For pipe fabrication shops, stainless steel pipe welding typically represents 15%–20% of their business. The pipe materials fabricated in these shops are primarily austenitic stainless 304L and 316L pipe. The quality requirements in stainless pipe fabrication shops are determined by performance requirements for service applications in low temperature, high temperature or corrosive environments. To enable the performance required in these applications, codes, standards and recommended practices for welding are frequently written from a conventional GTAW or SMAW welding paradigm. In addition, for the root pass and the first fill pass made with GTAW, an inert backing gas is always recommended to minimize or eliminate the discoloration or oxidation on the ID surface of the pipe near the root pass. The use of GTAW with inert backing gas adds significant time, complexity and cost to the welding of stainless pipe. In stainless pipe shop fabrication, very few welding practices recognize or encourage the use of GMAW welding solutions for these applications, even though it is known to be a more productive and economical welding process. Moreover, the absence of a consistent and proven GMAW welding solution in terms of either no backing gas GMAW, alternative options for expensive shielding gases, implementing unique welding waveforms etc., proves to be a hindrance in the adoption of GMAW solutions for the welding of stainless pipe. In this paper, we discuss advances that have been made in producing acceptable stainless pipe welds with a 1G GMAW welding solution using an STT ® waveform for the root pass and a unique “Rapid X™” waveform for fill passes with no use of backing gas. One goal of this project was to also find a shielding gas mixture to provide acceptable welds from root to cap that takes into account both welding process performance as well as fabrication of defect free welds. Six different shielding gas mixtures with varying amounts of Ar, He, CO 2 and N 2 were evaluated. Results indicate that STT/RAPID X™ welds made with 97%Ar/2%CO 2 /1%H 2 provide very promising results in terms of weld appearance and other conventional metrics such as radiography, bends and tensile properties. However, assessment of the corrosion performance in comparison to welds made with conventional GTAW requires development of a better test protocol than the ASTM G48 Method A test for it to be relevant and meaningful.

Recently, a simple screening technique based on the quantitative evaluation of the hydrogen embrittlement (HE) sensitivity of the metallic materials using an in-situ small-punch (SP) test method was developed by the author group. The in-situ SP test can be easily carried out even under a high-pressure hydrogen gas environment. It makes possible to investigate the HE behaviors of metallic materials quantitatively adopting as a characterizing performance factor of the relative reduction of thickness (RRT) measured at the fractured parts of specimen after SP tests. In this paper, the application of the newly established in-situ SP test method for the hydrogen compatibility screening of austenitic stainless steels was performed at room and low temperatures. The influence of punch velocity on RRT of the HE sensitivity was examined for various austenitic stainless steels. Their HE sensitivities were evaluated quantitatively using RRT and checked by comparing to a factor, the relative reduction of area (RRA) obtained by SSRT tests.

In Japan, Japan Atomic Energy Agency has developed a probabilistic fracture mechanics (PFM) analysis code, PASCAL4, for probabilistic evaluation of reactor pressure vessels (RPVs) in pressurized water reactors (PWRs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. Besides severe PTS events, however, transients associated with normal operations, such as the cooldown and heatup transients associated with reactor shutdown and startup, respectively, should also be considered in the integrity assessment of RPVs in both PWRs and boiling water reactors (BWRs). With regard to a heatup transient, because temperature is at its minimum, and tensile stress at its maximum on the RPV outer surface, outer surface crack and embedded crack near the RPV outer surface should be taken into account. To extend the applicability of PASCAL4, we improved the code to include analysis functions for these cracks. The improved PASCAL4 can be used to run PFM analyses of RPVs subjected to both cooldown (including PTS) and heatup transients. In this paper, improvements made to PASCAL4 are firstly described, including the incorporated stress intensity factor solutions and the corresponding calculation methods for vessel outer surface crack and embedded crack near the outer surface. Using the improved PASCAL4, PFM analysis examples for a Japanese BWR-type model RPV subjected to thermal transients including a low temperature overpressure event and a heatup transient are presented.

