As offshore drilling technology advances and wells become ever deeper, the problem of corrosion increases proportionately. The presence of hydrogen sulphide, carbon dioxide and chlorides creates a potentially catastrophic corrosive mixture. Add to this the extremely high product temperatures from deep wells and there are significant problems that need to be overcome.
When assessing the corrosion protection of any production system, piping and process engineers have a number of options to consider. The effectiveness of each will vary dependent on a number of factors including: the aggressive nature the product; pressure and temperature; size and complexity of the system; well-life expectancy; available development period and the budget.
A production pipeline, from wellhead to topside processing, will typically include pipe, various types of connectors, fittings (tees, elbows etc.), complex valve blocks, pig launcher/receivers, etc., all of which will be subject to corrosive and possibly erosive attacks on their internal wetted surfaces. So how do engineers design a system to resist these attacks?
Protection methods where risk of attack is low and life-cycle short, may be as simple as an injected inhibitor used with conventional high-strength carbon or low alloy steel.
Where greater protection is needed corrosion resistant alloys (CRAs) such as austenitic (300 series); ferritic/martensitic (400 series); and duplex stainless steels or the more complex high nickel chromium alloys, must be considered.
With apologies to the manufacturers of austenitic stainless steels, it is unlikely they would have the resistance required for the very worst conditions. They would have to be used in very heavy wall section to match the pressure retention achieved by the carbon steels in common use (API 5L X60 or X65 for instance).
Duplex steels and nickel based alloys, such as alloy 625, are the only materials in general production which, when welded, will achieve the strength to match carbon steels. However, there are constraints to their use in solid form – namely cost, availability and the need for very rigid fabrication procedures.
Cost is particularly relevant where large quantities of pipe and fittings or large forgings or castings are needed. Wellhead valve systems and pipe bundle bulkheads are typical examples.
The use of carbon and low alloy steels clad with a corrosion resistant alloy has been common practice for some years and is a proven, economical and technical alternative to solid alloys.
The term ‘cladding’ covers a wide range of processes including: hot roll bonding, explosive bonding, diffusion bonding, centricast pipe, co-extruded pipe and weld overlay cladding.
Each has particular merits, so the processes are not necessarily competing for the same market. For example, whilst hot roll bonded plate, rolled and welded into pipe, may be economical for a 12m length, co-extruded or centricast would offer savings if 12km are required. Also, in periods of high demand, the lead times for some of these techniques may preclude them from use in a fast track or refurbishment project.
Weld overlay cladding
Weld overlay cladding technology presents the materials engineer with a wide choice of welding processes and immense flexibility. An almost infinite range of component shapes and sizes can be protected, with an equally wide range of base material/cladding alloy alternatives.
The combination of high strength low alloy steels (AISI 4130 or 8630 for example) and alloy 625 (Er-NiCrMo-3) is probably the most common for high pressure retaining wellhead equipment.
Weld procedures are normally qualified to ASME IX, as are the welding operators. Additional testing to prove conformity with API 6A and NACE MR01-75 is also completed, along with any contract specific requirements from the end user.
Selection of the most appropriate welding process is largely dependent on factors such as the size of the clad area; access to the area to be clad; alloy type, specified clad thickness; chemical composition limits; welding position; and NDT acceptance standards.
Welding processes in common use internationally include:
Given that the process used must be practical, viable and provide the mechanical and chemical conditions to achieve service requirements, economics dictate that the higher deposition rate processes should prevail. Details are available to optimise processes and deposition rates while taking into account the limitations that may apply.
Automated or mechanised processes generally offer the best deposition rates and provide the most consistent quality of deposit. This enables the finished cladding to closely match the results provided during procedure qualification testing. Mechanised equipment can also be designed to access areas that simply cannot be reached by manual methods – for example through a small-bore pipe.
GTAW processes can be used in bores as small as 15mm, and are ideal for components of varied geometry where the position of the welding head requires frequent adjustment, from a simple flange that needs to be clad through the bore and across the sealing face, to a complex valve body with several interconnecting bores.
Often equipment also needs cladding to RTJ grooves. The control available with the GTAW process means that cladding can follow the profile of the groove rather than filling it completely. This not only saves time and material but also reduces the cost of finish machining.
This flexibility also lends itself to cladding irregular shaped components such as pipefittings. Elbows and tees as small as 2” NB can be clad, particularly where specifications do not allow for a mixture of base materials – for example a carbon steel pressure vessel, where fittings in solid alloys are not permitted due to risks from the use of materials with different thermal expansion rates.
Using this process the chemical composition of the welding consumable can be achieved at 2.5mm from the base material/cladding interface (this can be reduced to 1.5mm in the case of 300 series stainless steels, where over alloyed wires are available).
