The new ECCC Datasheet for Alloy 617 - eccc-creep.com

The new ECCC Datasheet for Alloy 617: multi-regime models to cover a wide range of

temperature

Andrea Riva1, Michael Spindler2, Ronny Krein3, Oriana Tassa4, Eleonora Poggio1

1 Ansaldo Energia, Via Nicola Lorenzi 8, 16152 Genova, Italy

2 British Energy, Assessment Technology Group, Barnett Way, Barnwood, Gloucester GL4 3RS, UK

3 voestalpine Böhler Welding Germany GmbH, Hafenstraße 21, 59067 Hamm, Germany

4 RINA Consulting - CSM S.p.A., Via Di Castel Romano 100, 00128 Roma, Italy

Introduction

• Collation of data from worldwide sources• The data set is likely to be the largest assembled on Alloy 617

• The ECCC data assessments that followed were in accordance with the Recommendations in ECCC Volume 5• Two experienced ECCC assessors separately performed assessments

• Identification of the most accurate creep rupture model

• A new ECCC Alloy 617datasheet is issued

• Also, a separate ECCC Alloy 617B will be issued.

208/10/2020 “©2020 Copyright, Author Organizations

The material

• Alloy 617 is solid-solution hardened nickel-chromium-cobalt-molybdenum alloy used for components that in the range between 600 and 1000°C. Its oxidation resistance and high-temperature strength are the key elements that make this alloy widely used in combustion components in both aircraft and land-based gas turbines.

08/10/2020 “©2020 Copyright, Author Organizations3

E L E M E N T C O N T E N T E N C O N T E N T A S M E

Al 0.7-1.4 0.8-1.5

B <0.006 <0.006

C 0.05-0.1 0.05-0.15

Co 11-14 10-15

Cr 20-23 20-24

Cu <0.5 <0.5

Fe <2 <3

Mn <0.2 <1

Mo 8.5-10 8-10

Ni bal >44.5

P <0.01

S <0.01 <0.015

Si <0.2 <1

Ti 0.2-0.6 <0.6

The need of a re-assessment

• The most recent creep test results highlighted potential areas of improvement compared to the previous ECCC assessment, therefore ECCC-WG3C (Nickel Alloys) decided to activate the ECCC procedure that lead to a re-assessment of the material creep strength.

4

Rupture

Strength

(MPa)

EN ASME ECCC 2005 ECCC 2020

Ru,700°C,100kh 95 120.9 112 WAIT

AND

SEE…Ru,800°C,100kh 43 46.7 41

Ru,900°C,100kh 16 18.4 14.9


A new ECCC assessment

• Once ECCC WG3C (superalloy working group) agrees on the need of new assessment or update of a datasheet, the process is activated, consistently with ECCC Recommendations.

• Steps of the process: • Dataset collation

• Dataset pre-assessment

• Identification of the ECCC assessors

• Independent fitting of the models by the assessors

• Identification of the best assessment


A new ECCC dataset

6

• A new dataset was collated and pre-assessed

• 963 specimens

• 61 heats

• Temperatures between 550 and 1100°C

• Total tested time: 6.6 Mh

• Longest specimen test time: 90kh


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

A new ECCC dataset

• Many specimens have short duration

7

Temps No. of Test Durations

°C heats h h h h h h h

<10,000 10,000 to

20,000

20,000 to

30,000

30,000 to

50,000

50,000 to

70,000

70,000 to

100,000

>100,000

Number of test points available

550 1 5 (0) 2 (0) 2 (1)

593 3 6 (0) 2 (0)

600 5 15 (0) 1 (0) 1 (0) 5 (1) 4 (4)

649 6 14 (3) 2 (2) 2 (0)

650 5 17 (1) 5 (0) 2 (0) 3 (2) 2 (1)

700 5 17 (2) 6 (2) 3 (0) 2 (0) 4 (2) 1 (1)

704 2 5 (0) 2 (1)

750 3 10 (0) 1 (0)

760 7 16 (4) 4 (2) 1 (0) 2 (1)

800 9 50 (5) 7 (1) 1 (1) 12 (8) 3 (2) 2 (2)