ASME Code, Section XI, Nonmandatory Appendix G (ASME-G) provides a methodology for determining pressure and temperature (P-T) limits to prevent non-ductile failure of nuclear reactor pressure vessels (RPVs). Low-Temperature Overpressure Protection (LTOP) refers to systems in nuclear power plants that are designed to prevent inadvertent challenges to the established P-T limits due to operational events such as unexpected mass or temperature additions to the reactor coolant system (RCS). These systems were generally added to commercial nuclear power plants in the 1970s and 1980s to address regulatory concerns related to LTOP events. LTOP systems typically limit the allowable system pressure to below a certain value during plant operation below the LTOP system enabling temperature. Major overpressurization of the RCS, if combined with a critical size crack, could result in a brittle failure of the RPV. Failure of the RPV could make it impossible to provide adequate coolant to the reactor core and result in a major core damage or core melt accident. This issue affected the design and operation of all pressurized water reactors (PWRs). This paper provides a description of an investigation and technical evaluation regarding LTOP setpoints that was performed to review the basis of ASME-G, Paragraph G-2215, “Allowable Pressure,” which includes provisions to address pressure and temperature limitations in the development of P-T curves that incorporate LTOP limits. First, high-level summaries of the LTOP issue and its resolution are provided. LTOP was a significant issue for pressurized water reactors (PWRs) starting in the 1970s, and there are many reports available within the U.S. Nuclear Regulatory Commission’s (NRC’s) documentation system for this topic, including Information Notices, Generic Letters, and NUREGs. Second, a particular aspect of LTOP as related to ASME-G requirements for LTOP is discussed. Lastly, a basis is provided to update Appendix G-2215 to state that LTOP setpoints are based on isothermal (steady-state) conditions. This paper was developed as part of a larger effort to document the technical bases behind ASME-G.

It has been observed that steels which are operating in the ductile regime demonstrate greater resistance to tearing under conditions of reduced crack-tip constraint. Constraint is influenced by both geometry and load conditions. For example, fracture toughness specimens with shorter cracks relative to wall thickness, or those subjected to tension as opposed to bending, will demonstrate reduced constraint. Constraint may be quantified by an elastic T-Stress or the elastic-plastic Q parameter. R6, a set of structural integrity guidelines widely used in the nuclear industry, suggests that the effective fracture toughness of a material at reduced constraint may be calculated using a material-specific toughness locus. To define this locus, it is usually necessary to perform laboratory tests on the material at various levels of constraint, which are both expensive and time consuming. For cleavage (low-temperature) fracture, it is also possible to consult look-up tables, which require the calculation of the Weibull stress parameter. This paper details findings from an investigation into a method to determine the parameters defining failure loci for steels. The work involves the use of finite element analysis and two damage models which consider void growth in ductile materials. The first model is the Rice and Tracey model, which determines void growth based on stress triaxiality and plastic strain, and the second is the GTN local approach, which considers void initiation, growth and coalescence to define a yield surface for the material. The yield surface is governed by numerous parameters which enable the definition of the void volume fraction of the material at the various stages preceding fracture. Previous work has demonstrated independence of the parameters used to define the toughness loci to the critical void size when defined using the Rice and Tracey approach. The work presented in this paper demonstrates similar behaviour using the GTN model, with independence of the constraint benefit to the governing parameters. The toughness determined using the GTN approach is calculated from J-R type curves obtained by simulating crack growth in idealised constraint scenarios: specifically applying a T-Stress to boundary layer models, where a boundary layer model is an idealised high constraint scenario. It is shown in this paper that, whilst independence is demonstrated to the GTN parameters, there are discrepancies between the toughness loci derived using the GTN model and those using the Rice and Tracey approach. The reasons for this are discussed and are predicted to be due to load order effects, in that constraint reduces through loading, which may not be captured accurately using the boundary layer model. An introduction to the next phase of work, which does accurately include these effects, is also provided.