Where plain bores (in pipe or flanges for example) are greater than 250 - 300mm, the faster depositing electroslag and submerged arc processes can be considered. Equipment is available to enable pipe lengths of 12m to be successfully clad.
The electroslag process utilises a large weld pool that requires substantial base metal backing (generally a minimum of 20mm) to prevent burn through and support the edge of the weld pool to avoid collapse of the molten weld/flux covering.
It is ideal for areas of plain, open access. It is not ideal for cladding adjacent to convex or concave edges. The deposit thickness is nominally 5mm with the strip widths discussed here. With 60mm strip, deposition rates of up to 22kg per hour can be achieved.
To enable the chemical composition of the deposit to match that of the consumable specification within the first layer (3mm from the interface), over-alloyed strip and ‘loaded’ metal containing fluxes, are available.
Where a strict limitation is imposed on iron dilution into the cladding, a second layer can be added to give entirely undiluted weld metal. However, the use of a 9 -10mm thickness of cladding may negate the commercial advantage of the high deposition rate process.
In these circumstances additional production test plates have been produced, and corrosion tests carried out on the single layer to prove the acceptability of the material for known service conditions.
Another option is the use of a combination of processes. A recent example required a final layer of alloy 400 over a significant surface area. The first layer was pure nickel, deposited by spray GMAW. The second, with 30mm electroslag strip (to ER NiCu-7) ensured that the chemistry (in particular the low iron requirement) was achieved and a total thickness of 7mm was deposited. A material saving of up to 30% was achieved with only a small increase in production time over the two layers of strip.
Submerged arc welding using a solid wire consumable, while not as fast, is a useful ‘halfway house’ between strip cladding and slower GTAW and pulsed GMAW. The welding heads used are not as large as strip heads, and the consumable delivery method is much more flexible. Hence the ability to use this in smaller bore diameters. Traditionally larger diameter consumables (2.4mm +) have been used for this process, again resulting in the need for fairly thick substrates to accept the high heat and large weld deposits.
Recently, procedures have been developed using 1.2mm wires allowing use on thinner section components, and giving more controlled thickness of deposit while maintaining deposition rates of approximately 5kg per hour. As with strip cladding, consumable/flux combinations are available to make single layer deposits viable, especially with duplex and ferritic/martensitic stainless steels.
When weld overlay cladding was first employed, re-machining after cladding was the norm. However, as techniques and equipment have improved, the ‘as welded’ finish has become much smoother and many areas of clad equipment are now left ‘as clad’. This would not apply to sealing/gasket areas, which have to be produced to the very finest of tolerances.
Without doubt the GTAW (and PTA) processes give the least contoured deposits, so procedures have been developed to use the quicker submerged arc or GMAW processes for the first layer and finish with GTAW – combining the benefits of two processes.
When cladding high strength (and therefore more hardenable) low alloy steels such as AISI 4130, 21/4 Cr 1 Mo and, potentially, martensitic stainless steels such as A182 F6NM or AISI 410; PWHT is invariably adopted. This stress relief ensures that the layer of base material immediately below the weld (heat affected zone) is within the recommended hardness levels for the service conditions (as required by NACE).
Test procedures
The level of NDT will be in accordance with the specification to which the equipment is being produced, plus any client or contract requirements detailed in quality plans and purchase orders.
This will almost invariably include liquid penetrant inspection, usually after any machining has taken place. Ultrasonic inspection is less often required, but is used to confirm sound fusion and the absence of volumetric defects.
Chemical analysis of the clad surface is sometimes requested and can be tested in a number of ways, the most common being by analysis of swarf samples from the component, or by use of an X ray spectrograph (PMI) machine, or similar.
Where austenitic or duplex steels have been used, reporting the phase balance may be an additional requirement. This can be calculated from chemical analysis using one of the internationally recognised formulae, or by use of a suitably calibrated magnetic ferrite detector.
The ability to clad ‘off the shelf’ components of any shape and size with a wide variety of corrosion resistant alloys, has made weld overlay cladding the most adaptable and flexible in use - whether you need a one-off special or a large production run.
Advanced Insulation (www.aisplc.com)
Since its formation in 2007, Advanced Insulation has become a single source provider for insulation and fire protection systems to the oil and gas industry, and represents one of the most respected and progressive names in topside and subsea insulation worldwide.
Advanced Insulation offers a wide range of products to meet the growing demand for fire protection and thermal insulation systems adaptable for elevated service temperatures and pressures.
AL-KO Kober (www.al-ko-co.uk)
Since 1931, AL-KO Kober has been manufacturing premium, high quality components used in the Automotive, Commercial and Leisure industry.
The extensive range of chassis components, premium accessories and spare parts are engineered to last, ensuring whatever product you have purchased, you will benefit from the generations of development and enjoy a lifetime of service.
