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NDT CALIBRATION REFERENCE STANDARDS

4.0 REFERENCE STANDARDS

What are standards?

Standards are documented agreements containing technical specifications or other precise criteria to be used consistently as rules, guidelines, or definitions of characteristics, in order to ensure that materials, products, processes, and services are fit for their purpose. For example, the format of the credit cards, phone cards, and "smart" cards that have become commonplace is derived from an ISO International Standard. An important source of practice codes, standards, and recommendations for NDT is given in the Annual Book of the American Society of Testing and Materials, ASTM.  Nondestructive Testing is revised annually, covering acoustic emission, eddy current, leak testing, liquid penetrants, magnetic particle, radiography, thermography, and ultrasonic.

Calibration and reference standards for ultrasonic testing come in many shapes and sizes. The type of standard used is dependent on the NDE application and the form and shape of the object being evaluated. The material of the reference standard should be the same as the material being inspected and the artificially induced flaw should closely resemble that of the actual flaw. This second requirement is a major limitation of most standard reference samples. Most use drilled holes and notches that do not closely represent real flaws. In most cases the artificially induced defects in reference standards are better reflectors of sound energy (due to their flatter and smoother surfaces) and produce indications that are larger than those that a similar sized flaw would produce. Producing more "realistic" defects is cost prohibitive in most cases and, therefore, the inspector can only make an estimate of the flaw

 size. Computer programs that allow the inspector to create computer simulated models of the part and flaw may one day lessen this limitation.

 

There are many efforts on the part of the National Institute of Standards and Technology (NIST) and other standards organizations, both national and international, to work through technical issues and harmonize national and international standards.

 

4.1 AMERICAN WELDING SOCIETY (AWS)

AWS publishes codes on multiple aspects of welding and materials joining. The code books are assigned specific letters and numbers for easy reference, and many welders will refer to a specific code letter/number combination when referring to the code book. Different welding methodologies, inspection methods, and metals are published under different codes. For example, AWS B1.11 explains how to visually examine welds; AWS B2.1-1-004 explains welding carbon steel of thickness range of 18 through 10 gauge with semiautomatic metal gas arc welding; and AWS C2.20/C2.20M explains metalized zinc cathodic protection systems. Some codes also describe the standards used by AWS to certify welders, inspectors, and welding educators. All codes are available in hard copy, and in recent years AWS has started to make most codes available online. A very influential AWS code is AWS D1.1, which covers all general requirements for structural welding. This code has been adopted by ANSI as a National Standard in the United States.

4.1.1. IIW TYPE BLOCK

IIW is an acronym for the International Institute of Welding. It is referred to as an IIW "type" reference block because it was patterned after the "true" IIW block but does not conform to IIW requirements in IIS/IIW-23-59. Where IIW "type" blocks can be commercially obtained in a selection of materials. IIW "type" blocks may also include additional calibration and references features such as notches, circular groves, and scales that are not specified by IIW. There are two full-sized and a mini version of the IIW type blocks. The Mini version is about one-half the size of the full-sized block and weighs only about one-fourth as much. IIW type blocks are used to calibrate instruments for both angle beam and normal incident inspections. Some of their uses include setting metal-distance and sensitivity settings, determining the sound exit point and refracted angle of angle beam transducers, and evaluating depth resolution of normal beam inspection setups. Instructions on using the IIW type blocks can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments.

4.1.2. RC- Resolution Reference Block

The American Welding Society (AWS) Resolution Reference Block is used for checking resolution capabilities of angle beam transducers. Contains three sets of 1.6mm diameter through-holes for 45°, 60° and 70°. In accordance with American Welding Society (AWS) Welding Highway and Railway Bridges specification D2.0, and Structural Welding Code American National Standards Institute (ANSI)/ American Welding Society (AWS) D1.1.

4.1.3. DSC - DISTANCE AND SENSITIVITY REFERENCE BLOCK

A block that closely resembles the miniature angle-beam block and is used in a similar way is the DSC AWS Block. This block is used to determine the beam exit point and refracted angle of angle-beam transducers and to calibrate distance and set the sensitivity for both normal and angle beam inspection setups. Instructions on using the DSC block can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments.

