Rigid Pipe Research Articles

Effect of Bedding Thickness on Behavior of Rigid Pipes as Determined by Using Numerical Crack Modeling

Numerical analyses are performed to find the loading capacity of buried reinforced concrete pipes at different performance levels. Different geometrical and material parameters play an important role in the total behavior of the pipe system. The effects of bedding thickness, middle-bedding compaction level, steel cages, and pipe thickness are studied by using dynamic nonlinear analysis capable of modeling the complex cracking behavior of the concrete pipes. Contact elements are used for modeling the actual contact behavior between the pipe's surface and its surrounding soil. The Drucker–Prager plasticity model and the isotropic hardening plasticity model were used for soil and steel materials, respectively. Two structural performance levels are defined for pipes, the first one being the instance in which the crack initiates in the pipe's surface. The second-higher performance level is defined as the time in which the crack opens. The results of the study show that increasing the bedding thickness has a significant effect on the loading capacity of the system. This increase in capacity is more dominant for smaller-diameter pipes. Providing middle beddings with lower levels of compaction can also be effective in increasing the loading capacity of the pipes.

Experimental study of pressure fluctuations and flow perturbations in air flow through vibrating pipes

This paper discusses the results of an experimental study of the effect of pipe oscillations on the wall pressure field and flow rate through a metallic pipe with air flowing through it. The data presented in this paper show that the frequencies of pressure oscillations in a non-oscillating pipe are identical to the natural structural modes of the pipe suggesting the influence of structural properties on the fluid dynamics of the flow. The results presented in this paper also show that the wall pressure undergoes both a temporal as well as a spatial oscillation if the pipe is forced to oscillate periodically. The pressure oscillations are found to be harmonics of the pipe oscillations. There is a drop in the mean pressure when the pipe is subjected to periodic oscillations. The flow rate through the pipe is seen to undergo a periodic change over a range of almost 7 percent variation when the pipe is oscillated. The study presented in this paper elucidates the dominant effect of system dynamics on determining the flow behavior through a rigid pipe. The adverse effect of flow oscillations, induced by pipe motion, can lead to departure of the flow from the intended design conditions and can render the fluid supply system inadequate.

A refractive index-matched facility for fluid–structure interaction studies of pulsatile and oscillating flow in elastic vessels of adjustable compliance

The flow field in the respiratory and vascular system is known to be influenced by the flexibility of the walls. However, up to now, most of the experimental biofluidic investigations have been performed in rigid models due to the complexity and necessity of optical access. In this paper, a facility and measurement techniques for studying oscillating and pulsatile flow in elastic vessels will be described. The investigated vessel models have been adapted such that fluid-mechanical and structure-mechanical characteristics represent realistic blood flows in medium blood vessels. That is, characteristic parameters, i.e., the Reynolds and Womersley number, as well as mechanical properties of the flexible wall, i.e., the Young’s modulus and the material compliance, have been chosen to reasonably represent realistic flow conditions. First, a method to manufacture elastic models, which mimic the structure-mechanical properties of vascular vessels is described. The models possess a tunable compliance and are made of transparent polydimethylsiloxane. Second, the experimental setup of the flow facility will be elucidated. The flow facility allows to mimic pulsatile flow at physiologically relevant Reynolds and Womersley numbers. The precise form of the flow cycle can individually be controlled. Water/glycerine is used as flow medium for refractive index matching particle image velocimetry (PIV) measurements. The PIV recordings not only allow to assess the mean cross-sectional flow field but also further enable to simultaneously detect the movement of the flexible wall. Additionally, the local wall-shear stress can be obtained from the single-pixel line resolved near-wall flow field. To confirm the flow conditions of the oscillatory laminar flow inside the flow facility and to evaluate the ability to assess the flow field, measurements in a straight, uniform diameter, rigid Plexiglas pipe under identical conditions to those of the oscillating flow in the flexible vessel have been performed. The measurements of oscillating flow in the rigid pipe corroborate the experimentally obtained flow field and the wall-shear stress to well confirm Womersley’s analytical solution and thereby evidence the quality of the flow facility and of the measurement techniques. To further study the detectability of the vessel deformation, oscillating flow at Reynolds numbers based on the non-dilated vessel diameter D and peak velocities Re D ranging from 1,000 to 1,750 and at Womersley numbers α ranging from 5 to 17.5 has been investigated in an elastic vessel.

