Large Pressure Vessels Research Articles

Crack propagation characteristics and fatigue life of the large austenitic stainless steel hydrogen storage pressure vessel

Hydrogen-induced cracking or embrittlement can have a substantial and severe impact on the fatigue life of large austenitic stainless steel hydrogen storage pressure vessels. In this study, a dynamic model for the plastic zone in the crack tip considering the hydrogen diffusion was established and a correction factor for the stress intensity factor of the hydrogen storage pressure vessel was proposed for 316L stainless steel, which is commonly used pressure vessel material. The crack propagation characteristics and fatigue life of the stainless steel vessel were investigated. The results indicated that the shortest fatigue life under hydrogen pressure occurs at the intersection of the vent nozzle and the vessel head. The hydrogen environment not only reduces vessel service life but also makes the influence of pressure on cracks propagation more pronounced. It leads to a significant reduction in the fatigue life of pressure vessels when overpressure happens during operation. These research findings are valuable for the accurate assessment of the vessel fatigue life and improving the quality of large hydrogen storage vessel structures.

Consideration on the Applicability of Electron Beam Welding for the Manufacture of Small Modular Reactor

The overall technology required for the application of electron beam welding to ultra-thick plate pressure vessel in small modular reactors was considered. Electron beam welding has the advantage of reducing the manufacturing time compared with traditional arc welding, but it requires the construction of complex equipment and the establishment of related process technology. Based on the thickness of 150~250 mm, the electron beam welding equipment for application to SMR pressure vessel requires large-capacity equipment of 120~170 kV, 150 kW or more, which has never been commercially manufactured so far. A stable beam must be maintained for a constant time. Anti-arcing and seam tracking functions are also required. Electron beam welding of low-alloy steel has superior characteristics in terms of strength and toughness compared with arc welding. The welded area can be made into a base material by solution heat treatment. Cleaning and gap control are important for weld quality. Weld area should not be affected by magnetic fields. As circumferential welding overlaps in span at the welding start and end, it requires precise setting of welding parameters. For welding of large pressure vessel, customized cylindrical vacuum chamber or local vacuum chamber are suitable. It must be shielded from X-rays generated during welding.

Investigation of angular deformation control for T-joint rib using multi-point constraint method

The circular rib is a crucial component of large pressure vessels, and its cross-section is primarily a T-joint structure. The double-sided arc welding (DSAW) process is an advanced technology for T-joint connection. However, during the T-joint welding process, harmful deformation still occurs in the form of angular deformation, including web and flange angular deformation. This paper proposes an innovative multi-point array constraint method to control the angular deformation of the rib based on the DSAW process for circular ribs. The welding deformation of the T-joint rib under multi-point constraints is studied using both numerical and experimental methods. The results of the numerical and experimental are consistent, with a relative error of no more than 12%. The multi-point constraint method is found to control angular deformation effectively, with the maximum angular deformation of the web not exceeding 1.77 mm and that of the flange not exceeding 0.45 mm after welding and releasing the constraint. The deformation control is significantly better than that of the rigid jig. Moreover, the coupling deformation of the web and flange caused by double-sided heat source and multi-point constraint forms an overall bending deformation. The deformation trend of each welding process is the same, with the main deformation occurring in the stage of releasing the constraint.

High yield, large-scale synthesis of calcium-based microporous metal-organic framework and examination of the long-term stability for xenon adsorption applications

