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Project Title:

Influence of gaseous H2 with different purity on the characteristics of ferro steels of pipes

Ref.No.: 132

Project Type and Category:

Basic research

Project Duration:

1992 - bis 1998

Project Participants:

Staatliche Materialprüfungsanstalt, Dr. Deimel
Others of SFB 270 (See project no. 73)

Sponsor:

DFG

Project Budget and
Funding:

1 064 000 DM (Phase 2 – 4)

Project Description and Objectives:

An important question with respect to the safety of metallic components containing high pressure hydrogen is hydrogen embrittlement. Since large pressure vessels and long distance pipelines for hydrogen at ambient temperature were built due to cost restrictions with ferritic steels quite a number of investigations on hydrogen embrittlement of these materials were carried out mainly at room temperature [1]. Most of these tests were done using a qualitative method to simulate slow strain rates with simultaneous presence of high pressure hydrogen, the constant extension rate test (CERT). Derived from the results of this test hydrogen embrittlement of ferritic as well as austenitic materials is most pronounced in the surrounding of room temperature [1]. For aluminium alloys indications exist that hydrogen embrittlement could be possible [2].
For a materials related safety analysis of critical components the qualitative results of the CERT-tests are not sufficient. Fracture mechanics tests like the J-integral test are needed to characterize quantitatively the resistance against crack initiation and growth. For low alloy ferritic steels and gaseous hydrogen up to a pressure of 34,5 MPa critical J-integral values JIc derived from crack resistance (JR)-curves were published. A reduction of Jic up to a factor of three due to the influence of hydrogen was observed.

Technical Goals:

Since the published results and statements mentioned before are mainly deduced from investigations on base materials it is the aim of the contribution of the MPA Stuttgart to the Collaborative Research Center 270 to investigate and clarify the relevance of hydrogen embrittlement for weld joints of ferritic and austenitic materials as well as aluminium alloys in the range from room temperature up to 300°C. As a first step CERT-tests are performed to get information about the most critical region of the weld joints. Afterwards J-integral tests in the single specimen technique will be carried out for the critical region of the weld joint defined by the CERT-test. Also cyclic crack growth tests will be done.

Project Status

Final phase

Preliminary or Final Results:

First results were obtained for the base material from tensile and fracture mechanics tests at room temperature and for pure gaseous hydrogen with a pressure of 9 MPa on the ferritic steels StE 480.7 TM (X 70) and 15 MnNi 6 3 performed in the testing facility shown in Fig. 1. Comparing the necked profile of a tensile specimen tested in pure high-pressure hydrogen to one tested in argon the significant effect of hydrogen embrittlement becomes obvious, Fig. 2. This is also apparent in the micrographs of the fracture surfaces. In argon environment a pronounced reduction of area is accompanied by a completely dimpled fracture surface, whereas in hydrogen environment a much smaller reduction of area is combined with secondary cracks and a quasi-brittle fracture surface. This qualitative behaviour illustrated in Fig. 2 was quantified revealing a decrease of the reduction of area by a factor of about two due to the influence of hydrogen. The fracture surfaces originated during a J-integral test on a 20 mm thick compact tension specimen CT 20 at room temperature in argon as well as in hydrogen are shown in Fig. 3. In order to get a quantitative information on the transition region from the fatigue precracked region to the region of stable crack growth at the lines marked on the micrographs in Fig. 3 the profile of the fracture surface was determined using on automatically operating image processing system connected to a scanning electron microscope. A distinct difference is seen between the profile measured in argon environment and that for hydrogen environment. The stretched zone present in the case of argon is not existent for the test in hydrogen. With respect to the fracture mode the micrographs of the crack advance in top view show similar features like the corresponding ones in Fig. 2. Due to the fact that in the case of hydrogen environment a stretched zone could not be seen it is not possible to derive the J-integral Ji at crack initiation from the JR-curve. Using the standardized JIc-value to get a quantitative measure for the influence of the two different media a decrease in this value by a factor of about four due to high pressure hydrogen is seen. Since the JIc-value is not suitable to characterize the physical crack initiation consequences for a materials related safety analysis can arise.

