Offshore Piping Research Articles

Machine Learning Applied to Terahertz Signal Analysis For Hygrothermal Aging Characterization of Composites

Given their noncontact nature, ease of inspecting nonmetallic materials, and ability to detect small structural changes, terahertz waves were chosen as the study methodology for this project. Initially, characterization data was pretreated and standardized. The data were then reduced in dimensionality using principal component analysis and classified using other machine learning methods. The results demonstrated that the terahertz wave technique could accurately distinguish between different temperature and aging time scenarios. They also indicated that nondestructive in-service characterization of composite repairs is feasible and can provide invaluable information for decision-making. The main benefits of this approach include ensuring the safe operation of offshore piping and optimizing resources when deciding whether to replace the repair or keep it in service.

A fundamental study on structural strength assessment of U-bolts for expanded application to shipbuilding and offshore piping systems

The currently defined Safe Working Load (SWL) of the U-bolt has been determined excessively conservatively. To address this issue, this study conducted structural tests and numerical analysis on round type U-bolts of various sizes. The structural tests were conducted using a 2.5 MN actuator at the SURF R&D center, and the strain was measured through a uniaxial strain gage. The test showed the failure load greatly exceeded the design load with horizontal force. This necessitates a reevaluation and redefinition of load standards. Nonlinear numerical analysis was carried out, and these results were compared with the structural test results. When subjected to vertical loading, behavior was similar to uniaxial tension. On the other hand, using linear elastic analysis for determining SWL for horizontal loading was found to be irrational. A methodology was proposed for estimating the SWL of the U-bolt.

Flare Piping Material Selection for the Offshore Oil and Gas Industry

Optimal operation of offshore plants depends on the correct material selection for offshore piping systems. Flare systems, in particular, play a critical role in the safety of personnel in the plant. This study aims to determine the most suitable material for flare piping in order to prevent such failures in the future. In order to select the optimum piping material for flare systems, a systematic material selection process, called value engineering (VE), in conjunction with initial screening has been selected. Flare piping materials are selected according to six criteria: internal and external corrosion resistance, mechanical strength, cost, low-temperature resistance and availability. Using the VE method, the weight factor is determined by comparing each parameter pair-wise. A score is then calculated for each parameter for each material. For the flare system, five different types of material candidates were assessed in terms of performance. As a result, Inconel 625 was found to be the most suitable material for flare systems, while 6MO was the second choice.

Experimental investigation of residual stress distribution on girth welds fabricated at proximity using neutron diffraction technique

Maintaining minimum distance between repair and existing welds often becomes impractical due to the presence of compact layouts, original welds of branches, nozzles, etc. on offshore structural elements, pipelines, and piping. Although some international codes and standards provide criteria for maintaining a minimum distance between proximity welds, most of them lack technical justification in relation to their effect on the structural integrity of welded components. The development of residual stresses has a significant effect (i.e., a negative effect on tensile stresses and a positive effect on compressive stresses) on the integrity of the welds fabricated at proximity. Hence, it is important to investigate the residual stress distribution on welds fabricated at proximity, especially at a distance away from the weld toe. This study presents findings on the characterization of residual stresses by neutron diffraction at the proximity region between two girth welds. The two welds were fabricated at proximity, using two different welding procedure specifications and at three different distances, on a structural steel pipe, grade S355. The three different welding distances between weld toes were maintained at 5, 10, and 15 mm respectively. The neutron diffraction-based residual stress distributions were investigated at the POLDI neutron instrument at the Swiss spallation source SINQ in Switzerland. The axial, hoop, and radial components of the residual stresses were experimentally investigated between proximity welds. The findings revealed that residual axial stresses at a 5-mm proximity distance were increased beyond the yield strength of the structural steel, grade S355. The findings of this study enable practitioners to take remedial actions to minimize the residual stresses developed in girth welds fabricated at proximity. Also, the findings enable us to derive technical justification for maintaining a minimum distance and developing welding procedure for welds fabricated at proximity.