Scale-up synthesis of calcium-based microporous metal-organic framework (SBMOF-1) up to ∼400 g in a batch with a yield of >90 % was achieved by a solvothermal reaction of sulfonyldibenzoic acid (SDB) with an excess of calcium chloride. Here, we observed that recrystallization of unreacted SDB at a solvothermal condition caused a moderate reaction yield (40–50 %) at the reference condition of CCaCl2/ CSDB = 1 and CSDB/ CSDB(ref) = 1. Simply adding more reagents to the reactor did not increase the mass of product formed per unit volume due to a more pronounced loss of the yield at those conditions. By simultaneously changing the molar ratio of CaCl2 to SDB, CCaCl2/ CSDB, and the molar concentration of the SDB reagent, CSDB/ CSDB(ref), we explored %yield of the reaction. Interestingly, a linear improvement in the yield was observed from 21 % (at CCaCl2/ CSDB = 0.5) up to 78 % (at CCaCl2/ CSDB = 6) at a fixed ratio of CSDB/ CSDB(ref) = 2 and the yield leveled off after further addition. Unlike those at CCaCl2/ CSDB = 1, the yields at a high CaCl2 excess continued to improve with increasing the CSDB/ CSDB(ref). When a large pressure vessel (2500 mL EtOH, CCaCl2/ CSDB = 6, CSDB/ CSDB(ref) = 8) was used, about 415 g of SBMOF-1 with a yield of 92.3 % was produced, indicating 16 × the space yield improvement. The ability to synthesize SBMOF-1 on a large scale allowed us to examine the long-term stability of SBMOF-1 for almost 200 days in the presence of varying levels of relative humidity.

A continuous leakage real-time localization method based on space phase image of elastic wave field with improved CNN

To satisfy the requirement of real-time monitoring and locating of the leakage in large pressure vessels, a method of leakage source location based on improved convolutional neural network (CNN) is proposed in this paper. In this method, the polar coordinate model of elastic wave propagation excited by continues leakage is established, and the improved CNN is constructed according to its spatial field distribution, and the training set of the network is obtained by finite element simulation. The experimental results show that this method can be applied to locate the leak at any time after it occurs, and only a single sensor array is used. In the experiment of 1 m2 stiffened test plate, the absolute distance error was less than 0.1 m and the absolute angle error was less than 0.1 rad in 90.2 % of all samples.

Experimental analysis of boron dilution transient flow mixing characteristics based on planar laser induced fluorescence measurement

In Reactor Pressure Vessels (RPV), flow mixing between high and low concentration coolants will cause uneven distribution of boric acid. Severe cases will lead to boron dilution transient and re-criticality safe operation accident. Therefore, accurate measurement of coolant flow mixing characteristics and boron concentration distribution in RPV and study of the mechanism affecting the mixing process are of great significance to improve reactor operation safety. Based on the structural characteristics of large advanced pressurized water reactor pressure vessel, a large-scale visual experimental device was built by 1:6 scale modular design. Optical path correction scheme is used to solve the problem of optical path distortion existing in PLIF technology, and improved ratio calibration method is used to reduce the experimental error of concentration field distribution measurement. Flow mixing process and boron concentration field distribution in pressure vessel under single loop conditions were obtained based on plane laser induced fluorescence technique (PLIF). The influence of Reynolds number on boron diffusion behavior was studied. The experimental results show that during single loop operation, the localized eddy current formed in the left area of the lower head will result in a high concentration retention zone and a V-shaped boric acid concentration distribution in the core. With the increase of the ratio of cold tube flow to injection flow, the time when the high concentration coolant reaches the core hardly changes with the boric acid solution flow rate. The mixing diffusion behavior of boron concentration is the best when the ratio of injection to Reynolds number in the cold tube is at a certain value.

High accuracy and efficiency calculation model for predicting the reduction of residual stress on large pressure vessels by ultrasonic impact surface treatment

AbstractUltrasonic impact treatment (UIT) is a new surface strengthening method to reduce the residual stresses on large pressure vessels induced by surface and repair welding. An accurate and high efficiency calculation model is the key to accurately predicting the full‐field residual stresses on large pressure vessels under the UIT process. In this article, a full‐coverage impacting model is proposed to simulate the impacting process of the UIT pin. The effects of UIT on the residual stresses on repair and surface welded pressure vessels were investigated by explicit dynamic simulation. Experiments were also performed to verify the prediction results. Results show that the proposed full coverage impacting model can greatly improve the simulation precision and the calculation efficiency. The predicted residual stresses after the UIT process using the proposed model are consistent with the measured results. A remarkable reduction in residual stress was achieved in the zone subjected to UIT. The tensile residual stresses on the surface of the treated area were reduced to compressive stresses. With the increase of the impact velocity and the coverage rate, the residual stresses on the surface and transition layers decreased and then tended to stabilize. The impact coverage rate should not exceed 200% to avoid damage and save time.

