Negative air gap and wave slamming load on the deck box of drilling semi-submersible units in severe storm have received a great deal of attention, due to the COSL Innovator accident in 2015. Equally important is vertical slamming load on the MODU underdeck, which is less reported in the literature. The present paper attempts to derive characteristic vertical slamming pressure on the deck bottom, based on an extensive model test program for a drilling semi-submersible unit, CM-SD1000. A total of 96 3-hour wave impact tests were conducted including 4 sea states selected along the DNV steepness criterion curve in 3 wave headings. Two critical sea states were identified and each was tested with 16 random realizations in both the head and the beam waves. 8 force panels were installed on the under-deck to capture vertical wave impact events. It is found that the peak slamming pressures obtained can be fitted well with both Weibull and Gumbel probability function. The extreme vertical impact pressure predicted are of the same order of magnitude as the extreme horizontal impact pressure. The present study also shows that rise velocities of the wave surface relative to the deck bottom have a remarkable correlation with the wave slamming pressure in terms of probability distribution. The relative rise velocities can be properly derived from wave probe measurements. This offers an alternative approach to estimate the vertical impact pressure without resort to force panels. In contrast to horizontal wave slamming, the magnitude and frequency of vertical ones simply increases with significant wave height and wave steepness has much less effect. It is found that the extreme vertical impact pressure can be approximated well by a linear function of the significant wave height. The linear relationship, if validated by more tests, may help evaluate structural strength of the deck bottom before wave basin model testing.

This paper presents the development and testing of Gator, a hydraulic Power Take Off (PTO) being commercialised for the Aquaculture market. Gator uses a novel polymer bellows to pump pressurised water through a power take off system, while also providing a non-linear force response that reduces mooring line loads over traditional mooring lines. The Gator system is comprised of 4 distinct subsystems: The Gator pump, hydraulics, turbine, and electrical storage & control. The Gator pump is a polymer component that compresses under load, pumping water through check valves into the hydraulic system. The connected hydraulic system takes the pressurised water, regulates the pressure and flow rates with an accumulator, and provides a steady flow of water to the turbine, generating electricity. This paper will provide an overview of the technical development of the Gator system over several phases, which has focussed its adaptation for use in the aquaculture industry as an inline pump on cage mooring lines. A description of comprehensive testing undertaken on a linear test rig to simulate the variable loading that the system would experience in operation will be provided as well as some of the early characterisation results from this testing.

Model tests were performed with a model of the INO WINDMOOR 12 MW floating wind turbine in the Ocean Basin at SINTEF Ocean. The tests were done at a scale of 1:40. RealTime Hybrid Model testing was used for the modelling of the wind turbine rotor and aerodynamic loads. A subset of the results is analysed to study the influence of the wind on the platform motions, the acceleration at tower top, the loads at base of tower and the relative wave elevation. The study is based on the comparison of the quantities of interest for different tests with the same moderate sea-state but with different wind modelling: no wind, constant thrust force, turbulent wind of 11.5 m/s and turbulent wind of 25 m/s. The wind modelling has a minimal influence on the platform surge and pitch response in the wave-frequency range. On the other hand, the aerodynamic loads, including wind turbine controller dynamics and turbulent wind, has an important impact on the low-frequency surge and pitch response. The aerodynamic loads are important for the loads at tower base due to the dominance of the tower-RNA induced gravitational loads at low-frequency. Maximum relative wave elevation was found to be mainly dependent on the thrust induced mean pitch angle.

