THE OFFSHORE COATING TECHNIQUE Renato Sanchez, Engineering Manager, and Caroline A. Fisher, Technical Writer, CRTS, Inc., USA, examine the use of internal field joint coatings in unique, offshore locations. W hen building a pipeline of nearly 13 000 welds, corrosion management is naturally part of the design. Unfortunately, while the majority of pipelines are built with reasonable monitoring and inspection plans in place, little attention is paid to the bare steel on the internal field joints (IFJs) where leaks and internal corrosion often occur. This bare steel represents approximately 2% of the entire pipeline, yet easily becomes the pipeline’s weakest link if not protected. To prevent internal corrosion, one of the largest oil companies in the world awarded CRTS an offshore project in the Gulf of Arabia near Qatar in 2012. This pipeline crosses the Hasbah and Arabiyah gas fields and CRTS completed its corrosion prevention services in January 2015. The operation was based at the company’s facility in Abqaiq, Kingdom of Saudi Arabia, and at that time was the largest project ever awarded to CRTS. Why was IFJ coating chosen over other corrosion prevention methods? Corroded, leaking pipelines on the ocean floor are not a viable option for owners or the environment. Coating the IFJs provides the most mitigation for the money. Preventing corrosion from the inside out Designing a pipeline to endure a lifetime means employing corrosion prevention techniques that do more than meet the minimum standards; the pipeline should have built-in measures, such as corrosion prevention coatings, that prevent corrosion or greatly mitigate it. Built-in prevention does not exclude future inspection and monitoring; corrosion prevention coatings do however add many benefits such as: ) Maintain product purity. ) Increase pipeline longevity. ) Reduce internal corrosion. ) Reduce pipeline flow friction, which minimises pressure drop. ) Reduce pipe wall thickness requirements. ) Diminish or eliminate pipeline leaks. ) Protect the environment from leaks, ruptures or spills. These benefits are inherent to the parent coating of pipelines, but when also applied to the internal field joint, they create seamless, defect-free protection from internal corrosion. These benefits also address the gravity of internal corrosion consequences: deepwater pipelines need defect-free, continuous internal coatings to complement the expensive and complicated methods of monitoring and inspection. Customised equipment for best practice The sheer number of welds and impact on the marine environment with a project of this size is enough to warrant specialised equipment and testing. The complexity of keeping equipment running efficiently while performing also warranted
Transcript
THE OFFSHORE COATING TECHNIQUE
Renato Sanchez, Engineering Manager, and Caroline A. Fisher, Technical Writer, CRTS, Inc., USA, examine the use of internal field joint coatings in unique, offshore locations.
When building a pipeline of nearly 13 000 welds, corrosion management is naturally part of the design. Unfortunately, while the majority of pipelines are built with reasonable monitoring and
inspection plans in place, little attention is paid to the bare steel on the internal field joints (IFJs) where leaks and internal corrosion often occur. This bare steel represents approximately 2% of the entire pipeline, yet easily becomes the pipeline’s weakest link if not protected.
To prevent internal corrosion, one of the largest oil companies in the world awarded CRTS an offshore project in the Gulf of Arabia near Qatar in 2012. This pipeline crosses the Hasbah and Arabiyah gas fields and CRTS completed its corrosion prevention services in January 2015. The operation was based at the company’s facility in Abqaiq, Kingdom of Saudi Arabia, and at that time was the largest project ever awarded to CRTS. Why was IFJ coating chosen over other corrosion prevention methods? Corroded, leaking pipelines on the ocean floor are not a viable option for owners or the environment. Coating the IFJs provides the most mitigation for the money.
Preventing corrosion from the inside outDesigning a pipeline to endure a lifetime means employing corrosion prevention techniques that do more than meet the minimum standards; the pipeline should have built-in measures, such as corrosion prevention coatings, that prevent corrosion or greatly mitigate it. Built-in prevention does not exclude future
inspection and monitoring; corrosion prevention coatings do however add many benefits such as:
) Maintain product purity.
) Increase pipeline longevity.
) Reduce internal corrosion.
) Reduce pipeline flow friction, which minimises pressure drop.
) Reduce pipe wall thickness requirements.
) Diminish or eliminate pipeline leaks.
) Protect the environment from leaks, ruptures or spills.
These benefits are inherent to the parent coating of pipelines, but when also applied to the internal field joint, they create seamless, defect-free protection from internal corrosion. These benefits also address the gravity of internal corrosion consequences: deepwater pipelines need defect-free, continuous internal coatings to complement the expensive and complicated methods of monitoring and inspection.
Customised equipment for best practiceThe sheer number of welds and impact on the marine environment with a project of this size is enough to warrant specialised equipment and testing. The complexity of keeping equipment running efficiently while performing also warranted
exceptional design. While the customised equipment may seem excessive at the outset, the long-term OPEX savings, protected public and marine environment demonstrate that every detail is essential.
Offshore, there are electronic challenges: the robotic equipment uses telemetry and it had to be robust enough to transmit not only through external welding-generated electrical noise, but also through a massive internal laser welding lineup clamp. Altogether, 60 printed circuit boards and 11 microprocessor boards were onboard each set of robotic equipment.
