Piping Components Research Articles

A Simple Measurement Method of Pressure Pulsations Using Outer Surface Strain in Piping Systems

This study proposes a method to measure pressure pulsations in piping systems easily and directly for their accurate evaluation of occurrence location and pressure amplitude. In the proposed method, the pulsations were estimated by combining the strain measurement result on the pipe outer surface with the calculated formula result for thick-walled cylinders. The proposed method was validated experimentally using a mock-up piping system. It was demonstrated that the method could measure the amplitudes and behavior of pressure pulsations with a practical accuracy. The factors influencing the measurement accuracy of the method were also discussed. The method is expected to contribute to more efficient plant maintenance to prevent fatigue failure of piping and plant components because the pulsations that the method measures are the main cause of vibration fatigue and acoustic noise in piping systems.

Short-Term Creep Behavior in P91 Heat-Resistant Steel at Low Stress

P91 heat-resistant steel is widely used in the high temperature of piping components of thermal power plants and nuclear power plants. In these conditions, the typical failure of P91 is mainly caused by creep at low stress. In this investigation the short-term creep behavior in P91 at low stress was investigated by helicoid spring creep test due to its high strain-sensitivity. The helicoid spring creep was based on the assumption of pure torsion. The mechanics field was firstly studied by ANSYS finite-element simulation to find the establishing conditions of pure torsion. Secondly, the creep properties of P91 were studied under the conditions of the temperatures of 0.38Tm<T<0.46Tm and the stresses of 14.6 MPa, 25 MPa, 34 MPa, respectively. The ANSYS finite-element simulation shows that the creep deformation is considered to be pure torsion when the pitch spacing of coil is between 2mm to 4mm. The creep curves show "Normal type ", and “the stress exponent” is n=0.9.

An IIW residual stress profile estimation scheme for girth welds in pressure vessel and piping components

Over the years, one major objective of IIW Joint Working Group (JWG) on residual stresses and distortion prediction (RSDP) has been the development of consistent residual stress profiles for supporting fitness-for-service assessment of welded components. As a result of the JWG activities and further in-depth investigations, this paper presents a major development on a novel full-field residual stress estimation scheme that can be used for describing through-thickness residual stress profiles not only within a weld region, but also at any location away from a weld in pressure vessel and piping components. Within weld region, a systematic parametric finite element analysis is used to establish key parameters that govern through-thickness residual stress distribution characteristics by introducing membrane, bending, and self-equilibrating based decomposition technique. Away from weld region, a shell theory based method is developed for describing through-thickness residual stress distribution at any distance away from weld toe. This paper presents detailed results for single “V” joint preparation with pipe wall thickness varying from 6.25 to 250 mm and wall thickness to pipe radius ratio (r/t) varying from 2 to 100. The residual stress estimation method can be applied for double V and narrow groove joint preparations for girth welded components since all three joint preparations have been shown to follow a similar functional form to that seen in single V joint preparation.

Fracture studies on carbon steel elbows having part-through notch with and without internal pressure

Elbows are one type of components widely used in various industrial applications in conventional and nuclear power generating plants, chemical processing plants and petroleum refineries. Due to the complexities of geometric structure, elbows are one of the piping components that are prone to failure in the piping system of nuclear power plants (NPPs). In service, the piping components are subjected to internal pressure in addition to bending loads, and the internal pressure is known to have significant effect on the load carrying capacity of these components. Hence, fracture studies were carried out on 406 mm diameter elbows with and without internal pressure. The investigations have shown that the location of notch plays an important role in the load carrying capacity of the elbows and their failure behaviour. The internal pressure reduced the load carrying capacity of the elbow when the notch was located at the intrados in circumferential direction and the behaviour is vice-versa when the notch was located at the intrados in an axial direction, when subjected to opening moment, in both the cases.

