FP7-FCH-JU MATHRYCE Material Testing and Recommendations for Hydrogen Components under fatigue

Transcription

1 FP7-FCH-JU MATHRYCE Material Testing and Recommendations for Hydrogen Components under fatigue Deliverable Nature Dissemination D2.6 Existing codes and standards Final update Report PU D2.6 Existing codes and standards Final update Foreseen submission date Project Month 34 Actual submission date Project Month 36 Author(s) Jader FURTADO Air Liquide Olivier BARDOUX Air Liquide Béatrice FUSTER Air Liquide Paolo BORTOT TenarisDalmine Randy DEY CCS Laurent BRIOTTET CEA Version number for EC Doc ID Code V1 MATHRYCE_D2.6 Contract Start Date Duration Project Applicant 36 months CEA - LITEN FCH Joint Undertaking Collaborative Project Project funded by the European Commission 1

2 Project Number FP7- FCH JU Project Acronym Title MATHRYCE Material Testing and Recommendations for Hydrogen Components under fatigue Deliverable N D2.6 Due Date Project Month 34 Delivery Date Project Month 36 EXECUTIVE SUMMARY In previous deliverable D2.5, several regulations, codes and standards dealing with (or in some cases without) hydrogen effect on fatigue design of pressure components used for the containment of high pressure hydrogen have been analyzed. This deliverable provides a summary of the ANSI/CSA CHMC standard [1],, a recent testing methodology for evaluating metallic material compatibility in compressed hydrogen applications. The standard refers to the applicability of current testing methods to verify the degradation of mechanical properties of materials used in contact with hydrogen. Three mechanical properties are evaluated: ductility, fracture toughness and fatigue properties. The central idea of the standard is to measure the required mechanical and fatigue properties in hydrogen gas, as exemplified below: Ductility reduction: through the ratios RNTS or RRA obtained through slow strain rate testing. A material is considered compatible with hydrogen if RNTS>0.90 or RRA>0.90 (see cl 6.2.2). If RNTS 0.50 the material is eligible for qualification using clause plus 6.3 or 6.4. Fatigue life test: The safety factor (SF) multiplier is the largest of the four ratios determined through the statistical analysis of fatigue results. It is mandatory to perform statistical analysis of the fatigue data as explained in Annex F, which follows ASTM E739. Fatigue crack growth rate: fracture mechanics based design is allowed and R-ratio effect is considered through a correction using an effective value of the cyclic stress intensity factor, K*. Document Control Title: Project: D2.6 Existing codes and standards Final update MATHRYCE Type: Report Dissemination PU The information contained in this report is subject to change without notice and should not be construed as a commitment by any members of the MATHRYCE Consortium. The MATHRYCE Consortium assumes no responsibility for the use or inability to use any procedure, protocol, which might be described in this report. The information is provided without any warranty of any kind and the MATHRYCE Consortium expressly disclaims all implied warranties, including but not limited to the implied warranties of merchantability and fitness for a particular use. Authors Doc ID Amendment History Jader FURTADO Air Liquide (AL), Olivier BARDOUX AL, Béatrice FUSTER AL, Paolo BORTOT TenarisDalmine, Randy DEY CCS, Laurent BRIOTTET CEA MATHRYCE_D2.6 Version Date Author Description/Comments V1 Sept 30, 2015 Jader Furtado Final 2

3 Table of contents 1 REMINDER OF THE PROJECT MAIN OBJECTIVES DELIVERABLE S CONTEXT NOMENCLATURE AND/OR DEFINITIONS INTRODUCTION ANSI/CSA CHMC STANDARD APPLIED TO MATERIAL COMPATIBILITY ANSI/CSA CHMC STANDARD APPLIED TO FATIGUE LIFE TESTS ANSI/CSA CHMC STANDARD APPLIED TO FRACTURE MECHANICS BASED FATIGUE TESTING 10 8 CONCLUSION REFERENCES

