Oil & Gas treatment and petroleum refining involve aggressive environments containing aqueous hydrogen sulfide (H2S). Carbon-manganese steels used in these industrial sectors may be susceptible to various kinds of cracking phenomena namely Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC) and Stress Oriented Hydrogen Induced Cracking (SOHIC). The HIC risk can be avoided by a strict control of the chemical composition of the steel (sulfur, phosphorus, oxygen) associated to a specially-adapted production route. SSC can be limited by a careful control of the hardness level of both the parent material and the heat affected zone as well as a low impurity level and appropriate PWHT. SOHIC is a critical problem in the Oil & Gas industry since it has been involved in many in-service failures. This phenomenon can be described as a combination of both SSC and HIC. Previous studies have shown that the measures taken to counter HIC and SSC are not sufficient to protect carbon-manganese steels against SOHIC. The SOHIC susceptibility of SA516 Grade 70 carbon-manganese steel was studied according to NACE MR0175/ISO15156-2 standard by means of the four-point-bending and constant load test methods. Both base metal and welded specimens were investigated. The results show that the microstructure also plays an important role and that only quenched and tempered steels with appropriate PWHT can offer SOHIC resistance when combined with an optimized chemical composition and steel fabrication route.

Changes in energy situation around the worldwide oil crises have brought about an increase in demand for Liquefied Natural Gas (LNG) which is a promising alternative energy source, providing for lower CO2 emissions than coal and petroleum with a huge geographical resource base. The onset of shale gas production, the consideration of LNG as a ship engine fuel and the expansion of the petrochemical industry are other drivers of demand for similar infrastructure. The structural materials used for cryogenic tanks and vessels are tailored to combine high strength to minimize wall thickness, with good fracture toughness to prevent catastrophic failure at cryogenic temperatures. The cryogenic structural 9% nickel steel grade has been largely used as a main material of the inner walls of LNG tanks and LNG transportation vessels for more than 50 years thanks to its excellent properties at very low temperature. Industeel has developed a premium experience in the metallurgy of this material to supply excellent as-delivered quenched and tempered steel specifically designed to be user-friendly in terms of forming and weldability, as well as to provide for the safest in-use properties. With that extensive know-how, Industeel has developed new alternative solutions to further cater for the evolving demand, aiming towards safe and economical construction materials. This paper reports the research and development results on 7% nickel quenched and tempered steel, now introduced in ASTM Standard A553/A553M as Type III and adopted by ASME in Code Case N°2842 to provide for rules of construction . At the time of writing it is under ballot for incorporation into API 620 Appendix Q and will be considered for naval classes. 7% nickel steel plates provide an excellent level of strength, toughness properties and a very good ability to arrest brittle cracks at very low temperatures, equivalent to those of 9% nickel. The developed 7% nickel steel, branded CryElsoTM 7 is more economical, and the reduction of nickel content also significantly contributes to save natural resources. 7% nickel steel is intended to be used for the construction of storage tanks for LNG, ethylene, ethane and other liquefied hydrocarbons, as well as for their transportation vessels and piping.

Wet hydrogen sulfide cracking of pressure vessel steels has been a major concern in petroleum refining as well as in the oil and gas industry since the 1950's. Nowadays, more and more H2S-containing oil and gas fields are exploited. Hydrogen sulfide is responsible for numerous corrosion phenomena in steels, such as Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC), and Stress Oriented Hydrogen Induced Cracking (SOHIC). During the last 30 years, pressure vessel steels with improved SSC, and furthermore HIC, resistance have been developed to resist H2S-induced degradation in upstream and downstream equipment. More recently, attention has been particularly directed on Stress Oriented Hydrogen Induced Cracking experiences in wet H2S operations. This paper reports the new results obtained on both normalized and quenched and tempered C-Mn pressure vessel and pipe plate steels. SOHIC resistance has been evaluated according to the requirements of NACE MR0175 / ISO 15156 Annex B.4. Results show that only quenched and tempered steels can offer optimized SOHIC resistance thanks to the fine bainitic microstructure provided by the use of adapted heat treatments combined with optimized chemical composition and steel fabrication route.

