In order to meet the increasing worldwide energy demand, there is a need to economically develop remote oil and gas resources. Construction of pipelines is required to connect these resource locations to markets. Such pipeline routes may cross areas of large ground motions such as regions of active seismicity, discontinuous permafrost, and offshore ice gouging. All of these features can subject pipelines to significant longitudinal strains. For these conditions a strain-based design (SBD) approach may be required to maintain pipeline integrity. Welding technology is a key component of pipeline construction. Significant pipeline construction cost savings are enabled with the use of higher strength steels (X80+). Higher strengths enable reduced pipe wall thicknesses, which reduces both weight and girth welding time. However, robust welding technology for high strength SBD pipelines remains challenging. Such applications demand welds with both high strength (>120ksi) and low temperature (−15°C) toughness, combinations that are at the limits of, or beyond, existing commercial technology. This paper discusses the development of an enabling welding technology which offers a superior combination of strength and toughness properties. An iron-nickel (FeNi) martensitic weld metal with a refined mixed cellular microstructure has been developed as a promising high strength weld metal that can be applied for field pipeline construction. This paper describes how this technology has been applied to create welds for X80 strain-based pipelines requiring significant weld strength overmatch and superior ductile tearing resistance. The welding technology can also be applied to X70 grade strain-based pipelines where high toughness is required. This approach has been developed for mainline girth, tie-in girth, and girth repair welding scenarios. Welding procedures are discussed and examples of the mechanical properties achieved and calculated strain capacities are described.

This paper describes the results of pressure vessel fracture test which called West Jefferson and/or partial gas burst testing using Grade API X65 linepipe steel with high Charpy energy that exhibits inverse facture in the Drop Weight Tear Test (DWTT). A series of pressure vessel fracture tests which is as part of an ongoing effort by the High-strength Line Pipe committee (HLP) of the Iron and Steel Institute of Japan (ISIJ) was carried out at low temperature in order to investigate brittle-to-ductile transition behavior and to compare to DWTT fracture behavior. Two different materials on Fracture Appearance Transition Temperature (FATT) property were used in these tests. One is −60 degree C and the other is −25 to −30 degree C which is defined as 85 % shear area fraction (SA) in the standard pressed notch DWTT (PN-DWTT). The dimensions of the test pipes were 24inches (609.6 mm) in outside diameter (OD), 19.1 mm in wall thickness (WT). In each test, the test pipe is cooled by using liquid nitrogen in the cooling baths. Two cooling baths are set up separately on the two sides of the test vessel, making it possible to obtain fracture behaviors under two different test temperatures in one burst test. The test vessel was also instrumented with pressure transducers, thermocouples and timing wires to obtain the pressure at the fracture onset, temperature and crack propagation velocity, respectively. Some informative observations to discuss appropriate evaluation method for material resistance to brittle facture propagation for high toughness linepipe materials are obtained in the test. When the pipe burst test temperatures are higher than the PN-DWTT transition temperature, ductile cracks were initiated from the initial notch and propagated with short distance in ductile manner. When the pipe burst test temperatures were lower than the PN-DWTT transition temperature, brittle cracks were initiated from the initial notch and propagated through cooling bath. However, the initiated ductile crack at lower than the transition temperature was not changed to brittle manner. This means inverse facture occurred in the PN-DWTT is a particular problem caused by the API DWTT testing method. Furthermore, results for the pipes tested indicated that inverse facture occurred in PN-DWTT at the temperature above the 85 % FATT may not affect the arrestability against the brittle fracture propagation and it is closely related with the location of brittle fracture initiation origin in the fracture appearance of PN-DWTT.

