Glenn Byrne

A constitutive equation of flow stress based on the Norton-Hoff equation has been developed for the high chromium and nitrogen containing super duplex stainless steel, ZERON® 100 (UNS S32760). This was then used to model, using the finite element method, the strain distribution within a uniaxial compression test under typical two-phase forging conditions. Predictions from the model were used to correlate deformation history to microstructure morphology. The microstructure consisted of austenite, γ islands (both primary and secondary) within a ferrite, δ matrix that contained chromium nitride precipitates. For deformation temperatures of 1050°C and 1120°C, the small secondary austenite was equiaxed, whilst at 1280°C the secondary austenite exhibited a Widmanstätten morphology. The highest level of nitride precipitation occurred at the highest deformation temperatures, i.e. highest volume fraction of ferrite, independent of strain rate. This suggests that nitride precipitation appears to be driven to a greater extent by thermal factors than deformation substructure.

The high resistance to corrosion of 22 Cr, 25 Cr and super duplex stainless steels in chloride containing environments is well known. In sour service, resistance to stress corrosion cracking, pitting and crevice corrosion in the presence of CO{sub 2} and H{sub 2}S is required. This paper presents the results of tests to determine the resistance of three duplex stainless steels to stress corrosion cracking, pitting and crevice corrosion at elevated temperature in a synthetic brine containing different concentrations of H{sub 2}S. The three alloys were UNS S31803, UNS S32550 (low Cu) and UNS S32760. All three materials were tested in the cold worked condition, and loaded to about the 0.2% proof stress. The tests were conducted with 93 bar (9.3 MPa) CO{sub 2} and either 0.125, 0.25 or 0.375 bar (12.5, 25 or 37.5 KPa) H{sub 2}S. The results showed that only the super duplex alloy, UNS S32760, was resistant to SCC at 80 C at all of the H{sub 2}S concentrations. Pitting and crevice corrosion occurred at 121 C only at the highest H{sub 2}S concentration on all the alloys. The depth and severity of attack varied from alloy to alloy and indicated that super duplex UNS S32760more » is more resistant than 25Cr, UNS S32550 (low Cu), which is more resistant than 22Cr UNS S31803.« less

There is an increasing use of CRAs (corrosion resistant alloys) for subsea flowlines. These pipes carry corrosive fluids at high temperatures and pressures, and insulation is usually, applied to prevent excessive cooling of the process fluids. The present tests were undertaken to investigate the effect of insulation defects on the susceptibility to localized corrosion of a super duplex stainless steel at different internal temperatures. Four different commercial coating systems were tested, Neoprene, EPDM, Polyurethane and Polyurethane foam. The results show that pitting occurred at an average temperature of 55 C for neoprene and EPDM, and at lower temperatures for the other two coatings. The reasons for this are discussed, and the implications for service applications.

Duplex and super duplex stainless steels are widely used by the Oil and Gas industry for handling slightly sour process fluids. These alloys have limits, beyond which sulfide stress corrosion cracking (SSCC) is likely. In NACE MR0175 the operating limits of alloys are usually defined by a maximum hardness and an H{sub 2}S limit. For one or two alloys another parameter may also be specified. The present paper has collected together a body of evidence, some of it previously unpublished, to show that the susceptibility to SSCC depends on a number of environmental variables, i.e. temperature, chloride, pH and H{sub 2}S, as well as several metallurgical variables e.g. microstructure and degree of cold work. The data for one alloy, a proprietary super duplex stainless steel, is used to show how these variables inter-relate, and where the alloy may be safely used. The results clearly show that NACE MR0175 is inadequate for specifying the limits of use of a duplex or super duplex stainless steel. The authors suggest that where an alloy is though likely to be useful and the conditions are outside the scope of MR0175, testing as specified in the European Federation of Corrosion document on CRA`s (Publication No.more » 17), should be carried out.« less

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.

The high resistance to corrosion of 22 Cr, 25 Cr and super duplex stainless steels in chloride containing environments is well known. In sour service, resistance to stress corrosion cracking, pitting and crevice corrosion in the presence of CO{sub 2} and H{sub 2}S is required. This paper presents the results of tests to determine the resistance of three duplex stainless steels to stress corrosion cracking, pitting and crevice corrosion at elevated temperature in a synthetic brine containing different concentrations of H{sub 2}S. The three alloys were UNS S31803, UNS S32550 (low Cu) and UNS S32760. All three materials were tested in the cold worked condition, and loaded to about the 0.2% proof stress. The tests were conducted with 93 bar (9.3 MPa) CO{sub 2} and either 0.125, 0.25 or 0.375 bar (12.5, 25 or 37.5 KPa) H{sub 2}S. The results showed that only the super duplex alloy, UNS S32760, was resistant to SCC at 80 C at all of the H{sub 2}S concentrations. Pitting and crevice corros...

