Pipelay Operations Research Articles

A Tank Experiment of the Autonomous Detection of Seabed-Contacting Segments for Submarine Pipelaying Operations

A Tank Experiment of the Autonomous Detection of Seabed-Contacting Segments for Submarine Pipelaying Operations

Use of response forecasting in decision making for weather sensitive offshore construction work

Response forecasting is an emerging technology for supporting decision-making during offshore construction work. The method aims to improve the reliability and efficiency of weather-sensitive operations. This article identifies the motivations, advantages, and challenges of implementing a response forecasting decision-support service in an offshore organization from the perspective of an installation contractor. In addition, a case study based on a recent pipelay operation exemplifies the method and its impact on decision-making.

THE CLASSIFICATION OF PIPE-LAY VESSELS AND HEAVY-LIFT CRANE VESSELS

Pipe-lay vessels, heavy-lift crane vessels and dual purpose heavy-lift and pipe-lay vessels are distinct in many ways from other types of ships or offshore units. The unique functions that these vessels carry out can impact directly on the overall safety of the vessel, the personnel on-board and the potential to pollute the environment. This paper outlines some of the hull and machinery safety assurance considerations for classification and design pertinent to pipe-lay and heavy-lift operations. The considerations that are discussed in this paper include the implications of classing the vessel as a ship or an offshore unit; the interaction between classification and marine warranty; general arrangement; station-keeping; structural assessment and the interaction between safety critical systems. Specific hazards for pipe-lay vessels and their use of chemicals on-board are also discussed.

Numerical Investigation of Deepwater S-Lay Pipeline Under Freak Waves

Abstract Freak wave is an extreme sea state with unexpected and huge wave height, which becomes a potential risk for lay barge and offshore pipeline during deepwater installation. In order to investigate the dynamic responses of deepwater S-lay pipeline induced by freak waves, this study developed a comprehensive numerical model with the particular consideration of the freak wave effect. An enhanced superposition method of combined transient wave trains and random wave trains was presented, and a series of freak wave trains were generated. The induced pipelay vessel motions were simulated by the use of displacement response amplitude operators (RAOs). The pipe–stinger roller interactions in the overbend and the cyclic contacts between the pipeline and seabed soil in the touchdown zone (TDZ) were fully taken into consideration. The developed S-lay model was subsequently utilized to calculate the dynamic responses of the pipelay vessel and offshore pipeline under random waves and freak waves for a comparison. The results illustrated the remarkable influence of freak waves on the systematic behaviors of deepwater S-laying pipeline, which offer a significant theoretical basis for the pipe structure design and pipelay operation safety.

Monitoring and Analysis of Wave Characteristics during Pipeline End Termination Installation

Pipeline end termination (PLET) installation is an essential part of offshore pipe-laying operation. Pipe-laying operations are sensitive to pipe-laying barge motion and marine environmental conditions. Monitoring the field environment can provide a reasonable basis for planning pipe-laying. Therefore, the measurement and analysis of sea wave motion is helpful for the control and operational safety of the pipeline and vessels. In this study, an environmental monitoring system was established to measure wave motion during PLET operation. Fourier transforms were used to process images that were acquired by ultra-high-frequency X-band marine radar to extract wave parameters. The resulting wave spectra, as measured each minute, were used to simulate real-time wave data and calculate wave characteristics and regressed wave frequency and direction spectrum throughout the PLET operation. The regressed frequency, spectral density, and direction spectra were compared with the theoretical spectra to evaluate their similarity and find the most similar spreading function in the operational area (the South China Sea). Gaussian fitting of real-time wave data was tested while using a classical method. The marginal distribution and joint density of the wave characteristics were estimated and then compared with theoretical distributions to find the most suitable model for improving marine environmental forecasting.

The Classification of Pipe-Lay Vessels and Heavy-Lift Crane Vessels

Pipe-lay vessels, heavy-lift crane vessels and dual purpose heavy-lift and pipe-lay vessels are distinct in many ways from other types of ships or offshore units. The unique functions that these vessels carry out can impact directly on the overall safety of the vessel, the personnel on-board and the potential to pollute the environment. This paper outlines some of the hull and machinery safety assurance considerations for classification and design pertinent to pipe-lay and heavy-lift operations. The considerations that are discussed in this paper include the implications of classing the vessel as a ship or an offshore unit; the interaction between classification and marine warranty; general arrangement; station-keeping; structural assessment and the interaction between safety critical systems. Specific hazards for pipe-lay vessels and their use of chemicals on-board are also discussed.