Laboratory Testing to Examine Deformations and Moments in Fiber-Reinforced Cement Pipe

Two 381 mm (15 in. nominal) diameter fiber reinforced cement pipes have been tested under embankment loading conditions to study pipe response in both low stiffness, fine grained backfill, and a high stiffness graded granular backfill. Pipe deformations and strains were measured and interpreted to provide insight into the effect of soil backfill on the deformations and moments that develop. Not surprisingly, the use of silty clay backfill resulted in greater pipe deflections while the stiffer granular backfill lead to greater load transfer to the surrounding ground. Calculations using elastic soil-pipe interaction theory were effective in estimating the observed changes in pipe diameter at typical service loads (overburden pressures of 100 kPa, i.e., 14.4 psi in the lower stiffness backfill and 200 kPa, i.e., 28.8 psi in the high stiffness backfill). Measured strain distributions show that the fiber reinforced pipe exhibited ovaling response similar to that seen for flexible and semiflexible pipes. As expected, tensile strains were observed on the outer surface at the springlines and the inner surface at the crown. Strains observed at the haunch were negligible, indicating that the bending moments within the pipe have conventional hourglass distribution, with negligible moments at shoulders and haunches. Differences in strain measured at the inner and outer surfaces were used with the elastic pipe modulus to calculate the experimental bending moments. Comparisons of those experimental bending moments with the bending moment calculated for a rigid pipe indicate that these FRC pipe structures are semirigid so that moments are reduced as a result of support provided by the surrounding soil. A design expression for moment arching factor (MAF or moment divided by the rigid pipe moments) developed in an earlier paper was found to provide reasonable estimates for the experimental moment values. Moment estimated using the design soil moduli of McGrath and MAF provide moment values that are reasonable and conservative relative to those that were observed.

Failure Mechanisms in Sand over a Deep Active Trapdoor

An experimental testing program was undertaken to investigate failure mechanisms induced by the active movement of a deep rectangular trapdoor underlying a granular soil. Reduced-scale models were tested under normal gravity as well as under an increased gravitational field using a centrifuge facility. Some models were used to evaluate the performance of both flexible and rigid pipes undergoing a localized loss of support. Failure mechanisms in the longitudinal direction of the models were characterized by a single, well-defined failure surface that developed within the limits of the trapdoor. However, failure mechanisms in the transverse direction of the models were characterized by multiple failure surfaces extending outside the limits of the trapdoor. Significant dilation of the soil located immediately above the trapdoor was identified in the failure of the models. The pattern of the failure mechanisms was found to be affected by the stress level and backfill density. Higher stress levels were found to lead to well-developed failure zones. The influence of backfill density was found to be more relevant in models involving flexible pipes. Pipes embedded within loose backfill were severely damaged after loss of support, while pipes embedded in dense backfill experienced negligible deformations. These results indicate that damage to pipelines caused by ground loss of support can be significantly minimized by controlling the compaction of the fill.

Special design of tuned liquid column-gas dampers for the control of spatial structural vibrations

The relevant low-frequency modes of plan-asymmetric tall buildings and those of bridges consist of coupled translational and torsional motions. We consider the locations of the modal centers of velocity of either the rigidly assumed floors or of the bridge cross-sections to be crucial for selecting the design and the “optimal” position of the liquid absorbers. Such a tuned liquid column-gas damper, TLCGD consists of a sealed rigid piping system that is partially filled with liquid (preferably water), whose dynamics can be derived using the nonstationary Bernoulli equation properly extended to account for the relative streamline in a moving reference system. Although both the construction and working principle of TLCGDs differ from tuned mass dampers (TMD), a geometric analogy exists between these absorber types. Consequently, in a first step modal tuning is performed by means of a transformation of the TMD optimal parameters, e.g., of the Den Hartog formulas, possibly followed in a second step by fine-tuning in state-space. Such a U- or V-shaped sealed liquid column-gas damper, i.e., with the gas-spring effect taken into account, is found suitable for applications in moderately plan-asymmetric buildings (the floors’ modal center of velocity falls outside of the floor plan) and for bridges with dominant horizontal vibrations. The novel design of a torsional sealed liquid column-gas damper, TTLCGD, turns out to have even higher efficiency in effectively damping strongly asymmetric buildings, where the floors’ modal centers of velocity lie inside of the floor plan: in that case of an alternative design, the mid-plane of the U-shaped TLCGD is bent to a cylindrical surface that might be “nearly closed” such that the trace in the floor becomes approximately a loop. For bridges with dominating vertical flexural vibrations, a novel pipe-in-pipe design of the VTLCGD provides the vertical control force rendering the additional efficient damping. The evident features of TLCGDs are no moving mechanical parts, cheap and easy implementation into civil engineering structures, simple modification of the natural frequency and even of the damping properties, low maintenance costs, little additional weight in those cases where a water reservoir is required, e.g., for the sake of fire fighting, and with a performance comparable to that of TMDs of the spring-mass- (or pendulum-)-dashpot type.

