9%Ni (as per ASME SA553 type I) is the reference material for the fabrication of large LNG flat bottom above ground storage tanks servicing at -163 degrees C/-260F and industry has then a long experience with that alloy. Considering the case of pressurized applications, the situation is largely different as only few examples of using 9%Ni can be found. AISI 304L austenitic stainless steel is in that case the material of choice, despite its low strength. On one hand, usual applications in LNG business as well as new low temperature applications linked to the Global Energy Transition could benefit of high performances coming with that alloy. Its high strength and allowable stresses - in comparison to ones on 304L - permit to significantly reduce the wall thickness of pressure vessels while keeping an excellent level of toughness and hence of safety. But on the other hand, experience with thick sections is very scarce and pressurized equipments fabrication require significantly thicker products than ones encountered in low pressure above ground flat bottom storage tanks. Consequently, demonstration of the industrial feasibility of such equipments needed to be done. The present paper aims at summarizing recent developments made to produce ultra-thick plates (up to 100mm/4inches thick) and properties achieved on such thick products. Base materials as well as welded joints have been extensively studied, in various thermal states able to replicate all industrial configurations required by customers involved in the fabrication of large cryogenic pressurized vessels. Materials properties after PWHT were measured, as some pressure vessel construction codes may require such treatments after welding or forming operations, depending on design conditions and on considered product thickness. Finally, heterogenous welds between 9%Ni and 304L austenitic stainless steel have been tested with the aim of enabling the use of conventional pressure vessel sub-components (such as nozzles, piping, flanges) with 9%Ni pressure vessels. Performances down to -196 degrees C/-320F have been addressed by the various tests made during the study. All results achieved are satisfactory and it is demonstrated to be safe to use 9%Ni for the fabrication of large pressure vessels.

Traditionally, the energy industries have driven the development of steel grades, to enable safe operations of mission-critical equipment under severe service conditions ranging from high and low temperatures, high stress conditions and corrosive environments. Industeel has been heavily involved in developing steels for such applications.

For many years, process licensors and/or end-users have frequently specified that the tempering temperature of C-Mn alloys and low alloy steels (i.e. Cr-Mo, Mn-Mo-Ni alloys) should be greater than the post-weld heat treatments (PWHT). Most of the time, tempering temperature is then required as much as 30°C (54°F) above the PWHT temperature, making it very difficult for steelmakers to be able to supply compliant materials, especially for heavy wall components. Application of rules in the applicable codes often leads steelmakers to request for deviations in cases where they become not compatible with material capabilities. This report is intended to illustrate the combined effect of tempering and PWHT on materials properties and to provide recommendations on how to tune smart the tempering treatment with the aim of proposing the most efficient complete heat treatment sequence. Data provided within this paper for C-Mn steels and low alloy grades (Cr-Mo and Mn-Mo-Ni alloys) prove that tempering can be performed at temperatures below, at or above one of PWHT without any adverse effect. Data from actual mill production records show that stringent material specifications can be met by steelmakers when they are allowed to tune smartly the heat treatment parameters (tempering temperature) in accordance with applicable construction codes. The data also demonstrate that limiting the tempering temperature in the lower range of allowed temperatures may be beneficial to customers as it gives more safety margins for fabrication and maintenance (i.e. potential repairs/modifications) of pressure vessels. It permits either to consider more cycles for PWHT or to perform PWHT at higher temperatures or for longer durations, while on the opposite, current trend imposing high tempering temperatures limits flexibility.

This contribution intends to present the development of a Charpy V-notched mastercurve to fit or extrapolate the transition of ferritic steels. Mastercurve is largely used to fit fracture toughness and can be derived for Charpy toughness. Some changes have to be performed regarding particular case of Charpy. This work is based on the assessment of a large database that covers a wide range of materials with yield strengths from 290 to 1180 MPa. The purpose of this mastercurve is to predict the correct shape of the Charpy transition with a reasonable safety margin on the basis of a limited amount of data. (C) 2015 Elsevier Ltd. All rights reserved.