816 6 21 (1) 1 (0)

850 18 89 (9) 10 (1) 6 (4) 6 (4) 1 (1)

870 2 4 (0)

871 10 47 (13) 3 (0) 1 (1) 1 (0)

900 13 66 (2) 10 (6) 2 (0) 4 (2) 3 (1) 3 (3)

927 3 7 (0) 2 (0)

950 10 57 (7) 2 (0) 1 (1) 1 (1)

982 7 20 (8)

1000 21 78 (5) 15 (2) 7 (4) 5 (2) 1 (0) 2 (2)

1038 1 5 (0)

1093 6 24 (4)

1100 1 2 (0) 1 (1)

Totals 32 575 (64) 70 (17) 33 (12) 41 (21) 13 (6) 15 (14)

( ) Figures in parentheses denote unbroken tests


The selected assessment


8

• The proposed model was assessed by Riva (Ansaldo Energia).

• A region splitting approach was employed to deliver the required accuracy across the whole temperature range

• How the fit was made: dataset splitting (threshold at 700°C), independent fitting, the joining is made thanks to the blending formula below.

Low temperature reference equation (OSD4)𝑙𝑜𝑔10 𝑡𝐿𝑇= 𝑎0,𝐿𝑇 + 𝑎1,𝐿𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 + 𝑎2,𝐿𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 2 + 𝑎3,𝐿𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 3

+ 𝑎4,𝐿𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 4 + 𝐵𝐿𝑇/𝑇

High temperature reference equation (OSD2)

𝑙𝑜𝑔10 𝑡𝐻𝑇 = 𝑎0,𝐻𝑇 + 𝑎1,𝐻𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 + 𝑎2,𝐻𝑇 ⋅ 𝑙𝑜𝑔10 𝜎 2 + 𝐵𝐻𝑇/𝑇

Low temperature coefficients (OSD4)a0,LT= 2.59144756e+02

a1,LT= -4.36973658e+02

a2,LT= 2.64640145e+02

a3,LT= -70.3322662

a4,LT= 6.79133846

BLT= 1.48898122e+04

High temperature coefficients (OSD2)a0,HT= -11.2060026

a1,HT= -1.04315354

a2,HT= -1.09867022

BHT= 2.23185498e+04

The formula to obtain the time to rupture at a generic temperature, combining the low and high temperature equations:

𝑡𝑢∗ = −1 + 10

−40𝑙𝑜𝑔10(𝑡𝐿𝑇+1)

−40+ 𝑙𝑜𝑔10(𝑡𝐻𝑇+1)−40


9

Not all the available temperatures are reported here, to preserve the image readability.




Temps 10,000h 30,000h 100,000h 200,000h

°C N/mm² N/mm² N/mm² N/mm²

600 326 283 237* 210*

625 283 241 195 169*

650 242 200 157* 134*

675 202 163 125* 108*

700 163 131 102* 89*

725 131 105 84* 74*

750 105 85 68* 59*

775 84 68 54* 46.3*

800 68 54 42.1* 36.1*

825 54 43.1 33.0 28.1*

850 43.6 34.2 25.9* 21.8*

875 35.0 27.2 20.2 16.8*

900 28.1 21.5 15.7 12.9*

925 22.5 17.0 12.1 9.85*

950 18.0 13.3 9.30* 7.42*

975 14.3 10.4 7.05 5.50*

1000 11.4 8.05 5.26 3.99** Values which have involved extended time extrapolation7)

( ) Values which have involved extended stress extrapolation7)

1

10

100

1000

550 600 650 700 750 800 850 900 950 1000 1050

Stre

ss (

MP

a)

Temperature (°C)

10000 h

30000 h

100000 h

200000 h

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11

The ECCC Post Assessment Tests (PATs,

described in ECCC Recommendation

Volume 5) were developed in the 90s in

order to support the ECCC assessor in the

evaluation of the performances and

accuracy of a given model. There are three

types of PATs:

• PAT 1: verification of the physical realism

of the predicted isothermal lines

• PAT 2: verification of the effectiveness of

the model prediction in interpolation

• PAT 3: verification of the repeatability

and stability of the extrapolations.


