A New Hydraulic and Thermal Steady-State Calculation Program for Multiphase Pipe Network

With the continuous development of offshore oil and gas resources, calculation software for multiphase flowing pipe network has become an important tool for the design and daily operation of multiphase flowing pipe network. Improved accuracy of hydraulic and thermal calculation is an engineering requirement for economic and efficient production. Therefore, a new program is developed for multiphase pipe network in this paper. This program contains a general data structure to describe the complex connection of a pipe network. The structure is based on the conception of the incidence matrix and the adjacency matrix in graph theory. Two processes, hydraulic equilibrium calculation and thermodynamic equilibrium calculation are successively taken in this program to gain the steady-state for a multiphase pipe network. For the hydraulic equilibrium calculation, applying flow equation to each pipe in the network gains a pipe flow vector. A nonlinear system of equations, which represent flow balance of each node, is obtained by multiplying the incidence matrix and the pipe flow vector. To solve these equations, the Newton-Raphson iterative algorithm is used and afterwards, the hydraulic parameters of the pipe network are obtained. For thermal equilibrium calculation, since all the temperature of source nodes is known, the key step is to find the solution order of other node temperature. The program obtains the order by transforming the adjacency matrix. Deng temperature drop formula is used to calculate the end temperature of each pipe. When a node has more than one inflow, an average temperature based on the heat capacity and mass flow is adopted after gaining each pipe’s outlet temperature. Combining hydraulic and thermal algorithms, a complete set of solution program for steady-state of multiphase pipe network is compiled. In the end, two cases are performed to check the accuracy of the program. In the first case, a pipe network is created by using the data collected from a condensate gas gathering network in the South China Sea. The result indicates that the program has a good agreement with the actual data. In the second case, the program is applied in a single-phase network and gains almost the same result calculated by PipePhase and PipeSim.

Standardization of Flattening Procedure of Transverse to Pipe Axis Strap Tensile Samples

Tensile testing on large diameter line pipe is generally done using strap samples obtained in the transverse to pipe axis (TPA) orientation of a pipe. The strap samples are then flattened and machined prior to testing. Although the standardized tensile testing is well documented, the variability in the reported TPA tensile properties of the same material tested within a lab or at different labs has always been an issue. Recent work conducted at EVRAZ NA research lab has identified flattening as the main source of the variability in reported yield strength (YS) values for line pipe. The lack of a standard procedure for flattening TPA strap samples is a major obstacle to obtaining consistent results. Therefore, the main objective of this current study was to establish a standardized flattening procedure for TPA strap samples. Both finite element analysis (FEA) and experimental approaches were adopted. Various flattening methods and fixtures were studied. Extensive flattening experiments were conducted on TPA samples from different line pipe products. Results showed that the spring back after flattening in a TPA sample is different for pipes with different gauge and grades. It was established that consistent flattening can be achieved using appropriate fixtures for differerent ranges of tubular products defined by grade, diameter and gauges. Evaluation of the flattening fixture designs and experimental results are discussed in this paper.

Pipeline Geohazard Assessment: Bridging the Gap Between Integrity Management and Construction Safety Contexts

Geohazards are threats of a geological, geotechnical, hydrological, or seismic/tectonic nature that may negatively affect people, infrastructure and/or the environment. In a pipeline integrity management context, geohazards are considered under the time-independent threat category of Weather-related and Outside Force in the American standard ASME B31.8S. Geotechnical failure of pipelines due to ground movement is addressed in Annex H and elsewhere in the Canadian standard CSA-Z662. Both of these standards allow flexibility in terms of geohazard assessment as part of pipeline integrity management. As a result of this flexibility, many systems for identifying, characterizing, analyzing and managing geohazards have been developed by operators and geotechnical engineering practitioners. The evolution of these systems, and general expectations regarding geohazard assessment, toward quantitative geohazard frequency assessment is a trend in recent pipeline hearings and regulatory filings in Canada. While this trend is intended to frame geohazard assessment in an objective and repeatable manner, partitioning the assessment into a series of conditional probability estimates, the reality is that there is always an element of subjectivity in assigning these conditional probabilities, requiring subject matter expertise and expert judgment to make informed and defensible decisions. Defining a specific risk context (typically loss of containment from a pipeline) and communicating uncertainty are important aspects of applying these types of systems. Adoption of these approaches for alternate risk contexts, such as worker safety during pipeline construction, is challenging in that the specific geohazards and threat scenarios considered for long-term pipeline integrity may or may not adequately represent all credible threats during pipeline construction. This paper explores the commonalities and differences in short- and long-term framing of geohazard assessment, and offers guidance for extending geohazard assessment for long-term pipeline integrity to other contexts such as construction safety.