Mechanical recovery techniques are used to clean up oil spills in marine environments; however, their efficiency is challenged when dealing with heavy oil, ice covered water and high sea states. Current mechanical recovery techniques are based on removing oil from the water surface, however, a significant amount of oil could remain in the water column below the surface due to turbulent ocean conditions, the density of heavy oil and oil escaping underneath the booms when the sweeping speed increases. To enhance the oil recovery effectiveness, oil particles in the water column need to be guided to the surface to be recovered by the skimmers. This paper focusses on the development of a test protocol and physical testing in C-CORE’s lab of a bubbler system for enhancing the harsh environment oil spill recovery. Air bubbles produce an upward flow in the water body, which guides the submerged particles to the surface. The air bubbles also attach to the oil particles, leading to an increase in the buoyancy and rate at which oil droplets rise to the surface. By adopting this technique for oil recovery, additional oil particles can be brought to the surface. In the study, the bubbler system was tested in both stationary and advancing conditions with medium and heavy oils. The results of the stationary and advancing tests indicate that the oil recovery ratios can be significantly enhanced by using an optimized bubbler system. Different types and configurations of bubblers were tested by varying the airflow rates and bubbler advancing speeds to determine the optimal solution. The optimal bubbler system has been observed to enhance the recovery ratio from 41.5% to 84.8% with airflow rates ranging from 0.05 to 0.20 CFM/foot. Furthermore, the effective integration of the bubbler system with a mechanical recovery system, its deployment and retrieval in a near field condition were demonstrated during tests in an outdoor tank.

While performing fatigue reliability analysis of the butt-welded joints it is vital to estimate the Stress Concentration Factor (SCF) at these joints. A common approach adopted by industry to estimate the SCF at weld toes is to perform Finite Element Analysis (FEA) of the welded joints for different pipe sizes, flanges, valves etc. The SCF are calculated for each size by separately when required and are very time consuming. Although FEA is known for its accurate SCF calculation, but due to its high computational expense and time-consumption, SCF evaluation for different parameters makes the aforementioned method quite laborious. As an alternative response surface models (RSM) may be used for accurate estimation of SCF. The two basic steps in constructing a RSM are training and testing. The first corresponds to fitting a model to the intelligently chosen training points, while the second step involves comparing the predictions of the RSM to the actual response. This paper examines the applicability of 12 different RSMs for estimating SCF. The training and testing data is generated using FEA in ANSYS. In order to compare the accuracy of the RSMs, three metrics, namely, Root Mean Square Error (RMSE), Maximum Absolute Error (AAE), and Explained Variance Score (EVS) are used. A case study illustrating the applicability of the proposed approach is also presented.

For subsea well drilling, the drilling rig is connected to the subsea well by a marine riser and subsea BOP equipped with a remotely controlled wellhead connector latched onto the subsea wellhead profile. The level of cyclic loading on subsea wellheads is steadily increasing due to use of increasingly larger drilling rigs with larger BOPs, the drilling of wells in harsher environments characterized by high waves. The remotely controlled wellhead connector forces a series of locking dogs into an externally machined profile on the wellhead. This external profile is generally referred to as a wellhead profile. The fatigue resistance of this safety-critical connector is typically estimated by finite element analyses (FEA). Due to the large size of the equipment, and high cost of testing, very limited fatigue testing, if any, has been carried out. A test method has therefore been developed, where a special test fixture is used to apply realistic boundary conditions and variable tensile loads to a small sector or segment of the wellhead connector. A primary objective is to generate fatigue-critical stress fields in the segments under tensile test load that closely replicates the stress fields in the full-scale wellhead connector. A secondary objective is to evaluate the possibility of using segment testing to determine the fatigue capacity of the full-scale connector. The testing of narrow sector segments allows the use of readily available test apparatus. It is thereby envisaged that the total cost of testing (specimens and test laboratory costs) can be substantially reduced in comparison with full-scale connector fatigue testing. This paper describes the fatigue testing of wellhead connector segments, and the test results in terms of cycles to failure and the failure modes, i.e. crack initiation point, and final crack geometry. The test scope consists of nine segments tested in-air at ambient temperature (nominal 20 °C), at a frequency of approximately 2 Hz under axial load of R = 0.1. At the time of writing this paper, six out of these nine tests have been performed. These six fatigue tests are presented in this paper. The test results are compared with estimates achieved by FEA of the test assembly and relevant S-N curves for the materials. It will be determined if the test results can be accurately predicted by the fatigue analysis methodology in Section 5.4 of DNVGL-RP-C203 (C203), including use of the new series of S-N curves for high strength materials in Appendix D.2 of C203. This design approach assumes that other failure modes (e.g. fretting or other local effects in the interface between components) do not govern the fatigue life, as this cannot be predicted by the fatigue analysis method applied here. The fatigue test set-up and the finite element analysis of the segment test is presented in the OMAE2020-18652 paper.

