High-temperature Pipe Research Articles

Type IV cracking of P92 steel welded joint used in China power plants

ABSTRACT P92 (9Cr-1.8W–0.5Mo-NbV) martensite steel is widely used in high-temperature pipes of ultra-supercritical boilers in China. During high-temperature operation, microstructural evolution of the heat affected zone (HAZ) across welded joint leads to type IV cracking failure. In this article, microstructural evolution and type IV cracking of P92 steel welded joint in an actual 605℃ supercritical boiler were analysed. The results show the cracking appeared in the fine-grained heat affected zone (FGHAZ). Laves phase and M23C6 phase clustered around the cavity. Their precipitation and coarsening promote the nucleation and growth of cavities. The Z phase was also observed in the heated affected zone. Compared with other zones, FGHAZ has lower dislocation density and more degeneration of tempered martensite lath, the coarsening of Laves phase and M23C6 phase is more severer in FGHAZ. These factors led to the deterioration of the creep properties and type IV cracking.

Analysis on Applicability of Type 316L Stainless Steel to 700℃ High-Temperature Piping

Analysis on Applicability of Type 316L Stainless Steel to 700℃ High-Temperature Piping

A flexible precontact CNT-Al2O3 fiber sensor resistant to extreme temperatures.

As a new soft electronic product, a flexible precontact sensor provides spatial position sensing ability. However, the properties of traditional polymer materials change in industrial environments with extreme temperatures, which can cause the sensor function to decline or even fail. In this study, we propose a flexible fiber sensor based on the capacitor principle, which achieves a stable spatial positioning function and is not affected by a wide range of temperature changes. The fiber element of the sensor is obtained through the deposition of a flexible Al2O3 ceramic coating onto the surface of a carbon nanotube fiber (CNTF) via atomic layer deposition (ALD) technology. Coatings of different thicknesses (100 nm, 200 nm, and 300 nm) show different colors. The temperature resistance and flame retardancy of Al2O3 keep the morphology of the composite fiber unaffected by flame or high temperatures. Even at extreme temperatures (-78 °C to 500 °C), the sensor's sensing ability exhibits excellent stability. In addition, the spatial perception of the fibers remained viable after repeated bending (10 000 times). We demonstrate the potential of the sensor to acquire position information during high-temperature industrial pipe docking.

Creep–fatigue damage assessment in high-temperature piping system under bending and torsional moments using wireless MEMS-type gyro sensor

Creep–fatigue damage assessment in high-temperature piping system under bending and torsional moments using wireless MEMS-type gyro sensor

Design of type 316L stainless steel 700 °C high-temperature piping

High-temperature design evaluations were conducted on Type 316L stainless steel piping for a 700 °C large-capacity thermal energy storage verification test loop (TESET) under construction at KAERI. The hot leg piping with sodium coolant at 700 °C connects the main components of the loop heater, hot storage tank, and air-to-sodium heat exchanger. Currently, the design rules of ASME B31.1 and RCC-MRx provide design procedures for high-temperature piping in the creep range for Type 316L stainless steel. However, the design material properties around 700 °C are not available in those rules. Therefore, a number of material tests, including creep tests at various temperatures, were conducted to determine the insufficient material properties and relevant design coefficients so that high-temperature design on the 700 °C piping may be possible. It was shown that Type 316L stainless steel can be used in a 700 °C high-temperature piping system of Generation IV reactor systems or a renewable energy systems, such as thermal energy storage systems, for a limited operation time.

High-temperature creep behaviors of polybutene-1 with different chain microstructure and molecular weight

The creep resistance of polymer determines the dimensional stability of product under stress. The isotactic polybutene-1 (iPB) with outstanding high-temperature creep resistance and stress-crack resistance is applied widely in the field of hot-water pipes. Although the chain information including weight-average molecular weight (Mw) and aggregate structures of isotactic polybutene-1 (iPB) influence the creep resistance, the crucial factor affecting the creep behavior greatly is unclear. In this work, a series PB samples with varied Mw, isotacticity and configurational sequence were synthesized and characterized based on Gel Permeation Chromatography (GPC), solvent fractionation and Nuclear Magnetic Resonance Spectroscopy (NMR). The Differential Scanning Calorimetry (DSC), Wide-angle X-ray diffraction (WAXD) and Small angle X-ray scattering (SAXS) were used to characterize the aggregation structures of PB samples. The stress-strain behaviors and 95 °C creep deformation of these PB samples were testes by tensile test and Dynamic Mechanical Analysis (DMA), respectively. It was found that these PB samples showed different chain microstructures like 88–99 wt% high isotactic PB (HiPB) fractions, 90–97.6 mol% tetra-meso placements (mmmm) in HiPB fraction, and 50 × 104-160 × 104Mw. Increasing the molecular weight, isotacticity or configurational sequence mmmm enhanced the creep resistance of PB, while mmmm configurational sequence played more important role in creep resistance of PB through adjusting the aggregation structure (crystalline domains) of the final product greatly. Exploring the influencing factors of creep resistance provided guidance for the synthesis of high-performance PB for high-temperature pipe application.

