for straight beam is set on the equipment using the IIW V1 block.
10.1.1 Distance - Amplitude Correction: The probe is positioned for maximum response from the hole that gives the highest amplitude and set to 80% (±5%) full screen height. The peak of the indication is marked on the screen with a glass marking pencil. Without disturbing the sensitivity controls of the unit, the probe is positioned for maximum response from the other two-hole indications and their peaks marked on the screen.
The screen marks are connected and extended through the thickness to provide the distance amplitude curve using side drilled holes.
10.2 Technique for Angle Beam Calibration:
The basic calibration block shall be used for distance amplitude correction and position calibration.
The sweep range is selected and the equipment is calibrated to the selected range using IIW - V1 and V2 blocks.
Distance - Amplitude Correction (DAC): To construct a DAC a basic calibration block having drilled holes at ¼T, ½T and ¾T shall be used. The gain is adjusted to provide an 80% ± 5% of full screen indication from the ¼T hole.
The peak of the indication is marked on the screen with a glass marking pencil. Without disturbing the settings, the probe is positioned for maximum response from the ½T, ¾T holes and T+¼T hole after the beam has bounced from the opposite surface. The peak marks of the indications from the side drilled holes are connected to provide distance amplitude curve.
When calibrated using notched specimen, indication form the root notch is brought to 80% of screen height and the sensitivity level is noted.
10.3 A calibration check on at least one of the basic reflections in the basic calibration block shall be made to ensure proper functioning of the equipment, at the beginning and finish of each examination or series of similar examinations, every 4 hours during the examination and when examination personnel are changed.
10.4 The sensitivity (in dB) used for DAC shall be evaluation sensitivity or reference level.
10.5 Transfer correction if any obtained, shall be added to test / evaluation sensitivity.
11.0 Examination Surface:
11.1 For straight beam examination the weld and base material shall be scanned progressively along and across the weld surface to the extent possible from at least one surface of the part.
11.2 Angle Beam Scanning:
11.2.1 Defects Parallel to the Weld: (Figure - 4)
The angle beam shall be directed at 90° to the weld axis, from two directions where possible. The probes shall be manipulated so that the ultrasonic energy passes through the required volumes of the weld and adjacent base material.
11.2.2 Defects Transverse to Weld (Figure -5) :
11.2.2
For detection of transverse defects the weld shall be examined using 45 deg. angle beam probe.
For butt joints the angle beam shall be directed essentially parallel to the weld axis. The probe shall be manipulated so that the angle beam passes through required volumes of the weld and adjacent base metal. The probe shall be rotated at 180° and examination shall be repeated.
12.0 Scanning Sensitivity:
Scanning sensitivity shall be a minimum of +6dB above the reference
level. However evaluation of indications
shall be
performed at the
primary reference level.
13.0 Examination Coverage :
For the angle beam examination the entire volume of the
weld inclusive of adjacent base metal shall be examined by moving the probe over the
examination surface.
During scanning, the probes shall be moved to and fro with swiveling action of 10° to 15° on either side with overlap between successive scanning.
Each pass of the probes shall overlap a minimum of 10% of the crystal element dimension perpendicular to the direction of the scan.
In any case the rate of probe movement for examination shall not exceed 150mm per second.
Calibration Confirmation:
A calibration checks as discussed in 8.3, shall verify the sweep range calibration and distance amplitude correction.
12.1 Sweep Range Correction:
If a point on the DAC curve has moved on the sweep line more than 10% of the sweep reading or 5% of full sweep whichever is greater, the sweep range calibration shall be corrected. All recorded indications since the last valid calibration or calibration check shall be re-examined with the corrected calibration and the value changed.
12.2 DAC Correction:
If a point on the DAC curve has changed 20% or 2dB of its amplitude, all recorded indications since the last valid calibration check shall be re-examined with the corrected calibration.
13.0 Evaluation:
Imperfections that cause an indication greater than 20% of the reference
level shall be investigated to the extent that the ultrasonic examination
personnel can determine their shape, identity, and location, and evaluate them
in terms of paragraph 14.0
14.0 Acceptance Standard:
14.1 Cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.
14.2 Other imperfections are unacceptable if the indication exceeds the reference level amplitude and lengths which exceeds the following :
¼ inch for t up to ¾ inch
1/3 t for t from ¾ inch to 2¼ inches
¾ inch for t over 2 ¼ inches.
Where
\t is the thickness of the weld being examined. If the weld joints two members having different thickness at the weld, t is the thinner of these two thicknesses.
15.0 Post cleaning:
After the examination is completed the couplant applied on the surface
shall be
removed to the pre-inspection condition.
16.0 Repair & Retest:
Repaired weld regions
shall be ultrasonically re-examined by the same
procedure used for original testing.
17.0 Report:
17.1 Details of inspection of original weld and repaired area shall be recorded.
17.2 Recording all reflections from uncorrected areas having responses that exceed 50% of reference level shall be made.
|
Weld Thickness (t) in. (mm) |
Calibration Block Thickness(T) in. (mm) |
Hole Diameter in. (mm) |
|
Notch Dimensions in. (mm) |
|
Up to 1 (25) |
¾ (19) or t |
3/32 (2.4) |
Notch Depth = 2% T Notch Width = ¼ (6.4) max. Notch Length = 1 (25) min. |
|
|
Over 1 (25) through 2 (51) |
1 ½ (38) or t |
1/8 (3.2) |
|
|
|
Over 2 (51) through 4 (102) |
3 (76) or t |
3/16 (4.8) |
|
|
|
Over 4 (102) |
t + 1 (25) |
** |
|
** For each increase in weld thickness of 2 in. (51mm), or fraction thereof over 4 in. (102 mm), the hole diameter shall increase 1/16 in. (1.6 mm).
GENERAL NOTES:
(a) Holes shall be drilled and reamed 1.5 in. (38 mm) deep minimum, essentially parallel to the examination surface.
(b) For curved surfaces, two sets of calibration reflectors (holes, notches) oriented 90 deg from each other shall be used. Alternatively, two curved calibration blocks may be used.
(c) The tolerance for hole diameter shall be + 1/32 in. (0.8 mm). The tolerance for hole location through the calibration block thickness (i.e., distance from the examination surface) shall be + 1/8 in. (3.2 mm).
(d) All three holes may be located on the same face (side) of the calibration block provided care is exercised to locate the holes far enough apart to prevent one hole from masking the indication of another hole during calibration.
(e) Minimum notch depth shall be 1.6% T and maximum notch depth shall be 2.2% T plus the thickness of cladding, if present.
FIG (1) NON – PIPING CALIBRATION BLOCKS
* Notches shall be located not closer than T or 1 in. (25mm), whichever is greater, to any
block edge or to other notches.
GENERAL NOTES:
(a) The minimum calibration block length (L) shall be 8 in. (203 mm) or 8T, whichever is greater.
(b) For OD 4 in. (102 mm) or less, the
minimum arc length shall be 270 deg. For OD greater than
4 in. (102 mm), the minimum arc length shall be 8 in. (203 mm) or 3T, whichever is greater.
(c) Notch depths shall be from 8% T minimum to 11% T maximum. Notch widths shall be ¼ in. (6.4 mm) maximum. Notch lengths shall be 1 in. (25 mm) minimum.
Fig 1(A) CALIBRATION BLOCK FOR PIPE
FIG. 1(B) – CURVED BASIC REFERENCE BLOCK