Weld repair of Grade 91 piping and components in power generation applications, creep performance of repair welds

Creep strength-enhanced ferritic steels, such as Grade 91, are the preferred material for much of the high-energy boiler tubing and piping components used in modern power generating plants. Weld repair techniques that achieve the necessary performance without the need for high-temperature post weld heat treatment (PWHT) offer particular benefits for Grade 91 steel. These benefits arise since there are many examples of poor heat treatment control which have resulted in component microstructures with below the minimum properties expected by design codes. Furthermore, even a controlled PWHT at temperatures at around 760 °C will further temper the base material. This is significant because excessive base metal tempering is one suggested criterion requiring component replacement. Successful demonstration of controlled welding techniques linked to minimal or no PWHT would alleviate these problems. This article presents results from a major project which is aimed at considering options for designing a ‘well-engineered’ repair. In this project, the creep performance of candidate repair methods was evaluated using large, feature test-type specimens containing the entire weldment including both fusion lines and heat-affected zones. The results show that the cross-weld life in Grade 91 steels does not appear to be a function of whether or not the welding procedures include PWHT. The results offer the potential to qualify ‘cold’ weld repairs in these steels.

Two-parameter fracture characterization of a welded pipe in the presence of residual stresses

In this paper two-parameter fracture characterization of elastic and elastic-plastic stress/strain field around a crack front is presented for a welded pipe component containing a circumferential through-thickness crack. A macro function programmed in PYTHON is used to compute the constraint parameters (T-stress, Tz and Q factors) of the specimen in the open source finite element package Code_Aster. Data obtained from literature was employed to support three-dimensional finite element models developed in this research to study the impact of high magnitude repair-weld residual stresses. Complete distributions of the T-stress, Tz and Q-factors were obtained along a 3D crack front in the presence of residual stresses. The effects of stresses (residual and operational) on the constraint parameters are studied. It is shown that a two-parameter methodology provides effective characterization of three dimensional elastic–plastic crack tips constraint.

Evaluation of risk levels in static mechanical equipment: a fuzzy expert system approach

It is necessary to evaluate the risk levels in piping components of offshore production and process facilities (OP&PFs) to investigate potential failures. In an OP&PF, piping plays a vital role within the static mechanical equipment. Inspection planners make recommendations on the thickness measurement locations (TMLs) to be monitored based on: historical data, risk-based inspection (RBI) analysis results, plant inspection strategy guidance, etc. The inspection plans made by inexperienced inspection planners are of poor quality compared to an inspection plan made by an experienced inspection planner. Hence, to mitigate the problem, it is vital to develop expert systems to support inexperienced inspection planners and minimise suboptimal decisions. This manuscript illustrates the use of a fuzzy inference system (FIS) as an expert system for making optimal in-service inspection recommendations based on the current status and trends of TMLs. The proposed FIS enables the expertise of experienced inspection planners to be incorporated via membership functions (MFs) and a rule base, which will maintain the quality of an inspection programme at the intended level.

Experimental and simulated displacement in cracked specimen of P91 steel under creep conditions

The assessment of crack initiation and propagation under creep conditions is important in the remaining life prediction of pipe components for power generation industry. One of the most successful analytical parameters for describing crack propagation under steady-state creep conditions is the C*-Integral that depends strongly on the material’s creep behavior and the resulting load-line displacement. This study deals with the determination and optimization of a creep model for a P91 grade steel operating at 600 °C. After a good fit provided by the model with uniaxial creep tests was found, the creep behavior of compact type C(T) specimens was modeled to predict creep crack growth (CCG) rates. A modified Cocks and Ashby power law creep controlled cavity growth model was used to compute the creep crack propagation rates. Load-line deflection was found to be strongly dependent on the primary creep strain rate. Lastly, good correlation between the experimental CCG results and the predicted CCG rates from the simulations were found.