Stress intensity factor prediction on offshore pipelines using surrogate modeling techniques

This study aims to predict the accurate stress intensity factor (SIF) of a crack propagating in offshore piping, which is one of the crucial factors used to assess the remaining fatigue life (RFL) of offshore pipelines. Four soft computing techniques are examined and evaluated in the modeling of SIF of a crack propagating in topside piping, as an inexpensive alternative to the finite element methods (FEM). In the training and testing stages, developed models of Functional Network (FN), Emotional Neural Network (ENN), Relevance Vector Machine (RVM), and minimax probability machine regression (MPMR) for SIF prediction were used and compared. Also, a comparative study was conducted for the developed models with the Adaptive Gaussian Process Regression Model (AGPRM). The load, crack depth, and half crack length have been adopted as input variables of the models, and the output variable is the SIF. All variables were simulated and determined based on the flat-plate FEM model. The analysis confirms that the RVM and MPMR models are superior to FN and ENN models for SIF prediction in the training and testing stages. In addition, the RVM and MPMR models show better than AGPRM for the prediction of pipe SIF in the testing stage. The MPMR accurately outperforms all models within 1.31% prediction error, and the majority of its error values at 99% confidence level fall within ±29.64 MPamm.

Laser surface texturing inhibits Biofilm formation

Biofilm development on surfaces leads to biofouling, which is an undesirable phenomenon in the marine industry. Marine fouling leads to an increase in fuel consumption and corrosion of propeller blades. Most of the antifouling technologies available today are chemical methods that have detrimental effects on the environment. The current work focused on producing non-toxic and effective antifouling systems to control biofilm formation on the titanium alloy surfaces, which has potentially wide range of applications in the marine industry, such as propeller blades, the hull of the ships, heat exchangers, and offshore piping systems. A laser micro-machining was used in this study for the generation of surface texture patterns on the titanium specimens. The contact angle of the untextured surface was 28°, but the wettability of the textured surface increased with a contact angle of 134° for a square pit and 112° for a triangular pit. Surface roughness of the untextured sample showed Ra = 3.811 μm, but post-laser-texturing, the Ra value increased to 10.66 μm and 9.55 μm for the square pit pattern and triangular pit pattern, respectively. Microbes formed biofilm on the untextured specimen but, the square textured surface showed no apparent biofilm formation, while the biofilm was found in triangular textured surface as seen under the fluorescence and scanning electron microscope. The biofilm biomass was significantly reduced in the square textured surface. This work showed that laser textured surfaces might be potentially used to reduce biofilm development on the surfaces. Unlike most methods used for reducing bacterial adhesion, this kind of physical alteration of the surface topography is non-toxic, and it will help to prolong the life of the components used in the marine environment.

Influence of Thermal Treatment on SCC and HE Susceptibility of Supermartensitic Stainless Steel 16Cr5NiMo.

A 16Cr5NiMo supermartensitic stainless steel was subjected to different tempering treatments and analyzed by means of permeation tests and slow strain rate tests to investigate the effect of different amounts of retained austenite on its hydrogen embrittlement susceptibility. The 16Cr5NiMo steel class is characterized by a very low carbon content. It is the new variant of 13Cr4Ni. These steels are used in many applications, for example, compressors for sour environments, offshore piping, naval propellers, aircraft components and subsea applications. The typical microstructure is a soft-tempered martensite very close to a body-centered cubic, with a retained austenite fraction and limited δ ferrite phase. Supermartensitic stainless steels have high mechanical properties, together with good weldability and corrosion resistance. The amount of retained austenite is useful to increase low temperature toughness and stress corrosion cracking resistance. Experimental techniques allowed us to evaluate diffusion coefficients and the mechanical behaviour of metals in stress corrosion cracking (SCC) conditions.

Assessment of Offshore Piping Composite Repair Technology for Life Extension Program Case in Pertamina Hulu Energy West Madura Offshore

The pipe work repair method such as clamps and pipe connector as the use of metallic repair component have been used for maintenance and repair application in oil and gas industry and cover the most common types of defect to pressurize system like internal and external corrosion and also cover situations where the damage is severe. On the other hand with a process safety precausion and production concern, in oil and gas facility the use of metallic repair is very challenging and most of the time will come as last option scenario. Composite repair which are now increasing in application to pipe repair situations may come as a solution. This paper provides assessment of offshore piping composite repair for life extension program of pressure system in West Madura Offshore. Assessment come to a conclusion that the composite repair at field PHE WMO which operate on envelop of 700 psi and temperature range of 20°C-80°C are still in good condition and retain the integrity of the asset, from where then the repair is considered to extent its lifetime.

