In recent years, ship hulls have become larger. And the welding has become more important technology in ship building. In other word, welding has become more important technology in shipbuilding. In Japanese shipbuilding, multiple electrode butt welding has been performed with large current and high speed to increase construction efficiency. However, the multiple electrode welding method may cause a hot cracking. X-ray or ultra sonic wave inspection and repair welding are necessary due to the generation of hot cracking. These will increase the production cost. Therefore, it is important to prevent hot cracking. It is known that hot cracking is generated by both metallurgical and mechanical factors. The authors propose a new evaluation method of hot cracking based on the modeling of both mechanical and metallurgical behaviors. In the developed method, from the metallurgical point of view, solidification growth direction is determined from the temperature gradient obtained by the heat conduction analysis to predict the position of hot cracking. Moreover, from the mechanical point of view, the possibility of the generation of hot cracking is assessed using plastic strain increment in Brittleness Temperature Range (BTR). In order to show the validity of the developed method, the developed method is applied to the analysis of hot cracking on automatic tandem butt welding through the comparison with experimental results. As a result, it is demonstrated that the hot cracking can be evaluated by using the developed method.

Nowadays welding is the most common way to connect metal parts and structures. One of the challenges connected to welding it that heat output from the welding alters the microstructure of the metal creating the heat affected zone (HAZ) near the weld. In steel welds HAZ is often harder and more brittle than the base material due to formation of martensite. This might cause hydrogen induced cracking and speed up the fatigue of the weld. To mitigate the martensite formation in the HAZ different heat treatments, like preheat, interpass and PWHT are often applied. However, for 4130 steel, preheat and interpass temperatures are not expected to restrict martensite formation due to materials slow transformation rate. Preheat and interpass temperatures are still important for hydrogen diffusion and reduction of tension in the weld. This paper investigates the effect of different heat treatments on the microstructure of AISI 4130 steel used in sour service pipes. The welding and sample preparation were performed in accordance with ISO 15156 and ASME B31.3 standards. Two sample sets were produced: one with and one without preheating. The hardness tests of weld profiles were performed in accordance with ISO 15156-2 international standard. Comparison of hardness profiles indicated that preheat had virtually no effect on hardness of the steel in HAZ, although it affected hardness of fusion zone. Preheated samples were further heat treated in a furnace simulating PWHT effect. Three different PWHT condition were tested. The hardness profiles indicated that PWHT led to noticeable changes in steel microstructure. In order to understand those microstructure changes, the heat treatment of the steel during production process was reviewed and microscopic investigations of the weld profiles were performed.

ASTM A131 Steel, grade EH36 is a high strength steel used extensively as structural parts in shipbuilding, Oil and Gas applications. In this work, additive manufacturing of a support node connecting the main platform and columns for semi-submersible offshore vessel was performed using Laser Aided Additive Manufacturing (LAAM) process to evaluate both technical feasibility and economic viability. Both coupon and component levels LAAM process study was carried out. Properties of printed EH36 steel are significantly determined by the printing process parameters. EH36 deposited with optimized LAAM process has shown better mechanical properties than conventional rolled EH36 material. A deposition strategy was developed to distribute the accumulated residual stress, to minimize substrate distortion and stress-induced cracking in the print part. A hybrid approach combining both substrate and AM, with a 60% print to hot-rolled substrate plate weight fraction was proposed to enable printability and to enhance efficiency. Near-net-shape node was printed without cracking/delamination using optimized printing strategy. Total printing weight is 70kg and total time spent is 90 hours. It was concluded that LAAM technology is feasible for fabrication of large load bearing structural steel sections.

Three dimensional (3D) FE models have been developed for simulation of the incremental forming processes employed in UOE linepipe manufacturing at Tata Steel Hartlepool 42” Pipe Mill, namely edge crimping (C-press) and pipe expansion (expander). Transitional zone behaviour resulted from both forming operations as previously identified in practice has been revealed, for the first time, by the 3D FE simulations and preliminarily analysed. It was demonstrated that the transitional zone features observed in both edge crimping and pipe expansion were initiated in the plate/pipe feed-in side/area of the dies, and then formed within the working length/face of the forming dies. Detailed examination and analysis of the FE results, in terms of plastic strain and residual stress patterns as well as contact pressure distributions, have shown that the initiation of the transitional zone features was due to the redundant plastic deformation caused by (cantilever) bending in the material feed-in area of the dies mainly along the longitudinal direction. It is therefore believed that minimisation/elimination of such redundant plastic bending effect in the longitudinal direction would lead to minimisation/elimination of the unfavourable deformation features in the so-called transitional zones, which could be achieved through improved die designs and possibly forming process parameter settings.

