Research Report Library

The American Petroleum Institute (API) initiated this project through Pipeline Research Council International, Inc. (PRCI), to apprise industry consensus recommended practices regarding reasonable and prudent crack in-line inspection (ILI) response criteria for hazardous liquid pipelines based on a comprehensive and informed consideration of current practices, processes, research, ILI performance and the industry's operating history. API Recommended Practice (RP) 1176, Assessment and Management of Cracking in Pipelines, are currently being prepared. A target date for a notice of proposed rulemaking (NPRM) from the U.S. Department of Transportation's (DOT) Pipeline and Hazardous Material Safety Administration (PHMSA) for Title 49 Code of Federal Regulation (CFR) §195.452 has not been communicated at this time, however it is anticipated by the industry that an NPRM addressing changes to pipeline integrity management is forthcoming. The objective of this research is to substantiate API's stated depth and failure pressure ratio (FPR) response criteria applicable to ILI reported cracking anomalies in hazardous liquid pipelines, as well as facilitate operator and regulator technical insight sharing.

A testing program was conducted to evaluate the effects of internal pressure during the installation of composite and steel sleeves repair systems on pipelines with plain dents. The testing program included cyclic pressure testing a group of 12.75-inch OD x 0.188-inch WT, Grade X42 pipe samples with plain dents having residual dent depths on the order of 3% to 4% of the pipe's outside diameter. The dent samples were repaired using four (4) different composite repair systems, type-A steel sleeves, and steel thermal compression sleeves. The composite repair systems included a carbon fiber wet-layup, an E-glass wet-layup, a system with precured plies, and a hybrid composite-steel repair system. To determine the effect internal pressure has on repair installation for dents, all repairs were installed with an internal pressure of 64% SMYS (793 psig) in the pipe sample. The dent samples were then pressure cycled between 8 - 80% SMSY (ΔP = 900 psig) until failure or reaching the runout condition of 250,000 cycles. Only three (3) out of the fourteen (14) repaired dents reached the 250,000 pressure cycle runout condition and these samples were all repaired using steel sleeves. The maximum number of cycles reached by any composite repair was approximately 200,000 cycles while the least number of cycles reached was approximately 24,000 cycles.

In addition to the dent repairs, two (2) 12.75-inch OD x 0.375-inch WT, Grade X42 pipe samples with a 6-inch x 8-inch corrosion defect were repaired with an E-glass wet-layup. These two (2) samples were a continuation of a previous study that investigated the effects of a 50% SMYS (1,235 psig) installation pressure on the fatigue performance of corrosion repairs. Both samples reached the runout condition of 250,000 cycles.

The body of work is seminal in that it is the first time that industry was evaluated a wide range of repair technologies to determine the effects of pressure during installation in reinforcing plain dents. It has been speculated for some time that internal pressure present during installation of composite repair technologies has an impact on fatigue performance. Although corrosion features do not appear to be a concern, the reinforcement of dents with internal pressure requires careful consideration. Because gas transmission pipelines do not experience aggressive pressure cycling, the effects of pressure present during installation are not a major concern. However, liquid transmission pipeline operators should be cognizant of the pressure effects and respond accordingly. Namely, pressure should be reduced during installation as much as possible.

Use of the pre-combustion chamber (PCC) as an ignition source in large-bore natural gas engines has shown promise in reducing emissions. By increasing the ignition energy and surface area via a turbulent jet, these devices can extend the lean operating limit of the engine and reduce oxides of nitrogen (NOx). This study aims to characterize the sensitivity of main chamber NOx formation to changes in the PCC jet. A CFD model of a Cooper-Bessemer GMV two-stroke lean-burn natural gas engine is used for this purpose. The temperature and chemical composition of the PCC jet are varied across several tasks, and the resulting changes in main chamber NO­x emissions are recorded. Three-dimensional plotting tools are used to determine where and when NOx forms in the engine during the cycle. Data on the chemical pathways to NO and NO2­­ formation and destruction is also presented.

The objectives of this research are to figure out how solid state decouplers (SSDs) influence the surveys related to pipeline cathodic protection (CP) and provide corresponding field guidelines on how to mitigate the adverse effects of SSDs.

Firstly, by combining the classical capacitor discharge theory and the equivalent circuit of the CP system, a four-stage physical model is built to explain how SSDs' discharge current pulse influences the CP related readings.

From the physical model, we can obtain the following conclusions: (1) The driving force behind the discharging of an SSD's capacitor, after CP currents are cut off, is the voltage drop in the pipeline; (2)There are two contributors to the CP instant-off potential spikes: self-induced pipeline current and SSD discharge current; (3) The time constant (Ï„=RC) of an SSD installation determines how fast the SSD finishes its discharging process; (4) The adverse effects of SSDs can be mitigated by making the SSD discharge time constant Ï„ small enough (3Ï„

Before performing numerical modeling, some commonly used SSDs are tested for their capacitances in the lab according to the classical capacitor impedance theory. The test results show that the typical SSD capacitance is between 0.15 F and 0.36 F.

The target pipeline for numerical modeling is a 50 km pipeline with different levels of coating quality, SSD grounding resistance, and SSD capacitance. An equivalent circuit model with ten parallel branches is built accordingly, and solved by an open-source electrical circuit software module. The numerical modeling results firmly support the primary conclusions drawn from the four-stage physical model. Moreover, the parallel analog circuit tests in the lab further prove the rationality of the four-stage model.

Finally, comprehensive field tests are performed to study how SSDs influence the CP install-off potential survey, close interval potential survey, direct current voltage gradient, and alternating current voltage gradient. Practical field guidelines on how to mitigate SSDs' influence are proposed.

Based on experimental characterization of the scavenging behavior of a cross-scavenged, piston-aspirated, two-stroke, natural gas engine in phase III of the current project, a computationally inexpensive simple scavenging model was improved in this phase. Experimental results using fast nondispersive infrared (NDIR) CO2 measurements from the cylinder and the exhaust, as well as experiments using unburned fuel pre-mixed in the scavenging chamber as a tracer for short-circuiting during scavenging, were used in this phase to validate the improved model. The model represents the fundamental phenomenological characteristics revealed by those experiments. The experiments and literature show that scavenging takes place by the following phenomena: blowdown, displacement of residuals by incoming air, mixing of residuals and air, and short-circuiting of fresh air. To reflect this, the improved hybrid model features the following: isentropic blowdown, non-isothermal perfect displacement, non-isothermal perfect mixing, and a concurrent direct short-circuiting of air (unmixed with residuals).

The validated improved hybrid model rectified the primary shortcoming of the phase III model. By adding the discrete short-circuiting zone, trapped mass could be modeled at both medium and high crankshaft speeds, whereas the phase III model could not capture the full scope of scavenging inefficiencies at medium speed using its perfect mixing stage alone. Furthermore, using the hybrid model to predict NOx using an exponential NO­x-TER curve fit revealed that the improved phase IV hybrid model predicts NOx approximately as well as the experimentally-calculated TER from the phase III experiments.

Additionally, GT-Power, a 1D fluid dynamics and engine simulation software, was used to identify whether hybrid model tuning could be aided by relatively inexpensive 1D simulation rather than CFD or fast NDIR experiments. Using three-pressure analysis (with in-cylinder, exhaust, and scavenging chamber pressures as boundary conditions) and scavenging profiles derived from the hybrid model itself, GT-Power was shown to be a plausible tool for scavenging model tuning.