assessment of creep rupture properties for the eccc 2019

Assessment of Creep Rupture Properties for the ECCC 2019 Datasheet for Grade 92

C. Bullough1, A. Norman2, S. Holmström3, M. Ortolani4, M. Schwienheer5 , M. Subanovic6, J. Hald7

1 GE Steam Power, Newbold Road, CV21 2NH Rugby (United Kingdom)2 UK Atomic Energy Authority, Culham Science Centre, OX14 3DB (United Kingdom), formerly at GE Power1

3 Joint Research Centre, Westerduinweg 3, 1755 LE Petten, (Netherlands)4 Tenaris, Piazza Caduti 6 Luglio 1944, 24044 Dalmine BG (Italy)5 Chair and Institute for Materials Technology, TU Darmstadt, Grafenstr. 2, 64283 Darmstadt (Germany)6 Vallourec Research Center, Theodorstr. 109, 40472 Düsseldorf (Germany)7 Technical University of Denmark, Department of Mechanical Engineering, 2800 Kgs. Lyngby (Denmark)

ECCC Webinar – P91, P92, ALLOY 617

8th October 2020

©2020 - Author Organisations08/10/2020 ECCC Webinar

Introduction – Topics

The ECCC 2019 datasheet for Grade 92 has been published and is being considered for use in EN standards.

The purpose of this presentation, and associated paper (submitted to ECCC 2021 conference / Materials at High Temperatures) is to:

• describe the collation and pre-assessment of test data from worldwide sources

• explain the assessment and post-assessment methods used for the derivation of the strength values

• consider the strengths in relation to other property sets, other materials

• note the associated derivation of other design properties (1% creep strengths, minimum creep rates, … see ECCC2021!)

2©2020 - Author Organisations08/10/2020 ECCC Webinar

ECCC Grade 92 Datasheet 2019In December 2019, the ECCC issued a revised Full Assessment Data Sheet on: • Grade 92 steel – X10CrWMoVNb9-2, W. Nr. 1.4901forwarding that datasheet to CEN for consideration for EN standards.

Current public ECCC datasheets (41 in total) can be accessed at: https://www.eccc-creep.com/eccc-data-sheets/New users should apply for access at: [email protected] stating their company / organisation- expected use of the datasheets- agreement that any use of the datasheet will be fully

acknowledged.

Membership of ECCC gives access to Confidential datasheets, technical reviews, material characterisation etc. If interested, please contact the secretariat.


https://www.eccc-creep.com/eccc-data-sheets/

mailto:[email protected]

Standard

Name

Number

wt% Min Max Min Max

C 0.08 0.12 0.07 0.13

Si 0.20 0.50 0.50

Mn 0.30 0.60 0.30 0.60

P 0.020 0.020

S 0.005 0.010

Cr 8.5 9.0 8.5 9.0

Mo 0.85 1.05 0.30 0.60

Ni 0.40 0.40

Al tot 0.02 0.02

Cu 0.30 -

Nb 0.06 0.10 0.04 0.09

Ti 0.01 0.01

V 0.15 0.25 0.15 0.25

N 0.030 0.070 0.030 0.070

B - - 0.001 0.006

W - - 1.50 2.00

Zr 0.01 0.01

Heat Treat.

Austenitize

Temper

Rp0.2

Rm

%Elong A5

KV2 (J) 20°C

440 MPa 430 MPa

630-830 MPa 620-850 MPa

19 (long) 17 (tran) 19 (long) 17 (tran)

40 (long) 27 (tran) 40 (long) 27 (tran)

+NT +NT

1040-1090°C Air 1040-1090°C Air

730 -780°C Air 730 -780°C Air

EN 10216-2

X10CrMoVNb9-1

1.4903

EN 10216-2

X10CrWMoVNb9-2

1.4901

Background & Assessment Need #1• Grade 92 was developed in Japan during the early

1990’s; grade name - NF616. • Production methods, and initial ASME Code Case

2179 based on Nippon Steel 1993 assessment published in Naoi et al [1], Masuyama [2], resp.

• Main use is tubing and piping, EN 10216-2, but also available in rolled and forged product (not covered by EN standards).

• Especially relevant to USC Steam Plant (<625°C), but used widely throughout power generation.

• Grade 92 composition (right hand columns) similar to Grade 91 (left hand) in EN 10216-2, except for reduction in Mo, compensated for by W; & deliberate addition of B.

• Heat treatment identical, release properties similar.