4 1 REMINDER OF THE PROJECT MAIN OBJECTIVES The main objectives of the MATHRYCE project are centered on the development and dissemination for standardization of a methodology for the design of hydrogen high pressure metallic vessels and for their lifetime assessment that takes into account hydrogen-enhanced fatigue. This needs to be achieved without requiring full scale component testing under hydrogen as this is not practicable considering the expected lifecycle and equipment size. The project therefore targets the justification of an approach where lifetime assessment results from combining the hydraulic cycling performance of the component with the appropriate knowledge of the performance of the metallic material in hydrogen under cyclic loading. This will be validated by comparing the lifetime prediction of a component calculated from the lab-scale tests to that obtained from large scale component tests. The analysis of the results, based on numerical simulations as well as on the scientific knowledge of the possible hydrogen embrittlement mechanisms, will allow to assess or to modify the proposed design methodology. Once the testing method as well as the associated design methodology is validated, specific recommendations will be proposed for implementations in international standards. To summarize, the main outcomes of the MATHRYCE project will be: - The development of a reliable testing method to characterize materials exposed to hydrogen-enhanced fatigue, - The experimental implementation of this testing approach, generating extensive characterization (microstructural and mechanical) of metallic materials for hydrogen service, - The definition of a methodology for the design of metallic components exposed to hydrogen enhanced fatigue and for the assessment of their service lifetime; this methodology being liable to be recognized for pressure equipment regulation, - The dissemination of this methodology, as a proposed approach for standardization, - The dissemination of prioritized recommendations for implementations in international standards. 4

5 2 DELIVERABLE S CONTEXT This deliverable 2.6 is a final update of Task 2.2 Review of existing codes and standards on H2 vessel design. In this report is reviewed the North American standard ANSI/CSA CHMC1-2014, which was recently published and deals specifically with the design of metallic pressure components subjected to hydrogenenhanced fatigue. Work package number 2 Start date or starting event: Month 1 Work package title From End User specifications to experimental approach Activity Type RTD Participant number Participant short name CEA AL VTT JRC CCS CSM Tenaris Person-months per participant Objective The objective of WP2 is to characterize service life conditions for selected components (e.g. pressure vessel for refuelling station buffer), in order to define tests to be conducted in the following work packages (WP3 and WP4). The other goal of WP2 consists in a review of existing scientific data and codes and standards for hydrogen pressure vessels design, in particular to design components to be used for WP4 tests. Description of work Task 2.1: Component selection and operation specifications (M1-M3) Participants: AL (task leader), Tenaris One or several components undergoing hydrogen pressure cycles, and exposed to high pressure hydrogen ( bar) in the hydrogen energy applications will be selected for the project. Thus, operational data (e.g. pressure ranges, pressure cycles, temperature) describing the solicitations on the component(s) will be gathered, and compared to model solicitations already considered in similar projects. AL will provide data on the operation mode of hydrogen refuelling station (e.g., for buffer tank, time under pressure, number and amplitude of cycles ). Tenaris will add its comments and observations based on AL input data. Task 2.2: Review of existing codes and standards on H2 vessel design (M1-M34) Participants: CCS (task leader), AL, Tenaris A review of existing codes and standards for hydrogen pressure vessels design will be made, in order to gather information on the different possible approaches. In particular, the limits of each code or standard will be highlighted, and particular attention will be paid to high pressures and to fatigue-based design. CCS will collect existing RCS information relevant to the project. AL contributing to many activities in the RCS field with hydrogen technologies will analyze the limits of existing standards. Tenaris will present its point of view, including comments on the approaches used for fatigue design and qualification of gas cylinders, based on the experience gained during participation to different ISO committees. Task 2.3: In service stress analysis (M2-M4) Participants: CEA (task leader) Data collected in Task 2.1 will be transformed into data useful to define tests carried out in WP3. In particular, stress analysis will be based on component design and conditions of use (e.g. pressure), to define loads applied during the tests. CEA will provide finite element calculations using a model of hydrogen diffusion which couples mechanical stress and plastic strain to hydrogen diffusion. Thus, stress analysis as well as hydrogen concentration and localization in pressure vessels for conditions of use will be investigated in order to define experimental conditions (hydrogen pressure...) and global specimen geometry to use for in service representative lab mechanical tests. Task 2.4: Defect design for component testing (M9-M12) Participants: CEA (task leader), CSM, AL, Tenaris Based on the scientific data review for the selected grade of steel, and on microstructural analysis performed in WP3, defects (either microstructural such as inclusions or precipitates, or cracks) will be introduced in Task 2.3 stress analysis, to obtain new conditions of tests for WP3. Indeed, it is well known that microstructural defects can play the role of stress concentrators, and initiate cracks in the presence of H2. In addition, stress analysis will be performed on components to be tested in WP4, with several sizes of defects. 5

