Study on Key Parameters of Two-Stage Pressure Reducing Valve for 70MPa Hydrogen Supply System

With the increase of endurance mileage, 70MPa hydrogen supply systems are used more and more widely, in which pressure reducing valves are the key component. The flow field and the key parameters of 70MPa two-stage pressure reducing valve for hydrogen are studied in this paper. The two-stage pressure reducing valve with cone and flat valves is simplified to two-dimensional model, which is used in condition of high pressure difference with medium of hydrogen gas. Based on NIST real gas model and state equation of modefied Bennedict-Webb-Rubin (BWR), flow field simulation model is developed. A stepwise initialization method for convergence of calculation is proposed in the paper. The numerical simulations for the flow in two-stage pressure reducing valve are carried out. A set of structural parameters is obtained, which is reasonable for 500km hydrogen fuel cell electric bus.

Design and Testing of an Explosively Loaded Pressure Vessel System for Proton Radiography

A containment system is being developed to expand the capability of proton radiography of small-scale shock physics experiments at Los Alamos National Laboratory (LANL). The detonation of high explosives (HE) drives materials to extreme loading conditions, which are imaged using a proton beam and an imaging system. A qualified confinement and containment boundary needs to exist between a high-explosive experiment and the environment, and is comprised of the Inner Pressure Confinement Vessel (IPCV) and the Outer Pressure Containment Vessel (OPCV). The Inner Vessel is designed to the criteria of the ASME Boiler and Pressure Vessel Code, Section VIII, Division 3, Code Case 2564. The vessel contains an Experimental Physics Package, fragment mitigation structure, and radiographic windows. The windows need to minimize radiographic blur contribution (thin, radiographically transparent material such as Beryllium) over the field of view for imaging, but also need to maintain the pressure boundary during and after the dynamic event. Further, the vessel covers need to seal before, during, and after the experiment . In addition, the covers have miscellaneous feedthroughs, to enable high-voltage signal (for HE detonator), instrumentation and control signals (e.g. valves, pressure and vacuum gauge, optical fibers). We present the preliminary design, analyses, and testing of the Inner Vessel components.

Fracture Mechanics Integrity Assessment of Stud Bolts Subjected to Cathodic Protection

Exposure of metallic parts to cathodic protection (CP) in sea water leads to production and diffusion of atomic Hydrogen into the metal matrix. Absorption of atomic Hydrogen into the metal could lead to hydrogen embrittlement (HE). In order to study the influence of stresses related to HE, FEA and Fracture Mechanics (FM) assessments were performed on a stud bolt threaded geometry. Effects of manufacturing tolerances, interface between nut and stud bolt and a defect in the form of a semi-circular crack placed in highest stress location of a thread root were also considered. Investigations of stress profiles when tension or bending are applied in test samples for measurement of HE threshold were also done, aiming at showing gaps on ASTM F1624-12 [1]. Tolerance assessment shows a relative maximum increase of 260% of nominal linearized membrane plus bending (NLMB) stresses regarding the nut runout [2] and for the proprietary nut geometry, such relative increase drops to 126% of NLMB stresses. Highest Hydrogen concentrations could be observed in the neighborhood of the first loaded thread root. FEA of cracked geometry shows that Hydrogen concentration could increase by around 283% around the crack tip, when compared to stud bolt in unloaded condition. Integrity assessment according to API 579-1 [3] or BS 7910 [4] and tests conducted according to ASTM F1624-12 [1] show less conservative results.

Investigation on Typical Failure Mode of High-Pressure Hydrogen Cylinders for Vehicles

Compressed hydrogen gas cylinders with an aluminum liner and carbon fiber wound are currently used as main storage containers in hydrogen fuel cell vehicles region, such cylinders filled with hydrogen gas have the advantages of light weight, high pressure resistance etc. Owing to the fact that cylinders are generally pressurized to 35MPa-92MPa, they may have a vital impact on life and property if failure of the cylinder occurs. For risk prediction, a series of comparative experiments have been carried out and some tests results have been analyzed, where the typical failure mode of such hydrogen cylinders are summarized as irreversible failure, recoverable failure and preventable failure. Irreversible failure refers to the failure mode such as leakage, rupture and penetration, etc, which could cause the cylinder not to restore its original function. Recoverable failure includes thread damage, security attachment startup and so on. The original function of the cylinder could be repaired by repairing the thread and replacing the safety accessories. Preventable failure would be found under the condition such as load at extreme ambient temperature for a long time, filament wound layer cracking caused by surface damage, chemical corrosion and serious impact etc, which could decrease the cylinder strength. In case of existing the preventable failure, cylinders should be monitored in use and the service life would be reduced.

