Further Extension of the Unloading Compliance Method to Measure J-R Curves Based on CMOD Data

Laboratory testing of fracture specimens to measure resistance curves (J-Δa) have focused primarily on the unloading compliance method using a single specimen. Current estimation procedures (which form the basis of ASTM 1820 standard) employ load line displacement (LLD) records to measure fracture toughness resistance data incorporating a crack growth correction for J. An alternative method which potentially simplifies the test procedure involves the use of crack mouth opening displacement (CMOD) to determine both crack growth and J. This study provides further developments of the evaluation procedure for J in cracked bodies that experience ductile crack growth based upon the eta-method and CMOD data. The methodology broadens the applicability of current standards adopting the unloading compliance technique in laboratory measurements of fracture toughness resistance data (J resistance curves). The developed J evaluation formulation for growing cracks based on CMOD data provides a viable and yet simpler test technique to measure crack growth resistance data for ductile materials.

Experimental Study of Fatigue Crack Overload Retardation in X80 Grade Steel

The tests of fatigue crack overload retardation were performed to gain a some what deeper understanding of overload retardation. We present an experimental investigation of fatigue crack retardation behavior caused by intermediate single peak tensile overload under constant amplitude cyclic loading. The compact tension (CT) specimens of API grade X80 pipeline steel were used in fatigue test. The results show there was an instant crack extension during overloading for the tested overload ratios. As soon as the overload cycle was removed, instant delay in crack growth occurred. The results should be of interest for fracture mechanics prediction models on fatigue crack growth under variable amplitude loading and overloading effect for oil and gas pipelines.

Preliminary Failure Assessment for Spiral Welded Defects of Pipeline

The spiral welded defect of steel oil transmission pipeline is one of the main causes resulting in pipeline leakage accident. Hence the failure assessment for known-size spiral welded defects is an important step to ensure the safety of defected pipeline. Lack of suitable criterion for assessing the spiral welded manufacture defects of pipeline network in China, is a difficult technology problem to be solved desirably. This paper first summarized the basic idea of preliminary failure assessment (Grade 1A of code BS 7910:2005) with some insight of our own understanding, and then applied the preliminary failure assessment to the spiral welded defects of oil pipeline, with the use of ultrasonic inspection data of Daqing-Tieling old pipeline from LingYuan to XinMiao, Northeastern China. The calculation of both fracture and plastic collapse failure for spiral welded defects indicates some detected flaws of pipeline are not safe as the internal pressure is greater than 4.5 MPa. A leakage accident of spiral welded pipeline in Western China is also assessed through fractography analyses and failure calculations. This paper concludes that the preliminary failure assessment provides useful outcome for reference in making decision of inspection, integrity assessment and repair of spiral welded pipeline, and hence is a step of fundamental importance and practical significance before more accurate data becomes available for higher grade assessment.

Predictive Assessment of External Corrosion on Transmission Pipelines

Oil and Gas operators have to deal with the ageing process of their transmission pipeline grid. Some of these pipelines can be inspected using In Line Inspection (ILI) tools. In order to maintain an acceptable integrity level, re-inspection operations have to be performed. This process needs to be optimized in terms of resources and cost. Gaz de France R&D Division has developed a methodology which prioritizes rehabilitation operations on a pipeline after in-line inspections, and determines the optimal interval for re-inspection. A reliable help decision software tool which applies the methodology has also been developed. Dealing with defects assimilated to external electrochemical corrosion, the developed methodology is based on: • pigs information in order to assess a probable corrosion growth rate; • probabilistic distribution of input parameters (geometrical characteristics of defects, characteristics of the pipe and corrosion growth rate); • probabilistic methods of calculation : the probability of failure is calculated with the Monte-Carlo method. The convergence of the calculation is accelerated with the Cross Entropy method. The calculation results take the form of three probabilities of failure: • a punctual probability of failure for each defect; • an annual probability of failure for each defect; • an annual probability of failure per kilometer of pipe. To interpret the results, the annual probability of failure per kilometer of pipe is then compared with threshold values.

Performance of Corrosion Inhibitors at High CO2 Pressures

The objective of this study was to evaluate the performance of two corrosion inhibitors (CI-A and CI-B) under conditions similar to the second PTT’s offshore pipeline. The experiments were carried out in flow-loop system, 36 m long, 10.16 cm diameter at 10.5 and 14 bar of carbon dioxide pressure, a temperature at 50°C. The performances of corrosion inhibitors were examined under conditions of superficial liquid velocity of 0.03 m/s and gas velocities of 6, 8 and 10 m/s in 0 and 3 degree inclinations using the ER probe and X65 weight-loss coupons for corrosion rate measurement at the top and bottom of pipe. According to flow characteristics, it was found that the smooth and wavy stratified flow occurred in 0 degree. For 3 degree inclination, wavy stratified flow with big waves was dominantly presented for all conditions. Corrosion inhibitor B showed a better performance than inhibitor A in all cases. For inhibitor B, the target corrosion rates of less than 0.1 mm/yr were achieved in all conditions with 50 ppm of inhibitor concentration whereas the amount of 75 ppm inhibitor concentration was required for CI-A. The color, turbidity, and emulsion tendency with corrosion inhibitors will be also discussed in this paper.