Research on the Pump–Vessel Combined Ore Lifting Equipment for Deep-Sea Rigid Pipe Mining System

Abstract It is known from the principle that the pump–vessel combined ore lifting method has high head, large ores lifting capacity, and long-term working reliability. When applied to the deep-sea rigid pipe mining system, the main pump and power equipment installed on the mining ship is more convenient to operate and maintain. According to Bernoulli’s equation and two phases of hydrodynamics theory, the ore lifting equipment parameters have been calculated and analyzed. It is known that the pump head H of 1000m sea mining system is 124–172m and that of 5000m sea mining system is 652–760m. It is known that the pump–vessel combined lifting method is feasible in both theory and practice, therefore it is an ideal ore lifting method for a deep-sea rigid pipe mining system.

A conservative model for unsteady flows in deformable closed pipes and its implicit second-order finite volume discretisation

We present a one-dimensional model for compressible flows in a deformable pipe which is an alternative to the Allievi equations and is intended to be coupled in a “natural way” with the shallow water equations to simulate mixed flows. The numerical simulation is performed using a second-order linearly implicit scheme adapted from the Roe scheme. The validation is performed in the case of water hammer in a rigid pipe: we compare the numerical results provided by an industrial code with those of our spatial second-order implicit scheme. It appears that the maximum value of the pressure within the pipe for large CFL numbers and a coarse discretisation is accurately computed.

Can an intermittent pneumatic compression system monitor venous filling in the leg?

Objective: Intermittent pneumatic compression (IPC) systems are used for prophylaxis of venous thromboembolism. Both legs are wrapped with inflatable sleeves connected to a pneumatic controller to allow compression of the legs causing expulsion of venous blood. Venous refill between inflation periods causes leg expansion, which can be tracked by measuring pressure changes in the sleeve. The aim of our study, which utilized the SCD RESPONSE compression system in conjunction with an independent pressure transducer, was to investigate whether factors such as temperature changes within the sleeves during inflation and deflation affect the measured venous refill time (VRT).Methods: Transducers were used to measure air pressure in the middle chamber of the sleeve. A thermocouple was also inserted into the bladder to measure temperature changes. Inflation, deflation and refill measurements were made with the sleeves around model systems (static, rigid plastic pipes or compliant paper rolls, and dynamic, latex tubes inserted between a rigid pipe and the sleeve to simulate veins) and on 10 subjects in semi-recumbent, supine and sitting positions.Results: In all the experiments the maximum temperature change was 0.023°C. With the static model systems, the pressure in the venous refill measuring bladder fell from the inflation pressure of 40 – 50 mmHg to 9 ± 1 mmHg, but then rose by 2.1 ± 0.2 mmHg (rigid pipes) and 1.4 ± 0.2 mmHg (paper rolls). These pressure changes were associated with reported ‘filling times’ of 21 – 24 s (rigid pipes) and 22 – 29 s (paper rolls). In experiments on dynamic filling of the latex tube, there was a strong linear relationship between the filling time indicated by the SCD system and the time to empty the filling reservoir. In 170 measurements on human subjects, there were only three VRTs less than 30 s and 36 less than 35 s. VRT increased in all subjects when going from supine (34.6 ± 1.8 s) to semi-recumbent (38.9 ± 1.9 s) to sitting (42.6 ± 0.9 s) positions.Discussion: In all cases, temperature changes during the refill phase were too small to result in significant pressure changes that would affect VRT. The pressure increases observed with the static models after deflation appeared to be due to viscoelastic relaxation. Viscoelastic responses were present in human subjects, but the effect on VRT was negligible. This indicates that the increased VRT observed in humans is due to blood return. Body position affected VRTs, indicating the system's ability to detect changes in filling times and venous blood volume.