Repeated weld joints leaks were observed in newly commissioned non insulated low temperature carbon steel anhydrous ammonia pipes after few months of operations. A detailed investigation was carried out to identify the root cause which found to be usage of high strength filler wire which leads to stress corrosion cracking (SCC) and weld joints failure. Also, An Online advance inspection via Phased Array Ultrasonic Test (PAUT) was conducted to assess the condition of weld joints in anhydrous ammonia pipe loops. Moreover, three different samples of leaked weld joints were submitted for metallurgical failure analysis laboratory. The paper explains the root cause of the damage, Online PAUT inspection and the challenges faced during development of the rectification procedure and implementation.

The structural steel in a nuclear facility experiences significant degradation due to the accumulated neutron irradiation. Particularly, the long-column type reactor pressure vessel supports have been focused since they resist considerable loading to maintain the primary coolant system in their position and experience high neutron irradiation in low temperature, which is an unfavorable condition for the fracture toughness. This study implemented the API 579-1/ASME FFS-1, fitness-for-service (FFS) method to consider both irradiated mechanical properties and multiple loading cases. A three-dimensional (3D) finite element model of long column type reactor pressure vessel support was built for the linear analysis. The metallurgical properties of reactor pressure vessel support for assessment were estimated by empirical equations. This study provides the structural margin of long-column type reactor pressure vessel support by levels of the loads and levels of the neutron fluence.

Energy demand will increase due to global population growth in the future. As one of solutions for the demand, it will be necessary to operate petroleum service plants more efficiently. To improve refining efficiency, operation at higher temperatures is required of reactors used in high-pressure hydrogen service at the plants. 9Cr-1Mo-V steel has excellent creep strength compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel, which have been conventionally applied to reactors, and has been already put into commercial use for boilers of thermal power plants, etc. Further application of 9Cr-1Mo-V steel is expected for reactors at petroleum refining plants. As materials applied to reactors, low-temperature toughness should be considered for weld joints in addition to creep strength. However, 9Cr-1Mo-V steel has poor low-temperature toughness compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel. As for the welding methods applied to reactors, Submerged Arc Welding (SAW), Shielded Metal Arc Welding (SMAW), and Gas Tungsten Arc Welding (GTAW) can be used. The 9Cr-1Mo-V steel weld metals formed by SAW and SMAW have a high oxygen content, and their low-temperature toughness is inferior to that of the weld metal formed by GTAW. On the other hand, the GTAW weld metal has a low oxygen content and excellent low-temperature toughness. Therefore, GTAW is an effective way to improve the toughness of the weld metal. However, GTAW has low productivity compared with others, so it is necessary to apply to a narrow groove and a hot wire method to improve the productivity. In this paper, the application of narrow gap GTAW using the hot wire method was considered for welding of 9Cr-1Mo-V steel. When using the hot wire method, productivity of GTAW increases in comparison to the conventional method, leading to increased weld pass thickness. With the increase in pass thickness, the area of coarse grains increases because of decreasing thermal effect by the subsequent pass, then the low-temperature toughness decreases. Therefore, in order to improve the low-temperature toughness by refining the grains of the GTAW weld metal, the melt-run method, arc re-melting without adding fillers, was conducted after the former weld pass metal solidified. The weld metal from the melt-run method had finer grains compared with those of the weld metal without the melt-run method, and the low-temperature toughness increased. On the other hand, the melt-run method requires two processes: welding and melt-run. Therefore, a tandem electrode GTAW machine was produced in which an electrode for welding and the other one for melt-run were placed continuously to make it possible to execute welding and a melt-run without a time lag. As a result, it is possible to manufacture reactors made of 9Cr-1Mo-V steel for petroleum refining plants with sufficient low-temperature toughness by applying a welding method with narrow gap GTAW and a melt-run method combined.