6 As in Task 2.3, CEA will provide finite element calculations to analyze stress and hydrogen distribution in pressure vessels including defects (microstructural...). The size of the defects will be defined using the microstructural characterization performed by CSM in the task 3.2. Thus, specimen geometries and experimental conditions for representative lab-scale mechanical tests will be defined. Two sizes of components will be tested, a small one (10 to 30 l) and a full scale one. The small size components will have to be representative of damages (initiation and crack growth) occurring in real size component while it allows to test in parallel numerous pressure vessels. CEA will also design a new specimen geometry for disk pressure tests including notches designed upon data collected in WT2.3. The purpose is to obtain a stress field at the notch tip close to that existing ahead of a crack in a pressure vessel during service. Finite element calculations will be used to realize such a design. If this goal is achieved, this should provide a quite simple mechanical test for studying hydrogen enhanced fatigue with a hydrogen cyclic charging. Such test would have the advantage to test the material under cycling hydrogen pressure whereas the other tests are carried out at a constant pressure. AL will also follow the designing of this new specimen for disk pressure test to make sure that it is easy enough to implement for industrial purpose. CSM will contribute to the stress analysis, by FEA, of components including defects. In particular the activity will have a twofold aim. On the one hand the stress analysis will aim to define stress concentration factors deriving from the presence of defects as inclusions or microstructural defects. The results of the microstructural characterization performed in WP3 will supply the input information on possible defects shape and dimensions to be considered in the activity. On the other hand a devoted stress analysis will be performed in order to define suitable dimensions for defect to be manufactured on components for full scale hydraulic tests planned in WP4. Tenaris will give its feedback on possible imperfections and/or microstructural heterogeneities which can be found in a pressure vessel below the typical NDT detection limit Deliverables (month of delivery, Leader, Nature, Dissemination level) D2.1 Operational data AL, R, CO, M3 D2.2 Existing codes and standards CCS, R, PU, M7 D2.3 Stress analysis CEA, R, CO, M4 D2.4 Defect design CEA, R, CO, M12 D2.5 Existing codes and standards first update AL, R, PU, M21 D2.6 Existing codes and standards final update AL, R, PU, M34 6

7 3 Nomenclature and/or definitions Crack length, a linear dimension used to calculate fracture mechanics parameters, measured from the load line of the specimen to the crack tip. Fatigue crack growth rate, da/dn increment of crack extension per fatigue cycle. Force ratio, R the ratio of the minimum and maximum force applied in the fatigue cycle. R=P min /P max =K min /K max Frequency, f the number of times the complete fatigue loading cycle is repeated per second. J IH Elastic plastic threshold value of the J-integral determined near the onset of crack extension in gaseous hydrogen environments determined using the 0.2 mm offset intersect method. J IC - Elastic plastic plane strain fracture toughness K t - Notch severity K IH Linear elastic threshold stress intensity factor for crack initiation in gaseous hydrogen environments. K IC Linear elastic plane strain fracture toughness Maximum stress intensity factor, K max the stress intensity factor associated with the largest applied load during the fatigue cycle. Minimum stress intensity factor, K min the stress intensity factor associated with the smallest applied load during the fatigue cycle. Stress intensity factor, K amplitude of the stress singularity ahead of a crack tip in a homogenous, linear elastic body. Stress intensity factor range, ΔK: K max -K min the range of stress intensity factor applied during a fatigue cycle. Waveform refers to the shape of the fatigue cycle when plotted as load (or force or stress intensity factor) versus time. Relative notch tensile strength, RNTS the ratio of NTSH and NTSR. RNTS = NTSH/NTSR Notched tensile stress (maximum stress) in the reference environment, NTSR - the mean value of the measured NTSR in the reference environment. Notched tensile stress in hydrogen, NTSH - the mean value of the notched tensile stress measured in the hydrogen environment. Relative reduction of area, RRA = RAH/RAR RAR is the mean value of the RA measured after testing in the reference environment RAH is the mean value of the RA measured after testing in the hydrogen environment. Reduction of area (RA) is one minus the ratio of the final cross section area (A) of the specimen measured at the location of fracture divided by the original cross section area (A 0 ) of the specimen. RA=1-(A/A 0 ). 7