Effects of Duct Types and Emulsifiable Oils on Bond and Friction Losses in Posttensioned Concrete

Emulsifiable oils are often used in posttensioned construction to reduce friction losses and provide temporary corrosion protection for tendons prior to grouting. This paper addresses the effects of two emulsifiable oils and three duct types on bond and friction losses. Bond test results indicate that corrugated galvanized steel ducts provide better anchorage than corrugated HDPE ducts. Rigid steel pipes performed poorly because of failure at the duct-concrete or grout-duct interface. Bond test results also indicate that the ultimate strength of posttensioned specimens with oiled tendons is similar to or better than the ultimate strength of specimens with unoiled tendons. However, specimens with oiled tendons experienced greater slip at a given load than specimens with unoiled tendons. Friction test results indicate that current recommended design values for the coefficient of friction for steel pipes and galvanized ducts are accurate. However, the measured coefficient for HDPE ducts is significantly less than the AASHTO-recommended value. Friction tests also indicate that lubrication of the tendon reduces the friction coefficient by 15% in rigid steel pipes and HDPE ducts if stressing occurs while the oil is fresh.

Nontarget Image-Based Technique for Small Cable Vibration Measurement

In this paper, a proof-of-concept image-based technique is proposed for measuring small cable vibration. The technique analyzes an image sequence of a vibrating cable segment captured by a camera. An optical flow method is used to calculate variation of optical intensity of an arbitrary selected region of interest ROI on the cable image sequence. The obtained optical flow vector provides the direction of vibration for the ROI on the cable segment, which then can be used to estimate displacement of the ROI on the image plane. Furthermore, actual displacement of the ROI can be extracted when some conditions are met. The proposed technique is validated both in the laboratory using a rigid pipe and in the field on a small pedestrian bridge cable. Results show that the technique is able to measure the pipe motion and the cable vibration accurately. The proposed technique requires only one commercial camera, and no prior camera calibration is needed. In addition, the use of an optical flow method eliminates the need to attach any target to the cable and makes the technique very easy to implement. Despite these advantages, the technique still needs further development before it can be applied to long-span bridge cables.

Inexpensive Apparatus to Rapidly Collect Water Samples from a Linear‐Design, Plug‐Flow Hatchery Raceway

AbstractIn July 2001, we conducted a study to determine whether a target concentration of chloramine‐T (a waterborne chemical) could be achieved and maintained for 60 min in linear‐design, plug‐flow hatchery raceways (devoid of fish) via a “charged” flow‐through treatment methodology. In each of four independent trials, a raceway was charged to achieve the target concentration by turning off the inflow water (creating a static bath) and manually mixing in a premeasured volume of chloramine‐T stock solution. Water inflow was then turned on, and the target concentration was maintained by metering additional chloramine‐T stock solution into the inflow water via a calibrated chicken‐watering system. To help verify chloramine‐T concentrations during treatment, we built an apparatus to rapidly collect many water samples from throughout a raceway. The apparatus comprised three fixed sampling stations, each of which was equipped with 9 water collection devices (i.e., nine 60‐mL plastic syringes fitted with fixed‐length “suction needles” made of rigid polyvinyl chloride pipe threaded with flexible vinyl tubing) and 9–11 plastic bottles for storing the collected samples. During each of the four 60‐min trials, water samples were collected at elapsed times of 0, 30, and 60 min; thus, 12 sampling events were conducted during the study. During each sampling event, three people (working simultaneously but independently) collected a total of 29 water samples (27 for chloramine‐T dose verification and 2 for quality control). The time for one person to collect 9–11 water samples (50–60 mL per sample) from one sampling station averaged 1.5 min (SD = 0.382; n = 36) and ranged from 0.9 to 2.5 min. The apparatus was inexpensive, easy to build and use, and portable; it ultimately helped us verify the spatial and temporal distribution of chloramine‐T in linear‐design, plug‐flow hatchery raceways during 60‐min charged flow‐through treatments.

