Research on the welding technology of fillet weld

  • Detail

Research on the welding technology of the fillet weld of the pipe socket on the barrel of boiler and pressure vessel

the boiler barrel is a very important part of the boiler products. The welding quality of the boiler barrel has always been the most concerned by the boiler manufacturers, but in the past, people generally focused on the longitudinal seam and circumferential seam of the boiler barrel, as well as the centralized downcomer and water supply pipe Φ 133mm and Φ The welding of 159mm outlet pipe socket has not attracted enough attention, but with the continuous improvement of users' requirements for socket welding, the welding of drum socket has become the focus of attention in the boiler industry

in the past, in 220t/h and 420t/h drums Φ one hundred and thirty-three × 12. When welding the outlet pipe socket, the structural type of full penetration is selected. The welding adopts the inner hole argon arc welding back cover and manual electric arc welding cover. After welding, only the surface magnetic particle flaw detection is carried out. However, after the ultrasonic flaw detection is adopted, the one-time qualification rate of the fillet weld of the drum socket of two consecutive products is really unacceptable, which immediately attracted everyone's high attention. After the analysis of the physical anatomy, It is found that the welding defects of the drum socket are mainly distributed at the root of the inner hole argon arc back welding and the bottom of the manual welding seam, most of which are distributed in a whole circle, and the properties of the defects are incomplete penetration, slag inclusion and porosity

judging from the current production situation, the existing equipment, the processing accuracy of pipe sockets, the specific size of welding grooves, and the operating skills of welders can not meet the requirements, so the welding quality is difficult to meet the qualified standard of ultrasonic flaw detection. According to the analysis of the actual situation of the welding of the pipe seats of the first two boiler drums, we found that the blunt edge size of the pipe seat is too large or uneven due to the wall thickness, ovality tolerance and processing accuracy of the pipe seat. During the assembly of the pipe seat, due to the lack of careful control, the amount of misalignment is too large, resulting in the incomplete penetration and penetration of the inner hole welding at the root of the pipe seat, while the manual welding defects at the bottom of the pipe seat are mainly due to the small groove spacing, It is caused by factors such as improper operation of welders and poor operating environment

II. Improvement of pipe socket welding quality

1. Change the design groove type and complete the welding procedure qualification

due to the 1000t/h and 2000t/h drum Φ one hundred and fifty-nine × The groove types of 20 pipe sockets are all j-grooves with incomplete root penetration, which have been introduced by Johnson Matthey from CE company of the United States. It is expected that the sales of its catalyst business will slow down in the next few years, and it is difficult to meet the requirements of ultrasonic flaw detection. According to the requirements of 220t/h and 420t/h drums Φ one hundred and thirty-three × 12. According to the welding experience of the outlet pipe socket, the j-groove with incomplete penetration at the root is changed to the d-groove with full penetration, and the groove type meeting the requirements is redesigned, and the process evaluation is carried out again. In order to ensure the smooth progress of production, we have designed a new inner hole argon arc welding equipment, including the characteristics of the data testing machine, such as conductive rod, conductive nozzle, external protective gas sleeve, positioning mandrel and other tooling. The welding groove is also newly designed. In order to test the rationality of the redesigned tooling and welding groove, the process department has successively prepared nearly 100 pipe seat samples with the cooperation of the production workshop, adjusted the specification parameters and the specific size of the groove type while welding, summarized the experience while welding, and completed the test and process evaluation in a short time, meeting the normal progress of production

2. Refine the measures to improve the first-time pass rate of the fillet weld of the tube seat, which Airbus and Boeing are very interested in graphene at present.

in view of the extremely low first-time pass rate of the fillet weld of the tube seat, the relevant personnel of the process, workshop, flaw detection, standard and design have been organized for several times to have a consultation, and together with the workshop operators, the causes of the defects have been analyzed and discussed. According to the characteristics that the defects are mainly concentrated in the root and the whole circle, A new process plan has been formulated, and the following measures have been taken during the welding of the pipe seat of the third drum:

① for the excessive groove spacing, these enterprises basically obtain a small market by reducing profits. When processing the groove, there are often cases that the processing is not in place, so it is decided to change the groove angle on the drum from the original 30 ° to 15 °, and the size of the groove basin mouth must meet the size required by the drawing

② for the situation that the blunt edge size is too large or uneven, it is decided to bore all the inner holes of the pipe seat from the third set, and put forward higher requirements for the processing requirements of the pipe seat. The wall thickness of the pipe seat is appropriately thickened to meet the needs of internal boring

③ in view of the poor electrode transportation and difficult swing during manual welding, it is decided to manually weld the first layer from the original Φ 4.0 all welding rods are changed to Φ 3.2 welding rod

④ in view of the excessive misalignment, the positioning mandrel is used for assembly spot welding, and the longitudinal and circumferential deviations of the pipe seat are not assessed temporarily, so as to meet the needs of inner hole argon arc welding

⑤ disclosure shall be made to the welder before welding. During the welding process, the process personnel shall go to the site for follow-up and guidance to further master the first-hand information. The workshop will change the original production cycle from 2 days to 7-10 days to ensure quality

after 10 consecutive days of careful welding, the one-time welding qualification rate of the third boiler tube base was finally increased from 3 to 31 for the first set and 9 for the second set, but the qualification rate was still only 41.9%, which undoubtedly hit the confidence of welders and made many people wonder whether ultrasonic flaw detection can be used after tube base welding. With the care and support of the company's leaders, the process department and the production workshop cooperated to analyze the defects of the third drum socket, carefully observed and studied three pipe joints on the product, and let the operating welders watch together, so that the welders have an intuitive understanding of the location and nature of the defects. For this reason, we also organized the technicians to communicate with the welders. Through the communication, the process department fully listened to and analyzed the opinions of the welders, and made the following modifications to the welding process:

① change the original process of preheating into local preheating, so as to improve the operating conditions of the welders

Copyright © 2011 JIN SHI