4.1.4. DC- DISTANCE REFERENCE BLOCK

The DC AWS Block is a metal path distance and beam exit point calibration standard that conforms to the requirements of the American Welding Society (AWS) and the American Association of State Highway and Transportation Officials (AASHTO). Instructions on using the DC block can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments        .

4.1.5. DS – DISTANCE AND SENSITIVITY CALIBRATION BLOCK

American Welding Society (AWS) Distance and Sensitivity (DS) Block is used for calibrating of straight beam distance and sensitivity. The DS test block is a calibration standard used to check the horizontal linearity and the dB accuracy per requirements of AWS.

4.1.6. SC – SENSITIVITY REFERENCE BLOCK

American Welding Society (AWS) Type SC block is used for calibrating of shear wave sensitivity, in accordance with American Welding Society (AWS) requirements.

4.1.7. SUPPLEMENTAL REFERENCE BLOCK

Phased Array Calibration Standard used for angle beam verification, probe angle exit point, calibration for wedge delay, sensitivity, DAC/TCG for thicknesses up to 50mm. The three radii (12.5, 25, 50mm) allow for exit point verification, velocity, and sound path calculations. Block contains five holes at 1.2mm diameter drilled through the 25mm width, located at 2.5, 5.0, 10.0, 15.0, 20.0, 30.0, 35.0, 45.0, and 47.5mm from the respective scanning surface. Generous hole spacing eliminated "ghost" images from adjacent holes. Also includes an engraved scale from 30° to 70° associated with the 20mm hole for beam angle verification.

4.2 AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) STANDARDS

ASTM International has no role in requiring or enforcing compliance with its standards. The standards, however, may become mandatory when referenced by an external contract, corporation, or government. In the United States, ASTM standards have been adopted, by incorporation or by reference, in many federal, state, and municipal government regulations. The National Technology Transfer and Advancement Act, passed in 1995, requires the federal government to use privately developed consensus standards whenever possible. The Act reflects what had long been recommended as best practice within the federal government. Other governments (local and worldwide) also have referenced ASTM standards. Corporations doing international business may choose to reference an ASTM standard. All toys sold in the United States must meet the safety requirements of ASTM F963, Standard Consumer Safety Specification for Toy Safety, as part of the Consumer Product Safety Improvement Act of 2008 (CPSIA). The law makes the ASTM F963 standard a mandatory requirement for toys while the Consumer Product Safety Commission (CPSC) studies the standard's effectiveness and issues final consumer guidelines for toy safety.

4.2.1. IIW BLOCK (ASTM E164)

IIW is an acronym for the International Institute of Welding. It is referred to as an IIW "type" reference block because it was patterned after the "true" IIW block but does not conform to IIW requirements in IIS/IIW-23-59. Where IIW "type" blocks can be commercially obtained in a selection of materials. IIW "type" blocks may also include additional calibration and references features such as notches, circular groves, and scales that are not specified by IIW. There are two full-sized and a mini version of the IIW type blocks. The Mini version is about one-half the size of the full-sized block and weighs only about one-fourth as much. IIW type blocks are used to calibrate instruments for both angle beam and normal incident inspections. Some of their uses include setting metal-distance and sensitivity settings, determining the sound exit point and refracted angle of angle beam transducers, and evaluating depth resolution of normal beam inspection setups. Instructions on using the IIW type blocks can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments.

4.2.2. MINIATURE ANGLE BEAM REFERENCE BLOCK

The miniature angle-beam is a calibration block that was designed for the US Air Force for use in the field for instrument calibration. The block is much smaller and lighter than the IIW block but performs many of the same functions. The miniature angle-beam block can be used to check the beam angle and exit point of the transducer. The block can also be used to make metal-distance and sensitivity. Calibrations for both angle and normal-beam inspection setups.