08/10/2020 ECCC Webinar

Background & Assessment Need #2• Initial ECCC datasheet (Hald, 1999) based on

assessment of Japanese and European heats - 704 tests (JP/UK), max 43kh (many <500h)- PD6605 assessment (+1 other)- 100kh/600°C Rupture strength: 123MPa

• Followed by second ECCC datasheet (max 110kh test duration), Holdsworth 2005 [4]

- 48 heats, 831 tests (JP/UK), max 110kh - PD6605 assessment (+1 other)- 100kh/600°C Rupture strength: 113MPa

• Present 2019 assessment – collation 2017- JP/IT/DE/UK/FR/BE/NL, 61 heats (pipes, pipe

forgings/bends, tubes, plates, other forgings +bar). At 21 temperatures, 1037 tests, max 150kh (B), 198kh (UB)

- PD6605 assessment (+2 others)- 100kh/600°C Rupture strength: see later!

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Table 1: Distribution of Data Collated 2017

The ECCC gratefully acknowledges data supplied by outside organisations for the preparation of its datasheets, thereby aiding the development of reliable strength values for standardisation and design purposes.

©2020 - Author Organisations


Candidate AssessmentsECCC Volume 5 §2.2 [5], - At least 2 CRDAs, independent (- One CRDA has ECCC procedure document- ….

Assessments- Subonavic, ISO 6303 Manson-Haferd Polynomial order 5,

and Region Splitting 2 x Larson-Miller Polynomial order 3.- Schwienheer, DESA Manson-Haferd Polynomial order 3 - Norman & Bullough, PD 6605 Manson–Brown, rational

polynomial, 3rd order over 2.

Strength values close together (within ~+5% at 100kh)

… Norman & Bullough assessment selected by reviewers (WG3A).

6©2020 - Author Organisations


Assessment ApproachCollation and InitiationPre-assessment- Remove materials outside specification; remove duplicates, note atypical matls- Plot isothermals, identify/resolve/summarise anomalies- Select best-tested casts, identify inflections/sigmoidal behaviour

Main assessment (PD 6605)- Apply full set of models, parametric/algebraic/mixed/user defined (65)- Identify main relationships (eg linear T / reciprocal T models)- Initial shortlist models from main families; polynomials - optimise degree using

tests of significance; ECCC PAT1.1 visual check (~12-15)- Final shortlist models based on ECCC PAT1.2, 1.3 (physicality) PAT2.1, 2.2

goodness of fit full/isothermal - best-tested casts (~4-5).- Provisional model selection (1) extrapolate robustly / no influential casts

if none, consider further user-defined models; consider sub-populations –product/composition/heat treatment etc.

Post assessment- Apply ECCC PAT3.1,3.2 Repeatability & Stability of Extrapolation (sub-group, re-

iterate if necessary)- Report, review, approve.

7Figure Reference: BS PD6605-1, Figure 1



Standard Model SetSource: EN 13445-2 Annex R,

recently updated by ECCC.

Polynomial in log10[s] gives

greatest problems in stability of

extrapolation.

Alternative (non-standard) forms

considered –

1) "DESA" – stress raised to

power

2) Rational polynomials –

predictable / stable in

extrapolation

(Other "user-defined" models not

shown here; mainly algebraic /

region splitting/ Wilshire-type.) 8©2020 - Author Organisations


Maximum Likelihood Method• Assessment approach uses a combined Time & Stress left censor.

- tests less than 10h + tests at same temperature with same/higher stress removed

- censoring approach avoids undue bias of short-term tests

• Maximum Likelihood Estimation (MLE) for failure data

- “Hazard”/ “Survival” functions for failed / unfailed data resp.

- Using only failed data, and the same distribution, MLE and linear regression give

the same model coefficients! However,

- Linear regression ignores unfailed data & “right-censors” the data set; typically strong

heats are removed.

- Linear regression uses an inappropriate error distribution (long-tailed); for rupture data

the assumption that the residuals are independent of T, so is never met.

• Error function is heteroscedastic (“Funnel-shaped”)

- Weibull error distribution (optional - log-logistic); with shape parameter a

- Greater error in log10(tu) at high stress, high temperature fitted

T is the absolute temperature, so the initial stress, go … g2 fitted coefficients9©2020 - Author Organisations


Assessment Results - Isothermals

10

Fit: Manson-Haferd, To=0, Rational Polynomial 3-2


Fit: Manson-Brown, To=0, Rational Polynomial 3-2: better temperature flexibility.Selected model

Full dataset• Colours represent the

same temperatures as on the previous slide

• Open symbols are unfailed tests

• MB3-2 model - solid line• -20% stress line shown

dashed

• All of the test data exceed the -20% line.

• The unfailed test data –used directly - “support” the shape of the curve at lower stresses.


Assessment Results - Parameter


Identified outlier at -4s

By product• 20 pipes straddle the

median line. • 15 tubes generally have

higher strength than median (except at 625°C).

• Plate (9) , bar(2) and forgings (3), generally slightly below the median at high stress

• but begin to match the median stress at lower stresses/higher temperatures.