Related Reference Papers and Other Publications:

Similar projects: 121-125
[1] Deimel, P. und M. Hoffmann: Kapitel 5 der Studie ""Gefährdungspotential bei einem verstärkten Wasserstoffeinsatz"" im Auftrag des Büros für Technikfolgenabschätzung des Deutschen Bundestages (TAB), DLR Stuttgart, Februar 1992, 78-174.
[2]Nelson, H.G.: Hydrogen and advanced aerospace materials. SAMPE Quarterly 20 (1988), 20-23.
Kußmaul, K., Deimel, P. und E. Sattler: Einfluß von gasförmigem Wasserstoff Unterschiedlicher Reinheit auf die Eigenschaften ferritischer Rohrleitungsstähle. Kolloquium 1994 des Sonderforschungsbereichs 270 ""Wasserstoff als Energieträger"" der Universität Stuttgart, VDI-Verlag, Düsseldorf (1994) 267-286.
Deimel, P. und E. Sattler: Einfluß von Druckwasserstoff auf das verrformungsverhalten eines erst seit kurzem im Einsatz befindlichen modernen thermomechanisch behandelten austenitischer Stähle im Zugversuch bei Raumtemperatur. Werkstoffwoche '96, 28.-31. Mai
Kußmaul, K., Deimel, P. und E. Sattler: Wasserstoffversprödung von ausgewählten Schweißverbindungen ferritischer und austenitischer Werkstoffe sowie einer Aluminiumlegierung. Kolloquium 1997 des Sonderforschungsbereichs 270 ""Wasserstoff als Energieträger"" der Universität Stuttgart, Herausgeber: F. Philipps (September 1997) 271-291.
Deimel, P., Fischer, H., Sattler, E. und M. Hoffmann: Fracture mechanics in high pressure hydrogen for the thermomechanically treated steel X 70, Proc. of the Hypothesis II Symposium held in Grimstad, Norway, 18-22 August 1997, T.O. Saetre ed., Kluwer Academic Publ., Dordrecht, Boston, London (1998) 331-336.
Kussmaul, K., Deimel, P., Fischer, H. und E. Sattler: Fracture mechanical behaviour of the Steel 15 MnNi 6 3 in argon and in high pressure hydrogen gas with admixtures of oxygen, Int. J. Hydrogen Energy, 23, (1998) No. 7, 577-582.