Non-Contacting Bi-Axial Strain Measurement Method on Steel Pipeline

The StressProbe is a non-contacting electromagnetic tool that responds to material strain in ferromagnetic materials. Previous studies have concentrated on uni-axial strain measurements; in this study, we extend the scope of work by measuring bi-axial strains on a pipe specimen subject to internal pressure and to a displacement-controlled, axial tensile/compressive load. Specified pressure and load combinations were obtained, and measurements from the StressProbe were compared to those from tri-axial strain gauges installed on the pipe specimen. In this paper, we present the theory behind this measurement method and the results from this study. Also discussed are measurement applications both inside and outside the pipe specimen.

Understanding and Mitigating Under-Deposit Corrosion in Large Diameter Crude Oil Pipelines: A Progress Report

This paper is an exploration of factors affecting internal corrosion of transmission pipeline systems (<0.5% S&W), as well as a progress report on research aimed at improving chemical mitigation of this threat in heavy oil product streams. Typical pipeline corrodents and corrodent transport mechanisms are explored. Transmission quality hydrocarbon products are shown to carry micro-emulsified water, various solid particles, solid particles with micro-attached water, and bacteria. While micro-emulsified water can be considered benign owing its ability to be transported harmlessly without accumulation; water-wetted solid particles have sufficient density to reach the pipe floor. Patterns of internal corrosion on a transmission pipeline are used to demonstrate the significance of solids accumulation leading to under-deposit corrosion. Analysis of pipeline sludge reveals significant populations of different bacterial species indicating the existence of a robust biomass capable of creating or sustaining a corrosive environment. Corrosivity testing of pipeline sludges was performed using two static autoclave coupon methods. One test method demonstrated that the addition of chemical inhibitor directly to the pipeline sludge could reduce corrosion rates as effectively as batch treatment of a clean coupon. A rotating mechanical contactor was designed and built to facilitate the blending of corrosion inhibitor with pipeline sludge under ‘like-pipe’ flow conditions, but results of sludge corrosivity testing using this device are not yet available.

Integrity of Old Pipelines Buried in Petroleum Products Storage Terminals

This work aims to present the results obtained from the experience gained through the accomplishment of the inspection with the ultrasonic umbilical pig in a non-piggable internal pipe buried in the Transpetro Storage Terminal in Sa˜o Caetano do Sul, in Sa˜o Paulo, Brazil. The pipeline considered in this work is a line for marine fuel oil, which, because of its high viscosity, must be heated in order to flow. The oil is heated in the terminal by the steam produced in boilers. The heat transfer may occur in a heat exchanger or inside the storage tank, and the pipeline referred is thermally isolated. So that the line could be inspected, it was divided in two parts, one upstream of the pumps (suction), which is a 12-inch line, and the other downstream of the same pumps (discharge), which is a 14-inch line. This work has been developed by Transpetro’s Pipeline Operation, Maintenance, Inspection and Safety Departments together, since the planning phase, passing by the job execution and getting to the conclusion. To begin with, the operational liberation of the line had to be agreed between all the departments involved with the PIG inspection, which were mentioned before, and Transpetro’s Logistics Department. Once the PIG passage was scheduled, an initial cleaning had to be performed by the Operation Activity. Since this line is non-piggable, the installation of adaptations was necessary. After that, the passage of cleaning PIGs was possible, and the line sections could be enabled. The next step was the inspection of the pipeline with umbilical ultrasonic PIGs. After the passage of these PIGs, the adaptations had to be removed and the pipeline had to be conditioned for the operational return. After this part of the inspection was finished, the verification of the results issued was necessary. Once the theoretical results were available, ditches were opened for correlation inspection and temporary repairs in the most critical points for the operation were applied. The last part of the work consists in an analysis study of technical and economical viability for rehabilitation of the lines.

Electric Resistance Welded Seam Inspection Using Circumferential Flux

For conventional magnetic flux leakage (MFL) inspection where an excitation magnetic field is generated in the axial direction of a pipeline, axially oriented crack detection is impossible [1][2]. A new MFL tool design is presented that creates an excitation field in the circumferential or transverse direction, allowing for axial crack detection, as well as the more conventional metal loss detection. Design criteria that ensure detection include sufficient sensor density and magnetic field uniformity at sensor locations. The result is a new type of circumferential MFL inspection tool that can not only detect corrosion and other metal losses, but also axially oriented cracks. Based on the results of a series of inspection runs 22 crack-like features in the electric resistance weld (ERW) were investigated with 19 of those being verified as linear long seam features and were subsequently permanently repaired. Further information on the efficacy of this design is clarified in [2].

Results of Field Trials of Realsens™, An Airborne Natural Gas Leak Detection Technology

Detecting natural gas leaks from the worlds nearly 5 million kilometers of underground pipelines is a difficult and costly challenge. Existing technologies are limited to ground deployment and have a number of limitations such as slow response, false leak readings and high costs. Various remote sensing solutions have been proposed in the past and a few are currently being developed. This paper starts by describing the remote sensing concept and then will focus on a new technology developed by Synodon scientists. This airborne instrument is a passive Gas Filter Correlation Radiometer (GFCR) that is tuned to measure ethane in the 3.3 microns near-infrared band. The paper will then present the results of the first airborne field tests and conclude with a description of the service which Synodon will be offering to the transmission and distribution pipeline operators using the new technology.