There is increasing demand for subsea transport of well-produced fluids through corrosion resistant pipelines such as stainless steel or bimetallic pipes. The latter are made of carbon steel (CS) pipe and a thin (typically 3.0 mm thick) internal layer of corrosion resistant alloy (CRA) such as 316L, 625, 825 or 904L. The CRA and CS layers are adhered either metallurgically or mechanically by a means of an interference fit. Although less mature than other products, mechanically lined pipes (MLP) are more readily available and economical than both stainless steel or hot-roll bonded (HRB) metallurgically clad pipes. One of the gaps that remains to be filled relates to a reliable assessment method for confirming the MLP integrity during offshore installation and subsea service. The CRA liner in MLP is metallurgically bonded to CS at pipe ends by overlay welding, typically deposited using alloy 625 consumable. At the triple-point interface between the liner, overlay and host pipe, cracks may initiate from fabrication flaws and grow during installation or in service. Therefore, the engineering critical assessment (ECA) should be carried out to evaluate the risk of triple-point cracks breaching the CRA layer at any stage of the pipeline’s life cycle. Currently, no recognised ECA approach exists to allow completing such an assessment. Therefore, a bespoke integrity assessment procedure has been developed and validated both numerically and via laboratory testing. This paper outlines the ECA procedure for triple-point flaws in subsea MLP pipelines, which is undertaken through a combined analytical and numerical calculation and small-scale fracture testing. Fatigue crack growth due to cyclic loading is estimated using a geometry-specific stress intensity factor (SIF) solution derived by finite-element analysis (FEA). Ductile tearing during fracture load events is quantified by small-scale fracture testing on specimens with a representative geometry, designed to match the crack tip constraint of triple-point cracks in MLP.

An application of cyber-physical testing to the empirical estimation of difference-frequency quadratic transfer functions is presented. As an alternative to today’s procedure based on hydrodynamic tests with broad-banded or realistic (e.g., JONSWAP) wave spectra, tests in bichromatic waves are considered. The laboratory setup is the one developed by Sauder & Tahchiev (2020) that enables magnifying the sensitivity of the floater response to the low-frequency wave loading by adjusting the stiffness and damping parameters of a virtual soft mooring system. Bayesian experimental design is proposed to optimize the selection of the control variables (frequencies in the bichromatic wave and properties of the virtual mooring system) for a batch of cyber-physical tests. The experimental design algorithm is based on the recent work of Huan & Marzouk (2013). In a virtual yet realistic case study using an uncertain parametric quadratic transfer function, we demonstrate how the uncertainty of its describing parameters and other calibration parameters (low-frequency added mass and hydrodynamic damping) can be reduced. Results indicate that the proposed procedure has the potential for reducing experimental cost for calibration of hydrodynamic models.