High-alloy stainless steels, such as superduplex and 6% Mo, have been extensively used for seawater cooling systems and in reverse osmosis desalinaetion plants. Corrosion has been observed at flange faces that is not attributable to poor-quality material or excessively severe operating conditions. Various studies have investigated flange materials, while others have looked at different gasket materials. This article reviews the published data, presents some field experience, and recommends combinations to be avoided and the best choice of suitable gaskets.

There is an increasing use of CRAs (corrosion resistant alloys) for subsea flowlines. These pipes carry corrosive fluids at high temperatures and pressures, and insulation is usually, applied to prevent excessive cooling of the process fluids. The present tests were undertaken to investigate the effect of insulation defects on the susceptibility to localized corrosion of a super duplex stainless steel at different internal temperatures. Four different commercial coating systems were tested, Neoprene, EPDM, Polyurethane and Polyurethane foam. The results show that pitting occurred at an average temperature of 55 C for neoprene and EPDM, and at lower temperatures for the other two coatings. The reasons for this are discussed, and the implications for service applications.

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 1970s, 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.

The report presents the results for three alloys: carbon steel, 316L stainless steel and a proprietary super duplex stainless steel (UNS S32760), exposed in a marine mud off the south coast of England for 5 years. Analysis of the mud showed it to be very aggressive using a corrosion index developed at the University of Manchester. Carbon steel showed a typical corrosion rate for microbial attack with pits up to 0.64mm deep. The 316L stainless steel had extensive broad, shallow attack with a few, deeper pits. The Z100 parent pipe and weldments showed no evidence of corrosion attack.

INTRODUCTION The authors’ company has been heavily involved with the offshore oil and gas industry since the development of the North Sea oil and gas fields in the 1970’s. In particular there was a requirement for seawater injection pumps to maintain production rates. As the fields became larger and the pressures higher, austenitic stainless steel pumps became large and heavy and duplex stainless steels offered weight saving due to their higher strength. However, the 25Cr duplex stainless steels available in the 1970’s did not meet all the requirements in terms of strength and corrosion resistance. An alloy development programme resulted in a cast alloy named ZERON 100 (1), the first of the superduplex stainless steels1. This alloy became very successful for injection, seawater lift and firewater pumps and this created a demand for a wrought counterpart. The authors’ company developed production routes for all the commonly used wrought product forms (plates, pipes, forgings etc.) an...

The paper reviews the history of HISC failures of duplex and superduplex stainless steels when deployed subsea and subject to cathodic protection (CP) at potentials around -1V SCE. The test methods applied to investigate the problem and subsequently used to develop current design codes that deal with HISC are reviewed. Data from these investigations is compared with other testing using the same cast and batch of bar product, but where controlled shot peening is used to induce compressive residual stresses in the surface of the test samples. Parent pipe material and cross welded samples of seamless pipes were also tested. Peened material showed a 10 to 15% improvement in the threshold stress to initiate HISC. The paper also discussed the Advanced Forging Process (AFP) production route, recently developed to provide both increased notch toughness at low design temperatures and improved resistance to HISC in forgings used to make 10k weld neck and swivel ring flanges for subsea manifol...

Duplex and super duplex stainless steels are widely used by the Oil and Gas industry for handling slightly sour process fluids. These alloys have limits, beyond which sulfide stress corrosion cracking (SSCC) is likely. In NACE MR0175 the operating limits of alloys are usually defined by a maximum hardness and an H{sub 2}S limit. For one or two alloys another parameter may also be specified. The present paper has collected together a body of evidence, some of it previously unpublished, to show that the susceptibility to SSCC depends on a number of environmental variables, i.e. temperature, chloride, pH and H{sub 2}S, as well as several metallurgical variables e.g. microstructure and degree of cold work. The data for one alloy, a proprietary super duplex stainless steel, is used to show how these variables inter-relate, and where the alloy may be safely used. The results clearly show that NACE MR0175 is inadequate for specifying the limits of use of a duplex or super duplex stainless ...