Multiphysics coupling investigation of interphase heat transfer in gas-particle coaxial-jet swirling flow via CFD-DEM-CHT

The swirling particulate flows with heat transfer are widely encountered in the industry, yet the internal multiphysics coupling characteristics resulting from fluid, particle, and structure interactions are not well-understood. In present employment, a coupled method of computational fluid dynamics-discrete element method and conjugated heat transfer is constructed to provide insights into the thermal analysis in the industrial-scale annular pipe. The heat transfer behaviors between gas-pipe wall, gas-particle, particle-particle and particle-pipe walls are taken into account for the gas-particle coaxial-jet swirling flow. After verifying the mathematical model, the heat and momentum transfer behavior is analyzed, followed by a comprehensive exploration of fluid hydrodynamics, heat transfer characteristics, and particle properties under diverse swirler geometries. The results demonstrate that the presence of the swirler reinforces the forced convection between the jet and the high-temperature pipe wall. The heat exchange performance between the jet and the Wallcp-ann-cas enhances with the increase of vane angle and diameter of the swirler but decreases with the increase of swirler height. The impact of the swirler installing position on the thermophysical field can be neglected. An excessive number of swirler vanes adversely impacts the heat transfer process between the gas phase and pipe walls. The particle temperature increases with decreasing height, while the particle Nusselt number increases and then decreases with the decrease in height.

Non-Destructive Inspection of High Temperature Piping Combining Ultrasound and Eddy Current Testing

This paper presents an automated Non-Destructive Testing (NDT) system for the in-service inspection of orbital welds on tubular components operating at temperatures as high as 200 °C. The combination of two different NDT methods and respective inspection systems is here proposed to cover the detection of all potential defective weld conditions. The proposed NDT system combines ultrasounds and Eddy current techniques with dedicated approaches for dealing with high temperature conditions. Phased array ultrasound was employed, searching for volumetric defects within the weld bead volume while Eddy currents were used to look for surface and sub-surface cracks. The results from the phased array ultrasound results showed the effectiveness of the cooling mechanisms and that temperature effects on sound attenuation can be easily compensated for up to 200 °C. The Eddy current results showed almost no influence when temperatures were raised up to 300 °C.

STRESS ANALYSIS EVALUATION AND PIPE SUPPORT TYPE ON HIGH-PRESSURE AND TEMPERATURE STEAM PIPE

The design and analysis of piping systems are critical in the power and process industries. The steam pipe is one of the main requirements for the plant to be installed. High-pressure and high-temperature steam pipes in the piping system are critical lines that need to be subjected to stress analysis. This study aims to evaluate the stress and the effect of using pipe supports on the stress in the piping system. Stress analysis is needed to ensure that the piping system that is designed is safe and does not exceed the allowable stress under operating conditions. Data analysis used ASTM A335-P11 as a pipe material with a design pressure of 65 bars and a design temperature of 480 °C. Stress analysis was carried out using CAESAR II software, which refers to ASME B31.3 process piping standards and codes. The findings revealed that the type of support chosen, such as the gap and distance of pipe support, has a significant impact on the stress value in the piping system. The results of the analysis are carried out several times to get the stress value so that it does not exceed the allowable stress. The greatest stress value occurs at the expansion load condition in the steam pipe system design. The chosen piping system design has a ratio of 93.6%, which is located at node 220 with a stress value of 35889.1 psi and an allowable stress of 38327.2 psi. Because the stress value that occurs is below the allowable stress, the steam pipe system is safe to be installed and operated.