Continued Study on the Effect of Mean Stress on Ground Storage Vessels for Hydrogen Fueling

The use of high pressure vessels for the purpose of storing gaseous fuels for land based transportation application is becoming common. Fuels such as natural gas and hydrogen are currently being stored at high pressure for use in fueling stations. This paper will investigate the use of various levels of autofrettage in high pressure storage cylinders and its effects on the life of a vessel used for hydrogen storage. Unlike many high-pressure vessels, the life is controlled by fatigue when cycled between a high pressure near the design pressure and a lower pressure due to the emptying of the content of the vessels. There are many misunderstandings regarding the need for cyclic life assessment in storage vessels and the impact that hydrogen has on that life. Some manufacturers are currently producing vessels using ASME Section VIII Division 1 to avoid the requirements for evaluation of cylinders in cyclic service. There are currently rules being considered in all of ASME Section VIII Division 1 and Division 2, and even potentially for Appendix 8 of ASME Section X. Recommendations on updating the ASME codes will be considered in this report.

Proposal of Use of Mises Criteria for Elastic Analysis in Appendix 9 of ASME Section VIII Division 3

The stress evaluation by elastic analyses for protection against plastic collapse in Appendix 9 is based on maximum shear stress theory (Tresca theory). On the other hand, the stress evaluation by elastic-plastic analysis and design equations by flow stress for design pressure for cylindrical shell and spherical shell in KD-221 is based on distortion energy yield stress theory (von Mises theory). With regard to materials with low and intermediate Sy/Su, in particular the primary stress evaluation based on Tresca stress for elastic analysis in current Div.3 is much more conservative than that based on flow stress equations similar to elastic-plastic analysis from experimental results. In Section VIII Div.2, von Mises yield criterion is used for stress evaluation for elastic analysis because it matches experimental results more closely than Tresca yielding criterion and is also consistent with plasticity algorithms used in elastic-plastic analysis. Therefore in Div.3 von Mises stress should be used for elastic analysis in the same way as in Sec. VIII Div.2. For materials with high Sy/Su, the primary stress evaluation based on von Mises criterion for elastic analysis is less conservative than that based on flow stress equations similar to elastic-plastic analysis because of a difference in design factor of 1.5 for elastic analysis and 1.732 for flow stress equations. Therefore, we propose using von Mises criterion for protection against plastic collapse with design correction factor using Sy/Su in Appendix 9 in order to remove excessive conservativeness for materials with low and intermediate Sy/Su. The validity of this proposal is shown in this paper.

Subsea Flanges, Comparison Between Conventional API 6A Type 6BX Flange and SPO Compact Flange Designs

The API flange design is a well-known commonly used solution. The flange concept was developed in late 1920s and 1930s by Waters and Taylor. The design methodology of the flange was published in 1937[1], well known as the “Taylor Forge method”. This is still the basis of the present ASME flange calculation. The design is based on the simple elastic principles and linear stress analysis/calculations. The conventional flange type dimensions are described in API 6A [2] and analyzed in API 6AF [3] and 6AF2 [4]. On the other hand, the Compact Flange concept was presented first by Webjørn in 1989 VCF joint [5]. It is based on plastic theory equations and plastic collapse capacity. In 1989 the initial concept was adopted by the Steel Product Offshore (SPO) company for oil industry by equipping flange with HX seal ring for raiser and subsea use. After that a topside budget version (with simpler IX seal ring) was prepared by SPO and presented on PVP 2002 conference [6][7][8]. The Compact Standardized and simplified flange design with IX seal ring is defined and described in ISO-27509 [9]. As for today, along ASME B.16.5 [10] pressure classes range, SPO CF 5K, 10K, 15K and 20K rating flange classes were designed and are in use. The main advantages for CF design are reliability, low weight/compact dimensions and static behavior compared to the conventional design. The design is already well known and commonly uses for European region (mostly Norway). Despite its benefits, CF is still rare outside Europe region. A comparison between those two different concepts will be presented in this paper followed by the examples and Finite Element Analysis (FEA). In case of FEA the Compact Flange design is more suited to the plastic collapse analysis than to elastic stress evaluation as it is for API, therefore comparison between different FEA approaches will be studied in addition.