Passivity-preserving splitting methods for rigid body systems

A rigid body model for the dynamics of a marine vessel, used in simulations of offshore pipe-lay operations, gives rise to a set of ordinary differential equations with controls. The system is input-output passive. We propose passivity-preserving splitting methods for the numerical solution of a class of problems which includes this system as a special case. We prove the passivity-preservation property for the splitting methods, and we investigate stability and energy behaviour in numerical experiments. Implementation is discussed in detail for a special case where the splitting gives rise to the subsequent integration of two completely integrable flows. The equations for the attitude are reformulated on $SO(3)$ using rotation matrices rather than local parametrizations with Euler angles.

The Static Frictional Behaviors of Rubber for Pipe-Laying Operation

Experimental research is carried out to reveal the static frictional behaviors of rubber pipe contact systems. This research is motivated by deep water pipe-laying operations where rubber blocks are used to clamp the pipe to supply sufficient static friction. Within this context, a friction testing instrument has been designed to mimic a situation of the beginning of the pipe-laying installation. Using this instrument, the maximum static friction forces (F) of a rubber pipe contact system are tested. The results show that the ultimate values of the static frictions fluctuate due to the increasing rate of the tangential load (FT). The evolution of contact between rubber and polymethyl methacrylate (PMMA) pipe is observed to identify the formation and propagation of the folds within the apparent contact area. In addition, it is confirmed that the evolution of contact is influenced by the folds and creep of the rubber surface. The creep deformation takes primary effect in accelerating the separation of the interfaces of contact during relative high normal loads (20, 30, 40 N) and low increasing rate of FT; whereas for all of the testing normal loads (10–40 N), the propagation of the folds release the energy which is stored in the interface of rubber when the increasing rate of FT is high. Therefore, the fluctuation of the maximum static friction of the contact system can be regarded as a consequence of interaction of the creep and folds. Furthermore, the instability of the coefficient of static friction in this test has been examined, and it indicated that the creep and folds could affect the static friction distinctly within a certain range of a normal load. This research is beneficial for arranging appropriate normal loads and laying speeds to avoid pipes slipping during a pipe-laying operation.

The Reduction of Static Friction of Rubber Contact under Sea Water Droplet Lubrication

In this work, a series of experimental tests is carried out in laboratory conditions which set the rubber compound (soft and stiff), the normal load, and the direction of propagation of sea water droplets into the interface of rubber–steel pipe contact as variables. The results show that the maximum static frictions (F) of rubber–pipe contacts increase as the normal load increases in both dry and lubricating conditions, and the values of F for the softer rubber are higher than that for the stiffer rubber. However, significant reduction in static friction is found due to the lubrication of sea water droplets. The influence of lubrication is stronger when the droplets propagate into the contact interfaces at the tail edge than that at the front edge. Capture sequences of the contact region facilitate the lubrication of seawater droplets by accelerating the progress of separation in the contact interfaces, thus reducing the static friction force. This investigation improves our understanding of the lubrication of sea water droplets during pipe-laying operation, and it will help us to conduct further research on the accuracy and safety of offshore engineering.

A singular perturbation method for parametric investigation on J-lay installation of deepwater pipelines

The maximum bending moment or curvature in the neighborhood of the touch down point (TDP) and the maximum tension at the top are two key parameters to be controlled during deepwater J-lay installation in order to ensure the safety of the pipe-laying operation and the normal operation of the pipelines. In this paper, the non-linear governing differential equation for getting the two parameters during J-lay installation is proposed and solved by use of singular perturbation technique, from which the asymptotic expression of stiffened catenary is obtained and the theoretical expression of its static geometric configuration as well as axial tension and bending moment is derived. Finite element results are applied to verify this method. Parametric investigation is conducted to analyze the influences of the seabed slope, unit weight, flexural stiffness, water depth, and the pipe-laying tower angle on the maximum tension and moment of pipeline by this method, and the results show how to control the installation process by changing individual parameters.

A nonlinear PDE formulation for offshore vessel pipeline installation

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite extension, shearing, twist and bending, to apply for marine applications by adding the effects of restoring forces, hydrodynamic drag and seabed interaction. The model is validated against the natural catenary equation and the FEM code RIFLEX. The model is extended to include the pipelay vessel dynamics by applying a potential theory formulation of a surface vessel, suited for dynamic positioning and low speed maneuvering, as a boundary condition for the PDE. This system is found to be input–output passive and stable. Pipeline installation applications where the presented model is suited are e.g., analysis and simulation of the installation operation, operability analysis, hardware-in-the-loop (HIL) testing for vessel control systems, and automation of the pipelay operation.