During fabrication of large pressure vessels, thick plates are submitted to numerous process phases that may affect the initial (i.e. as delivered) properties of the material. Regarding the advantages (both technical and economical) of cold forming process, this technique is largely preferred and widely spread.Modern forming presses and rollers are now sufficiently powerful to roll very thick plates (typically up to 250mm thick) devoted to ultra-heavy pressure equipments. As force does not really constitute a limitation anymore, current limitations are now focusing on maximum admissible strain in materials. This particular limit is linked toIntrinsic maximum deformation admissible by the material (given by tensile tests),Regulation rules coming from construction codes.From a practical point of view, the actual limitation comes from the construction codes that are very severe.Main codes (ASME Boilers and Pressure Vessels Construction Code from American side and EN 13445 Unfired Pressure Vessels Construction Code from European side) both give a limit equal to 5% strain for using material in "as-strained" condition without any heat treatment. Above this limit, the philosophy differs from one code to another.While European Code requires a full quality treatment of the strained material (Normalisation or Austenitization / Tempering), American code only requires Tempering, allowing fabricators the possibility of using the mandatory Post Weld Heat Treatment (PWHT) (needed by welded zones) as a tempering treatment to improve welded zone toughness and to regenerate material properties.The purpose of this contribution is to review the effect of pre-strain on mechanical properties (Hardness, Tensile and Toughness transition curves) for different strain levels and to evaluate the ability of typical PWHT to regenerate material properties. Results presented in this paper are based on both recent studies on the most common up-to-date materials as well as on historical data collected in the last decades.This study clearly demonstrates that the required PWHT is efficient enough to regenerate all Material properties and that there is no need to apply a full quality heat treatment, even for the highest level of strain. This benefits both the fabricator and the end user as it implies reducing costs and risks of components deformation while maintaining the necessary level of service properties.

For some years, conventional 2¼Cr1Mo grade is less and less used for the fabrication of heavy refining reactors and is progressively replaced by 2¼Cr1MoV grade which offers much better mechanical properties at high temperatures. This change also offers large benefits on hydrogen resistance due to large differences in hydrogen solubility, diffusion and trapping behaviour between the two grades. Focusing more deeply on differences between the two previously cited grades, it appears that 2¼Cr1MoV offers an important gain in terms of hydrogen resistance but has also a very complex behaviour, strongly depending on charging method used to introduce hydrogen in material. Trapping and diffusion behaviours are particularly different when hydrogen is introduced using autoclave charging (gaseous hydrogen as in refining industry), using sour service environment (aqueous hydrogen sulphide as in gas treatment industry) or using cathodic charging. This paper proposes to explain the differences between the two previously cited grades when facing gaseous and aqueous hydrogen and then the consequences on fracture performance. This demonstration is based on actual hydrogen diffusion and solubility laws measurements associated to different kinds of mechanical tests.

Standard and Vanadium-alloyed 2,25Cr-1Mo steel grades (EN 10028-2 12CrMo9-10/ASTM A387 gr. 22 and 13CrMoV9-10/ASTM A542 tp. D) are commonly used for the fabrication of heavy pressure vessels for applications in petroleum refining plants.These reactors are made of heavy plates, forged shells, forged nozzles and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high temperatures and high hydrogen partial pressures). A primary concern for end-users is the definition of the Minimum Pressurizing Temperature (MPT) of the equipment. This temperature is the lowest temperature at which the vessel can be repressurized after shutdown and insures no risk of brittle failure of the containment body. The MPT is defined by fracture mechanics and/or CVN approaches and calculations.This second part of the paper presents the methodology of MPT determination and the particular case of vintage reactors. MPT determination methodology is explained by using a virtual pressure vessel representative of vessels found in petroleum refineries. A special focus is also set on the evolution of embedded defects. (C) 2013 Elsevier Ltd. All rights reserved.

Standard and Vanadium-alloyed 2,25Cr-1Mo steel grades (EN 10028-2 12CrMo9-10/ASTM A387 gr. 22 and 13CrMoV9-10/ASTM A542 tp. D) are commonly used for the fabrication of heavy pressure vessels for applications in petroleum refining plants.These reactors are made of heavy plates, forged shells, forged nozzles and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high temperatures and high hydrogen partial pressures). A primary concern for end-users is the definition of the Minimum Pressurizing Temperature (MPT) of the equipment. This temperature is the lowest temperature at which the vessel can be repressurized after shutdown and insures no risk of brittle failure of the containment body. The MPT is defined by fracture mechanics and/or CVN approaches and calculations.This first part of the paper presents the impact of thermal aging and exposure to hydrogen on materials' mechanical properties and consequently on the value of MPT. (C) 2013 Elsevier Ltd. All rights reserved.