Design and Analysis of Lightweight Automotive Component for Turbocharger Units

Nowadays global warming in parallel with air pollution is a significant problem. One of the major causes is the conventional fuel-powered automobile. This study focuses on reducing global warming caused by automobiles. This paper presents the results of redesign and analysis of piping component of a turbocharger unit from a new material in order to reduce the weight and unify the component from only one material. The existing component is composed of three different parts and materials. With the new design, in addition to the lightweight property, the component is designed in such a way that two separate parts of existing design are unified in a single part which simplifies the assembly of the component to the turbocharger unit. The design starts with choosing the convenient material to satisfy the necessary service conditions such as high temperature and pressure. Two different materials are considered for the analyses which are aluminium alloy and PA66+PA6-HI glass fiber reinforced plastic matrix composite material. Firstly, finite element analyses were performed by using a commercial software. The results of the finite element analyses showed that both materials showed resistance to tensile load of 4000 N and pressure of 0.4 MPa at 22℃ . However, if two separate parts were unified with a single part made of aluminium alloy, this component would fail under pressure of 0.4 MPa at 150℃ and 210℃, while the component made of PA66+PA6-HI glass fiber reinforced plastic matrix composite material resisted the pressure at higher temperatures. Tensile tests under 4000 N and pressure tests under 0.4 MPa at temperatures of 22℃, 150℃ and 210℃ were carried out on the component produced by PA66+PA6-HI glass fiber reinforced plastic matrix composite material. The same results were observed with those obtained by the finite element analyses. The design with the composite material satisfies both the mechanical and lightweight considerations.

Ultimate Strength of a Thin Wall Elbow for Sodium Cooled Fast Reactors Under Seismic Loads

With a purpose of identifying the failure mode and associating the ultimate strength of piping components against seismic integrity, many kinds of failure tests have been conducted for thick wall piping for light water reactors (LWRs). However, there are little failure test data on thin wall piping for sodium cooled fast reactors (SFRs). In this paper, a series of failure tests on thin wall elbows for SFRs is presented. Based on the tests, the failure mode of a thin wall piping component under seismic loads was identified to be fatigue. The safety margin included in the current design methodology was clarified quantitatively.

Experiences of utility microtunnelling in Irish limestone, mudstone and sandstone rock

There is currently no published guidance on the excavatability of Irish rock for microtunnelling applications. In this paper, new data and experiences of microtunnelling through rock (using a Herrenknecht AVN slurry shield machine with a rock head) at five Irish sites are presented and interpreted. The rock type is limestone at three of the sites, with mudstone/conglomerate and sandstone at the other two sites. The jacking forces are separated into face and friction (between the concrete pipe and rock) components. Useful relationships have been established between the excavatability index and the uniaxial compressive strength and brittleness index of rock. Cutter head wear is discussed in the context of rotational distance travelled and rock strength. In addition, the suitability of a number of prediction models documented in the literature for the prediction of microtunnel boring machine performance in Irish rock is examined.

Technical Basis for Application of Collapse Moments for Locally Thinned Pipes Subjected to Torsion and Bending Proposed for ASME Section XI

Piping components in power plants may experience combined bending and torsion moments during operation. There is a lack of guidance for pipe evaluation for pipes with local wall-thinning flaws under the combined bending and torsion moments. ASME boiler and pressure vessel (B&PV) Code Section XI Working Group is currently developing fully plastic bending pipe evaluation procedures for pressurized piping components containing local wall thinning subjected to combined torsion and bending moments. Using elastic fully plastic finite element (FE) analyses, plastic collapse bending moments under torsions were obtained for 4 (114.3)–24 (609.6) in. (mm) diameter pipes with various local wall-thinning flaw sizes. The objective of this paper is to introduce an equivalent moment, which combines torsion and bending moments by a vector summation, and to establish the applicable range of wall-thinning lengths, angles, and depths, where the equivalent moments are equal to pure bending collapse moments.

Effect of Pipe Bend Configuration on Guided Waves-Based Defects Detection: An Experimental Study

Ultrasonic guided waves is one of the most effective nondestructive testing techniques, which has been successfully applied for damage detection and evaluation of piping components. However, research about defects detection for pipelines with multiple bends is still limited. In this paper, effect of pipe bend arrangement on guided waves-based defect detection is investigated by experimental method, in which different configurations including space-Z type, U type, and plane-Z type are considered, respectively. Finite element (FE) simulation is used to explore the propagation behaviors of axisymmetric L (0, 2) mode in different bend configurations. On this basis, the detection sensitivity for different crack locations is experimentally investigated. Simulation and experiment results reveal that feature of guided waves propagation across the first and the second bend is totally different, and the defect detection sensitivity in the second bend is different from that in the first bend.

TOWARDS IMPROVED LEARNING OF FLUID MECHANICS VIA INTEGRATION OF A COMMERCIAL SOFTWARE PACKAGE INTO AN UNDERGRADUATE COURSE

The integration of software packages intochemical engineering courses is widely regarded tobenefit students in two ways. First, the active learningenvironment encourages a deep understanding of thecourse material. Second, it gives students practicalexperience with ‘state of the art’ tools that are used inindustry. However, surveys of chemical engineeringprograms have shown that the use of software packagesinto traditional fluid mechanics courses is quite low (lessthan 10%). Recently, the software package PIPE-FLO(from Engineered Software Inc.) was integrated into thesecond-year fluid mechanics course (ChE 2O04) atMcMaster. The software performs a full hydraulicnetwork analysis for a variety of piping configurationswith numerous piping components such as pumps,compressors, and control valves. The implementation ofPIPE-FLO as a simulation tool is in accordance with therecent initiative by the Canadian EngineeringAccreditation Board (CEAB) to determine directions forprogram improvement. A set of ten self-guided tutorialswere prepared to teach the students how to use the fullprofessional version of PIPE-FLO that was available inthe campus computer labs. Each tutorial was developedto enhance the understanding of the theory learned inclass and included references to the appropriateequations from the course textbook. Feedback from thestudents was overwhelmingly positive and encouragedgreater integration of the software into future offerings ofthe course.

These Pipes Have Passed

This article discusses need for introducing new standards for developing efficient piping systems. A barrier to wider adoption of the material has been the absence of non-metallic piping standards that could serve as a common language for manufacturers, fabricators, designers, and other stakeholders. The development of the new standards also reflects the growing international role of ASME standards. The intent of ASME NM-1 is to set engineering requirements for safe design and construction of thermoplastic piping installations. The ASMI NM-2 is expected to address pipe and piping components which are produced as standard products, as well as custom products designed for specific applications. The ASME NM-3 Standard intends to provide greater uniformity, consistency, and transparency for the identification and establishment of physical properties and allowable stress values for materials in non-metallic piping systems. The standards for thermoplastic and fiberglass reinforced plastic piping systems are being developed to fill the unmet need for comprehensive documents in these areas.

Low-Cycle Fatigue and Ratcheting Responses of Elbow Piping Components

The objective of this study was to investigate low-cycle fatigue and ratcheting responses of elbows through experimental and analytical studies. Low-cycle fatigue and ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquake and/or thermomechanical operation. Ratcheting and fatigue damage accumulation can cause failure of piping systems through fatigue cracks or plastic buckling. However, the ratcheting damage induced failures are yet to be understood clearly; consequently, ASME Code design provisions against ratcheting failure continue to be a controversial issue over the last two decades. A systematic set of piping component experimental responses involving ratcheting and a computational tool to simulate these responses will be essential to rationally address the issue. Development of a constitutive model for simulating component ratcheting responses remains to be a challenging problem. In order to develop an experimentally validated constitutive model, a set of elbow experiments was conducted. The loading prescribed in the experiments involved displacement-controlled or force-controlled in-plane cyclic bending with or without internal pressure. Force, displacement, internal pressure, elbow diameter change, and strains at four locations of the elbow specimens were recorded. This article presents and discusses the results from the experimental study. A sister article evaluates seven different constitutive models against simulating these elbow ratcheting and fatigue responses.

Constitutive Models in Simulating Low-Cycle Fatigue and Ratcheting Responses of Elbow

As stated in the sister article that the objective of this study was to explore the low-cycle fatigue and ratcheting failure responses of elbow components through experimental and analytical studies. Low-cycle fatigue and ratcheting damage accumulation in piping components may occur under load reversals induced by earthquakes or thermomechanical operations. Ratcheting damage accumulation can cause failure of components through cracking or plastic buckling. Hence, design by analysis of piping components against ratcheting failure will require simulation of this response with reasonable accuracy. In developing a constitutive model that can simulate ratcheting responses of piping components, a systematic set of elbow experiments involving deformation and strain ratcheting were conducted and reported in the sister article. This article will critically evaluate seven different constitutive models against their elbow response simulation capabilities. The widely used bilinear, multilinear, and Chaboche models in ansys are first evaluated. This is followed by evaluation of the modified Chaboche, Ohno–Wang, modified Ohno–Wang, and Abdel Karim–Ohno models. Results from this simulation study are presented to demonstrate that all the seven models can simulate the elbow force response reasonably. The bilinear and multilinear models can simulate the initial elbow diameter change or strain accumulation, but always simulate shakedown during the subsequent cycles when for some of the cases the experimental trends are ratcheting. Advanced constitutive models like Chaboche, modified Chaboche, Ohno–Wang, modified Ohno–Wang, and Abdel Karim–Ohno can simulate many of the elbow ratcheting responses well, but for some of the strain responses, these models simulate negative ratcheting, which is opposite to the experimental trend. Finally, implications of negative ratcheting simulation are discussed and suggestions are made for improving constitutive models ratcheting response simulation.

Production of rolled steel with specified surface roughness

The formation of microrelief on sheet, strip, pipe, and other rolled components is studied. With increase in the demand for high-quality products, requirements on the surface roughness are becoming more stringent. The influence of the rolling and tempering of sheet, strip, and tinplate on the impressions left by the roller surface on the product is considered. Recommendations are made regarding the selection of rolling conditions.

Experimental Validation of the Innovative Thermal Energy Storage Based on an Integrated System “Storage Tank/Steam Generator”

Abstract In the past years, an innovative thermal energy storage system at high temperature (up to 550C) for CSP plants was proposed by ENEA and Ansaldo Nucleare: a single storage tank integrated with a steam generator immersed in the heat storage medium. The idea is based on the exploitation of the thermophysical characteristics of the heat storage medium (a binary mixture of salts of NaNO3 at 60% and KNO3 at 40%) in order to maintain over time, in the single tank, a thermal stratification of the fluid. The thermal stratification is able to trigger, in the immersed steam generator, the natural circulation, shell side and downwards, of the hot molten salt cooled down by the water that flows upwards tube side, thus heating up and producing superheated steam. The advantages of such a system are: - efficient performances; - simple implementation; - compactness: - modularity; - and, overall, contained costs: only one storage tank instead of the two tanks and only one heat exchanger instead of the three exchangers of the classic configuration; reduced quantity of salt; minimization of piping, valves and other components. The technical feasibility of the proposed system, together with the stability over time of the stratification in temperature of the storage medium, have been already verified and assessed. This report has the aim of presenting the experimental results obtained by ENEA in the Casaccia Research Centre (Rome, Italy), with a small scale test section consisting of a 300 kWth steam generator inserted in a 8 m3 storage tank with molten salt at high temperature. The reported results relate to the behaviour of the system in steady state conditions, and show its promising performances.

Molten Salt as a Heat Transfer Fluid in a Linear Fresnel Collector – Commercial Application Backed by Demonstration

Abstract Motivated by the need of thermal storage, Novatec decided in 2012 to put the major product development focus on the development of the direct molten salt technology, applying molten salt directly as a heat transfer fluid (HTF)in Fresnel collector solar fields. After an intense engineering phase, Novatec started the experimental testing of molten salt specific issues in 2013. Several small-scale demonstrators with a cumulated pipe length in the order of 1 to 30 m have been built to gain first experience with salt-specific challenges such as Joule heating and salt freezing and re-melting. End of 2013, a demonstrator consisting of all piping and process components that will be used in future direct molten salt plants has been built, including over 550 m of solar receiver and connection piping. This paper presents the major challenges of future large-scale direct molten salt plants from today's perspective and how they were addressed experimentally including the testing results. To conclude: So far, all previously expected challenges related to the use of molten salts in Novatecs solar collector pipes have been experimentally tested. As a result, no point of concern for the use of molten salt as HTF was found. Even if freezing occurs, which likely can be avoided by night circulation or draining, measures have been proven to safely re-thaw the salt again. The testing was performed with HITEC® salt mixture.