Knowledge about flaw detection

Non-destructive testing, which is commonly used for flaw detection, includes X-ray testing, magnetic particle testing, dye penetrant testing, and ultrasonic testing. If you have only a basic understanding of these methods, you can refer to relevant books and materials

Whether for pressure vessel welds or pressure pipeline welds, the inspection ratio, the inspection methods to be used (ultrasonic testing UT or radiographic testing RT, including surface inspection, etc.), as well as the acceptance criteria or grades, are all clearly specified in the general specifications of the corresponding equipment layout drawings and process piping construction drawings. It is recommended that LZ consult the relevant drawings; in addition, he can also refer to the relevant sections of standards such as GB150 \"Steel Pressure Vessels\", GB50235 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\", and SH3501 \"Code for Construction and Acceptance of Piping Projects for Toxic and Flammable Media in Petrochemical Industries\". For reference!

There are many standards on the forum; the original poster can take a look at http://bbs.hcbbs.com/viewthread.php?tid=203835 http://bbs.hcbbs.com/viewthread.php?tid=203835#

You may refer to GB150 \"Steel Pressure Vessels\"

The proportion of weld inspection and the required inspection standards are clearly specified in GB150 \"Steel Pressure Vessels\". For those that require inspection, the proportion of inspections to be carried out and the acceptable standards are generally indicated in the construction drawings.

Typical manufacturing drawings will specify the standards used for flaw detection, the methods employed for such detection, and the acceptance criteria You can look up the corresponding standards according to the requirements in the drawings and proceed accordingly! Generally, JB/T 4730 is used for flaw detection operations in China; it contains criteria for rating the results of such detections, and based on these results it is possible to determine whether the manufactured equipment meets the required standards!