Measurement of electroacoustic transducer sensitivity in extreme hydrostatic pressure environments

The measurement and acoustic calibration of electroacoustic transducers for underwater sound under extreme pressures (to 10,000 psi / 7km depth) and variety range of temperatures is a great challenge. Specialized facilities consisting of large pressure vessels with pressure and temperature control do exist at Navy faciliites (www.navsea.navy.mil + USRD) but operate to moderate pressures, have limited availability, are expensive and limited access. An alternative or supplement is to measure the change in the electro-mechanical impedance of the of a transducer and use equivalent electrical cirucuit analysis to determine the resulting change in all electrical, electromechanical, and mechanical properties. Having the pressure and temperature depedence of all the consitutent parameters allows an accurate pediction of the transduer performance sensitivity and frequency response (such as TVR Transmit Pressure per Volt, and receive voltage per pressure sensitivity. We measured transducer performance of several devices in the laboratory pressure vessels up to 10 000psi and report on findings.

Constraint characterization and fracture initiation analysis for semi-elliptical surface cracks in reactor pressure vessel

The constraint and fracture initiation for semi-elliptical surface cracks in an actual large scale reactor pressure vessel (RPV) have been investigated by finite element analysis. The results show that the overall constraint level of the cracks increases when the crack depth a/t increases and crack aspect ratio a/c decreases. For most cracks with a/t = 0.25–0.8 and a/c = 0.2–2, the constraint level is higher than the standard plane strain specimen, and the conventional fracture assessment may possibly yield non-conservatism. The aspect ratio a/c has obvious effects on the distributions of the new unified constraint parameters Ad* and the elastic-plastic stress intensity factor KJ and the fracture initiation position along the crack fronts. For low aspect ratio cracks with a/c < 1.0, fracture initiation probably appears in the deepest region of the crack. For high aspect ratio cracks with a/c ≥ 1.0, fracture initiation is likely to occur in the near-surface region. To improve the accuracy of fracture assessment for cracks in the RPV, the constraint effect requires to be incorporated. The engineering estimation methods of the parameters Ad* and KJ at the crack initiation positions have been provided and verified.

Real-Time Localization Method of Large Pressure Vessel Leaks Based on Improved CNN and STCA of Elastic Wavefield

Real-Time Localization Method of Large Pressure Vessel Leaks Based on Improved CNN and STCA of Elastic Wavefield

A multi-objective discrete differential evolution algorithm for energy-efficient two-stage flow shop scheduling under time-of-use electricity tariffs

In response to the appeal for environmental protection and the efficient utilization of energy, local governments in China actively promote time-of-use (TOU) electricity tariffs for manufacturing enterprises. Motivated by a real-life industrial scenario of large special-purpose pressure vessel production, this paper addresses an energy-efficient two-stage flow shop scheduling problem under TOU tariffs to minimize the total electricity cost and the mean tardiness. Since the problem is computationally intractable, we focus on developing a multi-objective discrete differential evolution (MDDE) algorithm. Specifically, based on the optimal properties of the problem, we tailor an encoding scheme that consists of two job sequences and an idle time vector. The novel mutation and crossover operators are designed to generate the trail individuals, and the hypervolume contribution indicator is incorporated into the bi-criteria selection operator to measure the quality of the solution. Furthermore, two neighborhood structures are designed to iteratively improve the non-dominated solutions in the external archive set. We evaluate the performance of the MDDE algorithm via extensive computational experiments. The experimental results indicate that the MDDE algorithm can obtain the good approximate Pareto front, and it outperforms the well-known NSGA-II, SPEA2 and MOEA/D algorithms in solution quality.

A 3D leakage monitoring method for pressure vessel based on region segmentation and time difference estimation

Leak monitoring and location technology is an important guarantee for the safety of pressure vessels. However, the first-time capture of sudden leakage incidents and the structure of the revolving body have brought challenges to the full range of pressure vessel monitoring and location. In this paper, based on the structural characteristics of the cylindrical pressure vessel, a 3D monitoring and location method based on region segmentation and time difference estimation is proposed, which combines regional location and time difference location to improve the location speed and accuracy of the algorithm. The adaptive threshold is adopted to capture the first moment of leakage, and the regional cross-correlation calculation is used to locate the leakage source in the area. The performance of the method is verified by liquid leakage experiment based on distributed acoustic emission sensor. The results show that the proposed method has good adaptability. It can capture leakage events and locate the leakage events at different positions and apertures in the first time, with an average location error of 2.44 cm. This study will have a new understanding of the location technology of pressure vessels and provide a reference for the health monitoring of large pressure vessels.