Arc Energy Resources (www.arcenergy.co.uk)
Arc Energy Resources is one of the UK’s leading specialists in weld overlay cladding and fabrication for the oil & gas industry. The company’s expertise provides protection against corrosion and wear for a variety of process and pipeline equipment for use in any hostile environment.
The company recently made a major investment in two new Rotating Head welding machines costing £500,000. This has increased productivity and extended the size and scope of work it can handle, which now includes complicated component geometries for the full or partial cladding and fabrication of a huge range of component sizes weighing up to 15 tonnes. The company’s in-house designed cladding workstations feature state-of-the-art control systems developed to suit its customer’s specialised engineering requirements, and can clad bores up to four metres diameter and areas of restricted access within bores as small as 20mm diameter. Arc Energy also offers in-house test weld, heat treatment, PMI and NDT facilities.
Industry certifications include ISO 9001:2008 quality management, ISO 3834-2 fusion welding of metallic materials, and the internationally renowned ASME U and R Stamps, as well as ISO 14001:2004 environment management, Investors in People and OHSAS 18001:2007 Health & Safety management system.
Curtiss-Wright Industrial Group, which includes the legacy brands of Arens Controls, Penny & Giles, PG Drives Technology and Williams Controls, is a recognized leader in providing components and sub-systems which enable customer specific solutions for on- and off-highway vehicles. These include medium- and heavy-duty trucks, buses and motor coaches, construction and agricultural vehicles, materials handling, and other specialty vehicles, as well as sophisticated wheelchairs and scooters for medical mobility.
We are a leading provider of electronic throttle controls, transmission shifters and sensors for commercial off-highway equipment and heavy trucks, so helping to address the long-term trend towards attaining higher fuel efficiency and lower emissions. We also supply operator controls and advanced motor controllers for hybrid and electric vehicles, such as buses, forklift trucks, pallet stackers, wheelchairs and rehabilitation chairs.
With a proud legacy spanning more than 85 years, Curtiss-Wright is a global innovative company that delivers highly-engineered, critical-function products and services to the commercial, industrial, defense and energy markets. Building on the heritage of Glenn Curtiss and the Wright brothers, we have a long tradition of providing reliable solutions through trusted customer relationships.
Further information is available from the Curtiss-Wright Industrial website (www.cw-industrialgroup.com) or by calling +44 (0)1202 034000.
Euchner (UK) Limited (www.euchner.co.uk)
Safety for people, machines and products has been the maxim of this family-owned company since 1953. Stefan Euchner is the third generation to take the helm.
As specialists in industrial safety engineering, Euchner develops and manufactures products and solutions tailored to the requirements of customers from a wide range of sectors. Using its guards on machines and installations helps to minimise hazards and risks, which in turn protects people and processes. For its 800 employees around the world, safety is the watchword.
Further information is available from the Euchner (UK) Limited website (www.euchner.co.uk) or by calling +44 (0)114 256 0123.
Industry Superstore (www.industrysuperstore.co.uk)
Industry Superstore is a one-stop-shop for a wealth of budget-friendly, high-quality products tailored to industry!
Further information is available from the Industry Superstore website (www.industrysuperstore.co.uk) or by calling +44 (0)1892 664499.
Exmac Automation Limited has many years experience in the design, manufacture, and installation of unit conveyors, conveyor systems and associated materials handling equipment for most industry sectors.
Exmac Automation is part of the MacDonald Humfrey group of companies and are market leaders in the supply of automated materials handling equipment to the automotive, aerospace, white goods, warehouse & distribution, nuclear, pharmaceutical and food & beverage industries.
The group supplies to most industry sectors and have over 250 employees with many years experience in the design, manufacture and installation of unit conveyors, conveyor systems and associated materials handling equipment.
Projects have ranged from individual standard conveyors and bespoke handling applications, through to complete turnkey contracts involving conceptual and process design, installation and commissioning.
We are ISO 9001 accredited and constantly strive to achieve continuous improvements in the overall quality of our products and service.
Exmac Automation has has established a reputation for supplying high quality, robust systems at competitive prices.
In-house resources enable us to provide clients with a single source for complete systems integration including simulation, engineering, machining, fabrication, assembly, controls, installation & commissioning and after sales service.
Our 70,000 sq ft facility in Worcester has extensive design, manufacturing and assembly resources. Our skilled team of customer focussed automation professionals offers a broad base of knowledge and experience in a wide variety of industries.
A large workshop enables us to carry out comprehensive pre-installation assembly and factory acceptance tests on all projects.
