Engineering Critical Assessment Of Jacket KTY Node And Its Software Development

In the offshore oil and gas industry, jacket platform is one of the most widelyused platforms. The structure of the jacket contains a lot of great thickness KTY pipewelded joints, which are the weak link of the jacket structure. Post-weld heattreatment is often used to reduce residual stress level and improve the microstructure，so as to improve the ability to resist brittle fracture and fatigue of the structure in thefield of marine engineering. However, in recent years, it was found that the post-weldheat treatment may not be able to improve the fracture toughness of thicknessstructure in the engineering practice. At the same time, it is hard to do post-weld heattreatment in the KTY nodes of the jackets. Therefore, evaluating the structuralintegrity by ECA technology based on the theory of fracture mechanics anddiscussing whether they are exempted from the post-weld heat treatment receivedwidespread attention of the related industry.In this paper, according to FITNET and BS7910standards, we have a furtherstudy about the fracture toughness data processing of K/T/Y nodes, the calculation ofstress intensity factor, the formula for limit load and hot spot stress, then develop thefracture assessment software of KTY nodes of the jackets based on VB.NET platform.In the process of software development, the idea of modular programming is adoptedand the different steps and calculation contents of the fracture assessment of KTYnodes are written to the corresponding modules. According to the calculating contents,the corresponding modules are called in the main function, which reduces thecomplicated degree of the codes and provides a good foundation for revise or updatethe software.Fracture assessment for the specific project is performed with the developedsoftware to get the limit of crack sizes of the welded joints and the critical CTODvalues corresponding to different crack sizes, and contrasting the results with thecalculation results of crackwise developed by TWI and based on BS7910to test theaccuracy of the software. In addition, fracture toughness of FCAW welded joint ofDH36steel used in marine structures is studied in this paper. Results show that thejoint has excellent toughness, CTOD characteristic value of welding is0.2791mm and CTOD characteristic value of HAZ is1.0523mm.,which are both larger than thespecified minimum value0.15mm of DNV-OS-C401. Meanwhile, the owndevelopment ECA software is used to get the critical CTOD value corresponding todifferent crack sizes, which provides strong data support for whether the practicalproject would be exempt from post-weld heat treatment.