Study on the drag reduction performance of high-temperature exhaust pipe by spray cooling

The drag of the exhaust pipe greatly influences the engine power performance of an engineering vehicle. The engine power performance would decrease significantly when the exhaust drag is large. The drag reduction effect achieved by the existing drag reduction is relatively weak; thus, based on spray cooling, drag reduction technology is introduced to solve this problem. The present study aims to determine the influence of spray parameters on drag reduction using an electric heating test bench and to clarify why spray significantly reduces drag using numerical simulations based on Discrete Phase Modeling (DPM). The obtained results prove that increasing the flow value in the test spray flow range of 12–24 ml/s can significantly improve the drag reduction performance. When the spray inclination increases from 45° to 90°, the drag reduction remains, in the beginning, unchanged and then decreases. Under the synergistic effect of the frictional resistance reduction and the dynamic pressure reduction, the resistance downstream of the spray location is significantly reduced. Compared with the existing drag reduction, the spray drag reduction has obtained the ultimate drag reduction effect, and the drag reduction rate is as high as 90 %. To conclude, this research will help promote the application of spray drag reduction to engineering vehicles.

Estimation of Radiation Heat Flux in Open Pool Flames for Application of Fire Protection Walls

Petrochemical plants are characterized by various flammable substances and complicated processes. Moreover, flammable fluids are transported through high-temperature and high-pressure pipes. To reduce the potential damage inflicted on adjacent facilities owing to the risk of fire and explosion, it is necessary to consider installing a fire protection wall, which is a physical space partitioning method. Currently, in Korea, the Dangerous Substances Safety Control Act and High-Pressure Gas Safety Act define the technical specifications of fire protection walls. However, there is no performance standard for fire protection walls considering the many possible fire hazards of petrochemical plants. Therefore, the heat release rate based on the size of open pool flames, radiation heat flux, and temperature per distance were measured through an open pool fire test using n-heptane, which is commonly used as a solvent in the production processes at petrochemical plants. The experimental results were evaluated by comparing them with values calculated according to ISO 24678-7, which is the standard for the numerical analysis of radiation heat flux in an open pool fire.

Temperature effect on the axial behaviour of a pipeline buried in soft clay

Axial resistance is a key component to resist thermal buckling of an offshore oil and gas pipeline operating under a high temperature. The previous studies on the axial resistance of the pipeline were mostly performed under an isothermal condition, ignoring the temperature effect that would alter the strength of the seabed and modify the axial resistance of the pipeline. For this reason, a novel temperature-controlled experimental setup is developed in this study. Model tests were then carried out for simulating the axial interaction between clayey seabed and pipelines, which were heated to two typical temperatures (i.e., 15 and 55 °C) under the drained condition and then axially loaded under the undrained condition till failure. Additionally, the mobilized shear strain (and therefore mobilized shear stress) at the soil-pipe interfaces under the two temperatures are also investigated, based on a newly developed temperature-controlled interface shearing apparatus that has a transparent window for image recording and analysis. It is found that the pipeline with high temperature (55 °C) exhibits 20% larger initial axial soil resistance stiffness than the low-temperature pipeline (15 °C). This suggests the thermal consolidation has increased the soil stiffness around the high-temperature pipeline. Despite the increased undrained shear strength (s u) of the thermally consolidated clay around the high-temperature pipe, its peak axial resistance is 10% lower than that of the low-temperature pipe, the maximal normalized parameter of axial resistance α f max decreases from 0.90 to 0.70, when the temperature rises from 15 °C to 55 °C. This is attributed to the thermally induced suppression of the stick-slip (referred as “thermo-lubricity”) at the soil-pipe interface, which encourages the interface slippage prior to a full mobilization of s u around the pipes. Consequently, a temperature elevation from 15 to 55 °C has led to a reduction 36% (from 70% to 34%) of s u mobilization at the soil-pipe interface, which is observed in the interface shearing tests.

A novel insulation design for high-temperature pipe penetrating the walls of molten salt reactor cavity

The design of molten salt reactor has high-temperature pipes penetrating the walls of reactor cavity, the working temperature of which is about 530 K higher than the ordinary concrete wall. The insulation of high-temperature pipes is important to prevent local overheating of the walls of molten salt reactor cavity. A heat insulation scheme with multilayer different materials for the high-temperature pipe is analyzed. In order to verify the correctness and rationality of the design, one experimental set-up was built. The maximum relative deviation between the numerical results and experimental ones is 2.74% and the maximum relative uncertainty of the experimental results is 0.62%. The design scheme is used in a molten salt reactor and the maximum temperature of the ordinary concrete wall of the molten salt reactor cavity is 338.58 K, which is within the safety limit value of 343.15 K. The design of heat insulation for high-temperature pipe can also be used in other molten salt reactors.