The floating-roof tank has been the most widely used method of storage of volatile petroleum products since the first demonstration b Chicago Bridge & Iron Company (CB&I) in 1923. There have been many changes and design improvements to that first pan-style-floating roof. A floating roof is a complex structure. It must be designed to remain buoyant even when exposed to combined loads from varying process, weather and product conditions. There is a continued demand for improved floating-roof tanks to store a wide range of petroleum and petrochemical products in compliance with state and federal environmental regulations. Floating roofs are used in open top tanks (EFRT), inside tanks with fixed roofs (IFRT), or in tanks that are totally closed where no product evaporative losses are permitted for release to the atmosphere. This very special type of installation is referred to as a zero emission storage tank (ZEST). Products that might have been stored in basic fixed roof tanks must now utilize a floating roof to limit evaporative emissions to the atmosphere. High vapor pressure condensate service and blended heavy crude oils also present new design challenges to the floating roof tank industry. This paper will review the most prominent styles of floating roofs from 1923 to the present. Design and operating limits for current da floating-roof structures are presented. New trends in environmental regulations and the potential impact on the design and operation of floating-roof tanks will be presented. Current maintenance practices and the effect on Life Cycle Cost Management of the storage syste are also reviewed.

The integrity management of a pipeline with stress corrosion cracking was accomplished in two distinct phases. The initial phase, from 1993 to 1996, consisted of excavations that quantified damage (stress corrosion cracking & corrosion), fracture mechanics modeling and hydrostatic testing, with a short-term objective of restoring Maximum Operating Pressure (MOP). Limited testing was conducted to evaluate the hydrostatic line on the 610 mm (24″) diameter line. The second phase, from 1996 until present, included running a shear wave ultrasonic tool, a zero degree ultrasonic tool, fracture mechanics modeling and rehabilitation digs. The extensive data collection during rehabilitation was utilized to evaluate the relationships between cracking susceptibility and degree of Stress Corrosion Cracking (SCC) with parameters such as soil type, drainage, topography and magnitude of pressure fluctuations. Corrosion products predominantly consisted of iron carbonate, very much characteristic of the low pH SCC mechanism. Following the shear wave ultrasonic tool, a zero-degree compression wave ultrasonic tool was utilized to characterize the long axial corrosion locations with potential shallow cracking. A re-inspection plan was developed using crack growth rates, hydraulic simulations of pressure fluctuations and excavation data. The reliability of the pipeline was increased and the overall integrity management costs were reduced. Presently, hydrotesting is not being used to manage integrity of Rainbow’s system.

The quartz crystal microbalance (QCM) provides an extremely sensitive technique for detecting small changes in mass and viscosity on the quartz crystal surface. QCM can be used in oil, gas or water without the problems of high solution resistance. In order to use QCM to model pipeline corrosion, an iron quartz crystal electrode was prepared using an electrodeposition method. The reproducibility, effectiveness and accuracy of the iron QCM were tested in salt solution. The adsorption of amines was studied to investigate their effects on the corrosion behaviour of the iron QCM.

Coating disbondment on pipelines is a common phenomenon that leads to exposure of the pipeline metal to ground water solutions, promoting a corrosive environment which is associated with stress corrosion cracking (SCC). This investigation tracks the corrosion behavior of X-65 steel at different coating disbondments at Open Circuit Potential (OCP) conditions through weight loss tests, as well as SEM analysis. For the weight loss test, X-65 coupons were placed into a vertical coupon holder with varying gap sizes between the coupons and the shielding (2 mm 5 mm, and 10 mm) simulating the coating disbondment. The results of the tests suggest that the corrosion rate inside the gap is dependent on the mass transfer rate of CO 2 . For larger gaps, the corrosion rate inside the gap decreases almost linearly with position (highest at the top of the disbondment) and is dependent on the iron carbonate film deposition. For smaller gaps (≤5 mm) a galvanic effect was observed between the coupons at the top of the disbondment (anodic) which showed a high degree of general corrosion, and the coupons at the bottom of the disbondment (cathodic) which had very low corrosion rates. The experimental observations were related to the corrosion scenarios found in the field. Cathodic protection strategies with respect to the geometry of disbondment are also discussed.