The API 20S Standard is designed to play a crucial role in leveraging Additive Manufacturing (AM) to foster innovation in the oil and gas industry. The paper, in association with the standard, will facilitate the understanding of how AM will enable equipment design improvements, faster prototyping, and better inventory management. By way of discussing the progress, challenges, and lessons learned from the standardization process, the paper aims to encourage a safer, broader, and faster adoption of AM technologies in the mainstream oil and gas applications. The paper will summarize the streamlining process, feedback from the API 20S task group, and current status of the standardization efforts. Additionally, upcoming challenges and the potential for the oil and gas industry industries to contribute to the standard will be summarized. The paper will also showcase a novel tiered approach (Additive Manufacturing Specification Levels) to allow the users of the document to match different levels of criticality.

As offshore pipeline projects have expanded to deeper water regions with depths of more than 2 000 m, higher resistance against collapse by external pressure is now required in linepipe. Collapse resistance is mainly controlled by the pipe geometry and compressive yield strength. In UOE pipe, the compressive yield strength along the circumferential direction changes dramatically due to tensile pre-strain that occurs in pipe forming processes such as the expansion process. In order to improve the compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. As the mechanism of this effect, it is understood that internal stress is generated by the accumulation of dislocations, and this reduces reverse flow stress. Compressive yield strength is also changed by the thermal cycle associated with application of fusion-bond epoxy in pipe anti-corrosion coating by induction heating. In the typical thermal heat cycle of this coating process, the maximum heating temperature is from 200 °C to 250 °C. In this case, compressive yield strength increases as an effect of the thermal cycle, resulting in increased collapse resistance. Thus, for deep water application of UEO linepipe, it is important to clarify the conflicting effects of the Bauschinger effect and the thermal heat cycle on compressive yield strength. During installation of deep water pipelines by a method such as J-lay, curvature is imposed on the pipe axis, but the circumferential bending that leads to ovalization is determined by the interaction of the curvature of bending deformation. This bending deformation decreases collapse resistance. The interaction of external pressure and bending is also important when evaluating collapse. Against this background, this study discusses the collapse criteria for coated linepipe and their bending interaction against collapse based on a full-scale collapse test under external pressure with and without bending loading. The effect of the thermal heat cycle on linepipe collapse criteria is also discussed based on the results of tensile pre-strain tests with simulation of the thermal cycle and a collapse calculation by FEA.

Nowadays, sustainable development is becoming a worldwide growing concern for the shipping industry. The overall aim of this paper is to develop a holistic method to enhance sustainable design at the design stage of Offshore Supply Vessels. The process and practice of deciding on the alternative hull & structure materials are presented in the case study to verify and validate the method. The technique includes four main parts. Firstly, Life Cycle Sustainability Assessment, which was developed from Life Cycle Assessment, and which has been carried out to analyze the environmental, economic, and social impacts. Secondly, Monetary Valuation is used to convert the results of the Life Cycle Sustainability Assessment. Moreover, Life Cycle Sustainability Costing is used as an accounting tool to aggregate the results from the Monetary Valuation, including environmental cost, economic cost, and social cost. Finally, the results of Life Cycle Sustainability Costing have been analyzed through Sensitivity Analysis to interpret and make sound recommendations. The novelty of this research is the combination of the different methods, as well as its application to Offshore Supply Vessels.