New Leak Location Approaches for Gas Pipelines Using Acoustic Waves

Natural gas is a vital energy carrier which can serve as an energy source, which is extremely vulnerable to leakages from pipeline transportation systems. The required ignition energy is low. Although the safety of natural gas pipelines has been improved, the average economic loss of natural gas accidents, including leaks, is large. To solve these problems, an acoustic leak localization system is designed and researched for gas pipelines using experiments with methods proposed according to different application situations. The traditional method with two sensors installed at both ends can be improved by a newly proposed combined signal-processing method, which is applied for the case that it is necessary to calculate the time differences with data synchronicity. When the time differences cannot be calculated accurately, a new method based on the amplitude attenuation model is proposed. Using these methods, the system can be applied to most situations. Next, an experimental facility at the laboratory scale is established, and experiments are carried out. Finally, the methods are verified and applied for leak localization. The results show that this research can provide a foundation for the proposed methods. The maximum experimental leak localization errors for the methods are −0.592%, and −7.62%. It is concluded that the system with the new methods can be applied to protect and monitor natural gas pipelines.

Justification for Reducing In-Service Weld Inspection Delay Times for Liquid Pipelines

Welds that are made onto an operating pipeline cool at an accelerated rate as a result of the flowing pipeline contents cooling the weld region. The accelerated cooling rates increase the probability of forming a crack-susceptible microstructure in the heat-affected zone (HAZ) of in-service welds. The increased risk of forming such microstructures makes in-service welds more susceptible to hydrogen cracking compared to welds that do not experience accelerated cooling. It is understood within the pipeline industry that hydrogen cracking is a time-dependent failure mechanism. Due to the time-dependent nature and susceptibility of in-service welds to hydrogen cracking, it is common to delay the final inspection of in-service welds. The intent of the delayed inspection is to allow hydrogen cracks, if they were going to occur, to form so that the inspection method could detect them and the cracks could repaired. Many industry codes provide a single inspection delay time. By providing a single inspection delay time it is implied that the inspection delay time should be applied for all situations independent of the welding conditions or any other preventative measures the company may employee. There are many aspects that should be addressed when determining what should be considered an appropriate inspection delay time and these aspects can vary the inspection delay time considerably. Such factors include the cooling characteristics of the operating pipeline, the welding procedure that is being followed, the chemical composition of the material being welded and if any preventative measures such as post-weld heating are applied. The objective of this work was to provide an engineering justification for realistic minimum inspection delay times for different in-service welding scenarios. The minimum inspection delay time that was determined was based on modelling results from a previously developed two-dimensional hydrogen diffusion model that predicts the time to peak hydrogen concentration at any location within a weld HAZ. The time to peak hydrogen concentration was considered equal to the minimum inspection delay time since the model uses the assumption that if a weld was to crack the cracking would occur prior to or at the time of peak hydrogen concentration. Several factors were varied during the computer model runs to determine the effect they had on the time to peak hydrogen concentration. These factors included different welding procedures, different material thicknesses and different post-weld heating temperatures. The post-weld heating temperatures were varied between 40 F (4 C) and 300 F (149 C). The results of the analysis did provide justification for reducing the inspection delay time to 30 minutes or less depending on the post-weld heating temperature and pipeline wall thickness. This reduction in inspection delay time has the potential to significantly increase productivity and reduce associated costs without increasing the associated risk to pipeline integrity or public safety.

Near-Real-Time Seismic Monitoring for Pipelines

Earthquake hazard management for oil and gas pipelines should include both preparedness and response. The typical approach for management of seismic hazards for pipelines is to determine where large ground motions are frequently expected, and apply mitigation to those pipeline segments. The approach presented in this paper supplements the typical approach but focuses on what to do, and where to do it, just after an earthquake happens. In other words, we ask and answer: “Is the earthquake we just had important?”, “What pipeline is and what sites might it be important for?”, and “What should we do?” In general, modern, high-pressure oil and gas pipelines resist the direct effects of strong shaking, but are vulnerable to large co-seismic differential permanent ground displacement (PGD) produced by surface fault rupture, landslides, soil liquefaction, or lateral spreading. The approach used in this paper employs empirical relationships between earthquake magnitude, distance, and the occurrence of PGD, derived from co-seismic PGD case-history data, to prioritize affected pipeline segments for detailed site-specific hazard assessments, pre-event resiliency upgrades, and post-event response. To help pipeline operators prepare for earthquakes, pipeline networks are mapped with respect to earthquake probability and co-seismic PGD susceptibility. Geological and terrain analyses identify pipeline segments that cross PGD-susceptible ground. Probabilistic seismic models and deterministic scenarios are considered in estimating the frequency of sufficiently large and close causative earthquakes. Pipeline segments are prioritized where strong earthquakes are frequent and ground is susceptible to co-seismic PGD. These may be short-listed for mitigation that either reduces the pipeline’s vulnerability to damage or limits failure consequences. When an earthquake occurs, pipeline segments with credible PGD potential are highlighted within minutes of an earthquake’s occurrence. These assessments occur in near-real-time as part of an online geohazard management database. The system collects magnitude and location data from online earthquake data feeds and intersects them against pipeline network and terrain hazard map data. Pipeline operators can quickly mobilize inspection and response resources to a focused area of concern.

