Research on Structure Security of a Spherical Tank Under Wind and Seismic Effect

In the condition of the earthquake force and wind loads, there are many failure modes for the spherical tanks, such as the structure damage of the supports, uniform foundation settlement, displacement or upset, and the fracture of pipelines attached to the tank, etc. In this paper, more precise stress distribution of spherical tanks under wind loads and seismic force was obtained by finite element analysis. The safety assessment is carried out on a spherical tank. The weakness components of the spherical tank were found and the wind-proof performance and earthquake-proof performance of the spherical tanks could be improved.

Comparison of Strain Rate Calculation Methods for Environmental Fatigue Correction Evaluation

A Code Case for procedure to determine strain rate and Fen for environmental fatigue evaluation is under preparation in the ASME BPV Committee on Construction of Nuclear Facility Components (III). The draft Code Case is to incorporate two methods for strain rate calculation. One is based on NB-3216.1 “Constant Principal Stress Direction” that comes from the JSME Environmental Fatigue Evaluation Method. The other is based on NB-3216.2 “Varying Principal Stress Direction” that was proposed by M. Gray et al. In this paper, both methods are explained and compared by using a sample problem.

Elastic Follow-Up Factors to Estimate C(t) Under Secondary Loading

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.

Development on Predictive Maintenance Intelligent Management System of Static Equipments

The ability to forecast equipments failure is vital to reducing maintenance costs, operation downtime and safety hazards. In this paper, first, RBI application status in China is discussed. Through analyzing the existing condition of RBI technology on equipments, the necessary of dynamic risk management based on RBI is pointed out. After that, the development Status of RBI Software in China is put forward. Considering the shortcoming of these pieces of software, Static Equipment Predictive Maintenance Intelligent Management System is built by China Special Equipment Inspection & Research Institute (CSEI). The system integrates 8 core modules, including corrosion monitoring and management module, the remaining life evaluation calculation module, damage mode discrimination module, material upgrade management module, the analysis and prediction of erosion areas of the pipes module, risk analysis and dynamic updates module, safe operation of warning based on GIS module, the generation of the inspection scheme module. It provides timely the equipments operation condition information for the plant management departments, realizes the combination with plant management and condition monitoring. Finally, the scheme and the thoughts of the system are introduced in details. And the characteristics and functions of the proposed system have been demonstrated.

Guided Wave Testing: Maximizing Buried Pipe Corrosion Knowledge From Each Excavation

Excavation and Direct Examination of buried piping using conventional non-destructive examination (NDE) has been the traditional inspection approach for decades and remains the only quantitative method for piping evaluations in plants when internal in-line inspection tools cannot be used due to geometry or other constraints. This “difficult to assess” piping presents many challenges, including limited effectiveness of traditional indirect inspection tools, high cost and operational concerns associated with excavations, and the ability to evaluate only a small sampling of a piping system. Many inspection technologies exist for buried pipe assessments; however, no indirect techniques provide the ability to yield quantitative wall loss values suitable for ASME fitness for service calculations beyond what’s exposed in the excavation. An evolving technology, guided wave testing (GWT), has many applications including the ability to provide assessment information beyond the excavation. In this paper, the application of GWT for buried piping inspection will be discussed. We will review: principles behind its operation; the competitive technologies on the market; challenges for the technology; management of data within the Electric Power Research Institute (EPRI) industry standard buried pipe database (BPWorks™ 2.0); trending; case histories showing how GWT can be used to extend the knowledge gained during an excavation by screening adjacent areas for more significant corrosion than observed in the excavated and exposed area; coupling GWT results with other inspection technologies to gain an enhanced interpretation of the overall condition of the line; and how to incorporate this data into an effective structural and/or leakage integrity program as part of the reasonable assurance process.

Research on Ultrasonic Inspection of Cast Austenitic Stainless Steel Piping

Japan Nuclear Energy Safety Organization (JNES) has been carrying out the research program entitled “Nondestructive Inspection Technologies for the Cast Stainless Steel Piping” since 2009FY to comprehend the unique ultrasonic wave propagation in the Cast Austenitic Stainless Steel (CASS) and to confirm detection and sizing capability for cracks in the material by currently available ultrasonic testing techniques. The research is also intended to provide inspection staff with the fundamental information of ultrasonic wave propagation in CASS, for educational purpose. In this research program, specimens whose material, size, dimension and welding method are identical to the main coolant piping system in Japanese pressurized water reactors (PWRs) are examined. Results from the study on the capability for inspection of CASS and the unique wave propagation phenomena such as beam skewing are discussed in this paper.