Generic Approach for Risk Assessment of Offshore Piping Subjected to Vibration Induced Fatigue

Abstract Vibration induced fatigue (VIF) failure of topside piping is one of the most common causes of the hydrocarbon release on offshore oil and gas platforms operating in the North Sea region. An effective inspection plan for the identification of fatigue critical piping locations has the potential to minimize the hydrocarbon release. One of the primary challenges in preparation of inspection program for offshore piping is to identify the fatigue critical piping locations. At present, the three-staged risk assessment process (RAP) given in the Energy Institute (EI) guidelines is used by inspection engineers to determine the likelihood of failure (LoF) of process piping due to VIF. Since the RAP is afflicted by certain drawbacks, this paper presents an alternative risk assessment approach (RAA) to RAP for identification and prioritization of fatigue critical piping locations. The proposed RAA consists of two stages. The first stage involves a qualitative risk assessment using fuzzy-analytical hierarchy process (FAHP) methodology to identify fatigue critical systems (and the most dominant excitation mechanism) and is briefly discussed in the paper. The fatigue critical system identified during stage 1 of RAA undergoes further assessment in the second stage of the RAA. This stage employs a fuzzy-logic method to determine the LoF of the mainline piping. The outcome of the proposed RAA is the categorization of mainline piping, into high, medium, or low risk grouping. The mainline piping in the high-risk category is thereby prioritized for inspection. An illustrative case study demonstrating the usability of the proposed RAA is presented.

Comparison of Various Surrogate Models to Predict Stress Intensity Factor of a Crack Propagating in Offshore Piping

This paper examines the applicability of the different surrogate-models (SMs) to predict the stress intensity factor (SIF) of a crack propagating in topside piping, as an inexpensive alternative to the finite element methods (FEM). Six different SMs, namely, multilinear regression (MLR), polynomial regression (PR) of order two, three, and four (with interaction), Gaussian process regression (GPR), neural networks (NN), relevance vector regression (RVR), and support vector regression (SVR) have been tested. Seventy data points (consisting of load (L), crack depth (a), half crack length (c) and SIF values obtained by FEM) are used to train the aforementioned SMs, while 30 data points are used for testing. In order to compare the accuracy of the SMs, four metrics, namely, root-mean-square error (RMSE), average absolute error (AAE), maximum absolute error (MAE), and coefficient of determination (R2) are used. A case study illustrating the comparison of the prediction capability of various SMs is presented. python and matlab are used to train and test the SMs. Although PR emerged as the best fit, GPR was selected as the best SM for SIF determination due to its capability of calculating the uncertainty related to the prediction values. The aforementioned uncertainty representation is quite valuable, as it is used to adaptively train the GPR model (GPRM), which further improves its prediction accuracy and makes it an accurate, faster, and alternative method to FEM for predicting SIF.

Minimizing hydrocarbon release from offshore piping by performing probabilistic fatigue life assessment

Abstract Topside piping is the major source of hydrocarbon release (HCR) on offshore oil and gas (OOG) platforms in the North Sea region. Since 21% of piping failures are caused by vibration induced fatigue (VIF), an accurate remnant fatigue life (RFL) assessment has the potential to minimize the chances of HCR from an operating piping system. BS-7910 gives two possible approaches for performing a RFL assessment: the S–N curve approach and the fracture mechanics (FM) approach. Since there are large number of uncertainties (such as uncertainty due to the crack growth model, future loading, material and geometric properties, etc.) involved in the RFL calculation process, therefore it is vital to consider the aforementioned sources of uncertainty in order to arrive at an accurate RFL estimate. Nevertheless, BS-7910 provides limited guidance on how to handle uncertainty in RFL assessment. The most common way of dealing with the aforementioned uncertainty is to evaluate RFL probabilistically. This manuscript thus explains the procedure of the probabilistic RFL assessment of offshore topside piping, with an emphasis on uncertainty quantification, propagation and management. Uncertainty quantification handles the identification and characterization of the different sources of uncertainty that may influence the future behavior of the piping component and, in turn, the RFL estimate. Thereafter, uncertainty propagation employs the formerly quantified uncertainties and utilizes the aforementioned information to estimate the RFL. Finally, uncertainty management deals with performing sensitivity analysis to find the individual contributors to uncertainty in the estimated RFL. A numerical case study illustrating the deterministic and probabilistic RFL assessment of topside piping is presented. Afterwards, probabilistically predicted RFL is used to demonstrate the calculation of an inspection interval. Finally, the implications of probabilistically estimated RFL on HCR from process piping is discussed.

