Research On Safety Assessment Of Hydrogen Storage Pressure System

Hydrogen Storage Pressure System is a small device used to injection, storage and transfer of hydrogen gas. In life cycle, the safety of product is focus of attention. Pressure System has a complicated structure and many welds, so structure flaws are unavoidable. In regard to these flaws which may be found in process of manufacture or operation, we can follow the principle of "Fitness for Service" and take fracture mechanics theory to detect and analyze, then assess the product's safety. It is a rational and effective method for engineering application. FAD(Failure Assessment Diagram) method based on J-integral theory is a international mainstream way to assess safety of structure with flaws, because of its precise theorization and fitness for failure modes effect analysis. This theory is the base of the research on safety assessment of Hydrogen Storage Pressure System.In this paper, following the standards of BS7910, SINTAP and GB/T 19624, and depending on characteristics of Hydrogen Storage Pressure's structure, manufacture, materials and loads, the procedure and items of safety assessment were drawn up firstly. Secondly three research works were made. They are flaws detecting and characterizing, performance parameter of material and solving of structure stress. Finally, FAD was established depending on Ainsworth FAC(Failure Assessment Curve) method, two general FACs and plastic limit rule of GB19624 and BS7910. Various assessing points of different flaw parameters were calculated and drawn in FAD. So the conclusion of safety to Hydrogen Storage Pressure System was made. On this basis, the safety factor and the limit loads was calculated. The main conclusions of this article are as follows.The main flaws of the Hydrogen Storage Pressure System is Lack of Penetration(LOP). It is characterized to rectangular section circumferential notch for the need of conservatism and operability of practical projects. FeCrNi Austenitic Stainless Steel is possessed of good strength, plastic and fracture toughness, but plastic and fracture toughness will be decreased after hydrogen charging. Performance of the region of electron beam welding is the same as base material on the whole, and Failure mode is plastic instability. The maximum equivalent stress is in the region of LOP bottom margin under pressure and centrifugal load environment. The maximum equivalent stress increases with the increase of flaw depth, and decreases with the increase of flaw width. The depth of LOP is primary influence factor to maximum equivalent stress because of notable stress concentration effect. Deep narrow notch should be controlled and eliminated. When the depth of LOP is less than 1.5mm(60% shell thickness), the structure is safe. The safety factor is 1.9 to 4. Structure fail mode is plastic instability. After long-time hydrogen storage, the fracture toughness decreases and flaw depth increases. Failure mode converts to elastic-plasticity fracture. Structural strength will get close to safety boundary when centrifugal load increase. On condition that depth of LOP is 1.5mm and width of LOP is 0.1mm, structural strength will reach critical state under 190g centrifugal load while using yield stress for Lr, or reach critical state under 270g centrifugal load while using flow stress for Lr.The research on safety assessment of Hydrogen Storage Pressure System is a system engineering work. It covers knowledge of many subjects like manufacture, Nondestructive Testing, material and mechanics. This research has many deficiencies because of the limitation of our ability and time. For example, thermal stress of welding region, the matching of weld and base material, the exact solutions to K under non-uniform stress distribution, and date dispersivity in practical model were not taken into account in this paper. It will be considered at follow-up work.