Numerical modelling of the Arctic ocean dynamics with real-time simulation capability is useful for designing, developing, testing, and validating the performance of Dynamically Positioned (DP) and Autonomous ships/offshore platforms. Advanced simulation technology needs to be developed to predict the expected loads on these systems due to the complex interactions with environmental disturbances. This paper presents models of waves, currents, wind, and ice that comply with the real-time simulation requirements and adequately capture the dynamic characteristics of the most relevant physical processes. A 3D dispersive numerical model is deployed to predict the wave parameters to be utilized to compute the wave loads on a ship with known Response Amplitude Operators (RAO). A uniform current load is then incorporated in a superposition manner by using a combined wave-current field dispersion relation capable of expressing the wavenumber of an interactive wave-current field. The mean and the gust wind components are added to the resultant force components. A multiple regression-based ice model is used to predict the loads caused by an ice field characterized by varied ice thickness, concentration, floe size, drift speed and directions. The stationkeeping performance of a generic DP-controlled ship subjected to environmental disturbances is evaluated for a range of environmental conditions. The proposed models can help design, develop, and evaluate dynamic positioning and autonomous ship controllers’ performance. Another application may be developing a realistic simulation environment to train conventional, DP-controlled and autonomous ship operators.

It has been observed that, although submarine power cables have a critical role to wind power arrays and power export to shore, they are often overlooked at early stages of projects and oversimplified during late stages. This leads to lack of attention given during cable design and planning, as well as pressured schedules during manufacturing, testing and installation. The significant number of incidents attributed to offshore submarine cables during construction has increased overall project risk, lowered system average power availability and increased insurance costs. Lack of proper routing can also result in an inability to maintain asset integrity for the project design life. Despite the attention that submarine power cables have received over the past few years, the number and cost of incidents does not appear to be decreasing. A comparison can be made between offshore HVAC and HVDC cables used for wind power and offshore umbilicals and MV cables used in the oil and gas sector. These umbilicals are often similar in weight, size and bending stiffness, and have similar design, manufacturing, routing and installation challenges, but with a fraction of the incidents observed with offshore wind array and export cables. An additional caveat is that the offshore oil and gas sector has achieved a reliable track record while installing and maintaining these umbilicals and cables in fully dynamic conditions (ultra-deep water) as well static conditions. One primary difference between how the oil and gas sector executes these systems are design, planning and specification from an early stage of the project. Significant attention is given at an early stage to quality control, including offshore routing and umbilical testing specifically to avoid incidents resulting in umbilical damage due to the tension and crushing forces during installation as well as ambient seawater and seabed interaction. Management of these risks are documented, and optimal mitigation strategies are implemented early in the design phase. This paper will discuss the types of incidents which have been observed during construction and installation of submarine HVAC/HVDC cables in the wind power sector and how they could have been prevented by normal practices of the offshore oil/gas sector from early design and planning all the way to installation and commissioning.

Residual stresses are internal self-equilibrating stresses that remain in the component even after the removal of external load. The aforementioned stress when superimposed by the operating stresses on the offshore piping, enhance the chances of fracture failure of the components. Thus, it is vital to accurately estimate the residual stresses in topside piping while performing their fitness for service (FFS) evaluation. In the present work, residual stress profiles of girth welded topside sections of P91 pipes piping are estimate using a machine learning approach. The training and testing data for machine learning is acquired from experimental measurements database by Veqter, UK. Twelve different machine learning algorithms, namely, multi-linear regression (MLR), Random Forest (RF), Gaussian process regression (GPR), support vector regression (SVR), Gradient boosting (GB) etc. have been trained and tested. In order to compare the accuracy of the algorithms, four metrics, namely, Root Mean Square Error (RMSE), Estimated Variance Score (EVS), Maximum Absolute Error (AAE), and Coefficient of Determination (R^2) are used. Gradient boosting algorithm gives the best prediction of the residual stress, which is then used to estimate the residual stress for the simulated input parameter space. In the future work authors shall utilize the residual stress predictions from Gradient boosting algorithm to train the Bayesian Network, which can then be used for estimating less conservative through-thickness residual stresses distribution over a wide range of pipe geometries (radius to thickness ratio) and welding parameters (based on heat input). Furthermore, besides topside piping, the proposed approach finds its potential applications in structural integrity assessment of offshore structures, and pressure equipment’s girth welds.