8 4 Introduction In previous review, namely D2.5, several regulations, codes and standards dealing with (or in some cases without) hydrogen effect on fatigue design of pressure components used for the containment of high pressure hydrogen have been analyzed. The current update looks at the North American standard ANSI/CSA CHMC [1], which was recently published and deals specifically with the design of metallic pressure components subjected to hydrogen-enhanced fatigue. 5 ANSI/CSA CHMC standard applied to material compatibility The development of this standard started in 2002 after discussion with the U.S. Department of Energy, Renewable Fuels Group in Washington, D. C. to discuss standards development opportunities in hydrogen technology area. CSA undertook the development of such a standard based on industry needs and feedback [1] : There were no comprehensive standards available for material suitability in hydrogen applications. Automotive OEMs driving the application of hydrogen as a fuel for vehicles expressed concern over results from demonstration projects in the field. Quoting ref. [1] : The focus of the Test Method for Evaluating Material Compatibility in Compressed Hydrogen Applications standard established uniform test methods for evaluating material compatibility with compressed hydrogen applications. The results of these tests are intended to provide a basic comparison of materials performance in applications utilizing compressed hydrogen. This standard is not intended to replace the targeted testing which may be necessary to qualify the design of a component manufactured for use in hydrogen applications. An important feature of the ANSI/CSA CHMC standard is the possibility to experimentally derive a safety factor multiplier (SFM) to account for the degradation of mechanical and fatigue properties of metallic materials in contact with hydrogen. It is well known that hydrogen reduces the resistance of metallic materials to crack initiation and propagation, with reduction of ductility. The mechanisms that explain the hydrogen embrittlement mechanisms are still a matter of discussion, and will not be treated here. The methodology proposed by ANSI/CSA CHMC standard is described in Figure 1. Four classes of metallic materials are specified in the standard: Ni-base alloys, 300 series Cr-Ni austenitic stainless steels, carbon and low alloy steels and aluminum alloys. The flowchart shown in Figure 1 provides the rationale of the qualification process of metallic materials used for the containment of high pressure hydrogen. The verification of compatibility of the metal or alloy with hydrogen is verified through reduction factor ratio obtained with slow strain rate tensile testing of notched or smooth specimens according to ASTM G129 [2] and ASTM E8 [3] standards. 8

9 Figure 1 : Flowchart outlining the methodology and requirements of the qualification process of metallic materials used for the containment of high pressure hydrogen. A material is considered compatible with hydrogen if RNTS>0.90 or RRA>0.90 is verified per clause If RNTS 0.50, the material is eligible for qualification using clause plus clause 6.3 or ANSI/CSA CHMC standard applied to fatigue life tests In clause 6.3 Determination of safety factor multiplier an experimental procedure is described in order to derive a safety factor to assess fatigue properties. According to the standard, a safety factor multiplier 9

10 (SF) shall be multiplied to existing design safety factors of any component to account for the detrimental effects of gaseous hydrogen 12. An example of such method is shown in Figure 2. Fatigue tests shall follow ASTM E466 [4] for force controlled fatigue tests or ASTM E606 [5] for strain controlled fatigue tests. Notched tensile specimens are also recommended and shall follow ASTM G142 [2], but it is highlighted to use notch severity, Kt, greater than or equal to 3. A minimum of 12 tests shall be performed in hydrogen and 12 tests in air or inert atmosphere. Another recommendation is to conduct a minimum of 4 tests for each environment at load amplitudes that result in cycles to failure between 10 3 and 10 4 ; similarly 4 tests for each environment shall yield cycles to failure between 10 4 and 10 5 and 4 tests for each environment shall yield greater than 10 5 cycles to failure [1]. It is mandatory to perform statistical analysis of the fatigue data as explained in Annex F, which follows ASTM E739 [6]. The safety factor (SF) multiplier is the largest of the four ratios determined through the statistical analysis of fatigue results. Figure 2 : Schematic representation of the results of the safety factor multiplier method [1] Clause 6.4 Design qualification by testing allows to design a component using a published design code or any documented design rules so long as the method considers the possibility of failure by fatigue. The design rule may consider fatigue crack growth (e.g. fracture mechanics based design) or it may consider traditional fatigue analysis (stress based or strain based design). Fatigue life properties required by the design code/rules shall be measured in accordance with either stress or strain controlled techniques as described in clause 5.7. Alternatively a fracture mechanics based approach can be used. 7 ANSI/CSA CHMC standard applied to fracture mechanics based fatigue testing In this case, as usual, it is considered that the component has an initial crack and that the cyclic load fluctuations due to hydrogen pressure variations will provide the driving force for the crack to propagate. The component failure will occur when the fracture mechanics parameter (K IC or J IC ) associated with the crack exceeds a critical value [1]. According to the standard, any fracture toughness property required by the chosen design method, e.g. K IC or J IC, shall be measured in accordance with Clause 5.5 Hydrogen Assisted Cracking Threshold Stress Intensity Factor, as K IH or J IH, and shall follow ASTM E1820 [7]. 10

