Pipe Laying Operation & Pipe Laying Barge

Introduction:
Offshore Pipelines is one of the most important sectors of the offshore industry. Design and implementation of development planning and implementation of industry have an important role in the development of offshore industry. Today, using modern technology, various advanced techniques to install pipelines are done.
Pipe-laying vessels, according to the work area and climatic conditions are different. It serves to connect oil production platforms with refineries on shore. To accomplish this goal a typical pipe laying vessel carries a heavy lift crane, used to install pumps and valves, and equipment to lay pipe between subsea structures.

History of Pipe Laying:
History of submarine pipeline dates back to after the Second World War. The first company in the industry, "Kerr-McGee Oil Industries, Inc" is to help "company Brown & Root" of the oil-producing offshore platforms completed in mid-1947. This day was designated as the birth of modern offshore industry.
By 1969, the tools used to lay the pipelines exclusively includes flat-bottomed barges of which were controlled by the anchors. In addition, until then a relatively shallow waters and calm seas most pipelines were laid. In the early 70s, the need for pipelines that must be laid in deep water and harsh environmental conditions was seen.
In the mid-1970s, the third generation of Pipe-Laying Vessels entered the market. This time to the success of large-diameter main lines lay to a depth of 600 meters. By continuing to work in the early 90s by J-lay (in front of S-lay) was developed that can be installed in deep-water and ultra-deep pipeline created.
 Note: Definition of deep water among different companies and different countries are various, but the most accepted standard is higher than 1,500 feet and 5,000 feet of deep-water and ultra-deep waters and more for.

Various Methods of Pipe-Laying:
From the beginning pipe laying in the decade 50 many different methods have been used for the installation of pipelines on the seabed. For transportation of energy resources from offshore to the onshore there are many ways to install the pipeline. The most common ones are:

I. Reel (Reel Barge Method)
II. Pull & Tow (Pull & Tow Method)
III. Barge (Lay Barge Method)

Definitions:

1. Reel Barge Method:
In this method, pipes after preparation and welding at the coast, on a large reel drum that is located on a barge, wrapped and then put in place on the seabed are preset (installed). The maximum diameter of the pipe to install in this method is 16 inches.

2. Pull & Tow Method:
Preparations for welding and testing operations carried out on the coast and to install it in the sea with towing float, one of the following methods can be used:

1.2- Surface Tow
2.2- Below Surface Tow
3.2- Bottom Tow
4.2- Off-Bottom Tow

3. Lay Barge Method:
The most common way to install Offshore Pipelines is "Lay Barge Method". In this method, required pipes transport by barge and pipes are stored in the warehouse (Pipe Rack). Then these pipes will go into production line by the crane barge. After preparing the pipe and chamfer grinding two ends of pipes enter into the station (Line-Up as a first station) and will ready for welding. After completion of the welding and final "NDT" test (Non Destructive Test), Pipes at the next station (Field Joint Coating), using a special polyethylene anti-corrosion coating (and sometimes concrete cover). Then cross the tensioner devices whose role is to maintain minimal tension on the pipe arc is allowed and prevent pipe buckling, the barge moves forward the pipes into the Stinger and then placed on the sea bed.
Lay Barge Method is divided into two parts:

J-Lay Method:
Of this method mostly used in water depths up, the pipes are welded together on a large hinged mast and then after crossing the tensioner the pipes will lay on seabed. Given the depth of the water and also according to perpendicular the stinger on the production line, so be tensioner devices must have the ability to exert greater tensile force. This procedure is for that the pipeline do not getting the plastic deformation or diagonal buckling in the Sag Bend area.

 S-Lay Method:
This method has been widely used in pipe laying; pipe laying speed depends on: diameter pipe, water depth, equipments and type of the barge. Most of these methods are used in the Persian Gulf. The maximum operating depth for each barge depends on factors such as: mooring system capacity and its type, the type of Stinger, capacity of tensioner devices, pipe diameter and the thickness of it.
In this way the pipeline in the areas "Over bend & Sag bend" Is under tension, to prevent buckling of the pipeline must bending moment on it is within the allowable range. Bending in the area "over bend" By adjusting the angle of the Stinger and Its rollers and bending in the area "sag bend" By entering the appropriate tension on the pipeline by tensioner is controlled.