Hot rolled sections such as I- and H-beams are commonly used as structural elements in offshore platforms. They exhibit a superior fatigue life compared to welded sections due to smooth corners and the absence of welds between the flange and web plates. Hence, when loaded in fatigue, the butt welds joining different sections are the hotspots in the design. Due to the size of the rolling installations, the maximum height for such sections is limited. To overcome these limitations, a hybrid welded beam concept is studied. This concept consists of 2 hot rolled T-sections with a plate welded in between to form an H-beam with increased section height. The advantage of this approach is that it maintains the smooth corners of the hot rolled sections and places the longitudinal welds closer to the neutral axis of the beam where the stress levels in bending are reduced compared to the flange-web interface. Hence, the butt weld between different beam sections remains the hotspot instead of the longitudinal weld. In the present work the fatigue design of such hybrid welded beams is studied. As part of this research, an efficient experimental assessment methodology is proposed. Fatigue tests are performed on a large-scale resonant bending test setup allowing a testing frequency of around 30 Hz. Tests are performed on HISTAR HE girders with a section height of 696 mm and 524 mm. As a reference, fatigue tests are performed on hot rolled HE beams joined by butt welding. Hybrid welded beams will be tested in the same setup at a later stage. During the tests, fatigue crack initiation is detected using an acoustic emission system. Further crack propagation is monitored through local strain measurements and by intermediate inspections during the tests. In addition, the beach marking method is applied, allowing to investigate the evolution of the crack front by post-mortem analysis.

Hydrate plugging is an important factor affecting the safety and efficiency of flow assurance. Current prevention methods for hydrate plugging are costly or environmentally unfriendly or inefficient. In this work, an efficient method to prevent hydrate plugging during deep-water gas well testing was put forward, which is achieved by reasonably changing the testing orders of different gas production rates. The deposited hydrates in the tubing under low testing rates will be decomposed under high rates to reduce the risk of hydrate plugging without hydrate inhibitor injection. A case study is carried out to investigate the applicability of this method. The results show that the maximum dimensionless thickness of hydrate deposit reaches 68.14% under the conventional testing order, but decreases to 33.59% by using the proposed method. It is indicated that the proposed method can obviously decrease the risk of hydrate plugging without using hydrate inhibitor injection. Hence, the proposed method is a more economical and environmentally friendly method for hydrate plugging prevention, which can be applied as an alternative to the present prevention methods during deep-water gas well testing.

As the flexible pipe industry targets more on deepwater applications, collapse performance of flexible pipes becomes a key challenge due to the huge hydrostatic pressure during installation and service. The collapse strength of flexible pipes largely depends on the structural characteristics of carcass, pressure sheath and pressure armor layers. Therefore, the collapse prediction methodology involving a sound modeling of these layers is essential. Over the years, Baker Hughes have collected a large amount of collapse testing data. The prediction tool needs to be validated and calibrated against all the collapse tests for best accuracy. In this paper, the latest progress of the collapse prediction methodology and qualification tests are presented. A generalized collapse model was developed to predict the collapse pressure of flexible pipes. This model incorporates the advantages of both the weighted kNN regression technique and an analytical collapse model. It is able to reproduce the exact collapse pressure on the pipes tested and can predict the collapse pressure of other pipe designs not tested. As part of the qualification process, the capacity to prevent collapse must be demonstrated. Several flexible pipes were designed based on this generalized prediction methodology for deep water application, and pipe samples were manufactured using industrial production facilities for collapse tests. The results show that flexible pipes following current design guidelines are suitable for deepwater applications.