Effect of Torsion on Collapse Bending Moment for 24-Inch Diameter Schedule 80 Pipes With Wall Thinning

Piping items in power plants may experience combined bending and torsion moments during operation. Currently, there is a lack of guidance in the ASME B&PV Code Section XI for combined loading modes including pressure, torsion and bending. Finite element analyses were conducted for 24-inch diameter Schedule 80 pipes with local wall thinning subjected to tensile and compressive stresses. Plastic collapse bending moments were calculated under constant torsion moments. From the calculation results, it can be seen that collapse bending moment for pipes with local thinning subjected to tensile stress is smaller than that subjected to compressive stress. In addition, equivalent moment is defined as the root the sum of the squares of the torsion and bending moments. It is found that the equivalent moments can be approximated with the pure bending moments, when the wall thinning length is equal or less than 7.73R·t for the wall thinning depth of 75% of the nominal thickness, where R is the mean radius and t is the wall thickness of the pipe.

Fatigue Performance of Stainless Steel in NPP Service Conditions

Fatigue of Niobium stabilized austenitic stainless steel (X6CrNiNb1810 mod) is studied using specimens extracted from a solution annealed and quenched primary piping material sample. This paper reports and discusses new results complementing the data published in PVP2009 and 2011, where good long life performance was demonstrated and relevance of the new design curve in ASME III was questioned. Effects of temperature and operational loading sequences are in focus here. A typical case with steady state operation between fatigue cycles was roughly simulated in periodically interrupted tests. An extension of fatigue life due to hardening during the holds in elevated temperature was demonstrated and here we show that the hardening effect is generic. It occurs also in isothermal conditions, where straining and holds are both at 325 °C, irrespective of the phase within a cycle, where the hold is introduced, and also for other austenitic steel grades. Fatigue assessment based on standard fatigue data seems to underestimate fatigue performance of materials subjected to typical thermal transients in nuclear piping during operation.

Design of a New Bearing on the Large Net Shell Roof Tank

The structure of the plate rib roof can’t meet the need of the constantly enlarging storage tanks, thus more steel/aluminum net shell roofs have been used on the large storage tanks. The bearing between the roof and the tank wall is a key component, because it directly affects the strength and stability of the net shell roof. In this paper, a new type of net shell roof bearing structure is proposed in order to relieve the stress on the bearing and the net shell roof. The proposed structure has several features compared with the existing bearings: the net shell roof with the new bearing can allow a certain amount of radial displacement, and the bearing can also rotate within a certain angle. According to the actual loading status, strength and stability analysis of the overall net shell roof and the bearing’s partial structure are carried out respectively. The overall model of the net shell roof is established by ANSYS, and different boundary conditions are defined on the roof under two working conditions of “full-span live load” and “half-span live load”. Then the overall static strength calculation and stability analysis of the roof are completed. Based on the results of the overall analysis, the strength of the bearing’s partial model is analyzed in ANSYS Workbench. Research shows that when the net shell roof is under load, the roof is allowed to make radial displacement and the bearing to make angular displacement. Thus the burden on the bearing and the net shell roof is relieved, and the strength and stability of the overall roof meet the requirements. Moreover, many regions of the bearing can share the horizontal force, which helps to reduce the load on the bolts and improve the safety of the bearing structure. And the strength of the bearing meets the requirements.

Interaction Effect Evaluation of Multiple Through Cracks in Ductile Fracture Process

Study on the interaction effect of multiple cracks on the collapse load during ductile crack growth processes is important for the integrity evaluation of nuclear structure. The ductile fracture processes are well studied numerically by using Gurson’s constitutive equation and taking into account of void growth during plastic deformation. In this study, two through cracks are assumed to exist in a flat plate in tension and the interaction between two cracks is studied. The initial crack length, horizontal distance and vertical distance between two cracks are changed systematically. The interaction behavior between two cracks is studied precisely. Criteria to evaluate maximum load in the ductile fracture processes are discussed. The present study found H/l criteria can estimate the maximum load reasonably, and also the consideration of the effect of the horizontal distance between two cracks in H/l criteria may improve its estimation more reasonable. The effects on maximum load by changing the horizontal distance between two cracks are studied.