Marine Industry Development Procedures:

Item                                            Description                                                  Year

1.  The first offshore pipeline by "company Brown & Root" in the Gulf of Mexico 1954
2. The pipe-laying barge for the purpose of pipe laying (BAR 207) by "company Brown & Root" was designed and built. 1958
3. Flexible pipeline by "Shell" was installed in the US Gulf. 1959
4.  Dynamic positioning method was used for the first time executed by "company Eureka - H. Shatto" 1961
5. pipe laying was created with pulley by "Aquatic Contractors" 1961
6. The cause of the slot for underwater pipeline was built by "Orinoco/Phillips" 1961
7. The first float pipe laying spool trade barge was launched with the name of "U-303" 1962
8.  Deep pipe laying was reached to 264 feet by companies "California - shell" 1963
9. Second-generation pipe-laying barge by "North sea-Brown & Root" was used. 1966
10.  Twin pipelines cross water flow conditions at a speed of 8 knots by companies "McDermott - Cook Inlet" was laid. 1966
11. For the first time, Stinger and Tensioner pipe- lying was used in the operation. 1967
12. Pipeline hot-tap was created by "Ocean systems - Union Carbide". 1967
13. The first vessel was launched pipe lying with central ramps. Nominated "LB 22" by the company "McDermott" 1969
14. The first semi underwater pipe-laying vessel was built. "Choctaw I- Santa Fe" 1969
15. Implementation of pipe lying projects entered in depth of 1,000 feet by "Castoro V – Saipem" 1974
16. Pipe lying pulley projects entered into depth of 1,000 feet. Executed by "Chickasaw". 1975
17. Towing underwater pipeline installation method was tested. 1977
18. The first pipeline was installed by towing. Implementation by company "Statfjord". 1978
19.  Pipe lying projects entered into depth of 2,000 feet by company "Castoro VI – Sicily". 1979
20. The first pipe lying operation was performed in "J-lay" method by companies "McDermott-Shell". 1993
21. The first line (in field) /threaded installed by company "BP". 1993
22.  S-lay method of pipe lying depth of over 3,000 feet. Executed by companies "McDermott-Shell Brutus". 2000

Pipe Laying Barge:
One method of installing pipelines on the sea is pipe laying vessel, that on the deck of the barge; the pipes are welded together and during of vessel movement, cross the tensioner and stinger devices and then placed on sea bed. These kinds of barges are equipped with welding equipment, crane on deck, chamfer grinding machines (Beveling Machines), tensioner devices, abandonment & recovery winch and other equipment for the pipe-laying operation, including rollers of pipes holders? pipe davits, system mooring, survey &positioning and also diving operations.
How to install the pipe in the sea as well as needing equipments that are in the pipe-laying vessels are almost identical.

Operational Station:
The pipe-laying barge based on their design has several welding stations. The first station in each barge is called as "Bead Stall" or "Line Up". Where after Line up the pipes stage, welding passes Root & Hot is performed and in the rest of stations the welding passes are struck as Fill & Cap Pass. Number of welding station in each vessel to be adjusted based on pipe diameter and operating speed. In pipe laying barge, welding types (Auto or Manual) determines the type of equipment. 

Note: In order to achieve high efficiency and lowering the welder error, mostly automatic type used.

In the marine pipe-laying, all the welds must be 100% tested. Type of test (AUT "Ultrasonic Test") or (Radiography) is selected usually during pipeline design and also in accordance with existing standards. After testing the welds and ensure that they are safe and hale, in the last operating station, that is called Protective coatings station, the two ends of the pipe is covered with an appropriate layer of polyethylene. Type of pipe coverage depends on the salinity of sea water that the type and thickness will be determined during the design stages.

Tensioner Device:
The tensioner Hold the pipe and continuous acts of force and control the bending moment in sag bend area. Tensioners usually are installed on the barge, horizontally in the line of production and after NDT (Non-Destructive Test) station. In the case where the barge is not moving, tensioners exert force to protect the pipes from buckling actions. In the time of barge moving, automatically and maintaining the necessary traction, guides the pipe to front or rear.
In this regard, of tensioner and mooring winches co-ordinate together, to avoid problems for the pipe when the barge is moving.

Stinger:
Stinger is a steel structure, which will lead the pipes to the seabed under specified angle. Adjusting stinger angle to the horizontal during laying operation, is depending on *depth of water *pipe diameter * length of stinger and also extracted curve for pipes. By adjusting the angle of the Stinger and picking rollers, curved of pipeline and the stress are controlled in the area over bend.


Abandonment & Recovery Winch:
When to terminate the pipeline operation, at this time production operation is shutdown, and then pipes by using winch will place on the seabed.
Abandon the pipeline will happen according to one of the following reasons:
? Bad weather conditions at sea
? Machine malfunctions
? The end of pipe laying operation

Buckle Detector:
Means to identify detect buckling diameter of pipes that during the pipe laying operation are placed inside it. The location of it is in area sag bend or one/tow pipes after Touch Down Point.
Buckle detector contact by internal clamp and is restored by a winch inside the pipe. Buckle detector is one of the safe tools to control buckling when the pipeline is installed.

Compilation By: Saeed Mohammadi

Date: 27 January 2016