Ultrasonic Testing, English abbreviation UT(Ultrasonic Testing), it is one of the methods of non-destructive testing in industry.

When ultrasonic waves enter the object and encounter defects, part of the sound waves will be reflected, and the transmitter and receiver can analyze the reflected waves, so that the defects can be detected with exceptional accuracy, and the location and size of the internal defects can be displayed, and the thickness of the material can be determined.

Ultrasonic detection tips

1 Ultrasonic flaw detection method and scope of application

The National Standard of the People's Republic of China (ultrasonic inspection standard), this standard specifies the general method of inspecting weld and heat-affected zone defects, determining the location and size of defects, and evaluating defects, and the classification method of inspection results.

This standard is applicable to the pulse reflection method of manual ultrasonic inspection of the butt weld of ferritic steel with base material thickness of not less than 8mm.

This standard does not apply to cast steel and austenitic stainless steel welds; Steel pipe butt weld with outer diameter less than 159mm; Fillet welds with inner diameter less than or equal to 200mm and longitudinal welds with outer diameter less than 250mm and the ratio of inner to outer diameter less than 80%.

2. Reference standard for ultrasonic inspection methods

ZB Y344 ultrasonic inspection method is named by the probe type;

ZB Y231 ultrasonic flaw detection method with probe performance test;

ZB Y232 ultrasonic inspection method with No. 1 standard test block technical conditions;

ZB J04001 A type pulse reflection ultrasonic inspection system performance test method;

3 Terms related to ultrasonic flaw detection

3.1 Simplified horizontal distance l '

The horizontal distance measured from the probe front to the defect on the detection surface;

3.2 Defect indication length △l

In ultrasonic inspection of welding seam, the defect length measured by the moving distance of the probe according to the specified measurement method;

3.3 Probe contact surface width W

The width of the probe is used for annular seam inspection, and the length of the probe is used for longitudinal seam inspection.

3.4 Vertical Defects

Defects roughly parallel to the direction of the weld;

3.5 Horizontal Defects

Defects roughly perpendicular to the direction of the weld;

3.6 Geometric critical Angle β '

Inspection of cylindrical workpiece, refraction Angle when the axis of refracted sound beam is tangent to the inner wall;

3.7 Parallel Scanning

In bevel Angle detection, the probe is placed on the surface of the weld and the heat-affected zone, and the sound beam is pointed in the direction of the weld and moves along the direction of the weld.

3.8 Oblique Parallel Scan

In the bevel Angle test, the probe is at an Angle to the center line of the weld, which is equal to the scanning method of moving in the direction of the weld.

3.9 Inspection section

In serial scanning, as the inspection object, the section of the weld groove is generally taken as the inspection section.

3.10 List the base line

In serial scanning, the line used as the moving reference line with equal interval between one and two probes is generally located at a position with a distance of 0.5 span from the flaw detection section.

3.11 Guide Line

The position of the flaw detection section has been covered after welding, so before welding, a mark line should be drawn on the flaw detection surface at a certain distance from the weld groove, which is the reference line and will be used as the basis for determining the base line of series.

3.12 Horizontal Square Column Scan

A scanning method in which a set of probes are sent and received so that the incident points of the probe move equidistant and parallel to the reference line of the serial weld frequently;

3.13 Scanning the vertical Square column

A scanning method in which a set of probes are sent and received so that their entry points are always equidistant from the serial reference line and move perpendicular to the weld.

4 Inspection Personnel

4.1 Inspectors engaged in welding seam inspection must master the basic technology of ultrasonic inspection, have sufficient experience in welding seam ultrasonic inspection, and master certain basic knowledge of materials and welding;

4.2 Ultrasonic welding personnel shall undergo strict training and assessment in accordance with relevant regulations or technical conditions, and hold grade qualification certificates issued by relevant assessment organizations, and engage in inspection work related to the assessment projects;

Note: General welding inspection professional assessment items are divided into plate butt weld; Pipe butt weld; Seat fillet weld; Four kinds of joint welds.

4.3 The visual acuity of the ultrasound examiner shall be examined once a year, and the corrected visual acuity shall not be less than 1.0.

5 Flaw detector, probe and system performance

5.1 Flaw detector

The use of A type display pulse reflection flaw detector, its operating frequency range is at least 1-5MHz, the flaw detector should be equipped with an attenuator or gain controller, its accuracy is any adjacent 12dB error within ±1dB, each step is not greater than 2dB, the total adjustment amount should be greater than 60dB, the horizontal linear error is not greater than 1%, the vertical linear error is not greater than 5%.