The structural integrity of pressure vessels (PVs) is controlled by the application of various design and fabrication codes and standards. Within the European single market (ESM) design codes exist at both a European and a national level which can lead to variability in design procedures. The European standard EN 13445 has been updated several times to modify the design curves based on analytical modelling of high strength materials. The design curves in EN 13445 now differ significantly from those presented in the British national code that preceded it, namely PD 5500. As a result higher minimum Charpy test temperatures ( T 27 J ) are found using the EN 13445 procedure in comparison to those derived using the PD 5500 procedure. While the PD 5500 design curves have been validated experimentally it is generally accepted that they are overly conservative. This inherent conservatism in PD 5500 may account for some of the differences in the minimum Charpy test temperature, the analytical model used to generate the EN 13445 design curves however was validated with data from high strength steels only (σ y ≥ 420 MPa). It is not clear that the results can be applied directly to low/medium strength materials. This work identifies some of the disparities between the EN 13445 and PD 5500 procedures, for low temperature applications. A programme of work, at Imperial College London, is described. This programme of work, currently underway, is aimed at addressing concerns about the robustness of the updated EN 13445 design curves, especially for lower-strength steels in the as-welded condition.

Temper bead (TB) welding is often used as an alternative to post weld heat treatment (PWHT) for repair of pressure vessels and piping in the nuclear power industry. Historically, qualification of TB welding procedures has employed the Charpy V-notch test to ensure acceptable heat-affected-zone (HAZ) impact properties. The 2004 Edition of ASME Section IX provided a new provision in QW-290 that allows temper bead qualification using a peak hardness criterion. The peak hardness provision is appropriate for industries such as oil and gas, where peak allowable hardness is specified to ensure adequate resistance to sulfide stress cracking in sour service environments. However, a peak hardness criterion is not appropriate where impact properties are specified for resistance to brittle fracture during low temperature conditions that can occur during certain postulated accident scenarios at a nuclear power plant. Work at the Electric Power Research Institute (EPRI) and The Ohio State University (OSU) show that a hardness drop protocol can be used to demonstrate acceptable impact properties in the HAZ of a temper bead weld. This paper presents a quantitative correlation between hardness measurements and HAZ microstructures with presumed optimum impact properties using a hardness drop approach. The overarching goal is to develop a hardness test protocol for temper bead weld procedure qualification for applications where impact properties are specified.

Elastomers show a high versatility which makes them ideal materials for sealing applications in various fields. Especially under changing application conditions the high recovery potential of this class of material is beneficial to compensate temperature or pressure fluctuation, and geometrical changes resulting from mechanical loads in e.g. accident conditions. Out of these reasons elastomers are also used in containers for low and intermediate level radioactive waste and for spent fuel transportation casks. In casks designed for low and intermediate level waste elastomer seals can act as primary seal responsible for the containment function whereas in spent fuel storage and transportation casks (dual purpose casks (DPC)) elastomer seals are used as auxiliary seals to allow leakage rate measurements of metal barrier seals. An inherent prerequisite for this kind of application is the long time-scale of operation without or with limited possibility of seal replacement. In Germany an interim storage license for DPC’s is typically issued for 40 years, a timeframe which might increase in the future due to challenges of the final repository siting procedure. For low and intermediate level waste, also long time periods are required before final disposal can be achieved. Therefore, the performance of elastomer seals over extended time periods is, as for other applications, of high importance. A typical approach to ensure long-term functionality is to perform accelerated aging tests to calculate an estimated lifetime by assuming e.g. Arrhenius like equations for the timetemperature relationship. This approach requires a suitable end of life criterion considering the application of interest. This often can represent a challenge on its own. As BAM is involved in most of the cask licensing procedures and especially responsible for the evaluation of cask-related long-term safety issues we initiated several test programs for investigating the behavior of elastomer seals. Experiments concerning the low temperature performance down to −40 °C and the influence of gamma irradiation have been started first. Currently the thermal aging behavior of elastomer seals, which is the topic of this contribution, is examined. For our aging investigations we use a broad approach to first determine the property changes in different elastomer materials due to thermo-oxidative aging at elevated temperatures and secondly, we test how the typical methods of lifetime extrapolation can be applied to these results. This approach enables us to detect and exclude undesired side effects which very often influence lifetime estimations. In this contribution, our recent results are extended. The results show that lifetime estimation based on single material properties can be misleading and therefore a combination of several methods is recommended.