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Project Title: Influence of gaseous H2 with different purity on the characteristics of ferro steels of pipes		Ref.No.: 132
Project Type and Category:	Basic research
Project Duration:	1992 - bis 1998
Project Participants:	Staatliche Materialprüfungsanstalt, Dr. Deimel Others of SFB 270 (See project no. 73)
Sponsor:	DFG
Project Budget and Funding:	1 064 000 DM (Phase 2 – 4)
Project Description and Objectives:	An important question with respect to the safety of metallic components containing high pressure hydrogen is hydrogen embrittlement. Since large pressure vessels and long distance pipelines for hydrogen at ambient temperature were built due to cost restrictions with ferritic steels quite a number of investigations on hydrogen embrittlement of these materials were carried out mainly at room temperature [1]. Most of these tests were done using a qualitative method to simulate slow strain rates with simultaneous presence of high pressure hydrogen, the constant extension rate test (CERT). Derived from the results of this test hydrogen embrittlement of ferritic as well as austenitic materials is most pronounced in the surrounding of room temperature [1]. For aluminium alloys indications exist that hydrogen embrittlement could be possible [2]. For a materials related safety analysis of critical components the qualitative results of the CERT-tests are not sufficient. Fracture mechanics tests like the J-integral test are needed to characterize quantitatively the resistance against crack initiation and growth. For low alloy ferritic steels and gaseous hydrogen up to a pressure of 34,5 MPa critical J-integral values JIc derived from crack resistance (JR)-curves were published. A reduction of Jic up to a factor of three due to the influence of hydrogen was observed.
Technical Goals:	Since the published results and statements mentioned before are mainly deduced from investigations on base materials it is the aim of the contribution of the MPA Stuttgart to the Collaborative Research Center 270 to investigate and clarify the relevance of hydrogen embrittlement for weld joints of ferritic and austenitic materials as well as aluminium alloys in the range from room temperature up to 300°C. As a first step CERT-tests are performed to get information about the most critical region of the weld joints. Afterwards J-integral tests in the single specimen technique will be carried out for the critical region of the weld joint defined by the CERT-test. Also cyclic crack growth tests will be done.
Project Status	Final phase
Preliminary or Final Results:	First results were obtained for the base material from tensile and fracture mechanics tests at room temperature and for pure gaseous hydrogen with a pressure of 9 MPa on the ferritic steels StE 480.7 TM (X 70) and 15 MnNi 6 3 performed in the testing facility shown in Fig. 1. Comparing the necked profile of a tensile specimen tested in pure high-pressure hydrogen to one tested in argon the significant effect of hydrogen embrittlement becomes obvious, Fig. 2. This is also apparent in the micrographs of the fracture surfaces. In argon environment a pronounced reduction of area is accompanied by a completely dimpled fracture surface, whereas in hydrogen environment a much smaller reduction of area is combined with secondary cracks and a quasi-brittle fracture surface. This qualitative behaviour illustrated in Fig. 2 was quantified revealing a decrease of the reduction of area by a factor of about two due to the influence of hydrogen. The fracture surfaces originated during a J-integral test on a 20 mm thick compact tension specimen CT 20 at room temperature in argon as well as in hydrogen are shown in Fig. 3. In order to get a quantitative information on the transition region from the fatigue precracked region to the region of stable crack growth at the lines marked on the micrographs in Fig. 3 the profile of the fracture surface was determined using on automatically operating image processing system connected to a scanning electron microscope. A distinct difference is seen between the profile measured in argon environment and that for hydrogen environment. The stretched zone present in the case of argon is not existent for the test in hydrogen. With respect to the fracture mode the micrographs of the crack advance in top view show similar features like the corresponding ones in Fig. 2. Due to the fact that in the case of hydrogen environment a stretched zone could not be seen it is not possible to derive the J-integral Ji at crack initiation from the JR-curve. Using the standardized JIc-value to get a quantitative measure for the influence of the two different media a decrease in this value by a factor of about four due to high pressure hydrogen is seen. Since the JIc-value is not suitable to characterize the physical crack initiation consequences for a materials related safety analysis can arise.
Related Reference Papers and Other Publications:	Similar projects: 121-125 [1] Deimel, P. und M. Hoffmann: Kapitel 5 der Studie ""Gefährdungspotential bei einem verstärkten Wasserstoffeinsatz"" im Auftrag des Büros für Technikfolgenabschätzung des Deutschen Bundestages (TAB), DLR Stuttgart, Februar 1992, 78-174. [2]Nelson, H.G.: Hydrogen and advanced aerospace materials. SAMPE Quarterly 20 (1988), 20-23. Kußmaul, K., Deimel, P. und E. Sattler: Einfluß von gasförmigem Wasserstoff Unterschiedlicher Reinheit auf die Eigenschaften ferritischer Rohrleitungsstähle. Kolloquium 1994 des Sonderforschungsbereichs 270 ""Wasserstoff als Energieträger"" der Universität Stuttgart, VDI-Verlag, Düsseldorf (1994) 267-286. Deimel, P. und E. Sattler: Einfluß von Druckwasserstoff auf das verrformungsverhalten eines erst seit kurzem im Einsatz befindlichen modernen thermomechanisch behandelten austenitischer Stähle im Zugversuch bei Raumtemperatur. Werkstoffwoche '96, 28.-31. Mai Kußmaul, K., Deimel, P. und E. Sattler: Wasserstoffversprödung von ausgewählten Schweißverbindungen ferritischer und austenitischer Werkstoffe sowie einer Aluminiumlegierung. Kolloquium 1997 des Sonderforschungsbereichs 270 ""Wasserstoff als Energieträger"" der Universität Stuttgart, Herausgeber: F. Philipps (September 1997) 271-291. Deimel, P., Fischer, H., Sattler, E. und M. Hoffmann: Fracture mechanics in high pressure hydrogen for the thermomechanically treated steel X 70, Proc. of the Hypothesis II Symposium held in Grimstad, Norway, 18-22 August 1997, T.O. Saetre ed., Kluwer Academic Publ., Dordrecht, Boston, London (1998) 331-336. Kussmaul, K., Deimel, P., Fischer, H. und E. Sattler: Fracture mechanical behaviour of the Steel 15 MnNi 6 3 in argon and in high pressure hydrogen gas with admixtures of oxygen, Int. J. Hydrogen Energy, 23, (1998) No. 7, 577-582.