According to WorldOil.com, just last year the world's largest pipe-laying barge, the Chinese Vessel CPP 601, began its offshore operations. "Capable of laying pipes of 150mm-1,500mm diameter at a water depth of 5m-150m. The barge has a maximum hoisting capacity of 1,600 tons and can provide accommodation for 376 staff at the same time."
This mammoth barge would be unable to achieve its purpose, laying mile after mile of offshore petroleum pipeline, without tensioner machines to stabilize and control the distribution of the pipelines. Equally important on the machines are small rubber components which allow for flexibility within the metal parts of the machine and even distribution of weight as large sections of pipe groan their way into place below sea level.
The Role of Tensioners in Lay Operations
As Jan Buijvoets explains in a report from the 6th Pipeline Technology Conference (PTC) in 2011, barges in lay operation may have a single tensioner, or one in the stern and one at the stinger. The stinger is an extension that curves over the board of the stern of the barge which provides support during S-lay. These tensioners feed pipe into the pipeline system, laying new pipelines to facilitate the transportation of petroleum from offshore rigs.
Because the pipelines must be fed evenly and at specific depths, it is important that all machines run efficiently. Rubber tensioner pads facilitate the even and smooth distribution of pipe into the water through the tensioner machine.
When a lay barge is employed in submerging offshore pipelines Buijvoets notes, "there is a need for guarded buoyancy so the pipe can be launched in the water in a controlled way. Depending on the positioning system, the size of the tensioners, type of stinger and floating capacity of the barge the pipes can be lowered to a certain depth."
Even the smallest rubber tensioner pad plays a large role in offshore lay operations. Rigzone.com notes "Proper tension is integral during the S-lay process, which is maintained via tensioning rollers and a controlled forward thrust, keeping the pipe from buckling."
Without a well maintained tensioner, made flexible by with high quality rubber rollers and tensioner pads, sections of pipe will be unevenly distributed and may jerk or scrape against metal parts as they are fed through the laying mechanism. If these errors occur the pipe will buckle and may crack or snap. Such accidents cost both money and time in operations that are often racing to meet supply and demand of the booming petroleum industry.
How it Works
Described as one of the most challenging offshore operations, an article on offshore pipelaying published by the Laboratory of Computational Methods and Offshore Systems (LAMSCO) details the purpose and function of tensioner pads in the S-lay process.
"In the S-Lay method, as the laying barge moves forward, the pipe is eased off the stern, curving downward through the water until it reaches the touchdown point. After touchdown, as more pipe is played out, it assumes the ‘S’ shaped curve. To reduce bending stress in the pipe, a stinger is used to support the pipe as it leaves the barge. To avoid buckling of the pipe, a tensioner must be used to provide appropriate tensile load to the pipeline. This method is used for pipeline installations in a range of water depths from shallow to deep… The tension is applied to the pipe by tensioners on the barge which are usually arrays of rubber wheels or belts which surround the pipe and apply an axial force to the pipe through the friction generated between the tensioner and the pipe external coating.”
Like Buijvoets, the LAMSCO report also notes that without high quality rubber tensioner pads or rubber tensioner rollers, the tensioner may malfunction, causing irreparable buckling to expensive sections of pipe. Without the tensioner, a pipelaying operation may stray beyond the feasible operational range and control in the tension level of the pipeline can be lost.
Tension Pads Manufacturing
Because the sizes and shapes of pipes and pipelines vary greatly in response to geographical needs and production levels, tensioner pads are often made to customer specifications. Prototypes of these custom molded rubber tensioner pads are designed by engineers who work closely with the client. The tensioner pads then must pass friction and shear tests before large batches are produced.
Not only does Mark Tool & Rubber Company produce custom molder custom molded rubber tensioner pads and rollers, once our customers have produced a batch of parts, we keep their specific tension pads in stock for immediate shipment. At Mark Tool, we know how important it is to maintain the efficiency and safety of tensioners in order to protect crew members and reduce costly offshore accidents. Producing and shipping custom made, high quality custom molded rubber is our specialty.