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Duplex Usage in the Oil and Gas Industry

Introduction:

Over the past few decades, corrosive conditions in the Oil and Gas Industry have steadily grown in severity. The offshore oil industry continually pushes oil exploration to greater depths, which leads to higher pressure conditions and harsher environments. In addition, advanced technologies have enabled higher total production from domestic reservoirs, which in turn has increased both the life span of underground wells and the concentration of corrosive agents in those wells. As a field ages, the ratio of water to oil in the fluids produced increases to levels of 95% or even higheri. In order to adapt to these difficult environments, and also in order to safe guard against the high cost of component failure, it has become critical to ensure that the right alloys are chosen for applications within the oil and gas industry. This has created an excellent opportunity for Duplex 2205 and other duplex stainless steels.

Duplex stainless was first introduced to the Oil and Gas industry in the late 1970’s when it was selected for natural gas pipelines. At the time, this selection choice provided a critical commercial breakthrough for Duplex 2205 (UNS S32305/S31803). It helped pave the way for Duplex 2205 acceptance into not only the Oil and Gas industry, but also into many other industries as well. Now, more than 30 years later, Duplex 2205, lean duplexes, super duplexes and hyper duplexes all play an increasing role in both the onshore and the offshore oil and gas industries.

Oil and Gas Production:

Oil and gas production processes vary somewhat based on the environment, but the high level steps have remained relatively constant over time. Oil is found in reservoirs deep under the ocean or underground, and is extracted along with mixed gases and water using small diameter, high pressure tubing. Once the oil mixture reaches the surface, it goes through a well head, and then is typically fed through larger diameter, lower pressure, lateral piping until it reaches a separator vessel. In the separator vessel, the gases rise to the top, the water flows to the bottom, and the oils separate out in the middle. The gas is typically re-injected back into the reservoir, refined and marketed, or flared. The water is injected back into the reservoir. The oil is then sent to a pipeline for delivery to a refinery, tanker terminal, or transmission piping system.i

Benefits of Duplex 2205 and other Duplex Stainless Steels:

There are two significant benefits of duplex steel that make this material so attractive to the Oil and Gas Industry. First, it has excellent resistance to the various corrosive media that are typically found in both onshore and offshore environments. These mainly include CO2, H2S gases, chlorides, low ph conditions, and water. Duplex steel’s high resistance to chloride-induced stress corrosion cracking is of particular importance here. Secondly, its high strength is extremely beneficial in dealing with the high pressures encountered at great depths.

Duplex steels can also offer some material cost advantages as compared to alternative choices, but upfront cost is not usually a primary driver, especially for undersea extractions. The high cost of failure in oil fields of great depths makes it imperative that the best material for the job is selected upfront. Thus, it is critical that all cost calculations include lifetime maintenance and potential cost risks due to failures in order to truly evaluate costs when selecting materials.

Duplex Applications:

Duplex 2205 and other duplex grades are increasingly the material of choice for process piping systems, separators, scrubbers, pumps, manifolds, X-mas tree components, flowlines and pipelines transporting corrosive oils and gas. In cases were resistance to design stress is important, super and hyper duplex grades are preferred. Duplex grades have become standard in the inner tubing of flexible pipe, and in umbilicals. Not only do the duplex grades protect against corrosion, but they are capable of supporting their own weights in deep waterii.

Duplex 2205 Case Studies:

Duplex 2205 has been utilized in numerous applications within the oil and gas industry over the years. Here is one fairly recent example.

Duplex 2205: Petroleum Development Oman implemented Duplex 2205 stainless steel pipes for a natural gas flow line at the Burhan West field in Oman in 2007. Duplex 2205 was selected due to its high strength and corrosion resistance properties. Duplex 2205 typically performs well in environments that include the presence of carbon dioxide in the wet-gas stream. Also, it was selected due to material availability at the time.

The Burhan West Field pipeline is thirty-six kilometers long and passes through desert and wadis. The Duplex 2205 pipe diameters were specified at 8 and 14 inches for the outer dimension. They are designed to facilitate evacuation of a mixture of wet gas and condensate at the rate of 1.5 to 4 million cubic meters per day.iii

Super and Hyper Duplex Case Studies:

Super and Hyper Duplexes are gaining in popularity in the oil and gas industry, and are particularly useful in cases where resistance to design stress is important. There are many grades that have been designed for this purpose, including SAF2906 (UNS S32906), 3207HD (UNS 33207), and Super Duplex 2507 (UNS32750).

