Ordinary carbon steel is by far the most important alloy in the oil and gas industry because it accounts for more than 98% of the construction materials used in produced-water systems. As a general rule, every attempt should be made to use steel, such as modifying the process with corrosion inhibitors in the fluid or coating the steel. Proper material selection is critical for long operation life and minimal maintenance. A small increase in capital expenditure for an optimum material selection can greatly reduce the mean time to maintenance or failure, thus greatly saving on operating expenses. As a general rule, every attempt should be made to use steel, such as modifying the process with corrosion inhibitors in the fluid or coating the steel.
Operators are increasing capital budgets in the wake of tariffs and quotas initiated by the US government on steel imports, and the product exclusion process has revealed a host of other issues. If the tariffs are here to stay, what does industry hope to see moving forward? Supply and Demand in Unconventionals: Where Do Service Companies Fit? Service company executives examine how the oil price downturn affected supply and demand for their services in the unconventional sector, and strategies they have undertaken to stay afloat as operators adjust to uncertainty.
Operators are increasing capital budgets in the wake of tariffs and quotas initiated by the US government on steel imports, and the product exclusion process has revealed a host of other issues. If the tariffs are here to stay, what does industry hope to see moving forward? How will a US steel tariff affect the oil and gas supply chain? Industry criticism points to a noticeable effect on construction expenditure and jobs, but where will the pain be most felt?
A rupture of buckled steel pipes on the tensile side of a cross-section is studied in this paper as the most plausible case of ultimate failure for the pressurized buried pipelines under monotonically increasing curvature. Finite element simulation of full-scale bending tests on two pressurized X80 pipes with different yield-to-tensile strength (Y/T) ratios were conducted. The Y/T ratio and internal pressure were identified as the crucial factors that have a coupled effect on the ultimate failure mode of buckled pipes. That is, the high values of Y/T ratio and internal pressure mutually trigger the rupture of buckled pipes on the opposite side of the wrinkling.
Steel pipelines are so ductile and can accommodate a large amount of post-buckling deformations while preserving their operational safety and structural integrity. To benefit from this outstanding quality and prevent the buckled (wrinkled) pipelines from premature rupture, the postbuckling behavior of the steel pipes should be well understood.
Rupture is one of the major failure limits to the integrity of pipelines that endangers the environment as well as the public safety and property. Comprehensive experimental and numerical studies on the fracture of buckled steel pipes (Das, 2003; Sen, 2006; Mohajer Rahbari, 2017) show that under increased monotonic curvature, successive buckles (wrinkling) are formed on the compressive side of the wall, and the occurrence of rupture at the wrinkling location is unlikely because of the ductile nature of steel material. Rupture of wrinkling can occur once buried pipelines are subject to a very rare and changing boundary conditions accompanied by extremely large plastic deformations toward tearing the wrinkled wall (Ahmed, 2011). However, experiments have shown that the increasing curvature can easily trigger the postbuckling rupture of the tensile wall on the opposite side of the wrinkling (Sen, 2006; Mitsuya et al., 2008; Tajika and Suzuki, 2009; Igi et al., 2011; Tajika et al., 2011; Mitsuya and Motohashi, 2013; Mitsuya and Sakanoue, 2015). This mode of failure seems very likely to be the rupture limit of the wrinkled pipes, as it occurs following the same regime of monotonic bending deformations that have previously made the pipe buckle.
In joining technology, welding is one of the vital techniques used to make continuous pipelines in industry. The thermal and mechanical loading in the process has a profound impact on the integrity of the pipeline over its service life. An accurate and thorough assessment is needed on the associated residual stress and its effect on the structural properties of the pipeline. One of the novelties of this research is the understanding of the welded joints' temperature responses, as demonstrated by positioning high-temperature thermocouples at strategic points on the welded joints to capture the transient temperature response at different points. It is not enough to assume that the distribution of heat through the weld metal will depend on the distance from the thermocouples to the heat source only; the temperature profile must actually be studied to uncover any peculiar trends.
As the oil and gas industry and international shipping companies push their assets into high latitude marine environments, it is important to thoroughly understand the performance of construction materials exposed to extremely low temperature and / or subjected to high ice loads. In the past, the design considerations have addressed the uncertainty in these areas by adopting conservative approaches. While proven effective, there exists a need for additional testing to gain insight into the safety margin levels that have been implicitly included. The work presented has the potential to lead to a better understanding of how steel materials behave in long-term Arctic conditions.
This paper presents the results of mechanical property tests of aged steel samples from the Kulluk, an ice-class rated drilling barge. This barge was exposed to the Arctic environment for almost 30 years. The Kulluk was built in Japan in 1983, specifically for exploration drilling operations in the Arctic environment. When the barge was scrapped in 2014, hull steel was selectively harvested. The intent was to conduct tests to better understand the behavior of shipbuilding steels that have endured long-term exposure to Arctic environments.
As an initial project phase, four sample groups of hull plate, from four different locations of the barge (one below the waterline, one in the ice belt region and two above the ice belt), were chosen for testing. The laboratory tests included tensile tests, Charpy impact tests and hardness tests. The test results indicate that the yield strengths, ultimate strengths, toughness and hardness of the aged steels continue to satisfy the ABS Rules requirements. A degradation assessment of these samples was also performed using these testing results and the limited data available as tracked from the barge's construction stage.
It is observed that the yield strengths and ultimate strengths remain consistent within the scatter of original or time period data. With respect to Charpy toughness values no conclusions concerning degradation can be made conclusively as the scatter in the data is substantial, especially at low temperatures. The steel in this study that has aged in the Arctic environment appears to maintain its original mechanical properties.
Based on the study presented in this paper, further studies could be performed such as additional sample tests to increase the reliability of results, material properties test for steel samples with butt/fillet welds to understand the variation of the heat affected zone (HAZ) and Crack Tip Opening Displacement (CTOD) tests to get a better understanding of the material toughness.