Bacterial proliferation is a severe problem in many oilfield systems, especially in aging systems with high water cuts. Depending on the types of microorganisms present, they can cause microbiologically influenced corrosion (MIC) or biofouling of filters, membranes, and metal surfaces. Common oilfield bacteria include sulfate-reducing bacteria (SRB) that can generate hydrogen sulfide (H 2 S) and iron sulfide (FeS) as a by-product (iron sulfide can occur in different structural forms), acid producing bacteria that can secrete organic acids that lower the pH within the microenvironment of a biofilm, as well as general heterotrophic bacteria that are often important in biofilm formation and maintenance, amongst others. To prevent corrosion or biofouling caused by these organisms, biocides are commonly added to the production fluids. Some concern has arisen that common oilfield biocides may be inherently corrosive at high end use concentrations and could cause general corrosion in the assets they are protecting from MIC. Accordingly, it is important to understand the risk of MIC, souring, and biofouling versus general corrosion from the biocides themselves. To examine the killing efficiency of oilfield biocides versus their corrosive potential, laboratory work was undertaken with five biocide products including: Tetrakis (hydroxymethyl) phosphonium sulfate (THPS), glutaraldehyde, glutaraldehyde / alkyldimethylbenzyl ammonium chloride (ADBAC) mixture, 5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one (CMIT/MIT), and a cocodiamine (quaternary amine). Each biocide was evaluated at four different concentrations ranging from 10–100,000 ppm of product. Killing efficiency was determined via bacterial kill studies, while wheelbox and bubble cell testing examined corrosion rates. Corrosion rates varied quite substantially from one biocide to the next, especially at high concentrations. Some biocides were found to be only mildly corrosive even at high dosages, while other biocides were much more corrosive at high concentrations. In general, it was observed that biocide corrosivity is directly related to the dosage of the biocide, with higher dosages correlating with higher corrosion rates. On the other hand, biocides were shown to be effective at killing common oilfield bacteria at relatively low dosages. This data suggests that biocides can be effective at killing bacteria at concentrations that do not cause significant amounts of general corrosion. Additionally, the common practice of batch treating biocides minimizes contact time between the biocide and the metal surface, which is in turn expected to minimize any corrosion that would otherwise be attributed to the biocides themselves. Taken together, this data would suggest that the benefit of biocide treatment to prevent MIC and biofouling substantially outweighs any potentially negative impact on corrosion.

This paper investigates the long term corrosion behaviour of pretreated carbon steel under alternating anaerobic to aerobic cycles over 238 days. Changes in steel behaviour were observed electrochemically by monitoring the corrosion potential, and calculating changes to corrosion rate from linear polarization resistance. With increasing cycle number the corrosion process becomes localized at a small number of locations, consistent with the formation of tubercles. Periods of aerobic corrosion were associated with more positive potentials (between −500 mV to −350 mV) and high corrosion rates (70 to 120 μm yr −1 ); whereas anaerobic corrosion yielded more negative potentials (< −650 mV) and lower corrosion rates (40 to 50 μm yr −1 ). Upon termination of the experiment, corrosion product deposits were characterized by several techniques: scanning electrochemical microscopy to detect morphology; focused ion beam and cross sectioning to judge film thickness and film porosity; and Raman Spectroscopy to identify iron phases.

Edison Welding Institute (EWI) and Enterprise Products Operating LP (Enterprise) worked together to develop an in-service welding program. The objective of this project was to relax flow restrictions on current in-service welding procedures to allow for welding onto liquid pipelines with flow rates outside of current flow limits. Enterprise’s current products include liquid propane, liquid ethane, and propane and ethane mixes in addition to other refined products. The current Enterprise in-service welding procedures restrict welding onto liquid pipelines with a flow rate between 1.3 and 4.0 ft/s (0.4 and 1.2 m/s). The minimum flow rate of 1.3 ft/s (0.4 m/s) was used because it was Enterprise’s minimal operating flow rate. The maximum flow rate of 4 ft/s (1.2 m/s) was grandfathered into the procedures. When welding onto an in-service pipeline to repair a damaged section of pipe or to install a branch connection (i.e., hot-tapping) there are two main concerns (burnthrough and hydrogen cracking) and both concerns needed to be evaluated for both flow conditions. The results from the project allow welding onto no-flow liquid pipelines with wall thicknesses between 0.25 and 0.5 in. (6.4 to 12.7 mm). Even though welding onto a no-flow thin-walled liquid pipeline [i.e., less than 0.25 in. (6.4 mm)] would not increase cracking susceptibility, the risk of burnthrough and eutectic iron formation would make the procedure unacceptable. The results of this project also indicated that acceptable welds can be made onto a high flow liquid pipeline [up to 12 ft/s (3.7 m/s)]. It was recommended, however, that Enterprise only use the temper bead welding procedures for such applications. Proper use of the temper bead welding procedures (i.e., proper heat input, weld toe spacing and stringent low hydrogen welding practice) has been shown to produce acceptable, crack-free welds. It is important to note that none of the welds showed signs of cracking, but the hardness levels of the heat input control procedures all exceeded the critical hardness level for their intended carbon equivalent materials. Increasing the flow rate from 4 to 12 ft/s (1.2 to 3.7 m/s) does appear to increase the cooling effect but it is not possible to determine the magnitude of the effect from the results of this work.