Mission Architecture to Characterize Habitability of Venus Cloud Layers via an Aerial Platform

Venus is known for its extreme surface temperature and its sulfuric acid clouds. But the cloud layers on Venus have similar temperature and pressure conditions to those on the surface of Earth and are conjectured to be a possible habitat for microscopic life forms. We propose a mission concept to explore the clouds of Venus for up to 30 days to evaluate habitability and search for signs of life. The baseline mission targets a 2026 launch opportunity. A super-pressure variable float altitude balloon aerobot cycles between the altitudes of 48 and 60 km, i.e., primarily traversing the lower, middle, and part of the upper cloud layers. The instrument suite is carried by a gondola design derived from the Pioneer Venus Large Probe pressure vessel. The aerobot transmits data via an orbiter relay combined with a direct-to-Earth link. The orbiter is captured into a 6-h retrograde orbit with a low, roughly 170-degree, inclination. The total mass of the orbiter and entry probe is estimated to be 640 kg. An alternate concept for a constant float altitude balloon is also discussed as a lower complexity option compared to the variable float altitude version. The proposed mission would complement other planned missions and could help elucidate the limits of habitability and the role of unknown chemistry or possibly life itself in the Venus atmosphere.

Understanding DCPD signal changes when monitoring creep damage in metals

The electrical potential drop (EPD) technique has previously shown promising results using a combination of AC and DC EPD (or DCPD) on large pressure vessel creep tests, detecting final cracking as well as incipient creep cavitation damage in welded P91 steel, with DCPD showing subtle but steady rises of around 5% over ca 10,000 h of testing before rising exponentially at failure. The work presented here has attempted to shed light upon this using a simple numerical model. The model uses an array of spherical cavities to constrain the current path and hence raise the DCPD, however it was only able to show a modest rise in DCPD, and not match experimentally determined rises. Modelled DCPD values were a fifth of those experimentally observed, but both the nature of the model (simplified to aid timely computation) and the assumption that only cavitation is responsible for the changes seen, could be the reason for the discrepancies reported here. The possibility remains that other mechanisms are at play, which could magnify the measured DCPD – particularly those mechanisms that could be associated with embryonic or micro-crack formation, and these are discussed herein.

Collapse behavior of carbon-fiber epoxy cylinders subjected to long-term seawater exposure at seafloor depth pressures

The effects of simulated long-term exposure of carbon-fiber/epoxy (CFE) hollow cylinders to high pressure seawater were investigated experimentally. Utilizing accelerated life testing informed by the Arrhenius methodology, specimens were aged in 41.1 MPa (6000 psi) pressurized 3.5% saline water for durations representing 0, 193.5, and 516 days of service at 3 °C. Hydrostatically and explosively initiated implosion experiments were performed in a large pressure vessel simulating free field conditions. The events were recorded with high-speed stereo photography and analyzed using 3D digital image correlation (DIC) techniques. High frequency response pressure transducers captured a detailed pressure history of each event. Analysis of the collapse phenomena suggests that exposure to the abyssal environment at the timescales investigated had negligible effects on the response of CFE structures subjected to dynamic instability.

Analyse the effect of clad ratio on the stress-strain curve of titanium-clad bimetallic steel for different strain rates and temperatures using Johnson-Cook model