As a rapidly developing technology, the expanded capability of Additive Manufacturing (AM) allows implementation into the marine and offshore industries. Qualification of metal AM part may need detailed test plans and test results in order to meet the design requirements with a certain level of reliability. Approval may also be needed in accordance with regulation codes and class rules. However, challenges and gaps remain between the current metal AM technology level and marine and offshore applications. In this paper, two major categories of metal AM processes are discussed: powder bed fusion (PBF) and directed energy deposition (DED) with powder or wire as raw materials and laser, electronic beam (E-beam) or arc as heat source. The main challenges are also investigated in this study as follows: 1) Optimization of build cost and part quality by selection of appropriate process; 2) Performance of the part under static and cyclic loading; 3) Evaluation of the effects of corrosive environments (seawater); 4) Lack of standardization of the AM process for quality control. This paper addresses possible solutions for these challenges and provides qualification framework for metal AM parts to be implemented into marine and offshore applications.

In the construction of ships and ocean structures, thin steel plates are welded in order to join parts. Due to the welding, deformations and residual stresses may occur. These deformations and residual stresses can cause problems in the assembly process. Therefore, the prediction of welding deformations and residual stresses is necessary in advance of production. Welding deformations and residual stresses can be predicted using thermal elastic plastic (TEP) finite element analysis (FEA). However, solid elements are used in the conventional analysis method of TEP-FEA. The modeling of the thin-plate structures using solid elements is very complicated and difficult. In addition, the number of elements increases when using solid elements compared to shell elements. This leads to an increase in the required computing resources. Therefore, an efficient modeling method is necessary for thin-plate structures. In the present research, in order to realize an efficient welding mechanics analysis method for thin-plate structures, the authors proposed an efficient FEA method for the welding mechanics problem for thin-plate complex structures using the proposed shell-solid mixed analysis method. For the shell-solid mixed analysis method, the multipoint constraint (MPC) technique was used in the finite element analysis to connect shell elements and solid elements. In order to compare the analysis accuracy with the conventional analysis, which uses solid elements, the proposed shell-solid mixed analysis method was applied to the fundamental welding mechanics problem of thin-plate structures. The results revealed that the proposed method has approximately the same analysis accuracy as the conventional method. These results indicated that the proposed method can effectively analyze the welding deformations and residual stresses in thin-plate complex structures.

A PVDF grade typically used in off-shore applications was annealed at 70, 90 and 120°C. The samples were characterized and it was observed a small change in the crystallinity, but, on the other hand, the Elastic modulus of the sample annealed at 120°C increased from 1.52 to 1.85 GPa. The relaxations observed by Dynamic Mechanical Analysis (DMA) indicate that a morphological change took place at annealing process, which led to a stiffness rises of amorphous phase.

Design of Steel Catenary Risers (SCRs) requires the use of specialized connection hardware to mitigate the high dynamic bending moments at the hang-off location induced by host floater motion. Reliability of this connection hardware is imperative, especially in those applications involving high tension loads, high pressure and elevated fluid temperature. One option for connection hardware is a monolithic, metallic tapered stress joint. Because of its inherent density, strength, and stiffness properties, steel is not well suited for these applications due to excessive stress joint length and weight requirements. Titanium Grade 29 has been identified as an attractive material candidate for demanding service applications due to its unique mechanical properties including increased flexibility, excellent fatigue performance and corrosion resistance to sour fluids. This technology is well established in the offshore industry and utilized in over 60 SCR installations with operating lives exceeding 20 years of continuous subsea operation. Large titanium stress joints (TSJs) for deep-water applications are typically not fabricated as a single piece due to titanium ingot volume limitations thus making one or more intermediate girth weld(s) necessary to satisfy the overall length requirements. Fatigue testing of 38 mm (1.5-in) wall thickness girth welds, utilizing an optimized GTAW welding procedure to limit defect sizes to sub-millimeter, has previously been performed in seawater (OD exposure) under cathodic protection potentials and sour service (ID exposure) under galvanic potentials. Fatigue testing results fully verified the vendor S-N fatigue design curve, in addition, no appreciable differences in fatigue performance in environments were observed allowing project-specific testing to be limited to in-air testing. This paper presents in-air fatigue testing results of 51 mm (2.0-in) wall thickness Grade 29 girth welds, using the same optimized welding procedure, to assess thickness size effect on the vendor S-N fatigue design curve. Verification of the vendor fatigue design curve was demonstrated by testing curved dog-bone specimens, extracted longitudinally across the girth weld, with production level surface finishes on inner and outer surfaces in-air up to a predefined S-N fatigue target curve with 95% confidence level.