Comparison with previous assessments

12

The most important

change in the

Ru,700°C,100kh takes

place below 800°C, in

fact Ru,700°C,100kh changes

from 112MPa currently

published in the ECCC to

102MPa.

Rupture

Strength

(MPa)

EN ASME ECCC 2005 ECCC 2020

Ru,700°C,100kh 95 120.9 112 102

Ru,800°C,100kh 43 46.7 41 42.1

Ru,900°C,100kh 16 18.4 14.9 15.7


ASME/BPVC SECTION II-D (METRIC) - SECTION II-D PROPERTIES (METRIC) – MATERIALS 2019 – Table 1Bcalculated using:Ru,100kh=Max Allowable Stress/0.67

Comparison with previous assessments

13

Comparison of

models ECCC2005 vs

ECCC2020. The

yellow to red regions

represent areas in

which the 2020

assessment is more

optimistic than 2005.

Viceversa, the light

blue to blue areas

are where the 2020 is

more pessimistic


Metallurgical support to region-splitting

14

• IN617 is solid solution strengthened alloy.

• During high temperature exposition, gamma prime phase (Ni3Al,Ti) is formed, contributing to creep strength.

Thermodynamic calculations evidence that the

temperature stability field of ’ is limited:

✓ At temperature higher 800°C is not formed

✓ At temperature < 700°C a significant ’ fraction is formed independently by the alloy

composition

✓ In the range 700-800°Cthe ’ fraction can be considered not sufficient to affect significantly

the creep behaviour

’No ’

Low ’

Equilibrium calculation performed by JmatPro V.12


Focus on thin products

15

Evidence that thin products had a

different behaviour was found.

Only products with thickness

larger than 10mm were

considered to reduce the dataset

bias.

08/10/2020 “©2020 Copyright, Author Organizations In blue: thin products

Strong and weak heats distribution

16

All data plotted on the stress-

temperature diagram where the

colour of each dot is determined

on the basis of the strength of all

heats.

No temperature highlight a strong

agglomeration of very strong (or

very weak) heats. Therefore the

model obtained is not expected

to be strongly biased.


Residuals analysis


The logarithmic residuals are defined by:

x = log10 texp − log10 tcalc

• Image a: The model seems to be equally accurate at

both high and low stresses

• Image b: Error is homogeneous at high and low

temperatures.

a

c

b

• Image c: error is symmetrical at times longer than 10kh. There is a slight

optimistic bias at short term, but this is not relevant for design purposes.

Residuals analysis

18

• Several distribution functions fitted on

the empirical population of

logarithmic residuals. It can be noted

how the different models deliver

different estimation for the tails

thickness.

Only t>30kh

Cumulative Distribution Function

(Empirical and fitted)

focus on the weak tail

13/11/2020 “©2020 Copyright, Author Organizations08/10/2020 “©2020 Copyright, Author Organizations

Residuals analysis

19

• The best quantitative description of the

error is given by the logistic distribution

• Unfailed data not considered (potential

reason why the strong tail fit is poorer)

f x|μ, σ =e−

x−μσ

σ 1 + e−x−μσ

2

Mu -0.002309

Sigma 0.1520


Conclusions

20

• A large creep rupture dataset is collated using data from several organizations

worldwide.

• An assessment is delivered consistently with the ECCC guidelines and methods.

• A region-splitting model proved to deliver the sufficient reliability. Very thin products are

not represented by this model.

• The new assessment predicts a Ru,100kh,700°C of 102MPa, which is higher compared to the current EN values of 95MPa, but lower than ASME value of 120.9MPa.

• ECCC issued a new revision of his own datasheet on the basis of this new assessment.

• The dataset is characterized by large scatter. The error can be quantitatively described

by a Logistic distribution of the logarithmic errors, whose parameters are provided in the paper.

Additional notes• A revision to the Alloy 617B datasheet will soon be issued by ECCC.

• Several aspects of Alloy 617 behaviour were further investigated in papers submitted to

ECCC2021, Edinburgh, Sept 2021.


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The new ECCC Datasheet for Alloy 617 - eccc-creep.com