Verification of Stress Model in Dissimilar Materials of Varying Cladded Pipes Using a Similar Cladded Plate Model

This paper continues previous research performed by the authors on the modelling of dissimilar welded joints with varying clad thicknesses. This study aims to validate the use of a clad plate model as a replacement to the previous clad pipe model. To fulfill the hypothesis of the study, possible deformation or angular shrinkages occurring at weld joints have been simulated using a commercial finite element software. In parallel, angular shrinkages have been validated using the experimental data with the underlying concept of Gaussian transformation of plates into pipes. The welding of the two dissimilar materials has been carried out in-house with the aid of a Tungsten Arc weld with dynamic measurement of the temperature profile in the vicinity areas of the welding track using high temperature thermocouples. It was discovered that for each deformation angle of 11.5°, 22.75°, 40° and 45°, there exists shrinkage of the order of 0.01mm. Transient temperature curves have been generated for different cladding thicknesses (of stainless steel and mild steel). Comparison of the measured data versus the simulation results shows close agreement.

Fatigue Behavior of Metallic Pipes With Through-Wall Corrosion Damage Repaired With Bonded Metallic Patches

Composite repair systems have been gaining each time more space in industry, especially when it comes to repairing through-wall defects in pipes. They are simpler to apply, have no costly downtime and provide lower risks to the environment when compared to metallic repairs. ASME PCC-2 and ISO 24817 standards are responsible for defining the parameters necessary to a successful repair, however neither of them addresses a very common practice in such repairs, which is the addition of a bonded metallic patch over the defect. Several companies are adepts of such practice and it has already been proven that is actually the metallic patch and not the composite sleeve itself that sustains most of the load applied on the repair, and for that reason it becomes necessary to conduct further studies regarding the behavior of the patch alone. One important issue is to understand why the strength of similar repairs due to operation errors with very similar amplitude of pressure transients seems to vary randomly, with unexplained early failures. The present paper is concerned with an experimental study about how pressure variations can generate cyclic inelastic strains in the pipe, which can weaken the adhesion between pipe and patch, leading the repair to fail prematurely.

The Research on the Stress Analysis of Overhead Steam Pipeline

Industrial production is accompanied by a large number of physical and chemical reactions. Steam, whose heat was often used to carry out various production activities, is a common medium in industrial production. Steam pipeline has the characteristics of high temperature and high pressure. The pipeline has been in service at high temperature for a long time, which is prone to metal material degradation such as graphitization and spheroidization. Cause of the expansion of steam pipeline after heating, the natural compensation structure is generally adopted in the whole plant pipe gallery. In recent years, the accidents of steam pipeline occurred frequently, so we must pay more attention to the safety of steam pipeline. Periodic Inspection Regulation for Industrial Pressure Piping (TSG D7005-2018) explicitly requires stress analysis and checking in some cases to determine the safety of the pipeline. The traditional inspection method adopts a random sampling model which has the risk of over inspection and missing inspection. Taking a whole plant steam pipeline as an example, this paper introduced the stress check criterion of pipeline in ASMEB31.3.The model of the pipeline was established by the software, and the stress state and displacement of each node of the pipeline were calculated. According to the calculation results, a targeted inspection scheme was established and effective data support was provided for the regular inspection of steam pipeline.

Temperature Prediction of a Used Nuclear Fuel Cask With Different Gas Backfills

In this work, a two-dimensional (2D) geometrically-accurate model of the TN-32 cask is generated in ANSYS/Fluent to investigate the effect of backfill gases and their pressures on the peak cladding temperature (PCT). This model is similar to the cask being used in high-burnup (HBU) spent fuel data project lead by the Electric Power Research Institute (EPRI). Helium, nitrogen, argon, and water vapor fill gases are investigated at pressures ranging from atmospheric (∼105 Pa) to 100 Pa. Steady-state computational fluid dynamics (CFD) simulations that include the effect of gas rarefaction (temperature-jump) at the gas-solid interfaces are conducted. The PCT as a function of heat generation rate and pressure is reported as well as the heat generation rate that brings the cladding temperature to the radial hydride formation limit. The results show that there are competing effects between the temperature-jump and the thermal conductivity of the gas to increase the fuel rods’ temperature. The low pressures increased the PCT, with the increase being most significant for the helium backfill.

Mechanical Shock and Vibration Analysis of Spent Nuclear Fuel Carried by the Atlas Railcar

Researchers at Pacific Northwest National Laboratory have completed a structural-dynamic analysis of spent nuclear fuel subjected to the mechanical shock and vibration environment that is anticipated during normal conditions of transport in casks carried by the Atlas railcar. The Atlas railcar is a new railcar design that is being developed specifically for the purpose of carrying spent nuclear fuel casks. The analysis used best-estimate railcar dynamics models of the Atlas railcar and considered 17 different spent nuclear fuel transportation cask systems, representing the current fleet of cask options. This work used NUCARS, a specialized railcar dynamics explicit finite element code to calculate railcar dynamic response to prescribed speeds and track configurations. The railcar dynamics models provided cask transient motion for a wide range of speeds and track conditions, generating a relatively large database of potential cask motion. All of the cask motion transients were then applied as loading conditions to LS-DYNA structural-dynamic models of a single fuel rod. The analyses predict that the Equipos Nucleares S.A./U.S. Department of Energy (ENSA/DOE) multimodal transportation test of 2017 provided a relatively stronger vibration environment than is expected from the Atlas railcar. This paper describes the analysis methods, the analysis results, and compares the results of the Atlas transportation analysis to the test results and analyses of the ENSA/DOE multimodal transportation test of 2017.

