Duplex stainless steels were first manufactured early in the 20th century, but it was the introduction in the 1970s of the argon-oxygen decarburisation (AOD) steel making process and the addition of nitrogen to these steels, that made the alloys stronger, more weldable and more corrosion resistant. Today, duplex stainless steels can be categorised into four main groups, i.e., “lean”, “standard”, “super”, and “hyper” duplex types. These groups cover a range of compositions and properties, but they all have in common a microstructure consisting of roughly equal proportions of austenite and ferrite, high strength, good toughness and good corrosion resistance, especially to stress corrosion cracking (SCC) compared with similar austenitic stainless steels. Moreover, the development of a duplex stainless-steel microstructure requires lower levels of nickel in the composition than for a corresponding austenitic stainless steel with comparable pitting and crevice corrosion resistance, hence they cost less. This makes duplex stainless steels a very versatile and attractive group of alloys both commercially and technically. There are applications where duplex grades can be used as lower cost through-life options, in preference to coated carbon steels, a range of other stainless steels, and in some cases nickel alloys. This cost benefit is further emphasised if the design engineer can use the higher strength of duplex grades to construct vessels and pipework of lower wall thickness than would be the case if an austenitic grade or nickel alloy was being used. Hence, we find duplex stainless steels are widely used in many industries. In this paper their use in three industrial applications is reviewed, namely marine, heat exchangers, and the chemical and process industries. The corrosion resistance in the relevant fluids is discussed and some case histories highlight both successes and potential problems with duplex alloys in these industries. The paper shows how duplex stainless steels can provide cost-effective solutions in corrosive environments, and why they will be a standard corrosion resistant alloy (CRA) for many industries through the 21st century.
Groundwater dependent ecosystems (GDEs) require access to groundwater to meet all or some of their water requirements to maintain community structure and function. The increasing demand of surface and groundwater resources has seen the NSW Government put in place management mechanisms to enable the sharing of water between irrigators, the environment, industry, towns and communities via water sharing plans. The groundwater sharing plans aim to provide adaptive management of GDEs by prioritising for protection those that are considered the most ecologically valuable within each plan area. The High Ecological Value Aquatic Ecosystems (HEVAE) framework has already been adopted to prioritise riverine ecosystems for management in surface water sharing plans. Here, we provide a method developed using the HEVAE framework to prioritise vegetation GDEs for management. The GDE HEVAE methods provide a derived ecological value dataset for identified groundwater dependent vegetation that is used to inform the planning and policy decisions in NSW. These decisions are required to manage and mitigate current and future risks caused by groundwater extraction. This is achieved via the identification of ecologically valuable assets to then use as the consequence component in a risk assessment for the groundwater sources, to provide vegetation GDE locations for setback distances for new groundwater production bores, and for the assessment of impacts due to current and potential future groundwater extraction. The GDE HEVAE method uses recorded and predicted spatial data to provide weighted scores for each attribute associated with the four HEVAE criteria (distinctiveness, diversity, vital habitat and naturalness). The combined scores categorise the ecological value of each groundwater dependent vegetation community (depicted as geographic information system (GIS) polygon features) from very high to very low. We apply the GDE HEVAE method to three catchments in order to demonstrate the method’s applicability across the Murray–Darling Basin with varying elevation and climate characteristics. The ecological value outcomes derived from the methods have been used to inform planning and policy decisions by NSW Government processes to allow for protection in not only areas that are currently at risk but to also manage for potential future risks from groundwater extraction.
Austenitic cast iron has been used for many years for pump cases, column pipes and valves in seawater systems, particularly in the Middle East. Since the 1970’s failures have occurred by stress corrosion cracking, and there have been a number of research efforts to understand the problem and suggest means of preventing it. Cracking failures have continued and further research has been undertaken to try and understand the problem more thoroughly. This paper reviews the data from the early research, and presents the results of previously unpublished work, and its implications for the further use of austenitic cast iron in seawater, and alternative alloys.
As oil wells become deeper and run at higher temperatures and pressures, there becomes a need for high strength, corrosion resistant material that will withstand the more severe service conditions of these projects. Over the years many projects in various locations around the world have successfully used duplex and super duplex stainless steels for subsea pipe lines, flow loops, flow lines and manifolds to contain the high temperatures and pressures and more demanding corrosive service required with the High Temperature High Pressure (HTHP) wells. Additionally, operators have realized that they need to qualify the manufacturers of these materials following a number of problems experienced in the field. They see that the more severe conditions require a higher level of quality and security to go with the more demanding performance required. As such, the NORSOK M650 specification is seen as way to qualify the manufacturer and ensure a higher level of quality in the product. This has not solved all problems and a few operators are placing even greater demands on manufacturers to ensure they have the required metallurgical understanding and production facilities to produce parts in these more complicated alloys. There is also a recent development for super duplex stainless steels to meet service conditions beyond usual requirements. A number of operators have projects where minimum design temperatures are calculated to be as low as −70°C, which is near the lower shelf toughness level for duplex stainless steels. This paper discusses the properties that can be achieved by optimizing the forging route and therefore minimizing nitride precipitation in these alloys. The resultant properties are sufficient to meet the impact properties typically required at temperatures down to −70°C. In addition, the improved ductility and toughness also increase the resistance to HISCC due to cathodic protection. Several end users and OEM's have already used ZERON® 100 AFPTM to benefit from the improved toughness at design temperatures as low as −70°C. This paper will cover the metallurgy of duplex alloys and how improved understanding and processing can lead to less nitride precipitation, better morphology and austenite spacing that will have a beneficial effect on both toughness and HISCC resistance. The improved toughness values can also be seen across the full temperature range of most Oil & Gas projects with excellent properties at −50°C as well as at −70°C. Discussion of a few case histories also confirms the need for application of this Advanced Forging Process (AFP) of super duplex stainless steel.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.