To add mass to gas and oil reserves, numerous subsea pipelines happen to be installed and therefore are under operation within the oceans all over the world, for example in continental shelves and deep water regions. Additionally, cellular phone and operation of subsea pipelines in deep sea areas tend to be more complicated compared to shallow water. The circumstances in deep water are very harsh. For instance, a subsea pipeline should resist roughly 300-400 bar of hydraulic pressure and temperatures of 250-300 °C.
Roughly 50% of the several subsea equipment/facilities all over the world have observed failures within their subsea pipelines in recent decades. Failing accident could be categorized based on its mechanical/chemical aspects: corrosion, fatigue, and impact failures, that are caused by ocean water cyclic loads, for example from currents and falling objects, for example subsea piles, correspondingly. Numerous studies on failure accidents happen to be transported out. Included in this, corrosion and fatigue failures happen to be broadly studied. Particularly, many classification society rules happen to be set up, and lots of research papers happen to be written.
Xue (2006) examined the issue of buckle propagation in corroded subsea pipelines, the variation in propagation pressure based on the type of the pipe, and also the collapse mode inside a corroded pipeline. The finite element model was validated using Timoshenko’s classical solutions. Pinheiro and Pasqualino (2009) suggested a technique for any fatigue analysis of the broken steel pipeline under cyclic internal pressure. This technique uses the strain concentration factors, that are generally accustomed to customize the standard S-N curves of metallic structures within high cycle fatigue load. The authors conducted fatigue tests to judge the finite existence behavior of small-scale broken pipes under cyclic internal pressure. The outcomes of the fatigue analysis coincided well using the fatigue test results. Bazan and Beck (2013) suggested a non-straight line model, where the corrosion rates are symbolized like a Poisson square wave process. The resulting model represents the natural time-variability of corrosion growth and it was adjusted towards the same group of actual corrosion data for 2 inspections from existing corrosion models. The suggested non-straight line random process corrosion growth model brought towards the best fit up to now, and much more correctly represents the physics of the problem.
Furthermore, the look criteria for that corrosion and fatigue, among additional factors, are specified by rules for example ABS (2008), API RP 1111 (2009), API 5L (2008), ASME B31.8 (2010), CSA Z662-07 (2007), DNV OS F101 (2010), and ISO 13623 (2009).
Nonetheless, although numerous codes and research papers associated with two kinds of failure problems happen to be public-shed, there has been couple of reports on impact failures. Johnson et al. (1992) transported out a number of impact tests for any mild steel pipe by shedding a wedge-formed object. Particularly, the relationships between your kinetic energy and minimum internal and exterior diameters were investigated. Yang et al. (2009) conducted a pipe-on-pipe impact test to research the dynamic res-ponse of the pipe for that pipe impact problem. Within their study, the results from the impact location and pipe wall thickness were identified. Zeinoddini et al. (2013) evaluated the result of soil-pipe interaction around the structural response throughout a pipe impact event using finite element calculations. An altered-Drucker-Prager/Cap plasticity model was utilized to explain the seabed soil, as well as an FEA technique thinking about the soil-pipe interaction was suggested and validated via a comparison using the reported test results.
ASME B31.8 (2010) provides calculation formulae for the quantity of deformation and strain of the subsea pipeline under an effect load. Within this code, the stress around the internal and exterior pipe surfaces is evaluated in line with the bending strain both in the circumferential and longitudinal directions, as well as on the extensional strain within the longitudinal direction.
These research papers and code centered on the pipe impact phenomenon and it is connected structural behavior, but there is a significant limitation for the reason that the building blocks underneath the pipeline was postulated to be rigid. Additionally, in certain studies, the soil scale effect wasn’t investigated throughout the experiments and/or simulations. To be able to analyse the structural behavior from the subsea pipeline precisely, it’s strongly suggested the aftereffect of interaction between pipe structures and ocean-bed (soil) should be thought about within the statistical analysis (Yu et al., 2013).
Therefore, in our study, to visualize the pipe behaviors inside a subsea atmosphere, both precise pipe behaviors and also the failure characteristics were investigated by thinking about the soil effect, that is hard to predict and realize. Quite simply, a pipe impact test was transported out utilizing a soil chamber and dry drop impact mass. To think about the various seabed soil, three kinds of soil, i.e., clay with 60% and 80% moisture content and water-saturated sand, were adopted for that experiments. Throughout the test, a sizable scale soil chamber was utilized to prevent an abnormal reaction pressure generated through the narrow boundary conditions from the soil chamber.
Within the pipe impact simulation, the soil was described in line with the Mohr-Coulomb failure qualifying criterion. Additionally, the soil scale effect was identified via a parametric study with regards to the seabed soil length and breadth. Case study outcome was in contrast to the exam leads to validate the suggested simulation technique.
A number of statistical analyses were also conducted, and also the outcome was compared and among the present subsea pipeline-related classification society rules, e.g., ASME B31.8 (2010). The variations between your FEA results and rule cal-culation outcome was investigated, and modified ASME formulae were suggested to calculate the actual structural behavior of the subsea pipeline under an effect load when thinking about sand- and clay-based seabed soils.
LABORATORY SCALE IMPACT TEST
A parametric laboratory-scale impact test was conducted to simulate the failure phenomenon of the subsea pipeline. The laboratory-scale impact test utilized in this research, the first make an effort to simulate the outcome response of the pipe system within subsea atmosphere, requires a mix of two test methods. The very first technique is an effect test method use to judge the response from the target structure exposed for an impact load. The 2nd technique is a soil test method accustomed to find out the soil characteristics (Vesic, 1971 Terzaghi et al., 1996 Das, 1998 Poulos, 2005). It had been confirmed the mixture of the right impact make sure identification of soil interaction effect can be used an organized method of estimate the outcome behavior of the pipe system laid on the top of the seabed.