An indentation based investigation on the characteristics of artificially aged pipeline steels

An indentation based investigation on the characteristics of artificially aged pipeline steels

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Procedia Structural (2017) 172–175 Structural IntegrityIntegrity Procedia300 (2016) 000–000

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XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy

An indentation based investigation on the characteristics of artificially aged pipeline steels artificially aged pipeline steels

An indentation based investigation on February the characteristics of Portugal XV Portuguese Conference on Fracture, PCF 2016, 10-12 2016, Paço de Arcos, b Thermo-mechanicalGabriella modeling of aa*, high pressure turbine blade of an Bolzon Olha Zvirko a b Gabriella *, Olha Zvirko airplaneBolzon gas turbine engine Department of Civil and Environmental Engineering, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano, Italy a

ba b

Karpenko Physico-Mechanical Institute ofEngineering, the NationalPolitecnico Academy ofdiSciences Ukraine, 5 Naukova Street, 79060 Milano, Lviv, Ukraine Department of Civil and Environmental Milano, of piazza Leonardo da Vinci 32, 20133 Italy a b c Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5 Naukova Street, 79060 Lviv, Ukraine

P. Brandão , V. Infante , A.M. Deus *

a

Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa,

Portugal Abstract b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Abstract Portugal Thec decay of the mechanical properties of structural components operating in an aggressive environment can be detected by nonCeFEMA, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, destructive indentation tests. The effectiveness of this approach has been verified on artificially aged pipeline Indentation The decay of the mechanical properties of structural components operating in an aggressive environment can besteel. detected by nonPortugal tests have been performed at The different scales to of verify transferability the laboratory results aged to thepipeline field conditions, in view destructive indentation tests. effectiveness this the approach has beenofverified on artificially steel. Indentation of thehave possible in-situ diagnostic procedures. tests beendevelopment performed atofdifferent scales to verify the transferability of the laboratory results to the field conditions, in view © 2017 The Authors. Published by Elsevier B.V. procedures. of Abstract the possible development of in-situ diagnostic Copyright © 2017 The Authors. Published Elsevier Committee B.V. This is an Peer-review responsibility of Elsevier the by Scientific ofopen IGF access Ex-Co.article under the CC BY-NC-ND license © 2017 The under Authors. Published by B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). During their operation, modern aircraft engine components areEx-Co. subjected to increasingly demanding operating conditions, Peer-review under responsibility of the Scientific Committee IGF Peer-review under responsibility of the Scientific Committee of IGFof Ex-Co. Keywords: pipeline steel;pressure material turbine aging; mechanical characteristics; indentation especially the high (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, onesteel; of which is aging; creep.mechanical A model using the finiteindentation element method (FEM) was developed, in order to be able to predict Keywords: pipeline material characteristics; the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model 1. company, Introduction for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were 1. needed Introduction obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D The severe working conditions of gas pipelines induce material degradation with increased risk of uncontrolled rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The brittle and, therefore, economic losses andmaterial environmental actual margins Thefailure severe working conditions ofdisplacement gas pipelines induce degradation with increased risk ofsafety uncontrolled overall expected behaviour in significant terms of was observed, in particular at consequences. the trailing edgeThe of the blade. Therefore such a ofmodel thesefailure infrastructures depend on the evolution with time of their mechanical properties, which depend on a number brittle and, therefore, significant economic losses and environmental consequences. The actual safety margins can be useful in the goal of predicting turbine blade life, given a set of FDR data.

of these factors that include depend the material thetime environment conditions,properties, the external loading (Gabetta et al., infrastructures on thecomposition, evolution with of their mechanical which depend on a number 2016 The byNykyforchyn Elsevier B.V. et al., 2008; Nykyforchyn etPublished al., of©factors thatAuthors. include the2010; material composition, the2012). environment conditions, the external loading (Gabetta et al., Peer-review under of the Scientific Committee ofstatus PCF 2016. TheNykyforchyn reliable andresponsibility assessment of theet material can be facilitated by the implementation of non2008; ettimely al., 2010; Nykyforchyn al., 2012). destructive diagnostic procedures based on tests. Thiscan fastbe andfacilitated inexpensive can be performed The reliable and timely assessment of indentation the material status by experiment the implementation of nonKeywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation. directly on diagnostic the components, without the on need of extracting and working out specimens pre-fixed destructive procedures based indentation tests.material This fastspools and inexpensive experiment can beofperformed directly on the components, without the need of extracting material spools and working out specimens of pre-fixed