The growing economy of China has resulted in an increase in energy demands. This increased demand for energy has resulted in plans to expand the oil and gas transmission pipeline infrastructure throughout China. This transmission pipeline infrastructure expansion demands higher strength steels of API grade X70 and X80 for economical movement of the oil and gas. With most of the major natural gas supply in countries to the west of China and the major population centers of China in the east, long distant transmission pipelines from west to east have been built with additional capacity being designed. The first major natural gas transmission pipeline, 1 st West-East Pipeline was API X70. A parallel mainline of approximately 4950 km with 8 sub lines resulting in an overall total length of approximately 8800 km is being designed for construction in 2008. This line will be the 2 nd West-East Pipeline Project and will be built out of API X80. The major dimension of this line is 1219 mm OD × 18.4 mm wall thickness. Nanjing Iron and Steel Company (NISCO) in Nanjing, China commissioned a wide plate/coil Steckel mill in 2004 and has successfully developed API grades in plate and coil for the Chinese pipeline industry. Since 2004 NISCO has successfully ramped up production to where in 2007 anticipated delivery of API plate and coil will be approximately 350,000 mT. Over that time period NISCO has been developing API X80 plate and coil capabilities in anticipation of the 2 nd West-East Pipeline Project. The 2 nd West-East Pipeline specification major requirements for coil and plate mechanical properties include round bar tensile testing, YT maximum of 0.93 for round bar, ≥ 240 J @ −20 °C average TCVN and ≥ 85% DWTT shear average @ −15 °C. During the development process two alloy approaches have been identified for plate and coil to produce the ferrite/acicular ferrite microstructure required for API X80 pipe. This paper will describe Nanjing Iron and Steel Company’s development and results to produce API grade X80 plate and coil that successfully met the specification requirements of the 2 nd West-East Pipeline Project.

Economical movement of energy through densely populated regions of China to support economic growth has resulted in typical natural gas transmission pipeline designs of API grade X70 that utilize wall thicknesses in a range between 17 and 32 mm and OD at 1016 mm. The DWTT requirement for many of the specifications is ≥ 85% shear average at −10 °C to −15 °C in the plate or coil. Achievement of good fracture toughness, such as DWTT is heavily related to the total reduction from slab thickness to finish plate thickness. Ideally a total slab to finish plate thickness reduction in excess of 12:1 or at a minimum 10:1 is desirable to properly condition the austenite grains for good DWTT performance. Many of the Chinese steel producers, including Nanjing Iron and Steel Company (NISCO) have slab thicknesses less than 250 mm with several less than 200 mm, especially in wider widths to support the 1016 mm OD. This results in total slab to finish plate thickness reductions less than 10:1 and in some designs total reductions down to 7:1. This challenges the steel producer of plate or coil in achieving the required specification average DWTT percent shear on a consistent basis. For heavy gauge plate and coil in the widths required for the Chinese pipeline industry NISCO typically uses a 150 mm slab or a 180 mm slab. NISCO has to routinely use slab to finish plate or coil thickness total reductions less than 10:1. This paper will describe NISCO’s successful development related to production of heavy gauge API X70/X80 grade plate and coil meeting the DWTT percent shear requirement in China utilizing slabs that result in total slab to finish plate/coil reductions of less than 10:1.