Ships and offshore structures operating in Artic regions face specific challenges such as ice loads and seasonal low temperatures. In order to meet these extreme environmental requirements, the effect of temperature on material behaviour needs to be considered. It is well known that static material properties (yield strength, fracture toughness etc.) undergo significant changes with temperature. In recent studies, significantly higher fatigue strength was observed in welded joints in comparison to estimates based on international standards. Fatigue strength increased even for temperatures far below the allowed service temperature based on fracture toughness results; however, studies on fatigue strength of structural steel at sub-zero temperatures are scarce. Moreover, material selection for ships and offshore structures is usually based on empirical Charpy and fracture toughness relations at the design temperature, minus a safety margin. This study aims at introducing an S-N curve database for welded joints that can be used to verify the fatigue design approaches for ships and offshore structures subject to sub-zero temperatures. Therefore, the effect of temperature on the fatigue strength of butt-welded normal and high strength steel structures is analysed experimentally for sub-zero temperatures. For this purpose, fatigue test results of SAW and MAG welded joints for temperatures down to −50 °C are analysed and the potential for changes regarding material selection for ships and offshore structures are discussed.

Pipelines are commonly joined by girth welds. A centreline offset at a girth weld would inevitably be introduced due to either a difference in wall thickness of the pipes at each side of the weld or due to misalignment. An additional bending stress can result when the pipeline containing the girth weld is subjected to axial loading. This partly contributes to fatigue crack initiation from the weld toe. Therefore, the misalignment-induced stress concentration factor, K m , must be considered in fatigue design of girth welded pipelines. There are several solutions available to calculate K m including BS 7910, DNVGL-RP-C203 and Connelly and Zettlemoyer. In some cases, the difference in the stress concentration factors calculated using these solutions is significant. This paper reviews these and other solutions and verifies them by finite element results and experimental data obtained through strain gauge measurements. Based on the study, the most appropriate K m solution is recommended.

A high-performance polyamide grade of easy processability which presents excellent thermal and mechanical properties such as resistance to fatigue and creep is studied in this work. An accelerated aging of Polyamide 12 samples was performed in stainless steel autoclaves at 120°C in deoxygenated water at pH 8.7 in order to shorten the aging time and avoid oxidation. The samples were retrieved at distinct aging times which were enough to reach the asymptotic portion of the curve of corrected inherent viscosity (CIV) versus aging time. CIV measurements track modifications of the molecular weight due to hydrolysis. Afterwards, the samples were analyzed through their cross section in the core and edge layer in order to investigate changes due to diffusion effects. Differential scanning calorimetry (DSC) analysis assesses the degree of crystallinity and melting temperature. Thermogravimetric analysis (TGA) was employed in order to investigate changes in the thermal stability and the stage of degradation of the samples. Unlike conventional volumetric analysis techniques, the instrumented indentation tests (IIT) in micro-scale were performed to measure the mechanical properties such as elastic modulus (E IT ) and hardness (H IT ) along the thickness aiming to detect properties gradient between surface and core. The CIV measurements showed a decrease of 46.3% in the aged sample during the maximum aging time compared to the reference material.

Monitoring of fatigue crack propagation is very important in industrial fields. Stress-induced magnetic measurement is a newly developed non-destructive testing technique which can detect early failure of ferromagnetic materials in service. A lot of experiments demonstrate that magnetic measurement is more sensitive compared with other non-destructive testing technologies. In order to explore the correlation between crack propagation and magnetic hysteresis under cyclic stress in X70 pipeline steel, a series of stress-controlled tests were carried out and the changes in magnetic field around cracks during their propagation process were observed throughout the tension-tension fatigue tests. The variations of magnetic field and stress intensity factor K in the crack propagation stage were studied. The results obtained allowed the division of the magnetic behavior of the investigated steels into three stages corresponding to three distinct crack propagation stages. It was found that the magnetic field varies with crack propagation, and the stress intensity factor K increased with the increase of loading cycles. A strong correlation between the variation of the magnetic field and stress intensity factor was recognized, regardless of the loading conditions, maximum load or stress ratio. The results suggest that non-destructive evaluation of fatigue cracks would be possible using this relationship.