This paper intends to present the development of a Charpy V-notched (CVN) mastercurve to fit and/or extrapolate the transition curve of ferritic steels (including martensitic, bainitic and ferritic materials).The purpose of a mastercurve is to define a general mathematical model able to represent the overall behaviour:of a material for different test conditions,or for a set of materials for given tests conditions.The role of a mastercurve is then to allow extrapolating or interpolating values from other data on the basis of a robust model, thereby permitting to avoid execution of new tests. It is in general based on practical general observations and research for a common behaviour through a large database of experimental results.This kind of approach is largely used to fit fracture mechanics data and can also be used in the case of Charpy toughness. Some changes have to be performed in order to take into account specificities of Charpy (such as dependence of transition slope with strength of materials) as well as some verifications linked to statistical distribution of failure probability.This work is based on the assessment of a very large database collected for years at Industeel's Research Center (tensile results, Charpy transition curves). This database represents 286 Charpy V-Notched transition curves of ferritic steels. It covers a wide range of materials and applications. Yield strengths of studied materials are ranging from 290 to 1180MPa while ultimate tensile strengths are in the range of 480 to 1690MPa.The target of this mastercurve is to predict the correct shape of the CVN transition curve with a reasonable safety margin on the basis of a limited amount of data (tensile properties at room temperature at least and when available, few Charpy data).A brief description of the database used within this study is given in the first part of this contribution as well as a description of the concept and underlying models. Finally, a validation of the work will be given as well as an illustration of its performance in a practical industrial case.

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.

In late 2007 and early 2008, 2 1/4Cr1MoV heavy reactors fabrication has undergone some weld metal reheat cracking issues that became a serious situation as roughly 25 large vessels were affected. Strong efforts from the whole production chain were put in trying to isolate the root cause of the crack appearance and solve this particular matter. Many investigations were conducted by independent laboratories in the first months of 2008. In particular, a hot tensile Gleeble® test indicated a decrease in ductility in the critical temperature range of Intermediate Stress Relieving (ISR) treatment (650–680 °C) of the affected welding consumables compared to those that did not cause cracking. This mechanical test was successfully combined with high sensitivity chemical analyses (Glow Discharge Mass Spectroscopy – GDMS) to find the root cause of such batch-to-batch differences in ductility. A chemical composition factor, called Kfactor, was defined and statistically linked to the Gleeble® test in July 2008. Altogether, it permitted to solve the issue. Even if reliable and well documented, the Gleeble® test was originally developed to understand the root cause of the cracking. But due to lack of other solutions, its role was largely extended and it became a kind of standard test to qualify 2 1/4Cr1MoV SAW filler material. It was decided to optimize this test, keeping its general philosophy but making it feasible by a larger number of laboratories. In order to do that, a one-year Joint Industrial Program (JIP) was proposed to the community, accepted, sponsored and launched at the beginning of 2010. The target was to create a new test protocol able to discriminate batches of filler material. The objective of this paper is to summarize the investigations performed and the optimization of the original Gleeble® test during the project that led to the definition of a new hot tensile mechanical test successfully benchmarked by independent laboratories and now balloted to be incorporated in American Petroleum Institute (API) recommended practice API RP 934-A as a new appendix.

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

This section is concerned primarily with effects of hydrogen in steels in refining industry. The focus is set on steels, CrMo(V) alloys, used for fabrication of heavy reactors.In the first part, a short review of fundamental aspects of hydrogen diffusion and solubility in steels is carried out. In the second part, problems related to high temperature service, such as high temperature hydrogen attack (HTHA) and hydrogen-creep interactions, are discussed. The last part covers the problems occurring during and after cooling of the reactors, such as hydrogen-induced disbonding (HID) and effects of dissolved hydrogen on mechanical properties (tensile ductility, fracture toughness and Charpy V-notched impact toughness). The intent is to provide a review of the main problems occurring during service of heavy section reactors used in refineries and petrochemical plants.

CrMoV heavy reactors fabrication has undergone some weld metal reheat cracking issues during the end 2007 / beginning 2008. This paper addresses this particular problem and explains the methodology used to solve it. Usual techniques, such as chemical factors and required NDE, have shown their limits, underlining the fact that this problem was unpredictable. Special mechanical testing as well as very accurate chemical analyses have allowed the authors to find the root cause. Very small amounts of particular impurities were responsible for the cracking and a criterion is then proposed to ensure that the problem will not come out again.

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.