The overall efficiency of refining reactors is strongly linked to process parameters, i.e. service temperatures and pressures. For years, low alloyed ferritic materials - 2,25Cr1Mo and 2,25Cr1MoV steel grades mainly - are used to build heavy processing reactors, thanks to their good mechanical properties at high temperatures and under high hydrogen partial pressures. In particular, their good resistance to High Temperature Hydrogen Attack is of major interest for end-users. Depending on the grades, the ASME(1) Code gives limitations in terms of maximum allowable temperature that can limit the use of these low alloys in the case of advanced processes. Moreover, when these grades are allowed and above a given temperature, maximum allowable stresses are driven by time dependent mechanical properties (i.e. by their creep behaviour), leading to a strong reduction of the considered resistance and then to extra-thickness and weight when considering the vessels. Many developments have been done in the last decades to increase the efficiency of petrochemical/refining processes. In particular, this can lead to increase service temperatures and therefore the actual pressure vessel wall temperatures. Indeed, more and more temperatures around 500-510 °C are likely to be used, leading to a much reduced choice in terms of permitted steel grades. Regarding 2,25Cr low alloy family, the vanadium enhanced grade is not allowed whereas the usual grade has reduced creep allowable stresses. With a view to allowing strong improvements in admissible process parameters, Industeel1 developed a V-modified 9Cr1Mo Creep Strength enhanced material with advanced hydrogen resistance and improved toughness. Very thick plates (up to 200 mm thick) were produced and tested. This contribution reports both mechanical and metallurgical assessments performed on these heavy plates. Evaluation of hydrogen resistance (HTHA) as well as creep resistance under high hydrogen pressure is also reported.

Over the last few years, conventional 2,25Cr1Mo grade has been increasingly replaced by 2,25Cr1MoV grade for the fabrication of heavy refining reactors, offering better mechanical properties at high temperatures. This change also improves Hydrogen Induced Disbonding (HID) resistance due to large differences in hydrogen solubility and diffusion behavior between the two grades. The hydrogen trapping ability of 2,25Cr1MoV is also an important parameter to take into consideration. This paper proposes to explain the differences between the two previously cited grades when facing gaseous hydrogen and then the consequences on HID performance. This demonstration is based both on actual hydrogen diffusion and solubility laws measurements, hydrogen content profile simulations and actual HID tests to validate the conclusions. Disbonding tests are very often required during fabrication of hydro-treating vessels. This qualification test permits to assess the quality of the stainless steel overlay deposit procedure. As it is difficult to make the link between the testing conditions and the actual service conditions in the reactor wall, studies based on 2,25Cr1Mo grade were performed in the past and transferred into API 934-A1 recommended practice to better fit the test parameters to severity of actual field conditions and then avoid excessive safety.

The efficiency of petrochemical reactors is intimately related to process parameters, i.e. service temperatures and pressures. Low alloyed ferritic materials, such as 21/4Cr1Mo(V) and 3Cr1Mo(V) steel grades, are widely used for many years to build heavy wall reactors. This is mainly due to their good mechanical properties at high temperatures under high hydrogen partial pressures and good resistance to High Temperature Hydrogen Attack (HTHA). Depending on the grades, the ASME Code gives limitations in terms of maximum temperature that can limit the use of these low alloy grades. Moreover, above a given temperature, maximum allowable stresses are driven by the creep behaviour, leading to a strong lowering of the assumed resistance and hence to extra-thickness and weight.Many developments were done concurrently to increase the efficiency of petrochemical processes. In particular, this can lead to increase service temperatures and therefore actual pressure vessel wall temperatures. Indeed, more and more temperatures around 500 degrees C are likely to be used, leading to reduced choice in terms of permitted steel grades. The low alloy vanadium-enhanced grades are not allowed (except using specific code case) whereas the usual grades have reduced creep allowable stresses. With a view to allowing strong improvements in admissible process parameters, a vanadium-modified 9Cr1Mo creep strength enhanced material with advanced hydrogen resistance and improved toughness was developed. Very thick plates (up to 200mm thick) were produced and tested.This contribution reports both mechanical and metallurgical assessments performed on these heavy plates. Evaluations of hydrogen resistance (HTHA) as well as creep resistance under high hydrogen pressure are also reported.The V-modified 9Cr1Mo grade exhibits an excellent behaviour in hydrogen rich environment, showing therefore some advantages in terms of service conditions. The manufacturing of heavy plates has made significant progress in the recent years, allowing thick products to be manufactured with good homogeneity and mechanical behaviour. Taking into account the maximum use temperature as well as the allowable stresses as described in the ASME BPV Code section VIII division 2([1,2]), the V-modified 9Cr1Mo grade will