4.2.3. DC- DISTANCE REFERENCE BLOCK

The DC AWS Block is a metal path distance and beam exit point calibration standard that conforms to the requirements of the American Welding Society (AWS) and the American Association of State Highway and Transportation Officials (AASHTO). Instructions on using the DC block can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments

4.2.4. SC – SENSITIVITY REFERENCE BLOCK

SC block is used for calibrating of shear wave sensitivity, in accordance with ASTM E164

4.2.5. DSC - DISTANCE AND SENSITIVITY REFERENCE BLOCK

A block that closely resembles the miniature angle-beam block and is used in a similar way is the DSC AWS Block. This block is used to determine the beam exit point and refracted angle of angle-beam transducers and to calibrate distance and set the sensitivity for both normal and angle beam inspection setups. Instructions on using the DSC block can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments.

4.2.6. ASTM E127 Area Amplitude Set of 8

Set of eight flat-bottom hole blocks used to determine the relationship between flaw size and echo amplitude by comparing signal responses.

4.2.7. ASTM E127 Area Amplitude Set of 10

Set of Ten flat-bottom hole blocks used to determine the relationship between flaw size and echo amplitude by comparing signal responses.

4.2.8. ASTM E127 Area Amplitude Set of 19

Set of Nineteen flat-bottom hole blocks used to determine the relationship between flaw size and echo amplitude by comparing signal responses.

4.2.9. 30 FBH RESOLUTION BLOCK

The 30 FBH resolution reference block is used to evaluate the near-surface resolution and flaw size/depth sensitivity

 of a normal-beam setup.

4.2.10. ASTM E317 Block, Figure 1

ASTM E317 horizontal and vertical linearity block, Figure 1 is used for evaluating the horizontal and vertical linearity characteristics of ultrasonic pulse-echo systems.

4.2.11. ASTM E317 Block, Figure 6

ASTM E317 resolution block, Figure 6 is used for evaluating the resolution characteristics of ultrasonic pulse-echo systems.

4.2.12. ASTM E2491 PA Assessment Block (Type B)

Phased Array calibration block used for beam characterization and evaluation of system performance characteristics. Use it as baseline block to determine long-term instrument performance changes, generate DAC curves, and evaluate linear/angular resolution, focusing ability and beam steering capability. With a variety of targets, this small, lightweight block is also perfect for customer demonstrations of phased array ultrasonic capabilities. This block is also referred to as a “Type B” block.

4.2.13. ASTM TEST BLOCK

ASTM test block is also known as MPT test bar used in Magnetic particle inspection. It has 7 numbers of artificial flaws (side drilled holes). Easy to carry on site. Pocket friendly.

4.2.14. KETOS RING

Prior to the inspection, a system performance verifier is often used to ensure that the system is delivering the proper amount of current as called for during the inspection. Within the NDE industry there is a number of different standard process control specimens used to aid in verifying the performance of the electromagnetic system.  Some of the devices used include: the ISO ring (also known as Reference Block Type 1 (MTU-3)), ISO block (also known as MTU-2), and the AS 5282 ring (or similar Ketos ring). These items are a means to verify the operation of the system, and should be used on a periodic basis during the operation of the system.  Suggested times may be at the beginning of each shift change, or at the beginning of the inspection process if the bench is not used on a daily basis. For a system such as yoke, a prescribed test such as a dead weight test may be performed to ensure a proper amount of magnetic field is generated. The AS 5282 ring, and similarly the Ketos ring, is a ring that is made up of a series of pre-drilled holes at increasing depths below the surface used to simulate sub-surface defects. The distance of the holes to the surface increases as you move to holes of increasing number. Its original purpose was to demonstrate the ability to use MPI to find sub-surface flaws, but it has long since been used to perform regular performance evaluation of MPI bench systems.  The intensity of the indication depends on the depth of the flaw and the amount of current passed through a central bar conductor. Ketos ring indications when the magnetic particle fluid is applied, it contacts the surface with enough fluid flow to wash away any indications being formed by the magnetic leakage fields caused by the drilled holes.  For this reason, the indications are developed by a final magnetizing shot or shots, which are triggered immediately after the direct fluid flow is diverted.  Orientation of the ring with respect to the fluid flow can have a significant impact on which lines develop indications with lines near the area where the fluid is applied often proving more difficult for indications to develop.

