Non-destructive testing of welds on flanges with necks

The ultrasonic testing (UT) method can be used as a substitute for radiographic testing (RT). If conditions permit, magnetic particle testing (MT) or penetrant testing (PT) can also be considered as supplementary methods. When selecting an alternative method, please ensure that the chosen method meets the detection standards as well as the sensitivity and accuracy requirements of the project. .

In GC1-class pressure pipelines, when radiographic testing (RT) of the weld between the pipe and the necked flange cannot be carried out due to on-site constraints, the following alternative testing methods may be employed in accordance with relevant standards, provided that the testing capability of these alternative methods is equivalent to that of RT or has been approved through technical evaluation: 1. Ultrasonic testing (UT). Standard reference: In accordance with \"Non-destructive testing of pressure equipment – Part 3: Ultrasonic testing\" (NB/T 47013.3). Applicability: UT is effective for both volume defects (such as pores and inclusions) and surface defects (such as cracks and lack of fusion), and is particularly suitable for thick-walled welds. Attention should be paid to the impact of groove shape and material grain size on testing. Additional requirement: It is recommended to use phased array ultrasonic testing (PAUT) or TOFD (time-of-flight diffraction) to improve the detection rate, and the assessment should be carried out by personnel with Level III qualifications. 2. Phased Array Ultrasonic Testing (PAUT) Advantages: It enables scanning from multiple angles, covering the entire weld area; the data can be archived for subsequent review, and it is suitable for complex geometric structures. Standard reference: NB/T 47013.15 \"Non-destructive testing of pressure equipment – Part 15: Phased array ultrasonic testing.\" 3. Characteristics of Time-of-Flight Diffraction Ultrasonic Testing (TOFD): It provides accurate measurement of defect height, is suitable for detecting defects in the middle of welds, and is often used in combination with pulse-echo testing. 4. Penetrant testing (PT) or magnetic particle testing (MT): Suitable for use as a complement to surface defect detection; it needs to be used in combination with UT. PT: Suitable for surface opening defects in non-magnetic materials (such as stainless steel) (NB/T 47013.5). MT: Suitable for surface and near-surface defects in ferromagnetic materials (NB/T 47013.4). 5. Technical verification and approval: If non-standard methods are used, it is necessary to conduct a joint verification by the design unit, the owner, and the inspection party in accordance with the requirements of the \"Code for Pressure Piping – Industrial Piping\" (GB/T 20801) or the \"Rules for Periodic Inspection of Pressure Vessels\" (TSG 21), and obtain approval from the regulatory authorities. Precautions: Detection ratio: The detection ratio of the alternative method must not be lower than the original RT requirement (usually 100%). Personnel qualifications: Testers must hold a Level II or Level III certificate for the corresponding methods. Process evaluation: Process verification must be carried out prior to testing to ensure that all possible types of defects are covered. It is recommended that the final design take into account specific operating conditions (such as material, wall thickness, and properties of the medium), and comply with the relevant standards applicable to the project (such as GB/T 20801, ASME B31.3, etc.).

In a nutshell, use TOFD for ferromagnetic materials. For stainless steel, use ultrasound with special probes.

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