State-of-the-Art Assessment of Today’s Composite Repair Technologies

For almost 30 years composite repair technologies have been used to reinforce high pressure gas and liquid pipeline transmission systems around the world. The backbone of this research has been full-scale testing, aimed at evaluating the reinforcement of anomalies including, corrosion, dents, vintage girth welds, and wrinkle bends. Also included have been the assessment of reinforced pipe geometries including welded branch connections, elbows, and tees. Organizations sponsoring these research efforts have included the Pipeline Research Council International, regulatory agencies, pipeline operators, and composite repair manufacturers. Many of these efforts have involved Joint Industry Programs; to date more than 15 different industry-sponsored programs and independent research efforts have been conducted involving more than 1,000 full-scale destructive tests. The aim of this paper is to provide for the pipeline industry an updated perspective on research associated with composite repair technologies. Because of the continuous advance in both composite technology and research programs to evaluate their effectiveness, it is essential that updated information be provided to industry to minimize the likelihood for conducting research efforts that have already been addressed. To provide readers with useful information, the authors will include multiple case studies that include the reinforcement of dents, wrinkle bends, welded branch connections, and planar defects.

Leak Localization Algorithm Applied to Non-Isothermal Liquid Flow in Horizontal Pipelines

In the oil industry liquid pipelines are very important for the transport of liquids, particularly in long offshore pipelines. The operation of these oil pipelines is susceptible to the occurrence of leaks in the system. Localizing a leak in a very long oil pipeline is an important piece of information that needs to be obtained before mitigating actions can be taken. These pipelines are usually subject to the temperature gradients that exist in the bottom of the ocean, and the resulting heat transfer process may lead to wax formation and deposition. The single-phase flow that occurs in this type of offshore pipeline that presents one leak point and suffers the effects of an external temperature gradient is numerically simulated in this paper. We consider a one-dimensional mathematical model that includes conservation equations of mass, momentum and energy, and its associated numerical method to calculate the transient liquid flow inside the pipeline. We are particularly interested in testing a leak localization model based upon the intersection of the hydraulic grade lines emanating from the pipeline ends under the influence of a non-zero temperature distribution. This paper proposes to compare the results for a non-isothermal flow with the corresponding isothermal flow to study the influence of the temperature distribution upon the leak localization strategy. The flow that develops along the entire pipeline, upstream and downstream of the leak, strongly affects the pressure gradient and has a significant influence on the location of the leak. Our numerical simulations show results that allow the model sensitivity to be studied by changing the leak magnitude, for a given leak position. From this analysis, we may observe how these parameters affect the pressure gradients along the pipeline that develop upstream and downstream of the leak and the model’s ability to predict the leak location.

Validating a Single-Phase Flow Pipeline Simulation Model Against Real Data From a Vapor Collapse Event

Transient hydraulic conditions during a shutdown and subsequent start-up of a segment of a pipeline that runs through a mountainous region were simulated using commercially available hydraulic simulation software and a model of the relevant portion of the pipeline facilities. The segment of interest is located in an area where the pipeline is normally operated with vapor present (slack line flow conditions) due to the large change in elevation. Pressure data that was recorded by the pipeline’s data acquisition system indicated a pressure surge occurred when the line was restarted. The suspected cause of this pressure surge was the collapse of the vapor in this pipeline segment. Beginning with an estimate of the flow, pressure and temperature data for the pipeline segment at steady state conditions prior to the shutdown, the simulation was tuned to reasonably match the measured data. The resulting simulated data closely replicated the surge event. Examination of the simulated data provides insights into the hydraulic conditions in the pipeline at locations where pressure data is not measured, as well as during the time intervals between data acquisition scans. It also reveals impact of the timing of the mainline valve opening sequence. Further, since the simulated data does accurately replicate the actual measured data, the model can be used to evaluate how changes to facilities or operating conditions impact the formation and the collapse of vapor in this pipeline segment.

Experimental Evaluation of Blasting Near Pipelines

Construction blasting was proposed as a technique to create a trench for a new pipeline within the right-of-way (ROW) of an existing vintage pipeline where soil conditions consisted primarily of rock. Several field experiments were conducted to assess the potential loading conditions that the vintage pipeline could experience due to various blasting configurations as part of the nearby construction process. Two test pipe segments were constructed from segments removed from the vintage pipeline for use in these experiments. Each test segment contained two vintage bell-bell chill ring girth welds (GW) and were pressurized to operating conditions of the vintage pipeline for the duration of all blasting. Groups of eight resistive strain gages were bonded around the exterior surface of three distinct locations on each test segment. The three locations include one pipe body location and each of the two welds on each segment. Four separate experiments were conducted with each experiment focusing on a unique combination of trench backfill material, compaction level and separation distance from the test pipe segments and the explosive charges. The primary objective throughout these four experiments was to monitor and record the behavior of buried test pipe sections due to nearby blasting activities. Long range 3-dimentional (3D) laser scanning equipment was used to track movement of each test segment from test to test. High-speed video equipment was also employed to capture each blast. The high-speed video provided additional details on the blast energy transfer, verification of individual charge initiation as well as pipeline test segment movement where each pipeline segment was exposed. Peak particle velocity measurements were taken during each test blast. Strain data collected during each test was used to assess potential damage to the vintage pipeline test segments as a result of blasting. The combined information collected from the in-field testing showed that elevated strains and stresses may be observed during blasting activities near pipelines.