Design and implementation of the sea pipeline

Polyethylene pipe at sea

Undoubtedly, designing any project is one of the most important of project elements. In this regard, project design team, taking into account the general and specific nature of each project and considering of available facilities, will design a method for implementation and calculation of required requirements. Marine projects have unique complexity due to their maritime nature and difficult and unpredictable conditions, and for this reason, design team such a project requires considerable experience and skill. In this article, we have tried to study the importance of designing of a Marine pipeline, and recall more important subjects.

General of Marine pipeline design

Important points in the Marine pipeline design can be divided into two parts of basic concepts and operational method.

Designer of Marine pipeline in this section, investigates basics of the project, which can be mentioned as follows:

• Safety tips of plan
• Location of the plan implementation and initial and final conditions of the pipeline
• plan of fluid transmission system
• Useful life of plan
• Specifications of fluid inside the pipeline
• Transmission capacity and pipeline size
• Geometric shape of plan
• Functional requirements of the transfer plan
• Schedule of plan

In this section, Designer of Marine pipeline, according to the principles of the project, examines executive procedures and related requirements, and offers best option. Important points about this topic include:

• Safety tips of plan
• Project organization
• Project implementation phases
• limits and boundaries of the executive
• Equipment Required in suggested executive method
• Description of project operations
• Contractors
• Sellers and manufacturers of equipment and materials needed

Selection of Marine Line Route

Marine line route, to comply with safety tips, is selected for public and human aspects. In this regard, at least following items should be considered:

• Ships traffic
• Fishing activities
• Other marine installations
• Available marine cables and pipelines
• Offshore instability
• Sub-surface currents
• Seismic activities of Sea floor
• Maritime obstacles
• Mineral activities on the sea floor
• Military activities
• Environmental issues

In order to study this mentioned cases and determination of appropriate pipeline route, firstly, maps of the area and records of the previous projects are examined, and according to the information obtained from this section, hypothetical pipeline route is proposed, and then, through local visits and studies, route is finalized and selected.

Issues that are important in surveys and studies of the maritime pipelines route as follows:

• Sea floor topography in proposed corridor
• Sea subsurface inspections in the direction of the pipeline route for identification of probable obstacles
• Geotechnical studies of sea floor for investigation of loading and settlement conditions
• wind blow studies in the region
• Studies of marine waves status in the region
• Air temperature and sea water temperature
• Surface and Subsurface Flow Studies

Criteria of Marine pipelines design

In the design of maritime pipelines there are unique criteria, including:

- At intersection of the maritime pipelines, vertical distance of 2 pipelinesو should be at least 30 cm from each other.

- maritime pipeline should protect one of the following ways against the collapse of the fishing

• Concrete casing
• burial method
• Sand and gravel cover
• Mechanical methods

• Minimum of wall thickness

Except where the necessary measures to cover pipes are required against accidental loads, such as dropping objects or other external loads.

• Minimum of wall nominal thickness

Except where the necessary measures to cover pipes are required against accidental loads, such as dropping objects or other external loads, for pipes with a diameter of 8 inches or higher than high immunity, 12 mm is considered.

selection of pipe material

Pipe material with regard to the desired fluid, temperature and possible failure modes during the installation and operation are selected. In this selection, pipes and other components of the pipeline should be compatible. Most important parameters of effective in selection of material are as follows:

• Mechanical behaviors
• Mechanical behaviors
• fracture toughness
• Burnout resistance
• Weldability
• Resistance to corrosion

Design methods

Design methods can be done in two modes:

1- Load Antrel

2- Movement Antrel

- Reaction between pipe and sea bed in the design should be considered, In this regard, main parameters are shear strength and soil deformation behavior.

- Reaction between pipe and sea bed in the design should be considered, In this regard, main parameters are shear strength and soil deformation behavior.