11 For the calculation of fatigue crack growth rates (FCGR) the ASTM E647 [8] in conjunction with clause 5.6 is employed. The standard allows the use of experimental data used at R ratio values lower than the R-ratio that will be expected during the operation of the component (R comp ). In this case, the same idea of a safety factor multiplier is used to account for the effect of R-ratio on fatigue crack growth rate. In order to do so, an effective value of the cyclic stress intensity factor, *, which will be used in design calculations is provided by Eq. (1), and the corrected Paris equation is modified accordingly as in Eq. (2). K = ( 1 Rexp 1 R comp) Kexp (1) ( da dn )comp = C [( 1 Rexp 1 R comp) Kexp ] m (2) where R exp and K exp are respectively the stress ratio and the applied K during experimental tests. 8 CONCLUSION The ANSI/CSA CHMC provides a testing methodology for evaluating metallic material compatibility in compressed hydrogen applications. The standard refers to the applicability of current testing methods to verify the degradation of mechanical properties of materials used in contact with hydrogen. Three mechanical properties are evaluated: ductility, fracture toughness and fatigue properties. It is summarized in Table 1. The use of SFM method is also proposed bt Mathryce with the following differences: One concerning the experimental determination of the safety factor, which is based on the ratio of number of cycles obtained in inert environment or laboratory air and in hydrogen for the same R- ratio. The safe factor of MATHRYCE, named as hydrogen sensitivity factor (HSF) is applied to the number of cycles of the full scale hydraulic component test (Figure 3). The use of the safe factor is not the same. In the standard ANSI/CSA CHMC1-2014, SFM is related to the allowable stress level defined by design code used for the component. Figure 3. Recommendations of using a hydrogen sensitivity factor (HSF) coupled with full scale hydraulic fatigue tests. 11

12 HSF is obtained from laboratory scale tests, such as SEN (single edge notch specimen in bending or tension) and disc-fatigue tests. These recommendations were presented to the ISO TC197/WG15 [9]. Table 1. Advantages and drawbacks of standard ANSI/CSA CHMC Code ANSI/CSA-CSHMC-1 [1] H2 fatigue design method a) Material is considered insensitive to HE b) Fatigue tests on notched specimen (frequency 1 Hz) associated to the use of safety factor multiplier c) Combination of existing codes and tests performed under H 2 d) Allows also the use of fracture mechanics based approach as an alternative to fatigue life tests Advantages a) Several options possible b) Propose a way of considering the effect of the R- ratio Drawbacks a) Safety factor multiplier does not take into account scale effect, and it is over conservative regarding the number of cycles [10] The central idea of the ANSI/CSA CHMC standard is to account for the reduction in mechanical properties through safety factor multipliers, as exemplified below: Ductility reduction: through the ratios RNTS or RRA obtained through slow strain rate testing. A material is considered compatible with hydrogen if RNTS>0.90 or RRA>0.90 is verified per cl If RNTS 0.50, the material is eligible for qualification using clause plus clause 6.3 or 6.4. Fatigue life test: The safety factor (SF) multiplier is the largest of the four ratios determined through the statistical analysis of fatigue results. It is mandatory to perform statistical analysis of the fatigue data as explained in Annex F, which follows ASTM E739. Fatigue crack growth rate: a safety factor multiplier is used to account for the effect of R-ratio on fatigue crack growth rate. In order to do so, an effective value of the cyclic stress intensity factor, K*, which will be used in design calculations with a modified Paris equation. 9 References [1] ANSI/CSA CHMC Test methods for evaluating material compatibility in compressed hydrogen applications Metals, CSA Group, Ontario, Canada. [2] ASTM G (Reapproved 2006) Standard Practice for Slow Strain Rate Testing to Evaluate the Susceptibility of Metallic Materials to Environmentally Assisted Cracking. [3] ASTM E8/E8M-11 Standard Test Methods for Tension Testing of Metallic Materials. [4] ASTM E Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials. [5] ASTM E606/E606M-12 Standard Practice for Strain-Controlled Fatigue Testing. [6] ASTM E Standard Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-n) Fatigue Data. [7] ASTM E Standard Test Method for Measurement of Fracture Toughness. 12

13 [8] ASTM E Standard Test Method for Measurement of Fatigue Crack Growth Rates. [9] Briottet, L; MATHRYCE outputs General recommendations for standardization, MATHRYCE Dissemination Workshop, AFNOR, Paris, September 21, [10] Yamabe J, Matsunaga H, Furuya Y, Hamada S, Itoga H, Yoshikawa M, Takeuchi E, Matsuoka S. Qualification of chromium-molybdenum steel based on the safety factor multiplier method in CHMC International Journal of Hydrogen Energy 2015;40: