Full Pipe Research Articles

Improvement in Welding of Austenitic Stainless Steel Thick Pipe: Metallurgical, Mechanical & Full Scale Pipe Weld Tests

The paper aims at demonstration of reduction in residual stress, distortion and sensitisation in austenitic stainless steel pipe welds. The welding processes considered are Gas Tungsten Arc Welding (GTAW) and Shielded Metal Arc welding (SMAW) along with Hot wire GTAW with narrow gap welding technique. It was shown that residual stress is significantly reduced in case of hot wire GTAW. The reduction in residual stress is due to the low heat input and high deposition rate. Lower heat input leads to higher cooling rate giving more margins on sensitization in heat affected zone (HAZ). This has been confirmed by measuring temperature and cooling rate during welding in HAZ of the weld joints. Susceptibility to sensitization of the welds has been compared by carrying out ASTM E262 Practice A and E along with Electo-Potentiokinetic Reactivation (EPR) method. The results of the tests show that values are within acceptable limit for both the cases. However, hot wire GTAW has marginally better sensitization resistance. Fatigue crack growth rate and fracture resistance behavior of the above mentioned weld joints have been compared by carrying out tests on the specimens (Compact Tension) and full scale pipe welds with crack. Fatigue crack growth rate and fracture toughness of the weld joints (hot wire GATW) is superior to conventional GTAW and SMAW. The paper presents the details of the above mentioned studies.

Experimental investigation of entrapped air pocket in a partially full water pipe

The effect of air pocket during rapid filling of partially full pipe with dead end is investigated experimentally. The air–water flow patterns are observed with a high-speed camera. Pressure histories synchronously recorded are also presented to illustrate the relations between the air–water phase evolutions and the pressure oscillation patterns. Experiments indicate that tailwater is beneficial to reduce air pressure surge. Having the same air volume, the case with thinner or no tailwater can result in the larger pressure surge. The highest pressure fluctuates dramatically with the increase of initial air volume (involved in changing air length and tailwater depth). However, the trends of measured results show the maximum air pressure first increases and then decreases if initial air pocket volume increases at a given initial tailwater depth or air length. Moreover, the ratio of the maximum pressure to upstream inlet pressure increases as upstream inlet pressure increases.

Seismic fragility evaluation of piping system installed in critical structures

Seismic performance of critical facilities has been focused on the structural components over the past decade. However, most earthquake damages were observed to the nonstructural components during and after the earthquakes. The primary objective of this research was to develop the seismic fragility of the piping system incorporating the nonlinear Tee-joint finite element model in the full scale piping configuration installed in critical facilities. The procedure for evaluating fragility curves corresponding to the first damage state was considered the effects of the top floor acceleration sensitivities for 5, 10, 15, and 20 story linear RC and steel building systems subjected to 22 selected ground motions as a function of ground motion uncertainties. The result of this study revealed that the conditional probability of failure of the piping system on the top floor in critical facilities did not increase with increased level of story height and in fact, story level in buildings can tune the fragilities between the building and the piping system.

Combined numerical-experimental framework for strain based design and flaw assessment of girth welds

An increasing number of transmission pipelines have to be installed and operated in harsh conditions, due to the diminishing reserves of exploited fossil fuel sources. Under certain environment related circumstances, longitudinal plastic strains are imposed. When tensile, these may induce failure in girth welds in conjunction with the inevitable presence of weld defects. A large number of factors related to environment, material, geometry and operating conditions influence the tensile strain capacity and, hence, the acceptability of girth weld flaws. Therefore, a project specific development of guidelines in this strain based context is recommended. This paper provides systematic frameworks on (a) how to design pipelines under strain based conditions, and (b) how to assess girth weld flaws that were detected using non destructive testing. Attention is given to several technical and economical aspects related to the selection and qualification of pipe and weld metals, and to the evaluation of flaw acceptability. Both frameworks comprise a combined experimental-numerical approach, collecting project development reports from literature with research carried out at Soete Laboratory. Concretely, four in-house realizations are adopted: the UGent equation for strain capacity, the curved wide plate tension test, the UGent stress-strain equation and a finite element model of full scale pressurized pipe tension testing. The proposed frameworks aim to facilitate in performing thorough and economically justifiable strain based design and assessment processes.

Research of Drilling Gas Kick and Blowout Characteristic Based on The Volume of Fluid Model

The accident of drilling blowout out of control is a serious drilling accident. One of the measures that prevent this accident is detecting gas kick early. Mud pool liquid level method is one of the most widely used methods. But, due to the drilling bell mouth is exposed to the atmosphere, drilling fluid in the return pipe flow is not a full pipe flow but a free flow. When the gas kick was tiny, the change of mud pool level is unobvious and Liquid level detection device could not measure the level changes effectually. Drilling fluid return flow can’t be measured, and the error was so great that can’t detect the gas kick early. Air and drilling fluid (non-Newtonian fluid) were taken as mediums, to simulate the drilling fluid liquid level when drilling fluid return flow changed based on the Volume of Fluid multiphase flow model, then the characteristic of liquid level change in the return pipeline was analyzed with different gas rate in drilling fluid. It concluded that the liquid level in the bell mouth was changing obviously, when the drilling fluid has been changed with none gas. Give a suggest that Liquid level detection should be installed on the bell mouth in drilling fluid return pipe in order to find gas kick more accurately and effectively earlier. The gas kick rate has a great impact on the stability of the drilling fluid liquid level in the return pipeline.

Fatigue Crack Growth Behavior in Pipes and Elbows of Carbon Steel and Stainless Steel Materials

Abstract The objective of the present study is to understand the fatigue crack growth behavior and validate analytical procedures for austenitic stainless steel and carbon steel pipes, pipe welds and elbows. The study involved fatigue tests on actual components and specimens. The Paris law has been used for the prediction of fatigue crack growth life. Paris constants have been determined for pipe (base), pipe weld and pipe elbow materials by using Compact Tension (CT)/Three Point Bend (TPB) specimens machined from the actual pipe, pipe weld and pipe elbow. Analyses have been carried out to predict the fatigue crack growth life of these piping components having part through cracks on the outer surface. In the analyses, Stress Intensity Factor ( K ) has been evaluated through two different schemes. The first scheme considers the ‘ K’ evaluations at two points of the crack front i.e. maximum crack depth and crack tip end at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (KRMS) at deepest and surface points. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipes, pipe welds with part through circumferential crack. The tests have also been conducted on the full scale carbon steel elbows having part-through circumferential notch at intrados location and axial notch at crown location on the outer surface. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (KRMS) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme.

Transcribing the Venda tshikona reedpipe dance

Starting with the end result, the above transcription is the conclusion I came to after sitting with Laina Gumboreshumba for many hours, watching the videos she made during her recent doctoral research on the tshikona reedpipe dance of the Venda of Limpopo Province in the extreme north of South Africa. The transcription shown in Figure 2 is a skeleton version of the full pipe sound that contains all the information needed to grasp the structure of the sound and teach it or play it. There are always seven different pipes. A full tshikona group has far more than the seven pipes (nanga) shown, because all seven pipe numbers are doubled in every octave present in a group, so there may be up to four or more Pipe 1s, Pipe 2s, etc, of different sizes. All the Pipe 1s play the same pattern together, all the Pipe 2s etc. There are usually four octaves in all, with an incomplete octave of a few higher pitched pipes at the top (phalana). A popular size for a group according to group leaders (malogwane) is twenty eight pipes, which may include some pitch duplicates. A festive performance can number well over one hundred players. The music is heptatonic as you can see from the transcription, and hear for yourself from CD track 1 accompanying this issue of African Music. A chart showing the tuning is included as Figure 1 1 at the end of this article. This article does not address the pipe names; they are simply numbered Pipes 1 to 7, in the order of entry in Mr Netshivhale’s groups. The pipes are end-blown, closed tubes made of a special bamboo, or increasingly today of electrical or other tubing.3 (See Figure 3)

Influence and evaluation of constraint on fracture toughness in pipeline research

Accessing nowadays fossil fuel reserves requires a strain-based design approach. Within suchdesign, the ductile tearing resistance is a key parameter in assessing the defect tolerance. To determinethis tearing resistance, full scale (pressurized) tests can be performed. However, such approach would becostly and time consuming. Consequently, effort is made to select appropriate small scale test specimens.Most research has focused so far on the single edge notch bend (SENB) and tensile (SENT) specimen. Toevaluate the suitability of these test specimens, the crack tip stress fields can be examined or theresistance curves compared with full scale structures. This paper aims at comparing the trends observedusing these techniques. Furthermore, the suitability of the small scale test specimens is evaluated. It isconcluded that sufficiently long (length-to-width ratio equal to ten) clamped SENT specimens have thepotential to predict the tearing resistance of full scale pipes. In addition, the internal pressure does notsignificantly affect the fracture toughness. These conclusions are stated by both experimental results andfinite element simulations.

Impact of treatment on Pb release from full and partially replaced harvested Lead Service Lines (LSLs)

Release of lead from 80% partially replaced service lines was compared to full lead service lines using harvested–stabilized lead pipes and field brass connectors. After more than a year of stabilization, lead release was consistent with field samples. Over the relatively short duration partial replacement of lead pipe by copper pipe (3 months), generated high lead release, attributed to galvanic corrosion, resulting in a final outcome for lead release that was even worse than for a full lead pipe. Increased lead release was especially evident at higher flow rates. Orthophosphate reduced lead release from full lead pipes by 64%. For partially replaced samples with copper, lead concentrations were unchanged by phosphate dosing at moderate flow (103 ± 265 vs 169 ± 349 μg/L) and were increased to very high levels when sampled at high flow rates (1001 ± 1808 vs 257 ± 224 μg/L). The increase lead release was in the form of particulate lead (>90%). In comparison to the condition without treatment, increased sulfate treatment had little impact on lead release from 100%-Pb rigs but reduced lead release from partially replaced lead pipes with copper. Our results also raise questions concerning protocols based on short 30 min stagnation (as those used in Canada) due to their incapacity to consider particulate lead release generated mostly after longer stagnation.

Neutron diffraction residual stress measurements on girth-welded 304 stainless steel pipes with weld metal deposited up to half and full pipe wall thickness

The residual stress distribution has been measured in two girth-welded austenitic stainless steel pipe weldments using time-of-flight neutron diffraction. One had weld filler metal deposited up to half the pipe wall thickness, and one had weld metal deposited up to full pipe wall thickness. The aim of the work is to evaluate the evolution in residual stress profile on filling the weld, on which there is little experimental data, and where the selection of the correct hardening model used in finite element modelling can benefit greatly from an understanding of the intermediate residual stresses partway through the welding operation. The measured residual stresses are compared with those calculated by finite element modelling and measured using X-ray diffraction. The results show a change in the measured hoop stress at the weld toe from tension to compression between the half- and fully-filled weld. The finite element results show an overprediction of the residual stress, which may be a consequence of the simple isotropic hardening model applied. The results have implications for the likely occurrence of stress corrosion cracking in this important type of pipe-to-pipe weldment.

Modelling and simulation of gas dynamics in an exhaust pipe

The gas dynamics in an exhaust pipe is studied. In particular we focus on the warm up of the catalytic converter in very short times after the engine start. This is done by combustion a small unburnt part of the exhaust gas. This process is classically modelled by gas dynamic equations. Compared to the existing literature we improve the (one-dimensional) modelling approach using a small Mach number technique and a network ansatz for the full exhaust pipe. The final simplified model on one hand still describes the main features and on the other hand it is computationally a few orders of magnitude faster than the original model. Performing numerical simulations we compare the new model to the (classical) full model and to experimental results in the literature.

Local head loss monitoring using acoustic instrumentation in partially full sewer pipes

After an increase in capital investment in UK sewers to reduce hydraulic capacity problems, the proportion of sewer flooding incidents now linked to blockages has increased. It is clear that if sewer operators are to continue to reduce flooding incidents, then better blockage management is now required. Sewer blockage formation is poorly understood; blockages are intermittent and occur in a number of circumstances. This paper reports on the development of low-cost acoustic instrumentation that can identify the location of a pipe blockage and then estimate the local head loss as a result of the presence of a blockage. A set of experiments were carried out in two full-scale laboratory pipes. The pipes' condition was altered by inserting blockages of different sizes. Acoustic data were recorded and presented in terms of the acoustic energy reflected from the partially blocked pipe. The results of this study show that the total reflected acoustic energy correlates with the measured head loss. A new empirical relation between the reflected acoustic energy and head loss due to a blockage is derived. This knowledge can then be used to estimate the reduction in flow capacity resulting from a blockage based on a single remote measurement.

Parametric finite element model for large scale tension tests on flawed pipeline girth welds

The structural response of a pipe with a flawed girth weld, subjected to global plastic deformation is influenced by a large number of geometrical and material properties. Finite element models that aim to simulate this need to include all relevant influence factors, which causes high challenges in the creation of such models. In search for a high degree of flexibility, automation and ease of use, the authors have developed a parametric script that creates geometries for two common pipeline girth weld tension tests: the curved wide plate test and the full scale pressurized pipe tension test. The developed model allows to modify pipe geometry, test specimen geometry, flaw position (weld metal centre or heat-affected zone), flaw size, weld misalignment, pipe thickness variations, weld fusion line profile, and weld cap profile. The desired geometry is obtained by a coordinate transformation scheme that starts from a flat plate with a simplified weld geometry. A deliberate partitioning strategy is applied to obtain flexibility in the flaw location and full independence between a fine flaw mesh and a coarse body mesh. This article describes the approach, structure and governing equations of the model. An example geometry is discussed to illustrate the various possibilities. The proposed model provides inspiration for all who seek to develop parametric finite element models with a similar flexibility and ease of use.

Investigations of pulverized coal pneumatic conveying using CO2 and air

The pneumatic conveying experiments at the high solid–gas ratio (120–300kg/m3) were carried out to compare their conveying characteristics separately using CO2 and air as carrier gas. The differences between them are found to be related with fluidized state of pulverized coal in the feeding vessel and can be explained with material properties involving particle–gas interactions, permeability. Employing electrical capacitance tomography (ECT), the transition from full pipe flow to annular flow was observed with increasing the superficial gas velocity (3.0–8.5m/s) in the vertical pipe and the flow patterns with CO2 and air are found to be similar. The analysis shows there is a significant association between sharp fluctuations of the pressure signals and gas slug. When gas slug was observed in the pipe, there was a large pressure pulse. The occurrence of gas slug is also found to be higher in the transporting with CO2 as carrier gas. The pressure signals may therefore be used to identify gas slug appearing in the pipe. The energy analysis is presented to find that the energy consumption with CO2 is about 7.5% higher than that with air at the same gas flow rate, but the required energy with CO2 is increased by about 20% than that with air at the same solid mass flow rate.

Rapid detection of sewer defects and blockages using acoustic-based instrumentation

Sewer flooding incidents in the UK are being increasingly associated with the presence of blockages. Blockages are difficult to deal with as although there are locations where they are more likely to occur, they do occur intermittently. In order to manage sewer blockage pro-actively sewer managers need to be able to identify the location of blockages promptly. Traditional closed-circuit television (CCTV) inspection technologies are slow and relatively expensive so are not well suited to the rapid inspection of a network. This is needed if managers are to be able to address sewer blockages proactively. This paper reports on the development of an acoustic-based sensor. The sensor was tested in a full scale sewer pipe in the laboratory and it was shown that it is able to find blockages and identify structural aspects of a sewer pipe such as a manhole and lateral connection. Analysis of the received signal will locate a blockage and also provide information on its character. The measurement is very rapid and objective and so inspections can be carried out at much faster rates than using existing CCTV technologies.

Predictions for fatigue crack growth life of cracked pipes and pipe welds using RMS SIF approach and experimental validation

The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel pipes and pipe welds by carrying out analysis/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by using Compact Tension (CT) specimens machined from the actual pipe/pipe weld. Analyses have been carried out to predict the fatigue crack growth life of the austenitic stainless steel pipes/pipes welds having part through cracks on the outer surface. In the analyses, Stress Intensity Factors ( K) have been evaluated through two different schemes. The first scheme considers the ‘ K’ evaluations at two points of the crack front i.e. maximum crack depth and crack tip at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor ( K RMS) at deepest and surface points. Crack growth and the crack shape with loading cycles have been evaluated. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipe and pipe welds with part through circumferential crack. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor ( K RMS) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme. Fatigue crack growth in pipe weld (Gas Tungsten Arc Welding) can be predicted well using Paris constants of base material but prediction is non-conservative for pipe weld (Shielded Metal Arc Welding). Further, predictions using fatigue crack growth rate curve of ASME produces conservative results for pipe and GTAW pipe welds and comparable results for SMAW pipe welds.

Assessing the accuracy of fatigue life in surface-cracked straight pipes

The demonstration of leak before brake (LBB) based on fracture mechanics requires information on the initial size of a defect, initiation of crack growth from the inherent defect and subsequent crack growth rates. In the present paper the prediction methodologies have been tested for three different full scale pipes geometry experimentally tested data. The prediction accuracy of two SIF solutions available in the literature has also been judged. The effect of fatigue crack closure and corrections needed in the numerical prediction methodology using FEM have also been included. The results showed that the FEM could fairly predict the fatigue crack initiation and crack growth life of full-scale piping components having a constant depth crack profile.

Ezatollah Raeisi: Iran’s foremost professor of hydrogeology

The contribution of scientists born in Iran to both hydrological and hydrogeological sciences is substantial. However, one can call Prof. Ezatollah (Ezzat) Raeisi (pictured in Fig. 1), from Shiraz University, the father of groundwater hydrology in the country. He was born in 1944 in Ardekan, a small city in Fars province in southern Iran. With the exception of his PhD study, which was at Colorado State University, Fort Collins (USA), and a short period at Iran’s Scientific Research Centre, Prof. Raeisi has spent his entire academic career of 46 years, continuing to the present, at Shiraz University. Prof. Raeisi spent his periods of sabbatical leave, about nine months each, as visiting professor at the Mississippi State University (1995–1996) and the Western Kentucky University (2003–2004) in the USA. Similar to many high-profile hydrogeologists such as P. Witherspoon and W. B. White from the USA, Prof. Raeisi did not study geology as an undergraduate student. He completed his BSc (in 1968) and MSc (in 1970) in irrigation sciences at the Faculty of Agriculture, Shiraz University; then he switched to hydrology for his PhD studies at Colorado State University. This is why his first papers appeared in agricultural journals (e.g. Sepaskhah and Raeisi 1978). In 1984, he was employed as an Assistant Professor at the Department of Earth Sciences of Shiraz University; after 12 years he was promoted to the rank of Professor in 1996. In this institution, Prof. Raeisi formed a solid hydrogeology team and developed the curriculum for MSc and PhD studies in this field. He founded the MSc program in hydrogeology in 1988 and the PhD program in 1998. He has, so far, supervised more than 40 MSc and PhD students, a very valuable side-product of his extensive research career. His former students are now faculty members of a number of Iranian universities—e.g. Shahrood University of Technology, Shahid Beheshti University (Tehran), Tarbiat Moallem University (Tehran)—and senior research officers of consulting companies and government departments, and some are working in foreign countries in their field of expertise. Prof. Raeisi is a rather practical fellow. He has carried out countless research and consultancy projects. Excluding recently awarded grants, he has been successful in attracting funds for 13 large projects. The economic value of these grants is very high, especially when considering the economic situation and the low per capita gross domestic product for Iran (International Monetary Fund 2009). During his academic career, Prof. Raeisi has mainly focused on three different fields. Karst hydrogeology, especially around dam sites, is the first field which has been explored by Prof. Raeisi and his team (e.g. Raeisi et al. 1996; Ashjari and Raeisi 2006; Mohammadi et al. 2007a). Along these lines, one of his latest publications discusses the calculation of groundwater storage in karst aquifers with various types of boundaries without the need to drill boreholes (Raeisi 2008). Dye tracing for detection of leakage from dams forms his second area of research— note that Iran is said to rank among the first countries in the world in the field of dam construction (Khorasanizadeh 2008). In this regard, he has applied some basic research results to evaluate water tightness in several dam reservoirs in karstic regions (e.g. Mohammadi and Raeisi 2007; Mohammadi et al. 2007b, c; Karimi et al. 2007). Evaluation of karst springs based on the water-chemical composition and application of artificial tracers, as a way to understand groundwater behavior in karst regions, forms the third portion of Prof. Raeisi’s research (e.g. Raeisi and Karami 1997; Raeisi et al. 1999; Karimi et al. 2005). This approach, which was the focus of his early work, is now an established and widely adopted method of karst hydrology in Iran. In addition to the aforementioned three main fields, one of his former research areas was the characterization of caves in Iran (e.g. Raeisi and Kowsar 1997; Raeisi and Mylroie 1995), which led to the publication of a book, Iran Cave Directory, now in its second edition (Raeisi and Laumanns 2009). Prof. Raeisi has also touched on most other branches of hydrogeology such as artificial recharge (e.g. Raeisi and Koohyan 1998; Raeisi and Kowsar 1998), partial and full pipe flow Received: 7 June 2010 /Accepted: 15 November 2010

Evaluation of pipe bending reference stress equations

The use of a Failure Assessment Diagram (FAD) is widespread in the assessment of welddefects. To determine whether a defect is acceptable or not, this requires the calculation of a load ratio anda fracture ratio for the defect under consideration. Nowadays, many formulae are available to calculatethese two quantities and no clear guidance is given on which equation(s) should (not) be used. A partialclarification of this problem is achieved by comparing different reference stress equations. This article isconcerned with such comparison, for the specific case of welded pipes subjected to a bending load. A largeset of historical experimental data has been investigated in which defected pipes were subjected to anincreasing bending force until failure occurred. Two kinds of reference stress equations are considered, fullpipes subjected to a bending load and flat plates subjected to a uniform tension load. From the equationsunder consideration, the flat plate solution of Goodall & Webster and the empirical full pipe equations ofWilloughby and Wilkowski & Eiber describe the pipe failure in the most accurate way

A dimensionless number describing the effects of recharge and geometry on discharge from simple karstic aquifers

The responses of karstic aquifers to storms are often used to obtain information about aquifer geometry. In general, spring hydrographs are a function of both system geometry and recharge. However, the majority of prior work on storm pulses through karst has not studied the effect of recharge on spring hydrographs. To examine the relative importance of geometry and recharge, we break karstic aquifers into elements according to the manner of their response to transient flow and demonstrate that each element has a characteristic response timescale. These fundamental elements are full pipes, open channels, reservoir/constrictions, and the porous matrix. Taking the ratio of the element timescale with the recharge timescale produces a dimensionless number, γ, that is used to characterize aquifer response to a storm event. Using sets of simulations run with randomly selected element parameters, we demonstrate that each element type has a critical value of γ below which the shape of the spring hydrograph is dominated by the shape of the recharge hydrograph and above which the spring hydrograph is significantly modified by the system geometry. This allows separation of particular element/storm pairs into recharge‐dominated and geometry‐dominated regimes. While most real karstic aquifers are complex combinations of these elements, we draw examples from several karst systems that can be represented by single elements. These examples demonstrate that for real karstic aquifers full pipe and open channel elements are generally in the recharge‐dominated regime, whereas reservoir/constriction elements can fall in either the recharge‐ or geometry‐dominated regimes.