07MnNiMoDR is a widely used quenched and tempered high strength steel in fabrication of low-temperature pressure vessels in China. It can be used at/above −50°C according to the current design specification of GB 150. Some data show that this provision severely underestimates the performance of this material at low temperature, while others indicate that it overestimates the cryogenic performance of this material. In the paper, a series of tests including uniaxial tension tests, impact test and fracture toughness tests were carried out at low temperature to investigate the properties of 07MnNiMoDR with different thickness specimens. Fracture mechanics assessment procedures in API 579-1/ASME FFS-1 (Fitness-For-Service) is adopted to evaluate the low temperature design curve of 07MnNiMoDR, and the fracture toughness is obtained by master curve method (MC method) in the transition region. The results show that 07MnNiMoDR can be classified between exemption curve B and D in current edition of ASME Section VIII, Division 2.

In this present paper, the effect of specimen thickness on carburized layer thickness and surface residual stress of low temperature gaseous carburized AISI316L austenitic stainless steel was investigated by using specimen with thicknesses from ∼0.1 to ∼3 mm. After 15 and 30 hrs Low Temperature Gaseous Carburization (LTGC) treatment, the carburized layer thickness, surface residual stress and surface morphology were studied by optical microscope (OM), X-ray residual stress analyzer and scanning electron microscope (SEM). The results show that the specimen original thickness has no effect on the thickness of carburized layer. Surface compressive residual stresses are constant as about −1.6 and −2.1 GPa when the specimen thicknesses are not less than 0.485 mm for 15 hrs and 0.926 mm for 30 hrs LTGC treatment respectively. With the reduction of specimen thicknesses from 0.485 to 0.081 mm for 15 hrs LTGC treatment and 0.926 to 0.082 mm for 30 hrs LTGC treatment, the compressive residual stresses declined and finally reached about +0.4 and +1.0 GPa, respectively. Surface inter-granular cracking occurred on 0.082 mm specimen after 30 hrs LTGC treatment.

Pressure Strengthening (PS) is a technology widely used to increase the allowable stress and thus reduce the weight of Austenitic Stainless Steel (ASS) cryogenic vessels. Pre-strain and low temperature are two important factors enhancing the strength. However, standards such as EN 13458-2, ASME VIII-I, AS 1210 and ISO 21009-1, state that the strengthening is based on work hardening of ASS, while the effect of low temperature was ignored or not mentioned. Therefore, in this work, the influence of low temperature on cryogenic mechanical properties of S30408 stainless steel and its welded joints were studied firstly, then a numerical analysis on the influence of pressure strengthening of a large transportable cryogenic storage tank was conducted. Finally, after the technical significance of PS was discussed, a new understanding was proposed. Conclusions come that: (a) At room temperature, the strength of ASS can be increased by pre-strain; while at −196 °C, the strengthening of low temperature plays a leading role (2/3 or more) for strength increment; (b) The purpose of PS technique is to stabilize the dimensions of the internal vessel. It is unnecessary to consider insufficient strengthening or over strengthening at different location because the strength enhancement is mainly due to low temperatures.

Methods to qualify materials for hydrogen service are needed in the global marketplace to enable sustainable, low-carbon energy technologies, such as hydrogen fuel cell electric vehicles. Existing requirements for qualifying materials are not adequate to support growth of hydrogen technology as well as being inconsistent with the growing literature on the effects of hydrogen on fracture and fatigue. This report documents an internationally coordinated effort to develop a test method for qualifying materials for high-pressure hydrogen fuel system onboard fuel cell electric vehicles. In particular, consistency of fatigue life testing strategies is discussed. Fatigue life tests were conducted at three different institutes in high-pressure gaseous hydrogen (90 MPa) at low temperature (233K) to confirm consistency across distinct testing platforms. The testing campaign includes testing of both smooth and notched axial fatigue specimens at various combinations of pressure and temperature. Collectively these testing results provide insight to the sensitivity of fatigue life testing to important testing parameters such as pressure, temperature and the presence of stress concentrations.