Super Duplex 2507: Petro Canada recently implemented Super Duplex 2507 piping, along with Duplex 2205 code plus two®, in their oil field development off the coast of Newfoundland, Canada in order to combat saltwater corrosion with existing pipingiv. Super Duplex 2507 is a high alloy super-duplex steel for service in extremely corrosive conditions. Developed mainly for applications exposed to high stresses in chloride-containing environments like seawater, it contains high amounts of chromium, molybdenum, and nickel. It has high tensile strength, high impact strength, low thermal expansion, high conductivity, excellent stress corrosion cracking resistance, and high pitting resistancev.

Lean Duplex Case Studies:

Whereas the hyper and super duplex stainless steels are being utilized in areas that require advanced properties as compared to Duplex 2205, lean duplexes offer an opportunity for cost reduction when Duplex 2205 is overkill for an application. Also, lean duplexes have good weldability, which is very advantageous in the construction of flexible pipeline and umbilical tubing.iv Here are some case studies for lean duplexes LDX 2101 (UNS S32101) and AL2003™ (UNS S32003):

LDX2101: Technip utilized LDX 2101 for Total’s Dalia deepwater project off Angola. Also, RathGibson utilized LDX2101 in the construction of zinc-coated umbilical tubes.iv Lean duplex 2101, which is more corrosive resistant than 304, has double the yield strength and can provide significant savings in both cost and weight.

AL2003®: In 2007, lean duplex AL2003 was successfully used for the first time in unbounded flexible pipe. It was utilized by Murphy Oil in an oil field offshore of Sabah, Malaysia, referred to as the Kikeh Field. Unbonded flexible pipe is frequently used throughout the world to transport produce fluids from oil and gas fields under the ocean. These pipes typically consists of polymer and carbon steel materials that are extruded and heliacally wound around an inner stainless steel carcass. Duplex 2205 and austenitic steels have both been in use for the flexible pipe carcass for many years.

Flexible piping absolutely needs good corrosion performance. In addition, for deep oil fields, high strength is another critical component. As pipe stress levels increase, larger cross sectional areas are required, further increasing the weight. The Kikeh field at 1400m was effectively too deep to even consider 316L usage for the piping. Various tests were run to evaluate collapse resistance, erosion resistance, strength, corrosion resistance based on the expected environment, and fatigue resistance. Based on these tests, it was determined that AL2003 met or exceeded 316L in all qualification testing and is considered an improved alternative to 316L carcass in unbounded flexible pipe. AL2003 was also tested against Duplex 2205. While Duplex 2205 outperformed AL2003 in many areas, the results were such that this grade was considered satisfactory for the Kikeh environment. AL2003 offers a nice cost benefit over Duplex 2205 and is considered ideal for the high pressure demands of offshore piping systems that transport sweet to moderately sour oil and gas.vi

References:

  1. Appendix S – “Oil and Gas Exploration and Production.” www.corrisioncost.com. CC Technologies Laboratories. Web.
  2. Chater, James. “The Last Frontier: The Hunt for Deap Sea Oil and Gas.” www.stainless-steel-world.net. Stainless Steel World, June 2008. Web.
  3. “Duplex 2205 Stainless Steel Pipes | Outokumpu.” Stainless Steel for Industrial Use in Architecture, Building, Construction, Transportation, Chemical, Energy, Catering and Process Industry. | Outokumpu. Outokumpu. Web
  4. Chater, James. “Mount Everest in the Sea.” www.stainless-steel-world.net. June 2007. Web.
  5. “Case Study: Offshore Oil Field Development.” www.outokumpu.com. Outokumpu. Web.
  6. Dunn, John, David Hasek, Angus Cameron, and Richard Clements. “AL2003 Lean Duplex Case Study: Flexbile Flowlines for an Offshore Oil Field Development” www.stainless Steel World. KCI Publishing, 8 Nov. 2007. Web.

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Duplex Usage in the Oil and Gas Industry