Superduplex stainless steels have been used in seawater systems since 1986 as castings and since 1990 as wrought product. The performance has generally been excellent with few problems. However, seawater is a complex medium and, depending on the redox potential, stainless steels can adopt a wide range of potentials, spanning over a volt. Different methods of operation can lead to service potentials right across this range and the limits of use of superduplex stainless steel vary according to the potential. They cover the range from stagnant deaerated conditions, where the risk of microbially influenced corrosion is high, to chlorinated, flowing seawater, where the risk of crevice corrosion is high. The present paper describes some of the service environments commonly in use and the conditions that give rise to specific operating potentials. The limits of use under these conditions are described utilizing both laboratory and service experience. The results show the ability of superdu...

Duplex stainless steels are widely used by the oil and gas and chemical and process industries because of their combination of high strength and corrosion resistance. The alloys are usually used in the solution annealed condition and must be fast cooled from the annealing temperature to prevent the precipitation of third phases, such as sigma, chi, nitrides and alpha prime. Alpha prime precipitates in the temperature range 550 to 300°C. It forms less readily than sigma phase and other intermetallic precipitates and so is not normally found in commercially produced duplex alloys. However, poor cooling of duplex steels through this temperature range or repeated excursions in to this temperature range can result in its formation. Alpha prime dramatically reduces impact toughness and increases susceptibility to hydrogen induced stress corrosion cracking due to cathodic protection. However, corrosion resistance in chloride environments appears to be little affected by this phase. Alpha p...

The history and properties of Z100 superduplex stainless steel are discussed. The corrosion resistance in sulphuric acid is compared with some other common alloys. Four case histories are presented that show the use of Z100 over a range of acid concentrations and temperatures. Most of the applications have been both cost effective and successful. Such problems as have occurred have highlighted the importance of understanding the high influence of minor constituents in the environment in so far as their oxidising nature is concerned and working within the limits of the alloy.

The paper presents the properties of the author`s company`s proprietary super duplex stainless steel. Work is presented showing the development of a more realistic laboratory solution representing typical limestone slurries found in real flue gas desulfurization (FGD) systems. The importance of additions of metal ions such as Fe{sup 3+} and Mn{sup 2+} as well as partially oxidized sulfur species is demonstrated. Results are presented comparing the crevice corrosion resistance of super duplex stainless steel in these slurries with other commonly used wrought and cast stainless steels, for both simulated anthracite and lignite type slurries. Data from loop tests on the erosion resistance of a range of alloys in simulated FGD slurries is presented. The results clearly show the superior resistance of super duplex stainless steel to both crevice corrosion and erosion in FGD slurries. Finally the experiences in UK FGD systems with both cast and wrought super duplex stainless steel are pre...

Super Duplex Stainless Steels (SDSS) are utilised extensively by the oil and gas industry offshore, on fixed platforms, production vessels and subsea developments because they provide an excellent combination of; a) Strength, weldability, fracture toughness and structural integrity. b) Corrosion resistance in natural and chlorinated seawater. c) Corrosion resistance in CO2/ H2S/Cl process environments. d) Corrosion resistance in in marine atmospheres. e) They have high design strength, allowing weight savings through the construction of lower wall thickness, pipe work systems, process equipment and vessels. f) They are readily available in all cast and wrought product forms. g) They provide long life/minimum maintenance functionality to facilities that means that they are not normally manned and personnel are not exposed to the arduous offshore conditions. h) They provide lower level, cumulative, through life costs when compared with alternative material selection philosophies. As s...

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...

A constitutive equation of flow stress based on the Norton-Hoff equation has been developed for the high chromium and nitrogen containing super duplex stainless steel, ZERON® 100 (UNS S32760). This was then used to model, using the finite element method, the strain distribution within a uniaxial compression test under typical two-phase forging conditions. Predictions from the model were used to correlate deformation history to microstructure morphology. The microstructure consisted of austenite, γ islands (both primary and secondary) within a ferrite, δ matrix that contained chromium nitride precipitates. For deformation temperatures of 1050°C and 1120°C, the small secondary austenite was equiaxed, whilst at 1280°C the secondary austenite exhibited a Widmanstätten morphology. The highest level of nitride precipitation occurred at the highest deformation temperatures, i.e. highest volume fraction of ferrite, independent of strain rate. This suggests that nitride precipitation appears to be driven to a greater extent by thermal factors than deformation substructure.

The history and properties of Z100 superduplex stainless steel are discussed. The corrosion resistance in sulphuric acid is compared with some other common alloys. Four case histories are presented that show the use of Z100 over a range of acid concentrations and temperatures. Most of the applications have been both cost effective and successful. Such problems as have occurred have highlighted the importance of understanding the high influence of minor constituents in the environment in so far as their oxidising nature is concerned and working within the limits of the alloy.

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 n...