Analysis of the Suppression Device as Vortex Induced Vibration (VIV) Reducer on Free Span using Finite Element Method

Subsea pipeline is a transportation infrastructure of oil and gas as an alternative for ship tanker. The uneven topography surface of the sea floor resulting the pipe undergoes free span. The free span is a condition endured by the pipe where the pipe position has distance or gap with the seabed supported by two pivot. The free span is at risk of experiencing a vibration caused by the presence of dynamic load that is current and the wave. The vibration that occurs is the impact of the presence of the phenomenon of Vortex Induced Vibration (VIV). The Phenomenon Of VIV occur on a cylindrical component caused by ocean currents, causing the occurrence of vibration by the movement of fluid on the pipe so that it raises the vortex at the rear of the direction of oncoming flow. One way to dampen or reduce the impact of VIV is by adding suppresion device. VIV suppression device is a tool that is installed on the pipeline on offshore piping installationcthat serves to dampen or reduce the impact of VIV. One of the simulations used to know the characteristics of a fluid is to use (CFD) Computational Fluid Dynamic. With the addition of suppression device can add the rest of the operating time on a free span of affected VIV, on the condition of free span critical exposed VIV (Vortex Induced Vibration value) has a life time on plain pipe 44.21 years, on pipe with 53.09 years and Fairing on the pipe with the Helical strike 52.95 year.

IMU for Vessel and Offshore Piping Survey

“The Inertial Measurement Unit (IMU) is an electronic unit which records angular velocity and linear acceleration data which is fed into a central processing unit for data interpreting and logging. The unit constitutes of two independent sensors. The first sensor is the 3-axis gyroscope and second sensor is the 3-axis accelerometer. The IMU should also have a data interpreter that can draw the track it went through. This should enable the engineers to calculate the co-ordinates, based on longitude and latitude measures. To improve the effectiveness of the device, the device could possibly be designed to transfer the data wirelessly using Bluetooth technology to the nearby data logging machine, which can simultaneously calculate the algorithms to figure the correct of the vessel piping system.

Biaxial Failure Envelope and Creep Testing of Fibre Reinforced Plastic Pipes in High Temperature Aqueous Environments

Results are presented for a series of tests on filament wound glass fibre reinforced pipes which have been subject to prolonged exposure to high temperature water. Two materials systems in common use in offshore piping applications are tested: continuous fibre e-glass in a phenolic and an epoxy resin matrix, respectively. This is the first work on this type on water saturated GRP at very high temperatures up to 160 C. The results of water absorption tests on the two material systems at 95 C are presented. It is shown that saturated conditions can be achieved within seven days at this temperature. Creep modulus test results for the two material systems as a function of temperature up to 160 C are presented. The reduction in TG for the epoxy material in the saturated state is quantified and it is shown that the phenolic material is largely unaffected by water absorption. The results of biaxial tensile loading tests for the two material systems are presented in the form of failure envelopes at temperatures from 20to 160 C. The considerable weakening of the epoxy system, particularly under the matrix dominated loading conditions, is quantified and it is shown that the failure envelope for the phenolic system is largely unaffected by temperature. Finally, a comparison is made between the two materials as a function of loading condition and temperature as a design guide.

Large-scale rotating bending fatigue tests for offshore pipe connections

A testing apparatus featuring rotating bending fatigue techniques was designed and constructed to investigate the fatigue behavior of full-sized threaded connections used to couple offshore piping and structures. Rotating bending tests were performed where flexural loads are applied to the pipe with a hydraulic loading system while simultaneously rotating the pipe by belt drive attached to an electric motor. While rotating bending fatigue testing is not a new concept, the relatively large scale of the tests presented special problems that make the apparatus distinctive. This rotating bending apparatus allows more rapid testing than conventional closed-loop systems. Additionally, conventional closed-loop axial fatigue tests would have required a testing frame with fatigue load capacity exceeding 4455 kN (1,000,000 lbs). Several specially manufactured devices are featured that require large service loads combined with exacting machine tolerances. Currently, a fatigue frequency of 2.0 Hz has been achieved with an equivalent deformation range of 25.4 mm (1.0 in.). Faster speeds are believed possible.

Marine and offshore pumping and piping systems

Marine and offshore pumping and piping systems

Transient Analysis of Offshore Loading Systems

Transient fluid flow caused by power failure to pumps or by accidental flow stoppage in offshore piping systems may be significant. This paper discusses analysis procedures with particular emphasis on an efficient and convenient means of handling the transient behavior of the turbopump. The interaction of the turbomachine with the piping and other appurtenances in the system is also discussed.