There are also mechanical challenges unique to offshore work: CRTS engineers designed offshore-rated lifting frames for all of its robotic equipment, which included equipment baskets and compressor frames. The frames were designed in Tulsa and fabricated and load tested in our Abqaiq, Saudi Arabia location. Six sets of equipment were made, each set consisting of a crawler, battery cart, cleaner, vacuum and liquid coater. In total, with more than 100 45Ah batteries on each set of equipment, nearly US$1 million was spent on batteries alone.
Moving heavy pipe safely and efficiently is a safety concern on a laybarge. CRTS designed pipe rotators that were used to rotate the 36 in. pipe with a 1 5/8 in. wall. Each pipe piece was 80 ft long and was covered with 4 - 6 in. of concrete coating. These massive rotators had a lifting capacity of 50 t and were used to rotate the pipe during the preblasting process, which collects and recycles the abrasive blasting media.
Besides building coating equipment for the IFJs, CRTS perfected a recovery system in case any equipment rolled to the bottom of the S-bend. Although CRTS has coated thousands of offshore IFJs with no mishaps, the customer was adamant that a recovery system be in place, a safety practice approved by CRTS. A few simple mechanical components were added to the crawler features, such as a delatching mechanism for the 10 000 lb of equipment. CRTS also designed a safety winch as a fail-safe for retrieving runaway equipment. As expected, it was never used.
Preparing the IFJ for coatingOne of the main benefits of remotely controlled robotic equipment is that it identifies uncoatable (corrosion inviting) welds at the beginning of the corrosion prevention process. The wireless video system identified weld imperfections at the root pass, which made correcting them much simpler than finding them after all the welding passes had been completed. The visual inspection of the welding root pass is a valuable tool, regardless of whether the pipe is coated or not (CRTS has performed this function for clad steel). Cutting out pipe is one of the most expensive activities on a lay barge, especially if the faulty section is not found until after the pipe has been internally coated and is about to enter the stinger.
Preventing corrosion by applying coatings is easy; preparing the pipe surface for coating takes stringent effort. Since each weld is a potential source of corrosion due to its protrusion into the flow stream, before the pipe was welded together, handheld abrasive blasting equipment was used to create a surface roughness on the cutback area that met the coating manufacturer’s standard.
Once the surface roughness was measured and approved, the pipe was loaded onto the ready rack, then entered the first station, the bead stall. After this pipe was welded to another pipe, the cleaner and vacuum robots worked in tandem to provide the foundation of seamless internal corrosion prevention: superior surface preparation.
Figure 1. This train of equipment cleaned and coated nearly 13 000 internal field joints on a Middle East offshore project.
Figure 2. Factory-coated pipe strengthened with coated internal field joints enters the Arabian Gulf.
Figure 3. CRTS field technicians use telemetry to communicate with its robotic equipment while it is inside the pipe. This wireless communication includes receiving video and equipment parameters data from the equipment cameras.
World Pipelines / REPRINTED FROM AUGUST 2015
The robotic cleaner uses a high speed cleaning wheel to remove weld slag and other impurities generated by the welding process. The cleaner applied abrasive to the IFJ and then vacuumed and recycled the abrasive for use on the next IFJ. A visual inspection using an onboard camera ensured the proper level of cleanliness was achieved and no debris remained. The IFJ surface was then ready to receive the protective coating.
Coating the IFJ CRTS’ coaters are the heart of internal corrosion prevention and one of the most complex machines that CRTS designs and builds. Years of design and testing have culminated in machinery that uses various coating heads to precisely apply both FBE and liquid coatings on offshore and onshore projects. For this project, the customer chose SP 9888, a two-part liquid epoxy, to protect the nearly 13 000 submerged IFJs. The plural component liquid coater has infinite ratio adjustment with its range, allowing its use with many different types of materials. The coating operator set the pump speeds and oscillation distances to accommodate the pipe’s cutback lengths. This, along with its independent heat controls for the material components, allowed for mixing and application conditions as recommended by the coating manufacturer.
The liquid coater was also outfitted with wireless telemetry and video to allow remote operations. These features enabled the operator to remotely send the liquid coater to each IFJ for coating. The camera lets the operator view the weld to ensure it’s coatable (no abrasive or welding residue); line up to the weld; trigger and observe the actual coating sequence. Another feature of the
onboard camera is that it allows for instant visual inspection of the IFJ. Inspecting the coated IFJ at this stage meant that if a coated weld had any visual defects, it could be repaired before any product entered the pipe. CRTS also has a fusion-bond epoxy coater for FBE projects.
ConclusionCRTS applies its robotic technology to address the high cost of monitoring, repairing and rehabilitating pipelines by using a simple process of cleaning, coating and inspecting internal field joints and, if requested, the internal length of the pipeline. This foundation of internal corrosion prevention attempts to benefit the pipe owner, the public and the environment by addressing corrosion before it has a chance to form and wreak havoc on assets.
This seamless corrosion prevention system works alongside factory-coated pipe to meet PHMSA’s goal of reducing “the occurrence of defects that can lead to corrosion-induced failures.”1 While this PHMSA report focuses mainly on US transportation pipelines, it is a goal worthy of any pipeline project.
Part of the reduction goal on CRTS’ part is designing and building equipment that works efficiently with the project’s geographical and other challenges. For this particular customer, the additional preventive measures will result in lowered OPEX and repairs over a lengthy lifetime of production.