Physical mechanisms of phonation onset: A linear stability analysis of an aeroelastic continuum model of phonation

In an investigation of phonation onset, a linear stability analysis was performed on a two-dimensional, aeroelastic, continuum model of phonation. The model consisted of a vocal fold-shaped constriction situated in a rigid pipe coupled to a potential flow which separated at the superior edge of the vocal fold. The vocal fold constriction was modeled as a plane-strain linear elastic layer. The dominant eigenvalues and eigenmodes of the fluid-structure-interaction system were investigated as a function of glottal airflow. To investigate specific aerodynamic mechanisms of phonation onset, individual components of the glottal airflow (e.g., flow-induced stiffness, inertia, and damping) were systematically added to the driving force. The investigations suggested that flow-induced stiffness was the primary mechanism of phonation onset, involving the synchronization of two structural eigenmodes. Only under conditions of negligible structural damping and a restricted set of vocal fold geometries did flow-induced damping become the primary mechanism of phonation onset. However, for moderate to high structural damping and a more generalized set of vocal fold geometries, flow-induced stiffness remained the primary mechanism of phonation onset.

Hydrothermal dechlorination of PVC in the presence of ammonia

Poly(vinyl chloride) (PVC) powder and commercial rigid PVC pipe were dechlorinated hydrothermally in the presence of alkalis such as ammonia, sodium hydroxide, and potassium hydroxide in a semi-batch flow reactor, with comparison to dechlorination using water alone. Aqueous ammonia was the most effective among these solvents. Dechlorination with aqueous ammonia proceeded in three stages: initial incubation, major dechlorination, and slow dechlorination. In the initial stage the rates were very slow and scarcely affected by temperature or ammonia concentration. In the second stage extensive dechlorination took place, and the rates were affected by temperature and ammonia concentration. These higher rates were found to be significantly influenced by swelling, not alkalinity, when these various alkalis solvents were compared. In the last stage the rates were slower than in the previous stage, and were not significantly dependent on temperature or ammonia concentration.

Investigation on the Behaviour of Rigid Polyvinylchloride Pipes Subjected to Uniaxial Compression Loads

Investigation on the Behaviour of Rigid Polyvinylchloride Pipes Subjected to Uniaxial Compression Loads

Rapid crack propagation in loosely fitted PE liner pipe

Laboratory scale tests have been used to assess whether a loosely fitted PE liner within a rigid host pipe could, at any realistic working pressure, fail by rapid crack propagation (RCP). The standard 'S4' test method for RCP was modified, the usual cage of containment rings being replaced by a rigid, closed sleeve maintaining a predefined radial clearance from the unpressurised pipe. Pipe specimens of 125 mm diameter with wall thicknesses of 11·4 and 7·1 mm, made from a PE80 polyethylene in which RCP is normally possible at 0°C, were tested with three different clearances as well as with the usual S4 cage. For pipe having an unpressurised clearance down to 2% or so of the diameter, the RCP critical pressure was increased by ∼50% for both thicknesses; for smaller clearances, by progressively more. These results reinforce suspicions that pipe installation conditions may affect full scale RCP resistance.

Overview: Coiled Tubing Applications (June 2007)