Titanium–clad bimetallic steel plate finds its application in the construction of large pressure vessels which are used for storage and processing of petrochemicals. Mechanical properties can be imparted to any material according to its application by a technique known as cladding. To improve material, two main functions are performed by cladding. The finite element analysis (FEA) technique is an efficacious numerical method for solving several engineering problems. This technique not only provides reliable test results but also reduces the cost of the experiment. The aim of this report is to analyze the effect of clad ratio on stress–strain curves of titanium-clad bimetallic steels for different strain rates and different temperatures using the Johnson-Cook flow stress model. The ratio of the cladding layer thickness (tc) to the total thickness of Titanium-Clad bimetallic steel plate (t) is known as Clad ratio (α). In this report, Titanium Grade 5 is used as a cladding material and AISI 1006 is a parent metal. Furthermore, model constants were estimated from the analyzed result by using material constant for both cladding material and parent material from the research papers. The dimensions of the specimens were taken from GB/T228.1–2010 testing standard. The three-dimensional design of the specimens was created in Solidworks 20 and analyzed in Ansys Explicit Dynamics. A tension test was performed using Ansys for three different temperatures (293 K, 673 K, and 973 K) and for three different strain rates (1/sec, 10/sec, and 100/sec). In this paper, the reference strain rate was taken as 1/sec and the reference temperature as 293 K.

A Real Time Localization Technique Based on a Two-Dimensional Cnn and Spatio-Temporal Correlation Analysis for the Large Pressure Vessel

A Real Time Localization Technique Based on a Two-Dimensional Cnn and Spatio-Temporal Correlation Analysis for the Large Pressure Vessel

Weld line recognition and path planning with spherical tank inspection robots

AbstractPeriodic inspections are required for the safe operation of large pressure vessels such as spherical tanks. Inspection robots have been applied in large pressure vessels due to their low cost and high efficiency. This paper presents a robotic system for the inspection of spherical tanks, which can identify and track weld lines on the shortest running route. Two‐dimensional (2D) weld maps were prepared for robot path planning on the basis of the actual distribution of weld lines. In 2D weld maps, indispensable repetitive lines were added to form an Eulerian circuit that traversed all weld lines. In addition, an improved Fleury algorithm was proposed to solve Eulerian circuit and plan an optimal running route for robot inspection. To accurately identify weld lines, deep learning networks were constructed and trained with weld line data sets, which were captured by the camera mounted in the front of the robot. The laboratory experiments indicated that the inspection robot could identify weld lines within 0.2–0.25 s and track weld lines with a maximum offset of ±20 mm. The experiment results demonstrated that the robot could plan the shortest path to traverse all weld lines on the experimental platform. In the field tests, the virtual simulation of weld path planning on spherical tanks was explored in detail. The field tests of a spherical tank (3000 m3) verified that the robotic system could improve the efficiency and stability of inspection operations and replace manual inspection with automated weld line recognition and weld path planning.

ELECTRICAL POTENTIAL DROP FOR MONITORING CREEP DAMAGE IN HIGH TEMPERATURE PLANT

ABSTRACT Electrical potential drop (EPD) is a powerful technique to gauge crack depth in many contexts, including fracture, creep and fatigue testing, and in-field NDE, however it has only seen limited use for monitoring pre-crack creep cavitation damage. The authors have previously reported promising results using a combination of AC and DC EPD on large pressure vessel creep tests, even detecting incipient damage. However, that study lacked linkage to the underlying microstructural mechanisms. Here we present the results of a more fundamental creep study using EPD on P91 pressure vessel steel specimens taken from weldments, suffering HAZ-related Type IV cracking. This work confirmed that EPD could detect incipient damage, with ACPD being particularly sensitive to life fraction, but allowed linkage to changes in material properties, such as permeability and resistivity. Discussion of the implications for future off-line (in-field) NDE methods and on-line continuous monitoring of high-temperature plant components is also made.

A primary plus secondary local PWHT method for mitigating weld residual stresses in pressure vessels

Local post-weld heat treatment (PWHT) is often used for mitigating welding-induced residual stresses in pressure vessels and piping systems. As large and ultra-large pressure vessels are increasingly used in petrochemical and power generation industries, traditional local PWHT procedures stipulated in Codes and Standards become difficult to implement for some of the ultra-large vessels due to their very large diameter and overall length. In this paper, a new method referred to as primary-secondary heating based local PWHT technique (PS-PWHT) is proposed. Both finite element residual stress modeling and experimental residual stress measurements were performed for both validating the effectiveness of the proposed technique and elucidating the underling mechanisms. The results show that the PS-PWHT method can reduce welding-induced residual stresses in a significant manner, even leading to some level of compressive residual stresses at the vessel weld region.