Mechanisms of AC assisted corrosion of pipelines under cathodic protection (CP), and CP criteria for its mitigating remain still subjects of controversy. This paper presents a critical review of the fundamental understanding of the AC assisted corrosion phenomenon and also some laboratory investigation; such as the analysis of corrosion products obtained under carefully controlled AC corrosion tests using Raman spectroscopy, simultaneous recording of potential and current, and separation of this experimental overall current into its faradic and charging of the double layer capacitance contributions. For the latter, a simplified equivalent circuit model of the steel / solution interface, taking account of the interfacial and transport phenomenon was used. Results obtained are discussed: • to highlight the effect on corrosion rate and corrosion feature, of some critical parameters namely AC current density, AC voltage amplitude, CP level, soil resistance between the coating defect and remote earth, and development of iron oxide layers; • to devise some aspects on the mechanistic view of the phenomenon; and • to comment on the CP criteria currently in use, with a special focus on the dependency of CP protection level with AC current density and voltage amplitude.

Hydrogen plays a critical role in near-neutral pH SCC in pipelines, but the precise mechanism of its effect on crack initiation and propagation is still not well understood. Fundamentally, the process starts on the atomic level and at the root is dislocation formation and propagation due to various factors. In the present study a molecular statics simulation has been applied for the analysis of the contribution of hydrogen to the near-neutral pH stress corrosion cracking. A 3D crystal structure in which the interatomic forces between the hydrogen-iron and iron-iron atoms were defined, respectively, by the Morse and modified Morse potential functions was tested numerically. The model and the code developed were applied to both a hydrogen-free bcc iron crystal with the premade edge slit and to a bcc iron crystal with the hydrogen atoms aggregated near the crack tip. The width of the reference structure was chosen to be large enough to avoid any significant effects of free boundaries while preserving the basic properties of the structure. The edge slit was obtained by removing of a monolayer of iron; it was assumed that this slit was formed previously as a result of dissolution and the hydrogen-assisted cracking. Simulation results demonstrated that the presence of dissolved hydrogen causes severe distortion of the lattice and results in a weakened zone of interatomic bonds in the vicinity of the hydrogen atom even before the external load is applied to the structure. This phenomenon leads to the nucleation of nano-voids and later to the formation of edge dislocations array, and to the newly nucleated voids coalescing. Consequently the sliding processes start earlier (under the smaller load) leading to a 15–20% loss of residual strength in comparison with the hydrogen free sample.

This paper presents an evaluation of the thin film corrosion sensors that could be used in combination with a mobile, wireless platform to detect internal corrosion along a pipeline. The iron-copper, thin film interdigitated sensor was found to be appropriate for detecting the presence of corrosive conditions within the pipe. The sensor reading using DC resistance measurement method reflected the corrosivity of a number of electrolytes and was able to determine the corrosion rate of iron in these environments. The sensor readings were reproducible. The sensor was able to distinguish between bulk aqueous solution and condensed moisture film. The sensor response was relatively rapid (within 60 s), thus permitting it to be used as a transient, retrievable sensor. The sensor life in the presence of acid gases, CO 2 and H 2 S, was relatively short (less than a week). The sensor readings were only slightly dependent on sensor geometry.

The crack arrestability for high strength line pipe steels with tensile strength of 650 to 850 MPa was evaluated using precrack DWTT (pc-DWTT). Moreover, the effects of microstructure and texture on pc-DWTT energy were investigated. The pc-DWTT energy was remarkably affected by tensile strength. The pc-DWTT energy of ferrite and bainite/martensite dual phase steels was much higher than that of bainite single phase steels in comparison with the same tensile strength. The {100} plane is a cleavage plane in iron, so the brittle crack mainly propagates along the {100} plane. Bainte single phase steels indicated a high intensity of the {100} on the plane rotated 40° from the rolling plane with the axis of the rolling direction. On the other hand, ferrite and bainite/martensite dual phase steels indicated not only a high intensity of the {100} plane rotated 40° from the rolling plane, but also a high intensity of the {100} plane parallel to the rolling plane. Slant fracture could be easily formed by the high intensity of the {100} on the plane rotated 40° from the rolling plane if local brittle areas such as martensite and austenite constituent (M-A constituent), which became the initiation point of brittle fracture, existed. In contrast, separation tended to be formed by the high intensity of the {100} plane parallel to the rolling plane that was caused by the formation of ferrite and bainte/martensite dual phase microstructure. Thus, pc-DWTT energy and shear area were remarkably affected by microstructure and texture. Therefore, to control microstructure and texture is vay important for the improvement of pc-DWTT properties.