Monitoring the integrity of mooring lines on floating offshore platforms is one of the key factors in ensuring safe and productive offshore operations. Sensors, such as inclinometers, compressive load cells or strain sensors, can be used to monitor the inclination angles or tensions on mooring lines. An alternative method using only dry monitoring systems, such as DGPS (Differential Global Positioning System), Gyrocompass and/or IMU (Inertial Measurement / Motion Unit), can also be used to monitor the integrity of mooring lines. This method uses the measured motions and positions of a vessel without any information on the environmental conditions to detect mooring line failure. The detection of mooring line failure is based on detecting shifts in low-frequency periods and mean yaw angles as a function of vessel position, mass and added mass. The proposed method utilizes Artificial Neural Network (ANN) to recognize and classify patterns. The training of an ANN model requires examples/data associated with intact mooring lines and broken mooring line(s). Examples/data of broken mooring line(s) are practically available only from numerical simulations. Therefore, it is important to address these two key topics: (1) Is the real behavior of the floating offshore platform sufficiently aligned with numerical simulations? and (2) The effect of the accuracy of monitoring equipment on the performance of an ANN-based system. The first topic is reviewed briefly with its possible solution including some sensitivity tests, and this paper focuses on addressing the second topic. A system architecture is discussed in this paper along with the accuracy of the monitoring equipment. As an example, an ANN model has been trained to detect a broken mooring line of a spread-moored FPSO. This ANN model has been tested on its performance in dealing with a range of possible errors associated with the monitoring equipment. Furthermore, the tests have been carried out for a combination of variables that are not included in the ANN training, such as: vessel draft (mass), sea state conditions and directions. This paper presents the results of the tests for various variable sensitivities, which cover vessel positions, mean yaw angles and vessel drafts. These are essentially testing the tolerance of a trained ANN model against error or noise in the data. The results show that a trained ANN model can be error/noise tolerant.

In this paper fretting fatigue is addressed as a potential design consideration for wellhead connectors. The study of near-edge relative motion for frictional contacts under constant normal load is described using analytical, numerical and asymptotic methods. Based on published fretting fatigue experimental data an argument is drawn for a generalised fretting fatigue test design. We do this by reducing the parameters responsible for crack nucleation to the smallest number possible and thereby revealing the fretting fatigue strength as a material property independent of geometrical features. Easy to apply recipes are described and thoughts on a potential apparatus are shared with the reader. Commercial potential lies in the wide-ranging applicability of experimental results across many prototypes and loadings once an appropriate amount of fretting fatigue data has been generated for the material in question.

For subsea well drilling, the drilling rig is connected to the subsea well by a marine riser and subsea BOP equipped with a remotely controlled wellhead connector latched onto the subsea wellhead profile. The level of cyclic loading on subsea wellheads is steadily increasing due to use of increasingly larger drilling rigs with larger BOPs, the drilling of wells in harsher environments characterized by strong high waves. The remotely controlled wellhead connector forces a series of locking dogs into an externally machined profile on the wellhead. This external profile is generally referred to as a wellhead profile. The fatigue resistance of this safety-critical connection is typically estimated by FE analysis. Due to the large size of the equipment, and high cost of testing, very limited fatigue testing, if any, has been carried out. A test method has therefore been developed, where a special test fixture is used to apply realistic boundary conditions and variable tensile loads to a small sector or segment of a wellhead connector. A primary objective is to generate fatigue-critical stress fields in the segments under tensile test load that closely replicates the stress fields in a full-scale connector subject to bending loads. A secondary objective is to support the introduction of the practice of testing several segments cut from a single wellhead connector. The testing of narrow sector segments allows the use of readily available test apparatus. It is thereby envisaged that the total cost of testing (specimens and test laboratory costs) can be substantially reduced in comparison with full-scale connector fatigue testing. This paper describes the text fixture, the connector locking dog, and wellhead segments designed to replicate the stress fields in a full-scale wellhead connector. The test fixture and test specimens are designed to match conditions and fatigue stress of the full-scale connector. The test specimens are instrumented with strain gauges at fatigue hotspots. Digital image correlation (DIC) is used to measure the relative motion between the wellhead segment and the locking dog. The measured strains are compared with corresponding values from finite element analysis of the test. The DIC results are also used for estimating the coefficient of friction between wellhead profile and locking dog. Very good agreement is found between measured hotspot strains and strains from the FE analyses for consistent load conditions. The test fixture is therefore considered suitable for segment fatigue testing, where the test results can be used to estimate the bending fatigue capacity of a full-scale wellhead connector. Results from fatigue testing by this test method are presented in a separate OMAE2020 paper.

