17 August, 2016

Pipeline Design

TPP Technologies Ocean Engineering provides complete design services for marine pipeline projects. These services are normally provided in the following manner:

  • Pipeline planning, sizing and performance criteria.
  • Pipeline design and analysis tools.
  • Initial Site Survey
  • Preliminary design and opinion of probable cost.
  • Final design, specifications & cost estimate.

 

Pipeline Planning, Sizing and Performance Criteria

 

Pipeline performance requirements and design criteria are defined in terms of the client’s water needs. These criteria will include water temperature, water purity, flow, reliability, lifetime, location and budget restrictions. In most cases, all of these parameters are not fully defined at the start of the design process; pipeline flow, operating budgets, and even location are commonly dependent upon onshore facilities that are still in the planning, design and permitting phase.

A study is performed to quantify the choice of best pipeline length, diameter, wall thickness and operational lifetime for a given project’s flow rate, capital budget and operating budget. The results of the study often present the client with tradeoff decisions such as saving money on capital versus lowering operating costs. TPP Technologies assists the owner in finding the pipe dimensions that best meet his objectives. Other tradeoff studies are performed as necessary for each individual project to best economically and technically fit the pipeline into the client’s overall operation.

Even the location may be uncertain during the planning phase; since the pipeline costs are significantly affected by the location, TPP Technologies identifies and provides critical information relative to pipe site selection. Based on previous pipeline costs, TPP Technologies can price various pipeline and pumping options such that the client can be well-informed for these critical decisions.

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Pipeline Design and Analysis Tools

TPP Technologies uses a wide variety of analytical tools in the course of our ocean engineering design projects. TPP Technologies engineers understand the engineering and physical principles involved in designing lasting structures in the ocean, and are proficient users of several commercial and proprietary design, analysis, and data collection software. Below is a partial list of the software used at TPP Technologies on a regular basis:

 

  • 3D Design software:Solidworks, AutoCad.
  • Finite Element Analysis (FEA) software:Orcaflex, ANSYS, ABAQUS, OFFPIPE
  • Computational Fluid Dynamics (CFD) and related software:Fluent, Cosmos.

 

Initial Site Survey

 

Important site characteristics include bathymetry, bottom roughness, soil conditions, slope, current profiles, obstacle location, wave conditions, environmental restrictions and shoreline geometry; these and other site conditions greatly influence the pipeline design and cost. A review of all existing offshore data (including data from adjacent or related areas) plus a site visit and dive in the shallow water will frequently suffice for an initial survey.

If bathymetry and bottom data are not available, it may be necessary to conduct a survey for this information. In addition, depending upon how much is known of the oceanographic characteristics in the area, it may be necessary to commence current measurements at a few key locations.

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Preliminary Design

 

A preliminary design is performed that concentrates on the critical aspects of the project that most directly affect the pipeline’s performance and costs. The final output of the design includes preliminary drawings, pipeline routing, an initial opinion of probable construction cost and a conceptual method for the deployment. A quickly and easily deployed pipe is the key to an economically viable pipeline.

The importance of the deployment on the offshore pipeline cost and design cannot be overemphasized. The major pipeline costs occur during deployment, and there is an accompanying high concentration of activity and risk. This concentration of cost, structural loading of the pipeline and risk all occur in a relatively few days at sea. As a result, the deployment of the pipeline is often the major cost and design factor. Weights, loads, buoyancies and material strains are carefully balanced during the deployment such that the pipeline can both survive the deployment and serve properly once in place. Pipe joints are placed at critical points that ease pipeline handling and are avoided at points exposed to high loading.

An important aspect of the preliminary design is to evaluate whether the pipeline is feasible and whether it will meet the requirements of the client by delivering water within his performance and budget restrictions. In order to complete this determination, a variety of pipeline configurations may be studied. TPP Technologies often provides innovative but practical solutions to difficult technical and budgetary problems. The preliminary design gives the client a first cut at the overall performance and costs such that this information can be integrated with his overall project.

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Final Design

 

In the final design phase the design plans (drawings), specifications, and an opinion of probable construction cost are prepared. Careful attention is paid to every detail such that the hardware designed can be successfully deployed and operated over the desired lifetime. Details include wave loading, corrosion, pipeline fatigue, water flow dynamics on pump start-up and shutdown, maintenance, electrical routing, and deployment loads.

If the client wishes a formal contractor bidding process, the design plans, specifications, and deployment guidelines are suitable. TPP Technologies has also worked for clients who have selected the contractor prior to or during the design process. Either process has its advantages and disadvantages depending upon the size of the overall project, the client’s relationship with the contractor, and whether it is a public or private sector project.

During the design phase, TPP Technologies utilizes a variety of computer programs developed for deep water pipeline analysis and deployment. The drawings are also prepared and plotted using computer aided drafting (Autocad).

Most deep water pipeline designs use polyethylene as the pipe material. Its main advantages are its buoyancy in seawater, flexibility for installation, high strength, resilience to shock, corrosion resistance, high fatigue strength, and almost unlimited lifetime underwater. Polyethylene design, however, is quite different from design with other materials: polyethylene is a viscoelastic material with properties that are a strong function of both temperature and time. Acceptable design loads for a cool pipe for a short time are considerably different from design loads for a warm pipe over a long time. A design approach for a plastic pipeline that must reliably survive the deployment process must take into account these unique characteristics; this is a design strength of TPP Technologies.

The risks and costs of the at-sea portion of the installation can be quite high because of the concentration of critical tasks, the quantity and variety of equipment involved, and the number of personnel working. An unplanned delay results in significant additional costs and some mistakes could end up causing the loss of the pipeline. These problems are inherent with all marine construction; proper planning of the deployment is a critical step resulting in lower risks and cost savings.

A detailed deployment plan, written by the contractor, is necessary. The guidelines prepared by TPP Technologies form a basis for this plan, but the exact personnel, equipment, and scheduling of the contractor need to be included. A step-by-step procedure is written detailing each individual’s responsibility, materials required, and the major equipment involvement. TPP Technologies reviews this deployment plan for the owner to assure that the pipe is properly handled and that it will be correctly placed on the bottom.

 

 

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