A Robotic Approach to Nonlinear Dynamic Modeling of Offshore Pipelaying Operations

In this paper a robotic approach is taken to develop a dynamic nonlinear model of an offshore pipeline installation. A compact dynamic representation of the pipe and its kinematics, for effective implementation in a computer code is developed. The pipe model is used in simulations to compute the dynamic tension from the pipe on the vessel. The pipe tension is commonly computed by quasi-static methods based on the catenary equation, which lack the dynamic behavior and flexural effects of the pipe. The model can also replace computationally slower finite element models in applications with real-time requirements. The model is suitable for many applications, such as real-time decision support, training simulators, motion prediction systems, Hardware-In-the-Loop (HIL) testing, operability analysis, control applications and pre-design of ships.

Modelling and Control of Offshore Marine Pipeline during Pipelay

A model suited for control tasks is developed for a submerged offshore pipe during the pipelay operation. The pipe is fixed in the touchdown point at the seabed in one end and attached to a pipelay vessel in the other end. The developed model is discrete and is on the form of the robot equation with minimal coordinates. Thus the methods of controller synthesis and stability analysis can be applied directly. The model constitutes a hyper redundant system and it is shown that this system is passive. A PID-controller has been suggested. The simulation results are in agreement with the theoretical results.

Measuring Construction Stresses In Offshore Pipeline

During construction, a unique self-contained subsea package attached to an instrumented section of pipe recorded the pipe profile and bending stresses as the pipe traveled from the laybarge to the ocean floor. Barge motions, pipe tension, and pipe travel relative to the laybarge were recorded pipe tension, and pipe travel relative to the laybarge were recorded simultaneously on the barge. Introduction Offshore pipelines are usually installed using the laybarge-stinger (or "stove pipe") method. Stresses induced in the pipeline as it is lowered to the ocean floor during construction control the selection of the pipe wall thickness, the stinger design, the tensioner, pipe wall thickness, the stinger design, the tensioner, and, indirectly, the mooring system required for the particular pipeline installation. An analytical particular pipeline installation. An analytical procedure was developed' by Esso Production Research procedure was developed' by Esso Production Research Co. to predict static construction stresses during pipe-laying operations for given water depth, pipeline pipe-laying operations for given water depth, pipeline design, and laybarge equipment parameters. This procedure has been used as an aid in specifying pipe procedure has been used as an aid in specifying pipe wall thickness, coating weight, tension to be applied, and stinger length and deployment.Recognizing the need for accurate specification of pipeline design and pipelaying equipment parameters, pipeline design and pipelaying equipment parameters, Esso Production Research Co. and Esso Australia Ltd. considered it important to measure pipeline construction stresses during pipelaying operations in Bass Strait off Australia. The field measurement program consisted of two separate series of tests. The program consisted of two separate series of tests. The first was conducted in Nov.-Dec. 1969 from the Ingram DB-5 during construction, in about 200 ft of water, of a 24-in.-diameter crude-oil pipeline from the Halibut field to shore; the second was conducted in Jan.-Feb. 1971 during construction of a 20-in. diameter crude-oil pipeline from Halibut to Kingfish in 248 ft of water, using the Santa Fe Choctaw. The objectives of the DB-5 tests were to verify the static stress calculation procedure and to determine the significance of dynamic stresses in pipelaying operations. Since the DB-5 is a conventional, flat-bottomed barge (100 ft wide, 400 ft long, and 28.5 ft deep), it was expected that barge motion in operational seas in the Bass Strait would introduce observable dynamic stresses. In the DB-5 program, eight test runs were made using instrumented segments of pipe. In each test run, pipe strains, pipeline geometry, pipe. In each test run, pipe strains, pipeline geometry, barge motions, and other critical variables were measured as the instrumented pipe section moved from the laybarge to the ocean floor during normal pipeline construction. Analysis of the test results pipeline construction. Analysis of the test results indicated that measured static stresses agree closely with calculated values and that the motion-induced dynamic stresses were substantial (20 to 25 percent of yield stress).As a result of the DB-5 test, work was begun on analytical procedure to predict dynamic stresses during pipeline construction. In addition, it was decided that the Choctaw field measurement program should be conducted. The Choctaw, which is a semisubmersible barge 106 ft wide, 400 ft long, and 54 ft deep, was equipped with a unique, column-stabilized stinger 147 ft long, with columns as large as 48 in. in diameter rather than the more conventional buoyant stinger employed by the DB-5. JPT P. 261