Assessment Results – by Product


• Isothermal plots, with stress reversed on x-axis• Each colour/symbol represents the residual error

log(t_u) of a “best-tested cast”.• Each material behaves consistently, but differently• No particular overall trend – confirms validity of the

fitted line


Assessment Results - Residuals


08/10/2020 ECCC Webinar ©2020 - Author Organisations

ECCC Post Assessment Tests

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• A selection of the ECCC Post Assessment Tests are shown• Standardised residual in log(t-u). (Residual divided by the

standard error of the estimate.)• Non-uniformity of the error is confirmed (reduces as the

temperature is increased, as stress is reduced)• Cull tests not shown (“culled fits” are virtually

indistinguishable from full dataset)


ECCC 2019 Datasheet


Datasheet contains:-- materials /data summary- table of strengths- master equation/coeffs

Use within the range of the table!

Derived Strengths

16

ECCC 2005 Fit: Manson-Haferd , To=500 K, 4th order Polynomial - log(so)

ECCC 2019 Fit: Manson-Brown, To=0, Rational Polynomial 3-2

• ECCC 2005 polynomial suffers a turn-back at ~27MPa; overcome by use of Rational Polynomial in ECCC 2019.

• Otherwise little difference in recent derived strengths at >575°C. • ECCC 2019 - 100kh/600°C Rupture strength: 112MPa• Comment: ASME Code Case 2179-9 (approved July 2020) contains a revision

of grade 9Cr-2W; omitted here as not yet published.


Creep Ductility – Mayer et al 2017


Source: Mayer et al 2017 [6]

- Low ductility => property of the

material, specimen size effect, steel

cleanliness influence.

Potential viewpoint:

- Low ductility in high creep strength

heats somewhat inevitable as strain

concentrated at grain boundaries

- Less of a problem, as allowable

stresses much below material

property.

- Conversely, low ductility in low creep

strength heats (eg. d-ferrite / poor

normalisation, deleterious

segregation) more of a problem.

- Potential for greater life fraction

consumed in service.

Note, there is no evidence of embrittling

phases. Our view : no penalties or

possible exclusion from ASME code

cases are required.

Further papers in ECCC2021!

Conclusions

18

The ECCC has recently completed its assessment of steel Grade 92. The datasheet is available from the

website. The dataset analysed was made up of predominantly tubes and pipes, but with some plates/bars

and forged products. It comprises more than 1,000 tests, with a small but significant number of long-term

unfailed tests.

• The assessment method incorporates maximum likelihood estimation, user defined models and formal

treatment of failed/unfailed data. It also addresses the heteroscedasticity evident in rupture data.

• Nevertheless, even with a significant increase in test volume, the predicted strength values are only a

little changed (eg. decreased by ~1% at 100kh / 600°C) from those issued by ECCC in 2005. This is

believed to arise from the consistent rupture behaviour of Grade 92, and the stable ECCC assessment

and post assessment methods.

• The strengths in the datasheet are recommended for all products, though there is some evidence of

higher in tube products, at low temperatures that could fall away as temperature is increased. Some

products (particularly tubes/pipes) have low ductility at long-times, but this does not mean that they

show brittle behaviour. So far, it has been ascribed to general reduction in tertiary creep in high strength

steels, but needs to be investigated with respect to other influencing factors.

• Several other aspects of Grade 92 behaviour are considered further in papers submitted to ECCC2021,

Edinburgh, Sept 2021 – we hope to see you there!


References

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[1] Naoi, H., Mimura, H., Ohgami, M., Morimoto, H., Tanaka, T., Yazaki, Y., and Fujita, T., “NF616 pipe

production and properties and welding consumable development”, EPRI/National Power Conference, London

1995, pp. 8-29

[2] Masuyama, F., “ASME code approval for NF616 and HCM12A”, EPRI/National Power Conference, London

1995, pp. 98-113

[3] Bendick, W., Gabrel, J., “Assessment of the Creep Rupture Strength of the New Martensitic 9%Cr Steels

E911 and T/P92”, proc ECCC Creep Conference, London, 12-14 September 2005.

[4] Holdsworth, S.R., 2006. "Development and current status of ECCC creep property data sheets." proc

conference: “Advanced materials for power engineering 2006”, Liege (Belgium), 18-20 Sep 2006; Ed

Lecomte-Beckers, J. et al, 2006.

[5] Ed MW Spindler, “ECCC Recommendations - Volume 5 Part Ia [Issue 6], Generic Recommendations and

Guidance for the Assessment of Full Size Creep Rupture Datasets”, 2014. Available from https://www.eccc-

creep.com/.

[6] Mayer, K.-H., Kern, T.-U.,Scholz, A., Schwienheer, M. Wang, Y, Oechsner, M., Kauffmann, F.: “Influence of

Melting Methods on the Creep and Ductility Behavior of Boiler and Turbine Steels”, International ECCC

Conference 2017


https://www.eccc-creep.com/

Additional Information

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assessment of creep rupture properties for the eccc 2019

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