A high pressure material testing system (max. pressure: 140 MPa, temperature range: −80 ∼ 90 °C) was developed to investigate the testing method of material compatibility for high pressure gaseous hydrogen. In this study, SSRT and fatigue life test of JIS SUS304 and SUS316 austenitic stainless steel were performed in high pressure gaseous hydrogen at room temperature, −45, and −80 °C. These testing results were compared with those in laboratory air atmosphere at the same test temperature range. The SSRT tests were performed at a strain rate of 5 × 10 −5 s −1 in 105 MPa hydrogen gas, and nominal stress-strain curves were obtained. The 0.2% offset yield strength ( Ys ) did not show remarkable difference between in hydrogen gas and in laboratory air atmosphere for SUS304 and SUS316. Total elongation after fracture ( El ) in hydrogen gas at −45 and −80 °C were approximately 15 % for SUS304 and 20% for SUS316. In the case of fatigue life tests, a smooth surface round bar test specimen with a diameter of 7 mm was used at a frequency of 1, 0.1, and 0.01 Hz under stress rate of R = −1 (tension-compression) in 100 MPa hydrogen gas. It can be seen that the fatigue life test results of SUS304 and SUS316 showed same tendency. The fatigue limit at room temperature in 100 MPa hydrogen gas was comparable with that in laboratory air. The room temperature fatigue life in high pressure hydrogen gas appeared to be the more severe condition compared to the fatigue life at low temperature. The normalized stress amplitude ( σ a / Ts ) at the fatigue limit was 0.37 to 0.39 for SUS304 and SUS316 austenitic stainless steels, respectively.

With Oil and Gas exploration and production in low temperature arctic environment, new concerns arise concerning the application of the existing design rules for these conditions. Most codes and standards for bolted flange calculation do not include specific rules concerning application at low temperature. Especially, gasket performances under low temperature are neither tabulated nor easily available from other public sources. In this context, in collaboration with TOTAL, SCHLUMBERGER and SAIPEM sponsors, the CETIM has performed a program called ARCTICSEAL to characterize the flange gasket behavior in arctic environment. The goal is to check that gasket references, commonly used by these companies, are still usable under low temperature arctic conditions without main performance loss. The test program involves mechanical and sealing tests performed on 4 gasket types (sheet fiber based, sheet PTFE based, sheet graphite based and graphite spiral wound) with both NPS 8 and NPS 16 gasket sizes. Gasket performances are determined at −60°C, after loading at −25°C. Additional test involving hot/cold thermal cycling ageing (simulation of intermittent hot process fluid in the bolted flange) have also been performed. The result shows the ability of the tested gasket references to maintain good sealing behavior in most cases. Moreover, the hot/cold thermal cycling ageing improves the sealing performances for some of the tested gasket references. Moreover, a dedicated test stand has been developed to study the behavior of NPS 8 flange connection exposed to quick heat-up after exposure to low temperature environment.