During fabrication of Pressure Vessels, steels undergo several heat treatments that aim to confer the required properties on the entire equipment, including welds and base metal. Indeed, the production heat treatment of the base material, which leads to achieve the target properties, is most of the time followed by post weld heat treatment (PWHT). The aim of such treatments is to insure a good behavior of the welded zones in terms of residual stresses and obviously properties such as toughness. Generally, many simulated PWHT (up to 4 or more) are required for the testing of the base material, which can affect its properties and even lead to unacceptable results. In some cases for fabrication purposes an intermediate Stress relieving treatment can be required. Special attention is paid on C-Mn steels (e.g., SA/A516 from ASME BPV Code) with the effect of thickness and Ceq (International Institute of Welding Carbon equivalent formula: see page 3) requirements on the final compromise between properties and heat treatments. In particular, toughness and ultimate tensile strength (UTS) are the critical parameters that will limit the acceptance of too high PWHT. Although micro-alloying is a mean to increase the resistance to PWHT, this leads to difficulties in softening the heat affected zones. This solution is therefore not the best one considering the whole equipment optimization. Finally, the manufacturing process can play a major role when specifications are stringent. Quenching and tempering (Q&T) can indeed provide better flexibility in terms of PWHT and improved toughness for given Ceq and thickness. The case of Cr-Mo(-V) steels, which are widely used in the energy industry, is also addressed. Indeed, PWHT requirements for increasing the toughness in the weld metal can lead to decrease the base metal properties below the specification limits. For example, the case of SA/A387gr11 is very typical of metallurgical changes that can occur during these high PWHT leading to a degradation of toughness in the base metal. Another focus is made on the Vanadium Cr-Mo grade SA/A542D that must withstand very high PWHT (705 °C and even 710 °C) because of welds toughness issues. Optimization has therefore to be done to increase the resistance to softening and to guarantee acceptable microstructure, especially in the case of thick wall vessels. Some ways for improvement are proposed on the basis of the equivalent Larson–Miller parameter (LMP) tempering parameter concept. The basic philosophy is to fulfil the need for discussion between companies involved in pressure vessels fabrication so that the best compromise can be found to ensure the best and safest behavior of the equipment as a whole. In particular, the tempering operation can sometimes be done at lower temperature than PWHT in order to offer the best properties to the final vessel.

To face the future challenge of global energy supply, taking into account the depletion of fossil fuels and global warming issues, the main nuclear energy users are strongly involved in a research program to fourth-generation reactor technology. This new generation will work at high temperatures between about 450 °C and 550 °C. Extensive studies have been launched worldwide to assess steel grades able to meet these new operating conditions. One of the candidates is Vanadium enhanced 9% Chromium steel grade (EN 10028-2 X11CrMoVNb 9-1 – ASTM A387 grade 91 class 2 – ASME SA387 grade 91 class 2). To meet the future needs in nuclear energy, Industeel improved its conventional 9Cr1MoVNb steel devoted to the fabrication of steam lines in thermal power plants. Preliminary studies revealed the feasibility of thick plates in this enhanced grade. Thick plates, 140 and 210 mm thick, have been hot rolled from a 82 metric tons ingot. Welded joints have then been prepared. Tests performed on both base metal and welded zones proved the excellent mechanical properties of the grade, especially regarding toughness property. This work demonstrated the industrial feasibility of very thick plates made of grade 91 for nuclear applications. This contribution is a review of the work done as well as the results obtained on the plates.

