Welded joints as critical regions in pressure vessels -case study of vinyl-chloride monomer storage tank

Abstract

Welded joints are analysed as critical regions in a pressure vessel in respect to structural failure due to the elastic-plastic fracture/crack growth. To assess structural integrity of pressure vessels used in chemical industry the risk based procedure has been introduced and applied in the case of a large spherical pressure vessel used as a vinyl-chloride monomer (VCM) storage tank in HIP Azotara Pancevo. The risk matrix has been used, taking into account the basic definition of risk, being the product of the probability and consequence, and applied to different regions of welded joints, having different mechanical properties, i.e. crack resistance. To estimate probability, the failure assessment diagram (FAD) has been used, as an engineering tool, defined according to the position of the operating point for different regions of the welded joint, relative to the critical point on the limit curve. Generally speaking, consequence is estimated based on pressure vessel parameters, or by detailed analysis of health, safety, business and security issues, but in the analysed case, the worst case scenario is assumed, with the highest consequence due to potential disaster for environment and fatalities. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR 33044 and Grant no. 35017]

Effect of Over-Pressure on Pipeline Structural Integrity

“…RHPP "Bajina Bašta" presents new modified plant with a very high flexibility, i.e. high guaranteed power and large amount of accumulated energy from hydro power station, [4]. One of the crucial components is the pipeline, Fig.…”

“…Namely, there is a history of welded joint failures due to proof testing, e.g. spherical pressure vessels for liquefied natural gases [4], caused by unnecessary plastic deformation acting as crack initiation and propagation mechanism. Some details are given here, and more details can be found in [3].…”

Risk Management of a Hydro Power Plant – Fracture Mechanics Approach

“…Anyhow, the aforementioned approach is a bit more descriptive than engineering. Therefore, now we introduce a special procedure for risk analysis, based on fracture mechanics concept, [8][9][10][11].…”

“…Once these ratios are calculated, one can position the point on a diagram, which can be inside the safe area, or outside it, Fig. 2 This, classical fracture mechanics approach, has been used recently to estimate risk probability, [8][9][10][11], based on simple reasoning that the closer the point is to the limit curve the larger is the probability of failure. This approach was applied successfully in several cases of pressure vessels with detected cracks, including Pressure Vessels in RHPP BB, as shown in Fig.…”

Application of Fracture Mechanics Parameters to Spherical Storage Tank Integrity Assessment

“…As explained in [1], it was decided not to repair the storage tank, because of previous experience, indicating that more damage than benefit would be made, [2,3], mainly due to unfavourable microstructure of the steel, used for tank production, [4]. Namely, more cracks were found after repair welding than before, not only because of material, but even more important, due to unnecessary overpressurizing during testing, [5,6].…”