5.2 Probe

5.2.1 The probe shall be marked according to the provisions of ZB Y344 standard;

5.2.2 The effective area of the wafer shall not exceed 500mm2, and the length of any side shall not be greater than 25mm;

5.2.3 The beam axis horizontal deviation Angle should not be more than 2°;

5.2.4 When the probe main sound beam deviates from the vertical direction, there should be no obvious double peaks. For the test method, see ZB Y231;

5.2.5 The nominal refraction Angle β of the inclined probe is 45°, 60°, 70° or the K value is 1.0, 1.5, 2.0, 2.5, the deviation between the measured value of the refraction Angle and the nominal value should not be greater than 2°(the deviation of the K value should not exceed ±0.1), and the deviation of the front distance should not be greater than 1mm. If limited by the workpiece geometry or the curvature of the detection surface, other small Angle probes can also be selected;

5.2.6 When it is clear that it can improve the accuracy and reliability of the detection results, or can better solve the difficulties in general inspection and ensure the correct results, it is recommended to use special probes such as focusing.

5.3 System Performance

5.3.1 Sensitivity margin

The effective sensitivity of the system must be greater than 10dB of the assessed sensitivity.

5.3.2 Far-field resolution

a. Straight probe: X≥30dB;

b. Inclined probe: Z≥6dB.

5.4 Inspection of flaw detector, probe and system performance and cycle

5.4.1 The performance of the flaw detector, probe and system, except the sensitivity margin, shall be tested according to the method specified in ZB J04001;

5.4.2 The horizontal linearity and vertical linearity of the flaw detector should be checked once in the first use of the equipment and every 3 months;

5.4.3 Incline probe and system performance must be checked once within the time specified in Table 1.

6 Ultrasonic test block

6.1 The shape and size of the standard test block, and the technical requirements of the manufacture of the test block shall comply with the provisions of ZB Y232. The test block is mainly used to determine the performance of the flaw detector, probe and system.

6.2 See the appendix of the product for the shape and size of the test block

6.2.1 The test block shall be made of steel with the same or similar acoustic properties as the material to be tested.

When the detection surface and side of the test block are inspected at a frequency of more than 2.5MHz and under the condition of high sensitivity, defect echoes greater than 1/4 of the echo amplitude reflected back by the Φ2mm flat bottom hole 20mm away from the detection surface shall not appear.

6.2.2 Standard holes on the test block can be arranged or added in other forms according to the need of flaw detection, but it should be noted that it should not be confused with the reflection of the end Angle of the test block and the adjacent standard holes.

6.2.3 When testing a curved workpiece, if the radius of curvature of the testing surface R is less than or equal to W2/4, a comparison block with the same curvature as the testing surface should be used. The arrangement of the reflector can be determined with reference to the comparison block, and the width of the test block should meet formula (1) :

b≥ 2λS /De (1) b-- width of test block, mm;

λ-- wavelength, mm;

S-- sound path, m;

De-- Effective diameter of sound source, mm

6.3 For field inspection, other types of equivalent test blocks can be used to verify sensitivity and time baseline.

7 Inspection level (according to ultrasonic inspection standards)

7.1 Classification of inspection levels

According to the quality requirements of the inspection grade is divided into A, B, C three levels, the perfection of the inspection level A is lower, B is general, C is higher, the difficulty coefficient of the inspection work is increased step by step according to the order of A, B, C.

Should be based on the workpiece material, structure, welding methods, conditions of use and load bearing different, reasonable selection of inspection levels.

The inspection level shall be selected according to the technical conditions and relevant provisions of the products or selected through negotiation between the parties to the contract.

Note: The difficulty coefficient of level A is 1; Grade B is 5-6; Grade C is 10-12.

This standard gives the inspection conditions of the three inspection levels. In order to avoid the geometric shape of the weldment limiting the effectiveness of the corresponding inspection levels, designers and technicians should consider the feasibility of ultrasonic inspection on the basis of structural design and process arrangement.

7.2 Inspection range of inspection level

7.2.1 Class A inspection adopts an angled probe to inspect both sides of the weld, and only the section of the weld that is allowed to be scanned is detected.

Horizontal defect inspection is generally not required. When the thickness of the base material is greater than 50Mm, Class A inspection shall not be adopted.

7.2.2 Class B inspection in principle, an Angle probe is used to inspect both sides of the weld and detect the entire weld section. When the thickness of the base material is greater than 100mm, double-sided and double-sided inspection is adopted. Limited by geometric conditions, two kinds of Angle probes can be used to detect the weld on both sides of the half-day side. Horizontal defects should be inspected when conditions permit.

7.2.3 At least two kinds of Angle probes should be used for inspection on both sides of the weld, and transverse defect inspection of two scanning directions and two probe angles should be carried out. When the thickness of the base metal is greater than 100mm, double-sided side inspection should be used. Additional requirements are:

a. The residual height of the butt weld should be smoothed so that the probe can be scanned parallel on the weld;

b. The base metal part inspected by the inclined probe on both sides of the weld shall be inspected by the straight probe;

c. When the thickness of the weld base material is greater than or equal to 100mm, and the thickness of the narrow gap weld base material is greater than or equal to 40mm, it is generally necessary to increase the serial scanning and scanning method.