Material properties assessment at given temperature and thickness is of primary importance for steelmakers. Generally, a list of mechanical properties requirements, namely tensile, Charpy V-Notch (CVN), fracture mechanics, as well as chemical or heat treatments limits are furnished by customers. Subsequently, the best compromise has to be found by the steel producer in order to reach these requirements. Concerning tensile and CVN properties, experience is large and metallurgists are used to determine the best product optimizations so as to reach the requirements' values.However, optimization is generally more complicated regarding fracture mechanics. Tools are therefore needed in order to evaluate these properties with reference to conventional (i.e. tensile and CVN) properties.The objective of the present paper is to present some rules that can be used to extrapolate Crack Tip Opening Displacement (CTOD) values from CVN and tensile properties. Recent example is given to illustrate this methodology. In addition, special attention will be paid to the comparison of estimated and measured CTOD values.

Standard and Vanadium enhanced 2.25Cr1Mo plate steels (ASTM A387 gr. 22 and A542 type D) are commonly used for the manufacturing of heavy reactors for use in petroleum refining plants. These reactors are fabricated from heavy wall plates, forged shells (thickness up to 300-350mm), forged nozzles and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high pressure, high hydrogen partial pressure). A primary concern for end-users is defining the Minimum Pressurizing Temperature (MPT). This temperature is the lowest temperature at which the vessel can be repressurized after shutdown. This minimum temperature insures no risk of brittle fracture, and is defined by fracture mechanics and/or CVN approaches and calculation. This paper presents the methodology of MPT determination and the impact of ageing and exposure to hydrogen on material mechanical properties and on the value of the MPT. The MPT determination method is explained by using a virtual pressure vessel that is representative of reactor vessels found in petroleum refineries.

Processing equipment for oil and gas treatments is often exposed to the sour environments containing wet hydrogen sulfide (H2S), which is a naturally occurring component of crude oil and natural gas. A large part of this equipment is fabricated in Carbon-Manganese steels, which could be sensitive to wet H2S cracking. Hydrogen sulfide is responsible for numerous embrittlement phenomena in steels, such as Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC), and Stress Oriented Hydrogen Induced Cracking (SOHIC). Some parameters influence Carbon-Manganese steels behavior in sour service conditions, where wet H2S cracking mechanisms can operate. This paper provides recent experiences and HIC, SSC, SOHIC results on sour service resistant steel plates for pressure vessel construction. The effects of chemical composition, steel fabrication, heat treatments and steel plate’s thickness on cracking resistance in sour service environments containing wet hydrogen sulfide are analyzed. Optimized solutions for wet H2S service resistant steels are suggested.

Standard and Vanadium enhanced 2.25Cr1Mo plate steels (ASTM A387 gr. 22 and A542 type D) are generally used in high-temperature and high-pressure hydrogen environments. In such environments, significant quantities of hydrogen are soluble in the steel. The influence of hydrogen on mechanical properties during a shut–down operation and on creep properties has been considered. Mechanical property testing of steels exposed to the above stated environments was conducted in order to determine the effect of hydrogen. Tensile, Charpy V-Notch CVN, and fracture toughness values were determined after exposure to high pressure hydrogen at high temperatures, for base metal, heat-affected zone (HAZ), and weld metal specimens.

Stress corrosion cracking (SCC) sensitivity of the girth welds of supermartensitic stainless steels (SMSS) tubes seems closely linked to the thermal history encountered by the heat affected zones and chemical composition. The aim of the work presented in this paper was to investigate the influences of welding parameters (welding process, cooling rate …), chemical composition of the base plate and environment on the SCC sensitivity. Results of four point bend tests performed on plate with weld beads in simulated formation water with and without H2S are presented and discussed. It appears that the SCC mechanism is enhanced by a decrease in the pH value, an increase in the temperature and/or the presence of H2S. On the contrary a decrease of the cooling rate (high welding heat input) used for the last deposited bead or an increase of the chromium and molybdenum concentrations improves the SCC resistance. This study, supported by the European Community, was developed to improve the understanding of this new corrosion mechanism and to propose solution for the safer use of SMSS in oil and gas applications.