Fulton Limited (www.fulton.co.uk)
The Fulton name has been synonymous with steam since the company first introduced the vertical tubeless steam boiler in 1949 and Fulton was established in Bristol in 1966. Fulton is still one of the world’s leading manufacturers, producing an unrivalled range of multi-fuel steam boilers. But increasingly these are ordered by customers as part of bespoke turnkey systems designed to meet exacting specifications.
Today Fulton Limited is an important design and manufacturing base in Fulton’s global network that also includes production facilities in the USA and China. The company’s UK facility makes it possible to manufacture products more efficiently and assemble completed units for whenever and wherever they are needed throughout the UK and in export markets.
Once just a steam boiler manufacturer, Fulton now specialises in ready-to-ship skid mounted and fully packaged boiler plant rooms to meet the current demand for off-site fabrication. The company puts great emphasis in providing sales and application advice and a full commissioning and after sales service to a growing customer base in hospital and healthcare facilities, food and beverage processing, laundries and other applications.
Design and manufacturing resources are shared and coordinated around the world, but no matter where your product originates, it will always be produced to the highest quality in a facility that is wholly owned and managed by the Fulton Group, which remains a privately owned family business.
Fulton’s heating and hot water systems can be delivered as fully prefabricated plant rooms or complete skid-mounted units, built to fit a prepared location and connect direct to your services.
Using the latest CAD equipment its design team can accommodate the most sophisticated engineering specifications in surprisingly compact spaces, locating components in the best possible position to suit the installation.
In every sense, today’s Fulton boiler systems are solutions that fit the requirements of the modern age of steam.
Gast Group (www.gastmfg.com / www.jun-air.com)
Since 1921, Gast Manufacturing, Inc. has been designing and manufacturing quality air-moving products. Our vacuum pumps, compressors, air motors, gear motors, vacuum generators, regenerative blowers and Smart Air technology meet the many challenging applications of OEMs and end-users worldwide.
For industrial manufacturing, health care lab, or environmental cleanup applications, Gast provides a full range of ideally suited and cost-effective solutions to any pneumatic problem.
Monodraught (www.monodraught.com)
In the current climate of soaring energy prices and the fear of global warming, increasing attention is being focused on Monodraught’s range of energy-free products.
Monodraught has always sought to invent, explore and develop innovative technologies that harness the wind and sun. Products include Windcatchers, Sunpipes, Suncatchers, Sola-vents, Sola-boosts and Cool-phase.
Nexen Lift Trucks (www.nexenlifttrucks.com)
Disillusioned with the ever-increasing complexity of new forklift trucks and the failure of the major manufacturers to provide a high level of support to their dealer networks, the decision was taken to develop its own range of forklifts.
In 2003 Nexen Lift Trucks was established with the vision to design and manufacture its own range with a combined 70 years experience of the lift truck rental industry. Nexen's ultimate goal is to build worldwide brand recognition based on its product's design and build quality as well as outstanding reliability at competitive prices.
In 2007 Nexen completed the purchase of the second largest lift truck manufacturer in Taiwan, creating the Nexen Motor Corporation. Initially the existing models were improved whilst a European based design team was established to develop a completely new range of trucks from the ground up to meet Nexen's standards.
Q8Oils (www.Q8Oils.co.uk / @Q8OilsUK)
Q8Oils has become a major player in the global lubricants market. Our success is founded on significant corporate resources, a commitment to product development and uncompromising standards of quality and service.
Q8Oils has a unique and innovative approach producing some of the world´s finest quality lubricants. Manufactured in its state of the art plant at Leeds, West Yorkshire, Q8Oils represent the very best and latest in lubricant technology. With over 1000 grades of finished lubricants, base oils, process oils, extracts and waxes.
We are dedicated to serving the needs of our customers by striving to understand, anticipate and satisfy their needs faster and better than our competitors. To achieve this our objective is to develop and supply products and services which reflect customer demands in each of our market sectors.
TLV Euro Engineering (www.tlv.co.uk)
TLV Euro Engineering UK is part of TLV, an internationally-established designer, manufacturer and provider of steam traps, condensate recovery pumps, pressure reducing valves and other specialist steam solutions. The company plays a leading role in the promotion of efficient energy systems and increased environmental conservation on a worldwide scale through its products and consulting and engineering services.
Rockatek (www.rockatek.com)
Cheltenham-based Rockatek Ltd is an engineering consultancy that offers design, analysis and physical testing services that set it apart from others. Its directors have over 40 years’ experience in complex engineering product optimisation and development; and its engineers specialise in engineering solutions for harsh environments and value improving reliability and performance.
Verco (www.ver.co.uk)
Founded in 1965, Verco quickly built a reputation for supplying quality refrigerated glass door and open chill cabinets to supermarkets, convenience and forecourt stores. Verco is now a leading supplier of retail refrigeration and the largest UK manufacturer of glass door cabinets.