I. Non-destructive testing methods 1. Ultrasonic testing Equipment: ultrasonic flaw detector, probe, coupling agent, and standard test blocks, etc. Uses: Detection of cracks, delamination, and inclusions in forgings; cracks, pores, slag inclusions, lack of fusion, and incomplete welding in welds; cracks, delamination, inclusions, and folds in profiles; defects such as shrinkages, bubbles, thermal cracks, cold cracks, porosity, and slag inclusions in castings; as well as thickness measurement. Advantages: Highly sensitive to planar defects; the result is known immediately upon inspection ； Easy to carry ； High penetration power. Limitation: As it is a coupled sensor, the surface to be inspected must be smooth ； It is difficult to detect small cracks ； Reference standards are necessary; to interpret signals, inspectors are required to have high competence ； Not suitable for work with complex shapes or rough surfaces. 2. Acoustic emission testing equipment: acoustic emission sensors, amplification circuits, signal processing circuits, and an acoustic emission signal analysis system. Purpose: To detect dynamic cracks in components, crack initiation, and crack growth rate, etc. Advantages: Real-time and continuous monitoring, remote control capability, and the device is lightweight. Limitations: The sensor must be well coupled to the test specimen, which has to be under stress; ductile materials generate low-amplitude acoustic emissions, noise must not enter the detection system, the equipment is expensive, and high qualifications are required for the personnel. 3. Noise detection equipment: sound level meter, frequency analyzer, noise level analyzer. Purpose: To detect defects such as wear, impact, and fatigue in the internal structure of equipment, and to locate noise sources (fault sources). Advantages: The instrument is lightweight, offers fast detection and analysis speeds, and boasts high reliability. Limitations: The equipment is expensive, and it requires a high level of skill from the personnel. 4. Laser detection equipment: Laser holography camera. Applications: detecting minor deformations, the adhesion quality of honeycomb structures in splints, defects in pneumatic tires, material cracks, plasma diagnosis in high-speed physical processes, and high-speed collisions. Advantages: high detection sensitivity, large detection area, no limitations regarding materials, and results that are easy to store. Limitation: It is only applicable to the detection of near-surface defects. 5. Microwave detection equipment: Microwave computed tomography scanner (microwave CT). Purpose: Testing composite materials, non-metallic products, rocket casings, aerospace components, tires, etc ； Physical parameters such as thickness, density, and humidity can also be measured. Advantages: Contactless measurement, fast detection speed, and capability for automation. Limitations: It cannot be used to detect defects inside metal conductors; it is generally not suitable for detecting defects smaller than 1 mm, and its spatial resolution is relatively low. 6. Fiber optic inspection equipment: fiber optic endoscopes, fiber optic crack detectors. Purpose: To detect defects on the inner surfaces of boilers, pumps, castings, cannon barrels, pressure vessels, rocket casings, and pipelines, as well as the quality of welds and fatigue cracks. Advantages: High sensitivity, good insulation, corrosion resistance, and immunity to electromagnetic interference. Limitations: It is relatively expensive and cannot detect internal defects in the structure. 7. Eddy current testing equipment: eddy current flaw detector and standard test blocks. Purpose: To detect defects such as cracks, inclusions, folds, pits, and porosity on the surface and near the surface of conductive materials, and to determine the location and relative size of these defects. Advantages: Cost-effective and simple; it can automatically align for flaw detection, requires no coupling, and the probe does not come into contact with the test piece. Limitations: It is limited to conductive materials, has a shallow penetration depth, requires reference standards, makes it difficult to determine the type of defect, and is not suitable for non-conductive materials. 8. X-ray inspection equipment: X-ray source (unit) and power supply; equipment identical to that used for gamma-ray sources is required. Purpose: To detect under-welding, pores, and slag in welds, as well as shrinkages, pores, porosity, and thermal cracks in castings; it can also determine the location, size, and type of defects. Advantages: Adjustable power, better photo quality. The radiation level is high, allowing for permanent recording. Limitations: X-ray equipment requires a large initial investment, is not easy to transport, poses radiation risks, and needs highly skilled operators and radiographers. It is difficult to detect weld cracks and lack of fusion defects, and it is not suitable for forgings and profiles. 9. Gamma-ray inspection equipment: gamma-ray flaw detectors, film holders and film, lead shielding for radiation, film processing equipment, light sources for viewing films, exposure equipment, and radiation monitoring equipment, etc. Purpose: To detect welding discontinuities (including cracks, pores, lack of fusion, under-welding, and slag inclusions), as well as corrosion and assembly defects. It is most suitable for detecting thick-wall volumetric defects. Advantages: A permanent record is obtained for future review, and the gamma source can be located within objects such as steel pipes and pressure vessels. Limitations: It is unsafe; the equipment being irradiated needs to be protected, and the exposure level and dose of the radiation source must be controlled. Degrading radiation sources need to be replaced regularly. The output energy (wavelength) of gamma sources cannot be adjusted, the cost is high, and highly skilled operators and radiologists are required. 10. Magnetic particle inspection equipment: magnet head, yoke, coil, power supply, and magnetic particles. Certain applications require specialized equipment and ultraviolet light sources. Purpose: To detect cracks, folds, delaminations, inclusions, and other defects on the surface or near the surface of ferromagnetic materials and workpieces, and to determine the location, size, and shape of these defects. Advantages: Simple, easy to operate, fast, and highly sensitive. Limitations: It is limited to ferromagnetic materials; the workpiece must be cleaned before inspection. Excessively thick coatings can cause false readings. In some applications, it is necessary to demagnetize the workpiece after inspection, and it is difficult to determine the depth of defects. It is not suitable for non-ferromagnetic materials. 11. Penetrant testing equipment: fluorescent or colored penetrants, developer, cleaning agents (solvents, emulsifiers), and cleaning devices. If fluorescent coloring is used, an ultraviolet light source is required. Purpose: It can detect defects such as cracks, folds, looseness, and pinholes in metal and non-metal materials, and determine the location, size, and shape of these defects. Advantages: Suitable for all materials ； The equipment is lightweight, and the investment required is relatively low ； Flaw detection is simple, and the results are easy to interpret. Limitations: Surface layers such as coatings, dirt, and coated metals can conceal defects, and gaps on the surface of pores can also cause false readings ； The workpiece must be cleaned before and after flaw detection ； It is difficult to determine the depth of the defect ； Not suitable for loose, porous materials. 12. Visual inspection equipment: magnifying glasses, color intensifiers, rulers, micrometers, optical comparators, and light sources, etc. Purpose: Detecting surface defects, weld appearance, and dimensions. Advantages: economical, convenient, requires few devices, and inspectors only need minimal training. Limitations: It can only detect external (surface) damage, and the inspector needs to have good eyesight. 13. Industrial CT inspection equipment: Industrial CT scanner. Applications: defect detection, dimension measurement, assembly structure analysis, density distribution characterization. Advantages: It can provide tomographic images of the test specimen along with information on its spatial position, size, and shape; the imaging is intuitive ； High resolution ； Not restricted by the geometry of the test specimen. Limitation: High equipment cost.

The inspection methods, ratios, and acceptance criteria are clearly specified in the design drawings; if you want to understand the specific methods, you should first study Articles 81 to 93 of the relevant standards, as well as Requirement 10.8 in GB150 \"Steel Pressure Vessels\".

Thank you all for your guidance! Where can I download GB150 \"Steel Pressure Vessels\"? This post was last edited by shawkay on 2009-2-17 08:41]

Question: 1. When should flaw detection be carried out? What are the inspection ratio and acceptance criteria? 2. In what situations are various flaw detection methods applied?

See: http://bbs.hcbbs.com/viewthread.php?tid=3794&highlight=150-1998

GB150 provides detailed explanations in P128

Thank you to the two people above for their help! So many feelings. . . . . . :handshake :handshake

Regarding knowledge such as the timing for flaw detection, its scope of application, and its various characteristics, in addition to studying the relevant standards, it is recommended that the original poster read some comprehensive books on non-destructive testing. Of course, professional books on non-destructive testing are meant for those who work in this field; it’s sufficient for you to have a general understanding.