* Corresponding author. Tel.: +39-02-2399-4319; fax: +39-02-2399-4300. E-mail address:author. [email protected] * Corresponding Tel.: +39-02-2399-4319; fax: +39-02-2399-4300. E-mail address: [email protected] 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer-review underThe responsibility of218419991. theby Scientific Committee of IGF Ex-Co. * Corresponding author. Tel.: +351 2452-3216 © 2017 Authors. Published Elsevier B.V. E-mail address: [email protected] Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 2452-3216 © 2016 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of the Scientific Committee of PCF 2016.

Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 10.1016/j.prostr.2017.04.033

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geometry (Bolzon et al., 2012; Bolzon et al., 2015). The sensitivity of this investigation methodology to the decay of the material properties induced by aging has been be evaluated on pipeline steels of different composition and in different states. The transferability of the laboratory results to the operative environment has been verified by performing the test at different scales. The current state of this research is summarized in this contribution. 2. Materials Different pipeline steels have been considered for the present investigation. In particular, samples of 17H1S (Ukrainian code, equivalent to X52) steel were cut from a pipe of 529 mm diameter and 8 mm wall thickness, others made of X60 steel were extracted from a pipe 455 mm diameter and wall thickness t = 14 mm. The different production technology of these structural components was reflected by the material microstructure, significantly finer and more homogeneous in the case of X60 steel. Samples of both materials have been subjected to accelerated degradation processes, induced in laboratory under combined thermo-mechanical and hydrogen action. The machined specimens, shown in Fig. 1, were electrolytically pre-charged by hydrogen in an aqueous sulphur acid solution (pH2) at 20 m/m2 for 95 hours; then they were mechanically stretched up to 2.8% axial strain and finally exposed to 250º for 1 hour. This procedure permits to simulate, on a laboratory scale, the degradation of steel during long-term exploitation. Further details have been presented by Zvirko et al. (2016). 3. Tensile tests The investigated materials were initially characterized by means of tensile tests. The main mechanical parameters recovered from this survey are listed in Table 1. Degraded metals present a significant reduction of the overall elongation accompanied by a substantial variation of other bulk material properties like the initial yield limit and the ultimate strength. Ukrainian 17H1S steel reveals higher susceptibility to the artificial aging. All results are consistent with those recovered from former investigations (Gabetta et al., 2008; Nykyforchyn et al., 2009; Nykyforchyn et al., 2010; Fassina et al., 2012).

Fig. 1. Steel specimen broken by tensile test. Table 1. Mechanical properties experimentally observed for studied pipeline steels in as-received and degraded states. Steel type 17H1S X60

Steel state As-received Degraded As-received Degraded

Ultimate strength [MPa] 473 467 565 610

Initial yield limit [MPa] 304 426 489 551

Reduction of area [%] 66.1 46.4 77.6 71.3

Elongation [%] 21.1 10.9 21.9 16.4

4. Indentation tests The specimens traditionally employed for the mechanical characterization of pipeline steel are extracted from the pipe wall. The material samples are subjected to a laborious machining, which makes the approach time consuming and rather expensive. Indentation represents a faster and much cheaper testing procedure, which finds growing