Dynamic crack propagation in pressurized pipelines is usually investigated by means of lab-scale specimens due to its economic feasibility and material saving. More recently, new generation of pipeline steels have incredibly shown a combined fracture toughness and plastic strength capabilities with even more heavier wall thickness, for which current design standards and practice codes underpredict largely the actual material response under different strain rates. The Drop-Weight Tear Test (DWTT) is commonly used to characterize dynamic fracture behavior of pipeline steel and its numerical implementation with appropriate constitutive equations has become essential in the fundamental understanding of the interaction between fracture process and local stress-strain fields. In the present study, a X65 Q&T seamless pipeline steel is fully characterized under different strain rate levels and stress states for dynamic fracture initiation. A rate dependent phenomenological fracture criterion is proposed in the form of Modified Mohr-Coulomb (MMC) fracture model coupling with a multiplicative decomposition of the hardening law to describe strain rate effect on post-necking behavior. The model implementation is then validated through a drop-weight tearing analysis on standard and non-standard specimen configurations including different wall thickness.

A comprehensive experimental program is carried out to determine material parameters for fracture initiation and propagation in X100 pipeline steels. The quadratic Hill’48 yield function along with an isotropic hardening are used to describe plastic flow at large deformation and a phenomenological fracture criterion to predict fracture initiation. Fracture mechanics SENT specimens are used to calibrate post-initiation softening parameters necessary for ductile crack propagation in thick components. Once the material model parameters set is complete a final comparison is conducted with ring expansion test on same material.

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.

Accurate prediction of the fatigue strength of steels is vital, due to the extremely high cost (and time) of fatigue testing and the often fatal consequences of fatigue failures. The work presented in this paper is an extension of the previous paper submitted to OMAE 2019. The main objective of this manuscript is to utilize Artificial Intelligence (AI) to predict fatigue strength, based on composition and process parameters, using the fatigue dataset for carbon and low alloy steel available from the National Institute of Material Science (NIMS) database, MatNavi. A deep learning framework Keras is used to build a Neural Network (NN), which is trained and tested on the data set obtained from MatNavi. The fatigue strength values estimated using NN are compared to the values predicted by the gradient boosting algorithm, which was the most accurate model in the OMAE 2019 paper. The comparison is done using metrics such as root mean square error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R 2 ) and Explained Variance Score (EVS). Thereafter, the trained NN model is used to make predictions of fatigue strength for the simulated data (1 million samples) of input parameters, which is then used to generate conditional probability tables for the Bayesian Network (BN). The main advantage of using BN over previously used machine learning algorithms is that BN can be used to make both forward and backward propagation during the Bayesian inference. A case study illustrating the applicability of the proposed approach is also presented. Furthermore, a dashboard is developed using PowerBI, which can be used by practicing engineers to estimate fatigue strength based on composition and process parameters.

Recently, International Maritime Organization (IMO) reinforced the regulations for nitrogen oxide (NOx) and sulfur oxides (SOx) toward the reduced emission. To avoid serious environmental issues, the need for liquefied natural gas (LNG) fuel tanks arose for new constructed vessels. LNG fuel tanks are typically fabricated with low temperature materials that exhibit excellent fatigue performance at cryogenic temperature. In manufacturing of LNG fuel tanks, high manganese steel is known to be cost effective compared to other low temperature materials such as 9 wt.% nickel alloy steel, SUS304L and INVAR alloy. Therefore, extensive efforts are carried out to investigate the fatigue performance of high manganese steel. However, such investigations are yet limited to the constant amplitude load case only. In order to reflect loading or unloading condition of LNG vessels in terms of fatigue performance, this study investigates the fatigue crack growth characteristics of high manganese steel under overload condition. The main parameters considered are the overload ratio (OLR) and the mean stress. We employ the Wheeler approach for the estimation of fatigue crack growth characteristics. In general, the Wheeler approach consists of crack length, plastic zone size and shaping exponent. Among three parameters in Wheeler approach, we assess the relationship between OLR and shaping exponent and suggest a modified equation for the shaping exponent considering the mean stress effect. In order to predict the effect of overload, the estimated fatigue life based on the Wheeler approach with the modified equation was compared to that with a constant amplitude load.