After reviewing paper abstracts from many SPE venues for this last year, it became clear that coiled-tubing (CT) drilling is still generating much interest in the oil field. Yet with all the interest, few (perhaps with the exception the Canadians) are actually applying the technology in their wells. CT drilling is still striving for recognition, acceptance, and maybe just a little respect, as it has for longer than most would realize. While researching material for a presentation several years ago, I found it surprising to discover just how old the concept of CT drilling really is. Most would guess CT-drilling technology dates back to the early to mid-1990s, and some of the CT-savvy Canadians often will move that date back to the early 1970s. However, the US patent office contains information disclosing the idea of using reeled conduits for "well boring" with a filing date of May 1926. While this early concept discussed the use of hose as a conduit, the idea of using rigid pipe for "well drilling" has a filed date of February 1948. Interestingly, these ideas were not just paper patents—the technology was applied in various forms starting in the mid-1930s. Over the ensuing years, CT-drilling technology was used both onshore and offshore. Discussions of the success in this early work include a phrase that still is used to describe some CT-drilling activities today: "It was a technical success." While many will argue the merits of the use of CT-drilling equipment in an arena that often is considered the exclusive domain of rotary-drilling technology, fewer will question the value of CT to fill other completion voids previously performed by a drilling unit. One such example is CT fracturing, which gained rapid acceptance in many areas throughout the world as a viable tool to quickly, efficiently, and economically isolate and fracture numerous pay zones in well. And with the advent of high-angle and horizontal wells, many areas throughout the world use CT to perform tasks normally associated with slickline, wireline, or jointed-pipe techniques. Dozens of companies are providing new tools that enable CT to perform these needed functions economically, as documented in SPE papers. Considering history, CT-drilling units will not displace rotary-drilling units. Neither will CT units make slickline, wireline, or snubbing units obsolete. However, if properly engineered and applied, CT's versatility allows it to perform a wide variety of services throughout the drilling, completion, and intervention arenas. This year's SPE papers validate this claim. Coiled Tubing Applications additional reading available at the SPE eLibrary: www.spe.org SPE 101065 "Near a Kilometer of Perforating Guns, in a 71/2-km, Extended-Reach Well—Coiled Tubing Shows Its Mettle in New Zealand" by P. Bartholomew, Shell Todd Oil Services, et al. SPE 106907 "Successful Application of Underbalanced Coiled-Tubing Drilling in Horizontal Short-Radius Re-entry Well in Hassi Messaoud, Algeria" by Bachir Ben Amor, Sonatrach, et al. SPE 102608 "3D Managed-Pressure Drilling Around a Salt Dome Using Coiled Tubing: A Case Study—Challenges and Solutions" by Abdul Mujeer Abdul Rehman, SPE, Maharashtra Institute of Technology SPE 102661 "Fill Cleanout With Coiled Tubing in the Reverse Circulation Mode" by J. Li, BJ Services, et al. SPE 107113 "Fatigue Life of Coiled Tubing With External Mechanical Damage" by T. Padron, BJ Services, et al.

Soil–structure interaction for deeply buried corrugated steel pipes Part I: Embankment installation

The strengths of buried corrugated steel pipes were studied. There are considerable differences in the fundamental mechanics of earth pressure distribution on rigid pipes and flexible pipes. Corrugated steel pipes are categorized as semi-flexible. The mechanics of soil arching for corrugated steel pipes, therefore, are slightly different from rigid or flexible pipes. Predictor equations for arching factors, deflections, and maximum wall stresses of the corrugated steel pipes were formulated using numerically generated data from soil–structure models. These predictor equations, thus obtained, were compared with currently available equations in order to assess their validity and applicability. A pipe–spring model was used for buckling analyses. The spring coefficients in the pipe–spring model were calculated using the static analyses of soil–structure models. The ultimate and/or critical strengths determined from this study compare well with those from American Iron and Steel Institute (AISI) buckling equations.

Soil–structure interaction for deeply buried corrugated steel pipes Part II: Imperfect trench installation

The potential benefits of the imperfect trench installation method were studied for corrugated steel pipes. The imperfect trench installation method has mostly been used to reduce earth pressure on buried rigid pipes by inducing reverse soil arching over the pipe. Because corrugated steel pipes are relatively flexible, they induce a small amount of reverse soil arching. Therefore, there has been limited research regarding the effects of imperfect trench installation on flexible pipes such as those fabricated with corrugated steel. The objective of this study was to demonstrate the efficiency of the imperfect trench method for buried corrugated steel pipes. An optimum soft zone geometry for imperfect trench installation is proposed to maximize the reduction of the earth pressure on buried corrugated steel pipes. Predictor equations for arching factors, maximum stresses, and deflections of corrugated steel pipes were formulated that incorporate the proposed optimum soft material zone geometry. Parametric studies revealed that the proposed imperfect trench installation can reduce the maximum wall stress by as much as 69%.

Upwelling by a wave pump

A rigid open-ended pipe is submerged in the ocean below the troughs of the surface waves and held fixed in the vertical position, the lower end being at or below the depth of wave influence. When surface gravity waves propagate past the pipe, water flows up as long as waves are present. The steady upward vertical velocity in the center of the pipe is calculated to be proportional to the square of both the average wave steepness and the pipe’s radius. An application is to bring nutrient rich waters up into the sunlit surface layers of the open oceans.