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application for the diagnosis of metal structures. In fact, this almost non-destructive technique can be performed directly on the operating components. Results equivalent to those of traditional tensile tests can be recovered for maximum indentation force of the order of some kN (Bolzon et al., 2012; Bolzon et al., 2015). The maneuverability of the testing apparatus to be eventually operated in field conditions is however increased by reducing the load level. The representativeness of the results of indentation tests performed at different scales has been evaluated on the considered metal samples. Table 2 reports the characteristic penetration depths obtained from Berkovich indentation at 500 mN maximum force. The obtained results are somewhat dispersed, as for instance visualized by the graphs drawn in Fig. 2, and a systematic trend cannot be enucleated at this load level. Table 2. Berkovich indentation at 500 mN maximum load. Steel type 17H1S X60

Steel state As-received Degraded As-received Degraded

Maximum penetration depth, mean value [µm] fractured fractured intact near crack middle position 2.74 2.83 2.67 2.69 2.87 2.62 2.62 2.60 2.59 2.64 -

Residual penetration depth [µm] fractured fractured intact near crack middle position 2.33÷2.45 2.50÷2.58 2.25÷2.45 2.35÷2.43 2.55÷2.63 2.31÷2.35 2.29÷2.37 2.36÷2.40 2.28÷2.36 2.33÷2.53 -

Fig. 2. Indentation curves relevant to 17H1S steel in the as-received (left) and degraded (right) states; Berkovich tip, 500 mN maximum load

Fig. 3. Indentation curves relevant to as received and exercised X60 steel; Rockwell tip, 200 N maximum load

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The output of some preliminary tests carried out on X60 steel at 200 N maximum load is visualized in Fig. 3. The graph compares the indentation curves relevant to the same material sample in the as-received and exercised states. The output is rather repetitive and a shift toward larger penetration depths is observed for the exploited material. However, the two curve sets are partially overlapping. 5. Closing remarks The sensitivity to the decay of the mechanical properties of pipeline steels in as-received and degraded states has been be evaluated by indentation tests carried out at small and moderate load levels. The dispersion of the forcedisplacement curves recovered in this investigation does not permit to reach a sound conclusion. The reliability of the results can be possibly improved by the mapping of the residual imprint left on the material surface by the indenter tip. Further verification exercises will be performed in this sense in the next future. Acknowledgements The results presented in this paper have been obtained within the research project SPS G5055 “Development of Novel Methods for the Prevention of Pipeline Failures with Security Implications”. The work is supported by a gratefully acknowledged grant received from the NATO Science for Peace and Security program. References Bolzon, G., Gabetta, G., Molinas, B., 2015. Integrity assessment of pipeline systems by an enhanced indentation technique. ASCE Journal of Pipeline Systems Engineering and Practice 6(1), 04014010, 1–7. Bolzon, G., Molinas, B., Talassi, M., 2012. Mechanical characterisation of metals by indentation tests: an experimental verification study for onsite applications. Strain 48(6), 517–527. Fassina, P., Bolzoni, F., Fumagalli, G., Lazzari, L., Vergani, L., Sciuccati, A., 2012. Influence of hydrogen and low temperature on mechanical behavior of two pipeline steels, Engineering Fracture Mechanics 81, 43–55. Gabetta, G., Nykyforchyn, H., Lunarska, E., Zonta, P.P., Tsyrulnyk, O.T., Nikiforov, K., Hredil, M.I., Petryna, D.Yu., Vuherer, T., 2008. Inservice degradation of gas trunk pipeline X52 steel. Materials Science 48(1), 104–119. Nykyforchyn, H., Lunarska, E., Tsyrulnyk, O.T., Nikiforov, K., Gabetta, G., 2009. Effect of the long-term service of the gas pipeline on the properties of the ferrite-pearlite steel. Materials and Corrosion 60(9), 716–725. Nykyforchyn, H., Lunarska, E., Tsyrulnyk, O.T., Nikiforov, K., Gennaro, M.E., Gabetta, G., 2010. Environmentally assisted in-bulk steel degradation of long term service gas trunkline. Engineering Failure Analysis 17(3), 624–632. Zvirko, O.I., Savula, S.F., Tsependa, V.M., Gabetta, G., Nykyforchyn, H.M., 2016. Stress corrosion cracking of gas pipeline steels of different strength. Procedia Structural Integrity 2, 509–516