High-Temperature Ultrasound NDE Systems for Continuous Monitoring of Critical Points in Nuclear Power Plants Structures

High temperature pipe cracks are the root of a steam power failure in the EU typically every 4 years, resulting in loss of human life, serious accidents and massive financial losses. According to IAEA’s Reference Technology Database, such an event on a nuclear power plant has an average cost of €120 million, including outage costs, emergency repair costs, insurance and legal costs. Since only one growing crack is needed to cause a major failure, they have to be inspected and monitored thoroughly. Breakdowns at extreme conditions (e.g. 580°C, 400 bar) are a result of two major weld failure modes: a) creep cracks near pipe welds; b) fatigue cracks on pipe welds. Current maintenance practice is to proceed with repairs on a detected crack according to its severity. For cost reasons, cracks that are not judged as severe enough will not be repaired. Crack severity judgement is based on its probability to cause a failure and this probability is derived taking into account the crack size and operational lifetime. More variables such as operating temperature and vibrations may rarely be found in other studies. Recent data from fracture mechanics statistical studies shows this connection between the size of a crack on a nuclear power plant pipe and its probability to lead to a failure. To deal with the above problems two Structural Health Monitoring (SHM) systems have been developed and they are presented in this work. These systems are able to achieve continuous operation for an extended time period at operating temperatures of nuclear power plants. The developed systems employ novel phased array (PA) ultrasonic and ultrasound guided wave (UGW) probes able to withstand and continuously operate even up to 580 °C. The systems are designed to be permanently mounted on superheated steam pipes, at locations of known defects and to continuously monitor their size. However, this supposes that defects will have already been detected by a traditional method during an outage. The PA transducers are placed according to the Time-of- Flight Diffraction (TOFD) technique’s topology, thus creating a novel configuration, while the UGW transducers are placed on a stainless steel ring in a circular array configuration. These configurations can enable continuous tracking of cracks growth with high accuracy, enabling maintenance crews to estimate the severity directly and not through statistics.

A new on-line ultrasonic thickness monitoring system for high temperature pipes

On-line thickness monitoring of pipe wall is very important in petrochemical and power generation industries. There are two main reasons that the conventional ultrasonic transducers cannot withstand long-term on-line monitoring in high temperature. One is that the piezoelectric elements within transducers depolarize causes them to fail, the other is that the working medium inside the pipeline interferes with the ultrasonic wave results in the decline of measurement accuracy. In order to overcome these problems, an ultrasonic thickness gauge using a waveguide that can sustain a large temperature drop and effectively transmit the quasi-fundamental shear horizontal (SH0*) wave without causing dispersion is designed. The waveguide can isolate the vulnerable piezoelectric sensor from the high-temperature measurement zone, and the SH0* wave can avoid interfere of the working medium. Moreover, a monitoring system applying this ultrasonic thickness gauge is discussed and the application method of this system is introduced. The high temperature long-term reliability experiments carried out both in laboratory and on-site, and wall thinning measurement by corrosion experiments show that the designed thickness gauge has good accuracy and long-term stability, which can meet the needs of long-term on-line monitoring of high temperature pipes.

Study of a nondestructive inspection system by guide wave traveling to axis direction of a hot pipe using a long ultrasonic waveguide

Corrosion inspection of high temperature pipes for heat exchange installed in gas turbine buildings is important for safe operation management. Ultrasonic inspection is one of the promising inspection methods, but ultrasonic sensor systems are vulnerable to high temperatures. In this research, we aim to use an ultrasonic sensor system in a normal temperature environment by using a long waveguide to overcome this problem. For that purpose, we report the results of the ultrasonic sensor ability installed in the long waveguide, the propagation characteristics of the waveguide, and the ultrasonic wave characteristics from the waveguide to the pipe.