1- pipe surrender and Pipe burnout

2- Destroying of pipe cover

3- geometric constraints of pipe holders

4- Distance from other pipelines, structures or obstacles

Cover outside and inside of pipe

In order to selection and designing of the outer cover details of the pipe, external environment conditions associated with pipe should be considered as follows:

1- situation of pipe around environment: Buried or not buried

2- Gender and resistance of sediments and sea water

Other subjects that effect on determination of the pipe outer cover are:

• Maximum and average of fluid temperature in the pipeline
• Procedure for construction and installation of pipelines
• Requirements for mechanical protection and immersion weight and insulating temperature during operation
• Useful life of pipeline

Cover outside and inside of pipe

In order to selection and designing of the outer cover details of the pipe, external environment conditions associated with pipe should be considered as follows:

1- situation of pipe around environment: Buried or not buried

2- Gender and resistance of sediments and sea water

Other subjects that effect on determination of the pipe outer cover are:

• Maximum and average of fluid temperature in the pipeline
• Procedure for construction and installation of pipelines
• Requirements for mechanical protection and immersion weight and insulating temperature during operation
• Useful life of pipeline

Often, "the outer covering of marine pipes, Due to the provision of pipeline negative buoyancy and mechanical protection of the coating during installation and life of the pipeline, is a concrete weight coating that minimum requirements for these coatings are:

Minimum of concrete thickness: 40mm

Minimum of compressive strength: 40MPa

Max of Water absorption: % 8

Minimum density: 1900 kg / m 3

In order to selection and designing of the inner cover details of the pipe, external environment conditions associated with pipe should be considered as follows:

• Internal conditions of the pipe during storage, construction, installation, test pressure and during operation
• Maximum and average temperature / fluid pressure during the pipeline operation
• Speed and passing flow regime
• Fluid Compounds
• Chemical additives for periodic cleaning work of pipeline
• Possibility of erosion inside the pipe by passing fluid

Incoming loads to the marine line:

Incoming loads to the marine line are divided into 4 parts:

• Operator loads: Including weight, external hydrostatic pressure, temperature, component reaction, pipeline coating, inside pressure of pipe, sea floor reaction, permanent displacement of retaining structures and permanent changes due to land formation
• Environmental loads: include surface and sub- surface streams, wind, wave, ice and hydraulic loads
• Loads of construction times: Includes loads of transportation time, construction, installation, repair and maintenance
• Accidental loads: falling objects, explosions, fires and...

However, the marine pipeline designer will be able to analyze sea pipeline by analyzing of loads in the proposed plan and by determining of quantities of these loads.

Installation of marine pipeline

Installation method of marine pipeline due to the effect of loads on the pipeline at time of installation, it is one of the most important decisions of the designer.

Designer of marine pipeline, according to the project conditions, selects method for installation of marine pipeline. Effective factors in choosing of method for installation include:

• pipe length and diameter
• Depth of sea water in the pipeline route
• status of the sea bed along the pipeline route
• Accessibility possibility to required equipment
• time and duration of the project
• budget of performing project
• importance of the pipeline

Among the commonly used methods for installation of marine pipeline, is using from Barge. In this method, pipes are loaded from the quay onto the barge, and then pipe carrier barge go to the side of transition pipe barge, and placed near that, and during the installation, have role of supplier of pipe. On the other hand, pipe carrier barge, with coating of welds on the NDT, and providing of Fitup systems, welds itself, produces pipelines, and sends it into the sea continuously.

In differentiation of pipe carrier barges, power of intubation method using from pipe carrier barges is now very common, For example, we can refer to the intubation of different phases of the South Pars with using from this method. One of the other ways of installation of the pipeline, is pulling of pipeline into the sea. In this method, according to the maritime pipeline length, spools are constructed on the shore, and then, with the help of floating tanks, are taken to the sea by puller barge. In this method, spools constructed on racks, on the transmission line, which consists of rollers made at specified intervals, are pulled into the sea by a puller barge, respectively, and after a spool is pulled out, next spool is welded to this spool and transfer operation continues. Among the projects that are done in this way, Qeshm water pipeline project from Bandar Abbas, is to length of 10 kilometer.

Conclusion:

Although maritime industry is a native and young industry, however, we have significant progress in the implementation of marine projects, such as the installation of maritime pipeline, therefore, marine project design department have not synchronous growing with its executive department, and at present, an important company does not work in the design of marine projects in the country. This article tries to express special and important position of this sector of the industry with expressing of marine projects design, and in particular, marine pipelines design, and note basic points in the design of the maritime pipelines, and believes that proper design of marine pipelines can be a great help in the proper and cost-effective implementation of projects.

References:

• Offshore standard DNV-OS-F101, 2000
• Subsea Pipeline Engineering by Andrew Clennel Palmer
• Piping and Pipeline Engineering: Design, Construction, Maintenance, Integrity and Repair by George Antaki
• Pipeline Pigging Technology