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Extending the integrity of oil and gas infrastructure: refurbishment vs replacement

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Oilfield Technology,

While current oil prices seem to suggest that the industry is recovering from difficult times after years of weak prices, there is little doubt that the market continues to be a volatile one. The combination of unpredictable price fluctuations, ongoing debate about the future of fossil fuels and increasingly tumultuous geo-political trade issues means that the industry continues to face an uncertain future.

In fact, despite the apparent upturn, the International Energy Agency (IEA) has warned that the growing demand for oil, combined with the fact that investment was deferred during the downturn, could mean that supply will struggle to meet demand. Oil companies will need to boost their production, while keeping a watchful eye on the intrinsic volatility in the sector.

While this uncertainty has reigned in the marketplace, many operators have put off non-critical spending in order to reduce costs. As well as reduced CAPEX on new equipment, this cost reduction often took the form of deferring maintenance or adopting a safety-critical approach. Here, Mark Cattle at Surface Technology, looks at how maintaining the integrity of assets can extend equipment life and play a critical role in protecting an ageing infrastructure - particularly in times of uncertainty.

Repair, refurbishment and maintenance

Coating and plating can provide an ideal solution for the repair, refurbishment and maintenance of offshore and subsea equipment. With a wide range of solutions available ¬– from thermal spray, selective plating, and spot repairs to full asset re-coating, machining and grinding, non-destructive testing (NDT) inspection and pressure testing – it is possible to extend the service life of the asset and meet regulatory requirements without the need for CAPEX. Typical areas for efficiency and cost-savings include:

Valve applications. Pressure and flow control equipment such as valves are important oilfield assets that can often be repaired or refurbished to extend their service life. Typically, valve bodies and seats can suffer from corrosion and abrasive wear caused by particles being introduced between two moving surfaces. In addition to coating newly manufactured valve gates and ball valves to increase wear resistance, thermal spray can refurbish them to their original condition using high velocity oxy fuel (HVOF) coatings, and seat faces can be resprayed to ensure an effective sealing surface and extend their service life.

Drilling equipment. While equipment damage often results from the operating environment, issues with the manufacturing process can also lead to a need for component salvage. For example, Surface Technology received the sealing bore of an outer connector sleeve – a critical part of the drilling system – which had been scored during the manufacturing process. Replacement was an expensive option, but it was crucial that any potential solution would recondition the component to meet the manufacturer’s rigorous specifications.

Firstly the part was machined to remove surface defects – approximately 508 microns were removed from the sealing diameter. A HVOF thermal coating was recommended due to its wear, corrosion and oxidation-resistant characteristics. It required no heat treatment and therefore ensured that the outer connector sleeve was not at risk of distortion or any other metallurgical change. Once coated, the surface profile of the sealing bore was re-machined to meet the manufacturer’s original specification and comprehensive inspection and NDT took place to ensure the part had no microscopic cracks or inherent weaknesses. Overall there was a significant cost saving, and having in-house grinding and NDT testing, in addition to the HVOF process, expedited the repair process for the customer.

Christmas trees. Made up of a number of valves, spools and fittings, these are essential parts of any subsea and surface system used to control the flow, usually oil and gas, out of the well. Pipelines and Christmas trees, which are used in subsea oil drilling operations, are subject to hostile environments which can lead to tremendous surface wear and corrosion. For repairs to complex equipment like Christmas trees, abrasive blasting is often not a viable option due to problems of blast material ingress. As an alternative, the company use a bristle blasting method as it enables rapid spot repair to small and medium sized areas. It also delivers significant time and cost savings on component repair versus the complete strip down, blast and recoat, making it a highly cost-effective method for refurbishing Christmas trees and associated components.

Subsea/marine risers. Larger components with threaded connections such as risers and tethers for tension leg platforms present a coating challenge to the surface finishing industry due to their size and complex handling and resultant health and safety issues. The downtime associated with replacing one of these costly parts would be significant, which is why the case to repair is often clear-cut. The coatings used on these types of long components are normally sacrificial heat cured or thermally sprayed aluminium on the external surfaces, with anti-galling or low friction treatments on the connecting surfaces. Large oven capacity and preparation equipment is necessary for this type of work and this can often be perceived as a bigger issue than it needs to be. Surface Technology has developed a specialism in managing this type of component, particularly for the oil and gas industry, and has a facility in Renfrew, Scotland, specifically for handling larger and more complex work pieces.

BOPs. A blowout preventer (BOP) is a large high pressure valve used to prevent the uncontrolled flow of liquids and gases during drilling operations. A common industry problem is mechanical damage caused to the internal sealing diameter of the valve by the extreme, erratic pressures and uncontrolled flow emanating from a well reservoir during drilling. The most common method of repair is to weld clad with Inconel. This process, however, involves pre- and post-heat treatment which can affect the structural integrity of the component and, because of the safety critical function of the BOP valve, can only be carried out a maximum of three times to prevent stress related structural failure. A more dynamic application would be an HVOF thermal coating as the repair method due to the moderate transfer of heat to the powder particles and to the work piece, which remains relatively cool; this causes no metallurgical change to the surface of the internal sealing diameter. Additionally, this process does not require any time-consuming pre- or post-heat treatments.

In-situ repairs on a range of equipment: The SIFCO Process® facilities electroplating localised areas on components without the use of an immersion tank. As well as being able to focus on a specific area of a component, this selective plating process enables parts to be plated in-situ, helping to minimise downtime and production delays. This is particularly beneficial in an industry that has very large components that can be difficult to transport and where every hour of downtime can cost the platform operator thousands of pounds in lost production.

In contrast to tank plating, the SIFCO Process does not require extensive masking or special fixtures to plate the component and requires fewer chemicals. The length of time a plating operation will take is primarily determined by the amount of material that needs to be applied. SIFCO Process deposits can be plated at rates that are 30 to 60 times faster than conventional tank plating.

In summary, approaching and considering the selection of an appropriate coating for repair or refurbishment can be a daunting and complex task. With more than 50 years’ experience serving the global oil and gas industry, and a complete range of engineered surface coatings combined with extensive technical knowledge and application advice, Surface Technology is well placed to help oil and gas customers select coatings to repair and refurbish to the highest standard, increasing asset service life, reducing capital costs and improving profitability.

Author: Mark Cattle, Surface Technology

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