Stored Elastic Strain Energy of Pressure Vessels and Their Consequential Effect on High Speed Projectiles

The technological development of pressure systems is closely associated with the growth of various technologies in petrochemical, oil services, power, and aerospace industry. The closed boundary system such as a pressure vessel, pipe, tube, and barrel, in which an unforeseen ill design or installation imbalance between interior and external pressure conditions can result into a hazardous situation, and an unexpected catastrophic failure of the system. These accidental failures most likely lead to escalation of events due to hazardous projectiles impacting the surrounding environment. The kinetic energy contained in the projectile are dependent on the size of pressure vessel, density of the fluid (gas or fluid), and pressure of contained media. Numerous studies have shown the relationship between the contained media within the pressure vessel and fragment velocity. However, a gap still persists in regard to the effect of elastic strain energy of the vessel itself on the projectile velocity. In this study, we study the correlation between elastic strain energy of a pressure vessel and the projectile velocity. Several parameters, such as contained media, internal pressure, fluid nozzeling, volumetric expansion with respect to diameter and thickness of pressure vessel were considered to investigate their influence on the level of consequence in an accidental event. The findings of this study aim to provide important guidance for the design and operation of high pressure systems and testing.

Hydrodynamic and Structural Simulations and Measurements in an Explosively Loaded High-Pressure Vessel

A containment and confinement pressure vessel system is under development to expand the capability to perform small explosively driven physics experiments at the Proton Radiography facility at Los Alamos National Laboratory (LANL). Two barriers of this vessel system are the Inner Pressure Confinement Vessel (IPCV) and the Outer Pressure Containment Vessel (OPCV). To achieve high spatial resolution of proton images, radiographic windows (covers) of the Inner Vessel are located extremely close to the experiment containing high explosive (HE). While the Inner Vessel is designed to meet the ASME Boiler and Pressure Vessel Code, Section VIII, Division 3, Code Case 2564 criteria, the small separation between the explosive and the pressure-retaining boundary presents a unique requirement for designing dynamically loaded vessels. We present numerical simulations of HE detonation in the Inner Vessel for several HE configurations. Eularian hydrodynamic code is used to calculate pressure-time history on the inner vessel surface. The pressure-time loading is then imported into a Langrangian structural model, and high-fidelity structural dynamic simulations are performed to obtain stress and strain as functions of time. Simulations are compared against experimental measurements from dynamic testing. Dynamic experiments are conducted in a low-fidelity (LoFi) vessel prototype, to measure the pressure and strain in regions of interest in different vessel locations (body, radiographic windows, covers).

ASME Sec VIII Div. 3 and API TR 17TR8 Verification and Validation Methodology for Subsea Connectors

Wellhead connectors form a critical part of subsea tree production systems. Their location in the riser load path means that they are subjected to high levels of bending and tension loading in addition to the internal pressure and cyclic loading. As such, they are essential equipment and various industry standards influence their design and qualification requirements. This is particularly true of High Pressure High Temperature (HPHT) equipment where heavier blowout preventers and larger rigs are required to deal with this challenging environment. Industry standards that cover wellhead connectors include a range of verification techniques based on different base analysis codes each of which uses different factors to determine a design margin. Some of the different methods may therefore lead to different actual design margins on the connector from failure to a safe working load. In order to meet the requirements of the industry and to ensure product integrity a HPHT verification and validation methodology based on API 17TR8 [1] and ASME VIII Div. 3 [2] is presented here for subsea wellhead connector designs. The results from a series of verification and full scale validation tests for a subsea wellhead connector family are presented and discussed. The results prove the design margins of the connectors using this methodology and allow for a full understanding of the limits and true performance of the design.