Wave energy converters (WEC), particularly those of the oscillating paddle type, are one of the least utilized categories of marine energy harvesting devices. As such, the goal of this research is to develop improved WEC technology through numerical modeling that will inform future experimental testing, which is being carried out by the Pacific Marine Energy Center. A novel scheme using mesh distortion and re-meshing to simulate the rotation of a wave-driven oscillating wave surge converter is presented herein using only the default functionality of the OpenFOAM computational fluid dynamics software package as a framework to implement the scheme as a convenient tool for engineers to study OWSC performance. This scheme relies on the use of finite volume mesh quality parameters, namely mesh cell non-orthogonality and skewness, to control when re-meshing operations are undertaken, minimizing the number of re-meshing operations needed to accommodate OWSC motions while maintaining solution stability and accuracy.

The Rate of Penetration (ROP) is one of the key parameters related to the efficiency of the drilling process. Within the confines of operational limits, the drilling parameters affecting the ROP should be optimized to drill more efficiently and safely, to reduce the overall cost of constructing the well. In this study, a data-driven optimization method called Extremum Seeking is employed to automatically find and maintain the optimal Weight on Bit (WOB) which maximizes the ROP. To avoid violation of constraints, the algorithm is adjusted with a combination of a predictive and a reactive approach. This method of constraint handling is demonstrated for a maximal limit imposed on the surface torque, but the method is generic and can be applied on various drilling parameters. The proposed optimization scheme has been tested on a high-fidelity drilling simulator. The simulated scenarios show the method’s ability to steer the system to the optimum and to handle constraints and noisy data.

Understanding the interaction between the drilling fluid and the natural gas from a gas kick may be of great importance when predicting how a well control incident evolves during drilling operations. This is especially true for oil based mud, which has the ability to dissolve large quantities of gas under high pressure, thus potentially hide any volumetric impact of a gas kick. When the pressure of the dissolved gas decreases below the bubble pressure, free gas will start to emerge. Dangerous situations can occur if the bubble point pressure is low and located close to the surface. This may result in a rapid volumetric expansion of the free gas, as it emerges from solution, thus little to no time to react and initiate proper well control procedures. Most conventional well control simulators that takes gas solubility into consideration assumes an instantaneous vaporization of gas as the vapour-liquid phase equilibria changes. However, this assumption might not always be realistic. It may take some time before a new equilibrium is reached when the conditions are changed. This will thus affecting the rate of gas liberation from the liquid. To better understand this complex issue, an analytical expression for the transition rate of dissolved gas to free gas in a supersaturated liquid has been derived for low pressure systems. The analytical model is strongly dependent on the solubility coefficient, K h , and the transition rate factor, γ, and follows an exponential curve. In this expression, K h is a measure of how much the liquid is supersaturated at any given time and controls how much gas that will be liberated. γ determines how fast the system will reach a new equilibrium, i.e. how fast the gas will be liberated based on the size of the supersaturation. Both K h and γ are thought to be values given for a specific gas-liquid combination. In order to verify the analytical expression, experimental testing has been conducted. The experiment is carried out by pressurizing a tank partly filled with the base oil Exxsol D60 by feeding it with methane gas. Some of the gas will dissolve into the liquid. The rest will flow to the top as free gas and pressurize the tank. By quickly removing some of the free gas, thus depressurize the tank, the liquid will instantaneously become supersaturated, hence triggering liberation of free gas from the solution until a new equilibrium is established. By measuring the tank pressure throughout the degassing phase, values for K h and γ can be estimated and compared to the analytical model.