4.2.15 SHIMS FOR MAGNETIC PARTICLE TESTING

The standard flawed shims are typically used to establish proper field direction and ensure adequate field strength during technique development in magnetic particle examination. The Shims may be used to ensure the establishment and balance of field in the multi-directional magnetization method.

The Quantitative Quality Indicator (QQI) or Artificial Flaw Standard or SHIMS is often the preferred method of assuring proper field direction and adequate field strength. The use of a QQI is also the only practical way of ensuring balanced field intensity and direction in multiple-direction magnetization equipment. QQIs are often used in conjunction with a Gauss meter to establish the inspection procedure for a particular component. They are used with the wet method only, and like other flux sharing devices, can only be used with continuous magnetization. The QQI is a thin strip of either 0.002 or 0.004 inch thick AISI 1005 steel. A photo etch process is used to inscribe a specific pattern, such as concentric circles or a plus sign. QQIs are nominally 3/4 inch square, but miniature shims are also available. QQIs must be in intimate contact with the part being evaluated. This is accomplished by placing the shim on a part etched side down, and taping or gluing it to the surface. The component is then magnetized and particles applied. When the field strength is adequate, the particles will adhere over the engraved pattern and provide information about the field direction. When a multidirectional technique is used, a balance of the fields is noted when all areas of the QQI produce indications.

Some of the advantages of QQIs are: they can be quantified and related to other parameters, they can accommodate virtually any configuration with suitable selection, and they can be reused with careful application and removal practices.

Some of the disadvantages are: the application process is somewhat slow, the parts must be clean and dry, shims cannot be used as a residual magnetism indicator as they are a flux sharing device, they can be easily damaged with improper handling, and they will corrode if not cleaned and properly stored.

 4.2.16. STEP BLOCK AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) - E797

Step and tapered calibration wedges come in a large variety of sizes and configurations. Step wedges are typically manufactured with four or five steps but custom wedge can be obtained with any number of steps. Tapered wedges have a constant taper over the desired thickness range.

4.3 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) STANDARDS

ASME is one of the oldest standards-developing organizations in America. It produces approximately 600 codes and standards covering many technical areas, such as fasteners, plumbing fixtures, elevators, pipelines, and power plant systems and components. ASME's standards are developed by committees of subject matter experts using an open, consensus-based process. Many ASME standards are cited by government agencies as tools to meet their regulatory objectives. ASME standards are therefore voluntary, unless the standards have been incorporated into a legally binding business contract or incorporated into regulations enforced by an authority having jurisdiction, such as a federal, state, or local government agency. ASME's standards are used in more than 100 countries and have been translated into numerous languages.                                                                                                                            

4.3.1. ASME BASIC NON-PIPING CALIBRATION BLOCK

This block can be used as a calibration block with a compression probe; however, its main use is as a reference block with either compression or shear wave probes. Its most common uses are for setting test sensitivity prior to inspection, using various depth of individual Side Drilled Holes (SDH) as reference reflectors. The test sensitivity as set by means of Distance amplitude Curve (DAC) / Time Correction Gain (TCG). The block size and reflector locations shall be adequate to perform calibrations for the beam angle(s) and distance range(s) to be used. The block thickness (T) shall be varying according to test object.     

Acoustic signals from the same reflecting surface will have different amplitudes at different distances from the transducer. Distance amplitude correction (DAC) provides a means of establishing a graphic ‘reference level sensitivity’ as a function of sweep distance on the A-scan display. The use of DAC allows signals reflected from similar discontinuities to be evaluated where signal attenuation as a function of depth has been correlated. Most often DAC will allow for loss in amplitude over material depth (time), graphically on the A-scan display but can also be done electronically by certain instruments. Because near field length and beam spread vary according to transducer size and frequency, and materials vary in attenuation and velocity, a DAC curve must be established for each different situation. DAC may be employed in both longitudinal and shear modes of operation as well as either contact or immersion inspection techniques.

A distance amplitude correction curve is constructed from the peak amplitude responses from reflectors of equal area at different distances in the same material. A-scan echoes are displayed at their non-electronically compensated height and the peak amplitude of each signal is marked on the flaw detector screen or, preferably, on a transparent plastic sheet attached to the screen. Reference standards which incorporate side drilled holes (SDH), flat bottom holes (FBH), or notches whereby the reflectors are located at varying depths are commonly used. It is important to recognize that regardless of the type of reflector used, the size and shape of the reflector must be constant. Commercially available reference standards for constructing DAC include ASTM Distance/Area Amplitude and ASTM E1158 Distance Amplitude blocks, NAVSHIPS Test block, and ASME Basic Calibration Blocks

4.3.2. ASME BASIC PIPING CALIBRATION BLOCK

This block can be used as a calibration block with a shear wave probe, its main use is as a reference block for setting test sensitivity prior to inspection. Especially this block has manufacture for examine over curvature surface, which below 20” OD. Ultrasonic sound travel in curvature area, angle of propagation will differ when compare to flat area. In order to overcome this, American Society of Mechanical Engineers (ASME) standards have some set of curvature blocks for reference.

Sound Propagation of Angle beam into

the curvature surface, angle of

propagation will change

Sound Propagation of Angle beam into

the flat surface, angle of propagation

will not change

 

 

 

 

Sound Path

Sound Path

Search Unit

Search Unit

 

 

 

 

 

 

 

 

 


Examinations in materials where the examination surface diameter is equal to or less than 20 in. (500 mm), a curved block shall be used. A single curved basic calibration block may be used for examinations in the range of curvature from 0.9 to 1.5 times the basic calibration block diameter.

For example, an 8 in. (200 mm) diameter block may be used to calibrate for examinations on surfaces in the range of curvature from 7.2 in. to 12 in (180 mm to 300 mm) in diameter. The curvature range from 0.94 in. to 20 in. (24 mm to 500 mm) in diameter requires six curved blocks for any thickness range

8" x 0.9

Minimum OD 7.2"

8" x 1.5

Maximum OD 12"

OD 8"

 

 

 

 

 

 

 

 

 

 

 


American Society of Mechanical Engineers (ASME) standards requires six curved blocks to cover the curvature range of 0.94 in. to 20 in. (24 mm to 500 mm) in diameter.

 

 

Standard Calibration Block OD

Coverage of Pipe OD

Ø1"

Ø2"

Ø3"

Ø4"

Ø6"

Ø8"

Ø10"

Ø12"

Ø14"

Ø16"

Ø18"

Ø20"

OD Ø1"

 

 

 

 

 

 

 

 

 

 

 

 

OD Ø2"

 

OD Ø4"

 

OD Ø6"

 

 

 

 

 

 

 

 

 

 

 

 

OD Ø8"

 

OD Ø10"

 

 

 

 

 

 

 

 

 

 

 

 

OD Ø12"

 

 

 

 

 

 

 

 

 

 

 

 

OD Ø14"

 

4.3.3. CUSTOMIZED ASME BASIC PIPING CALIBRATION BLOCK

This block can be used as a calibration block with a shear wave probe; its main use is as a reference block for setting test sensitivity prior to inspection. Especially this block has manufacture for examine over curvature surface, which below 20” OD. NDE FLAW TECHNOLOGIES PVT.LTD. as customized set of block chosen from the American Society of Mechanical Engineers (ASME) standards to cover curvature range of 75mm to 500mm also these set of block will cover the thickness range from SCH 30 to SCH XXS.

Coverage of Pipe Curvature area(s)

Standard Calibration Block OD

Coverage of Pipe OD

Ø4"

Ø6"

Ø8"

Ø10"

Ø12"

Ø14"

Ø16"

Ø18"

Ø20"

OD Ø4"

 

 

 

 

 

 

 

OD Ø8"

 

 

 

 

 

 

OD Ø14"

 

 

 

 

 

 

Coverage of Pipe Thickness

 

Standard Calibration Block OD

Coverage of Thickness

SCH 10

SCH 20

SCH 30

SCH 40

STD

SCH 60

SCH 80

XS

SCH 100

SCH 120

SCH 140

SCH 160

OD Ø4" SCH 80

 

 

 

 

 

 

 

OD Ø4" SCH 160

 

 

 

 

 

 

 

 

 

OD Ø8" SCH 40

 

 

 

 

 

 

 

 

OD Ø8" SCH 80

 

 

 

 

 

 

 

 

OD Ø8" SCH 160

 

 

 

 

 

 

 

 

 

OD Ø14" SCH 30

 

 

 

 

 

 

 

 

OD Ø14" SCH 80

 

 

 

 

 

 

 

 

OD Ø14" SCH 120

 

 

 

 

 

 

 

 

 

OD Ø14" SCH 160

 

 

 

 

 

 

 

 

 

 

4.4. International Organization for Standardization (ISO)

This International Standard specifies requirements for principles for the qualification and certification of personnel who perform industrial non-destructive testing (NDT). The system specified in this International Standard can also apply to other NDT methods or to new techniques within an established NDT method, provided a comprehensive scheme of certification exists and the method or technique is covered by International, regional or national standards or the new NDT method or technique has been demonstrated to be effective to the satisfaction of the certification body. The certification covers proficiency in one or more of the following methods: a) acoustic emission testing; b) eddy current testing; c) infrared thermographic testing; d) leak testing (hydraulic pressure tests excluded); e) magnetic testing; f) penetrant testing; g) radiographic testing; h) strain gauge testing; i) ultrasonic testing; j) visual testing (direct unaided visual tests and visual tests carried out during the application of another NDT method are excluded).

4.4.1. BLOCK A2:

A2 Block is an International Institute of Welding. It is referred to as an IIW "type" reference block because it was patterned after the "true" IIW block but does not conform to IIW requirements. Where IIW "type" blocks can be commercially obtained in a selection of materials. IIW "type" blocks may also include additional calibration and references features such as notches, circular groves, and scales that are not specified by IIW. There are two full-sized and a mini version of the IIW type blocks. The Mini version is about one-half the size of the full-sized block and weighs only about one-fourth as much. IIW type blocks are used to calibrate instruments for both angle beam and normal incident inspections. Some of their uses include setting metal-distance and sensitivity settings, determining the sound exit point and refracted angle of angle beam transducers, and evaluating depth resolution of normal beam inspection setups. Instructions on using the IIW type blocks can be found in the annex of American Society for Testing and Materials Standard E164, Standard Practice for Ultrasonic Contact Examination of Weldments.

4.4.2. BLOCK A4:

The miniature angle-beam is a calibration block that was designed for the US Air Force for use in the field for instrument calibration. The block is much smaller and lighter than the IIW block but performs many of the same functions. The miniature angle-beam block can be used to check the beam angle and exit point of the transducer. The block can also be used to make metal-distance and sensitivity calibrations for both angle and normal-beam inspection setups.

4.4.3. BLOCK A5

Block A5 used for calibrates resolution check for angle beam transducer, also used for angle beam plotting, to plot beam divergence for shear wave transducer. Analysis of amplitude with respect to exit point is carried out for each angle using data points from depths corresponding to side drilled holes in an IOW block (British Standards A5). Graphed and tabulated results are analyzed for trends. This modeling analysis is then compared to actual lab results for refracted angle determination.

4.4.4. BLOCK A6

Block A6 is used for evaluating dominant frequency of compression wave transducer, calibration of pulse length, dead zone and resolving power for both shear wave transducer and compression wave transducer.

4.4.5. BLOCK A7

Block is used to calibrate the Resolution for checking shear wave probe resolution.

4.4.6. PAUT calibration block ISO-19675

At the first glance, the PAUT IIW block looks very similar to the former IIW conventional UT block, but it allows carrying out far more checking and calibration functions. Usages such as wedge delay, grating lobes assessment, active element assessment, sensitivity equalization, plotting check, element assignment, etc.

Beam angle (angle beam probe), First the delay law for the angle beam being assessed shall be configured. Then the probe index shall be determined, by positioning the probe to maximize the echo response from the 100mm radius. Using a fine-tip marker, a line is drawn on the wedge where the center point of the 100mm radius meets the wedge. Then the probe is moved to maximize the response from either the uppermost or lowermost 3mm diameter side drilled hole. Read the value of the angle indicated on the scribed markings to the nearest 0.5° to determine the actual refracted angle can now be read.

Element assignment - A B-scan of the delay law acquisitions is displayed and the amplitude and time of the back wall signal for each element in the array is observed. If the element #1 is nearest the end of the PAUT calibration block it will have the shortest arrival time in pulse-echo and all subsequent elements should display a monotonic increase in arrival time. B-scan from a 64 element probe with the response seen from the V surface of the block. The response from each element is slightly greater in time than its next adjacent element indicating correct assignment of elements.

4.4.7. HEMI CYLINDRICAL-STEPPED (HS) BLOCK

It shall be machined from a solid cylinder. After it is machined into cylindrical step shape, it is cut along the longitudinal axis and machined to the required surface finish. The radii of the hemicylindrical steps are 20 mm, 40 mm, 50 mm, 80 mm, 100 mm, and a slot of 85 mm and 91 mm. The width of the 20 mm to 80 mm radial steps is 25 mm; the width of the 100 mm step is 30 mm; the width of the 85 mm slot is 2 mm and the width of the 91 mm radius step is 28 mm. A line along the centre section of the slot (the x-axis), a centre line dividing the HS block in
symmetry (the y-axis), and boundary lines between adjacent steps, on the flat surface, shall be engraved. When in use, the block should rest on an appropriate support. The support frame shall cause neither mechanical damage to the block nor any acoustical damping effect due to the support.

4.4.8. SIDE-DRILLED-HOLE BLOCK

It is 300 mm long by 25 mm wide by 100 mm high with eight identical side-drilled holes 1,5 mm in diameter. They are identified as SDH2, SDH3, SDH4, SDH5, SDH10, SDH20, SDH30, and SDH456. The longitudinal axis of the holes shall be parallel to the top and bottom surfaces of the block. The surfaces of the block are identified as the T- (top), B- (bottom), R-(right) and L- (left), and F- (front) surface, which refers to either side of the large surfaces. The location
of the hole is measured from the center of the hole to the top, bottom, or end surface of the block. Short
lines on the edge of the F- and T-surfaces are engraved indicating the locations of the SDH center lines.
The location of the SDH456 is engraved on all the T-, B-, R-, and F-surfaces. Except for the SDH456 hole,
the number affixed to the SDH indicates the distance of the hole center to the T-surface. For example, the
distance from the SDH2 hole center to the T-surface is 2 mm. The distances from the SDH456 center to
the B-, R-, and T-surfaces are 40 mm, 50 mm, and 60 mm, respectively. The first hole, the SDH2, is 40 mm
from the L-surface, and the distance between the adjacent holes is 30 mm. Angles of refraction (0° to 70°)
are indicated by short lines engraved on the F-surfaces at the edge between the F- and the B-surfaces.
The nominal longitudinal and transverse wave velocities of the material, determined empirically after
the block has been machined, can be engraved on one of the F-surfaces of the SDH block.

4.5. AMERICAN PETROLEUM INSTITUTE (API)

API – American Petroleum Institute is the national trade association that represents all aspects of America's oil and natural gas industry. It has corporate members which range from multi-national oil companies to the smallest of independents and they cover all aspects of the industry: producers, refiners, suppliers, pipeline operators and marine transporters and service and supply companies. API maintains more than 500 standards and recommended practices which cover everything from drill bits to environmental protection. Increasingly, these API standards are being applied outside of the United States and some are being adopted by ISO.

4.5.1 API RP-2X LEVEL A BLOCK

The reference reflector for establishing the scanning sensitivity must be compatible with the flaw acceptance criteria
and provide sufficient sensitivity to ensure detection of the smallest discontinuity of interest. For ultrasonic examination at Level A acceptance criteria, the side of a 1/16-inch (1.6-millimeter) drilled hole provides an excellent reference for use with all transducers. The thickness and length of the block containing the drilled hole should permit evaluation of reference sensitivity at the lon