UNS N07718 (commonly known as Grade 718) is an age-hardenable nickel-chromium alloy which primarily has applications in aircraft components and engine parts, cryogenic tankages, and for downhole and wellhead components in oil and gas. It also has been used primarily as bolting for ASME Section VIII vessels, exchangers and other high strength applications. ASME SB-637, UNS N07718 (1) has the highest design allowable stresses of all the bolting materials in ASME Section II, Part D (2) , Table 3. There is a second industry standard which covers UNS N07718 components, namely API 6ACRA (3) , which was developed for Oil and Gas equipment. Since this standard is for very different applications compared to the ASME applications, the recommended heat treatments and required mechanical properties of the two standards vary considerably. Bolting to either standard can be specified to meet “NACE hardness limits” for wet sour services, but for the ASME materials, this requires strict controls of the various heat treatment steps as the “box” for meeting all the required properties is tight. The NACE standards and requirements for wet sour service are discussed in the paper, along with the specified heat treatments and mechanical properties required by the two industry standards. The paper will review the effect of the heat treatments on the expected microstructures and properties. By using testing results of N07718 materials specified to both the materials standards, the heat treatment and properties were optimized for a specific application that was specified to meet NACE hardness limits as well as ASME Code strength requirements. The paper also makes a recommendation to ASME and ASTM committees to consider incorporating an additional grade of N07718 bolting with lower yield and tensile strength requirements and subsequently slightly lower allowable stresses which will provide lower hardness levels, improved toughness and improved ductility, and make it easier to source a viable N07718 bolting that is endorsed by the Code for wet sour services, and improved for low temperature, cryogenic and other services.

Impact test exemption curves in ASME B31.3 [1] were adopted from ASME Section VIII Division 1 (VIII-1) [2] with subtle modifications. The VIII-1 exemption curves were generated based on early fracture mechanics methodologies and limited amount of test data with an assumption on maximum applied stress intended to correspond to the typical VIII-1 allowable stress criteria. The applicability of the exemption curves for low temperature applications of ASME B31.3 piping (such as blowdown events) is open to discussion because of potentially high longitudinal thermal expansion stresses that may exceed the VIII-1 allowable stress criteria. Additionally, unlike in VIII-1 and ASME Section VIII Division 2 (VIII-2) [3], there is no post weld heat treatment (PWHT) credit on Minimum Design Metal Temperature (MDMT) in ASME B31.3. Detailed fracture mechanics analyses have shown that PWHT can significantly reduce the risk of brittle fracture failures due to its relaxation effect on weld residual stresses, a major crack driving force. In this paper, a fracture mechanics-based methodology for establishing Minimum Allowable Temperatures (MAT) for low temperature applications of ASME B31.3 piping is presented. A state-of-the-art fracture mechanics methodology published in Welding Research Council (WRC) Bulletin 562 [4] is used to develop step-by-step Level 1 and Level 2 procedures for establishing MAT for low temperature applications of ASME B31.3 piping. For the Level 1 methodology, MAT screening curves are developed based on a likely conservative assumption that the stresses in the piping component are at the maximum code allowable stresses in both the hoop and longitudinal directions. For the Level 2 methodology, stress ratio verses temperature reduction curves are developed to consider the effect of lower operating stresses. Similar to VIII-2 [3] toughness exemption curves, the screening curves are generated for both As-Welded and PWHT conditions. The curves can also be used for impact tested materials. The established MAT can be directly coupled to different reference flaw sizes and integrated with an inspection criteria for piping components. Two examples of establishing MAT using both the proposed Level 1 and Level 2 methodologies are presented herein.

This paper is concerned with the low-cycled fatigue life of S30408 austenitic stainless steel at 77 K. Strain-controlled low-cycled fatigue tests were performed in a liquid-nitrogen bath covering a strain-amplitude range of 0.4%–1.0%. The role of the reduced temperature is examined during the low-cycled fatigue tests by comparing the fatigue performance to the one at ambient temperature that was obtained in our previous work. It is found that the cryogenic low-cycled fatigue life is significantly improved by a factor of 5–10 in the low strain-amplitude range of 0.4%–0.5%, resulting from the pronounced hardening effect due to the low temperature. However, the cryogenic improvement gradually reduces with the increasing strain-amplitude. At 77 K, the cyclic stress amplitude increases rapidly at the beginning of the fatigue test, and no cyclic softening is found due to the cryogenically constrained movement of the dislocations. The fatigue hysteresis loops and fatigue stress-strain curves shows that the cyclic plastic strain at cryogenic temperature accounts for a limited proportion in the total cyclic strain, and the damage may occurs explosively at the beginning of the cyclic load at 77 K.