Analysis on microstructure and properties evolution and life prediction of P92 steel in high temperature service

P92 steel (10Cr9MoW2VNbBN) is widely used in high-temperature steam piping and high-temperature header fabrications of ultra-supercritical units. In this paper, a follow-up study on the microstructure, mechanical properties and life of P92 steel steam pipes which are virgin, 31,000 h in service, 49,000 h in service and 71,000 h in service was carried out. The results show that the mechanical properties of the P92 steel drop significantly after 31,000 h of service, then decrease slowly with the increase of the service time. When the service time reaches 71,000 h, the high temperature yield strength, percentage elongation, and impact absorbed energy are all close to the lower limit regulated by the ASME standard. Moreover, the morphology of lath martensite becomes fragmentary, the width of the martensitic lath increases and carbide particles cluster and grow at the grain boundary. M23C6 phase coarsens and local Laves phase precipitates. Meanwhile, the dislocation density decreases to some degree. Furthermore, there is a good corresponding relationship between the room temperature hardness and the high temperature tensile strength of the P92 steel after a long period of service. The prediction model of the remaining endurance life of P92 components is proposed on the basis of the room temperature hardness.

A Special Thermal Fatigue Failure Mode of Pipe in Nuclear Power Plant and Its Countermeasures

Thermal fatigue phenomenon is well known and feedbacked in the nuclear power industry. Targeted screening principles has been developed and applied. However, a thermal fatigue failure, “Swirl Penetration” of small-diameter pipeline, was identified through a Reactor Coolant System (RCS) leakage in a nuclear power plant. Unexpectedly, this failure is not within the scope of previous screening principles of thermal fatigue. It is characterized in that the high-temperature main piping is connected downward with a certain length of vertical small-diameter piping, and then the vertical piping turns horizontally through an elbow. The reactor coolant in the lower pipeline does not flow under normal operation conditions. Subject to long-term cyclic thermal fatigue, cracks initiate and propagate in the elbow. Through researches, corrective measures are put forward to prevent, mitigate or discover it.

Health-Monitoring Methodology for High-Temperature Steam Pipes of Power Plants Using Real-Time Displacement Data

We developed a health-monitoring methodology for high-temperature steam pipes that estimated the life prediction of creep–fatigue interaction by directly measuring the displacement of hot parts. Three different methods (boiler code, design stress, and operating stress) were used to estimate the stress of the high-temperature pipe system. As a theoretical approach, the German boiler standard code calculates the stress according to the pipe shape, while design stress, which is also called allowable stress, was determined by a function of the operating temperature. The operating stress was immediately calculated using the surrogate model, with maximum displacement measured using the 3D displacement measurement system. To achieve the surrogate model, the stress was estimated by the pipe-stress analysis under the given displacements, and the surface-response model was developed to relate the stress and displacement. We showed that those methods are efficient methods to predict the stress and are applicable in health-monitoring methodology. Finally, the creep life and the low-cycle fatigue life were investigated using the Larson–Miller parameter equation, as well as the Smith, Hirschberg, and Manson equations. Our proposed monitoring system can be used to predict the fatigue and creep life of high-temperature steam pipes in real time, and we believe that the system can be applied to actual maintenance in thermal power plants.

Application of Nonlinear Elastic Wave Spectroscopy in the Field of Nuclear Energy

Abstract In the field of nuclear energy, two particular applications are considered—the measurement of biological shielding concrete and measurement of high-temperature high-pressure piping. For the measurement of biological shielding concrete, a special manipulator was developed, which is applied through the ionization channels of VVER-440 power plants. Biological shielding concrete is covered on all sides with an 11 mm thick steel liner preventing its assessment using any conventional test method. For the measurement of high-temperature high-pressure piping, acoustic emission sensors installed in the LEMOP system (NPP Temelin) are used for both excitation and data acquisition. In operation, this piping is covered with glass wool insulation, but installed sensors on the waveguides make it possible to assess pipelines without removing the insulation. To demonstrate the material degradation, a set of concrete test specimens and a set of steel test specimens were made. Nonlinear elastic wave spectroscopy is a test method based on measuring the elastic–plastic response of the material whose plastic component is caused by microcracks. Part of this response may be caused by inhomogeneity of the material itself or the nonlinearity of the test system used, which is to be minimized in the measurement. Due to degradation, the number of microcracks increases, increasing the total nonlinear response of the material. The aim of this approach is to monitor the degradation of concrete and metallic materials based on the response of the test system to ultrasonic excitation.