Structural Evaluation With Elastic and Inelastic Analysis Methods on a High Temperature Storage Tank Subjected to Static and Dynamic Loadings

The structural integrity of reactor components is very essential for the reliable operation of all types of power plants, especially for components operating at elevated temperature where creep effects are significant and where components are subjected to high-temperature alteration and seismic transient loading conditions. In this article, a molten salt storage tank in high temperature thorium molten salt reactor (TMSR) is evaluated according to ASME-III-5-HBB high temperature reactor code. The evaluation based on 3D finite element analyses includes the load-controlled stress, the effects of ratcheting, and the interaction of creep and fatigue. The thermal and structural analysis and the application procedures of ASME-HBB rules are described in detail. Some structural modifications have been made on this molten salt storage tank to enhance the strength and reduce thermal stress. The effects of ratcheting and creep-fatigue damage under elevated temperature are investigated using elastic analysis and inelastic analysis methods for a defined representative load cycle. In addition, the strain range and the stress relaxation history calculated by elastic and inelastic methods are compared and discussed. The numerical results indicate that the elastic analysis is conservative for design and a full inelastic analysis method for estimating input for creep-fatigue damage evaluation need to be developed.

Thermal Fatigue Cracking due to Intermittently Flowing Drain Water in Steam Piping

In a petrochemical plant, a steam leak incident happened due to a through-wall crack, which was found around the branch connection between the superheated steam pipe header and the branch pipe for the safety valve. Similar cracks had been observed in the Normally No Flow (NNF) line pipes sometimes. We decided to investigate the cause of these cracks. The crack was found along the circumferential welding line of the branch connection. According to the microfractography, the origin of the crack was internal surface of the pipe and it propagated through the thickness of the wall. Striations were observed on the fracture surface, and it showed the fatigue effect. All the NNF line pipes where the leak incidents occurred were installed upward and then connected to the horizontal pipe toward the safety valve. Infrared thermographic testing revealed that the steam drain pooled in the horizontal pipes was flowing intermittently toward the superheated steam pipe header. Cyclic thermal stress was sure to occur in the damaged area with calculation by FEM, and the cause was assumed to be thermal fatigue cracking due to intermittent dripping of drain water condensed in the NNF pipe. We decided to correct the slope of the horizontal pipe so that the drain was not pooled. Also, we checked all other NNF line pipes upwards and confirmed that there was no possibility of a similar incident due to drain in the horizontal pipe.

Analysis of Spent Nuclear Fuel Multipurpose Canister Dynamics During Rail Transportation

The primary mode of spent nuclear fuel transportation within the United States will be by railcar. One such system is the Atlas railcar, which is designed to transport 17 different spent nuclear fuel cask systems, including bare fuel systems and canister fuel systems. In the latter configuration, multipurpose canisters containing spent nuclear fuel may be placed within an overpack for storage, or within a cask for transportation. Compared to bare fuel systems, canister fuel systems have additional degrees of freedom for motion during transportation, because clearance between the cask and canister allows for some motion of the canister to occur relative to the cask. This work investigates the effect of canister motion on the shock and vibration imparted to the spent nuclear fuel within. Structural dynamic analyses have been conducted to identify the effects of canister to cask clearance, presence and type of dunnage, and loading direction and frequency. This modeling study calculates anticipated cask motion, canister motion, and spent nuclear fuel structural dynamic response to normal conditions of transportation railcar motion using finite element analysis methods that were developed to model the rail segment of the ENSA/DOE (Equipos Nucleares S.A., U.S. Department of Energy) multimodal transportation test of 2017.

Development of Valve Performance Qualification Methodology and Testing

Valves play important roles in piping systems. In the oil and gas industry, for example, they are used to control flow rates in pipes, isolate flow, and provide over pressure protection of equipment. Given the role of valves in process industries, it is important that valve end-users feel confident that the valves they procure meet the design and qualification requirements in the specification. This paper presents a case study where there have been breakdowns in the qualification of valves being offered by valve suppliers to the industry that did not comply with industry standards which can adversely impact plant operations and personnel safety. The loss of valve supplier credibility is a concern that rarely occurs in mature economies but seem to be more prevalent in countries where design and testing standards are either relatively new or non-existent. To address this issue, the author presents a systematic approach that can be used to ensure that valves supplied to end-users in oil and gas industries in emerging countries meet the design requirements and standards they are required to meet. The process used to control the manufacturers begins with a qualification plan which each supplier has to establish for its product line. Following compliance with the qualification plan, a valve type criticality matrix is introduced to the manufacturers that classifies the criticality of each valve in the system and the associated testing program(s) that the manufacturers need to meet. The qualification program is conducted by the national oil and gas company and acknowledged by the country’s regulator. The recently established program has shown some merit and could be applied to all manufacturers in emerging countries to ensure consistency. The details of the qualification program used and how the process is evaluated are covered in the body of the paper together with examples of how the process has worked.

The Process of Creating and Reviewing a Transient Surge Model

Transient surge modeling remains to be a specialized task and therefore quite unfamiliar to many engineers and designers. The process for discerning when to conduct a model can be vague. The process for how to conduct a model can be even more unclear and quite daunting. This paper serves as an introductory guide to an engineer or reviewing project manager new to surge modeling. The content within covers a brief overview of the physics behind transients, what information is required to create a computer surge model, the content within a surge report and how to interpret it. Included within this paper are several references and detailed plots derived from actual projects.