【Weekly Topic】What are the items for random inspections of on-site welding quality in boilers? (All participants receive a financial reward)
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This post was last edited by salesment on 2011-4-7 08:58. A newly installed 670/17.4-M power station boiler has the following main technical parameters: rated evaporation capacity of 670 t/h, superheated steam outlet pressure of 17.4 MPa, drum operating pressure of 18.67 MPa, and reheat steam outlet pressure of 3.8 MPa. Material for superheater tubes: 20G for low-temperature superheaters ； Screen superheater 12Cr1MoVG ； High-temperature superheater 10Cr9Mo1VNb(T91). Please answer: (1) What are the items for random inspections of the on-site welding quality of the low-temperature superheater, screen superheater, and high-temperature superheater during supervision and inspection? (2) The following are some details of the installation procedures provided by the installation unit. Please point out the errors and correct them. ① Radiographic or ultrasonic testing of the on-site welded joints in the low-temperature superheater is carried out on 10% of the total number of joints ； Radiographic or ultrasonic testing of the field-welded joints of the screen superheater and high-temperature superheater is carried out on 25% of the total number of joints. ② If non-conforming defects are found in the aforementioned welded joints, supplementary flaw detection inspections at twice the number of random samples shall be carried out. If the supplementary inspections still fail, flaw detection testing should be conducted on all joint connections. ③ Hydraulic test pressure: Primary steam system (boiler body): 1.25×17.4=21.75 MPa; Secondary steam system (reheater): 1.25×3.8=4.75 MPa. ④ The water level gauge is only used in the normal-pressure hydraulic test, not in the overpressure test. ⑤ After the hydrostatic test, the system undergoes an air pressure test at 0.5 MPa.
(1) Items for spot-checking of on-site welding quality: (3 points) ① Spot-check the quality of groove preparation at the welding joints (during on-site processing)； ②Randomly inspect the visual quality of welded joints ； ③Random inspection of the qualifications of on-site welders ； ④Inspect no less than 20% of the negatives, with a focus on those before and after repair, to check the quality of the negatives, the accuracy of defect assessment, and the quality of the welds as shown. For screen superheaters and high-temperature superheaters, the following items should be added: ① Conduct non-destructive testing on no less than 1% of the alloy steel weld joints through random on-site inspections ； ② If necessary, conduct random hardness tests on the heat-treated welded joints and heat-affected zones ； ③ Random spectral analysis of the welded joints shall be conducted, with a sampling rate of not less than 1%. (2) Judgment and correction of errors: (3 points) ① The inspection ratio for the low-temperature superheater is incorrect. It should be changed to: Radiographic or ultrasonic testing of the on-site welded joints of the low-temperature superheater shall be carried out on 25% of the total number of joints ； ② Error. It should be changed to: If the supplementary inspections still show non-compliance, flaw detection tests should be conducted on all butt joints welded by that welder. ③ Error. It should be changed to: The test pressure for the primary steam system (the boiler itself) is 1.25 times the operating pressure of the steam drum: 1.25×18.67=23.34 MPa. The test pressure for the secondary steam system (the reheater) is 1.5 times the operating pressure of the reheater: 1.5×3.8=5.7 MPa. ④ Correct. ⑤ Error. It should be changed to: Before the hydrostatic test, the system undergoes an air pressure test at 0.3 MPa.