I would appreciate it if experts could share their insights regarding the problems encountered during the actual construction of chemical plants.
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I. Case Background: At the beginning of March 2017, a fertilizer factory carried out its annual major maintenance. One of them is a high-pressure steam pipeline that has been in use for 12 years, with a base material of 12Cr1MoVG and specifications of Φ480×42 mm. The fertilizer plant commissioned a third-party testing company to conduct TOFD testing on the welds of that pipeline. The test results showed: \"Microcracks of varying degrees were present in the weld and heat-affected zone.\" ”Subsequently, the construction team and the relevant technical staff from the fertilizer factory worked together to develop a repair plan, involving partial repair of the defective welds or complete cutting of them. After the pipeline was repaired, it passed all TOFD inspections. The pipeline is now back to normal operation. The construction unit recovers and stores the welded joints of the overall pipe cuts. II. Questions for experts and scholars: At present, it is planned to conduct physical and chemical property tests on the recovered and preserved welded joints. Before conducting further physical and chemical tests, I would like to hear the opinions and suggestions of experts and scholars regarding such tests. Thank you for this!
This post was last edited by nj1952 on 2017-7-6 at 18:49. Determining the degree of microstructural aging and macroscopic property degradation of materials during their service life is of great significance for ensuring the safe and stable operation of existing equipment and pipelines. The samples should be subjected to: (1) chemical composition analysis. Samples from the base material and the welds are taken respectively for chemical composition analysis, in order to determine whether the material meets the standard requirements. (2) Hardness measurement (taking samples longitudinally along the sample): a. Changes in hardness in various areas such as the base material, welds and their heat-affected zones, as well as cracks ； b. The change in hardness of the material in the thickness direction, measured from the inner wall to the outer wall. (3) Metallographic analysis: a. Comparison of the metallographic structure of the base material, welds, their heat-affected zones, cracks, and other areas with the standard patterns for the material ； b. When viewing from the inner wall to the outer wall, the material structure is in the thickness direction of the wall. Regarding the above two inspections: changes in tissue morphology, changes in phase composition, coarsening of carbide phases, and changes in phase structure. (4) Assessment: Based on the inspection results, a comprehensive assessment is conducted of the degree of material aging and deterioration, and preventive measures are proposed. (5) The standards referenced are DL/T 438-2016 \"Regulations for Metal Technical Supervision in Thermal Power Plants\", DL/T 773-2001 \"Grading Standards for Spheroidization of 12Cr1MoV Steel Used in Thermal Power Plants\", DL/T 884-2004 \"Technical Guidelines for Microstructural Inspection and Evaluation in Thermal Power Plants\", and GB/T 13298-2015 \"Methods for Inspecting Metal Microstructures\"