Characterization of metallic alloys for Oil & Gas applications · 2020. 1. 27. · [2] M-630,...
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Doctoral Programme in Mechanical Engineering Characterization of metallic alloys for Oil & Gas applications Doctoral Thesis of Francesca Tavasci - Supervisor: Prof. Barbara Rivolta XXX Cycle, Materials Investigated Material Results References Mecc PhD Doctoral Programme in Mechanical Engineering Programme Coordinator prof. Daniele Rocchi Department of Mechanical Engineering Via La Masa 1 20156 Milano info and contact [email protected] Conclusions Introduction Different Duplex Stainless Steel grades have been developed during the years and are, nowadays, available on the market. The most promising one in terms of tensile and toughness properties is the F55 grade [1], which is characterized by an amount of Chromium of 24-26% and Nickel of 6-8%. It stands out for the low temperature toughness, nowadays tested at -46°C, as the NORSOK standards [2] require: Charpy V-notch testing according to ASTM A370 [3] standard at -46°C, with minimum absorbed energy of 45J average and 35J single. The actual trend of the Oil & Gas market is to exploit all the available natural resources, even aiming for Poles drilling. For reaching this goal, no limits from the material should come: the actual working condition of the F55 grade is outdated and the material Forged bars with medium-Nickel content (7,00%) have been also investigated for comparing the toughness behavior of the high-Nickel (7,63%) F55 grade with the most spread condition available on the industrial market. Influence of Nickel on the A/F ratio and on the mechanical properties of the high-Ni F55 steel in case of ideal quenching Influence of the cooling rate during quenching on the impact toughness of the high-Ni F55 steel Study of the high temperature precipitation phenomena of F55 steel Crack path and fracture surface analysis of F55 grade Q1 st = 280 kJ mol -1 Q2 nd = 201 kJ mol -1 High-Ni amounts in the chemical composition of the F55 grade are beneficial for the material, which has a good impact toughness even at -80°C, if the solution temperature is properly chosen (A/F ratio) and the cooling rate is sufficiently high for avoiding precipitation phenomena. Such result is industrially limited by the poor material conductivity, but a higher Nickel amount assures bigger margin on the material toughness requirements. The precipitation of secondary phases during isothermal aging at 980°C starts within 5 minutes. After 10 minutes soaking at 980°C, σ- phase (280 kJ mol -1 ) is present in the microstructure of both high and medium Ni F55 steels. Finally, from the analysis performed on the tested Charpy specimens, the intra ferritic contribution is the main one on the total crack path, and it is in the range from 70 to 80%. The fact that the crack predominantly propagates in the ferritic matrix, despite of the almost perfect equilibrium between the two phases (A/F ratio close to 1), suggests that the material toughness is mainly determined by the ferrite behavior. Objectives The major target of this experimental research is the improvement of the F55 grade toughness for extending its low temperature applicability field until -80°C, without worsening its tensile properties, by optimizing the heat treatment parameters of a high-Ni (7,63%) F55 alloy. Because of the pronounced tendency of the F55 grade to precipitation, the main high temperature precipitation phenomena have been studied as minor research target, not only by traditional aging treatments in the laboratory furnace, but also by dilatometry. Analysis of the tested Charpy specimens: crack path and fracture surface. Medium-Ni_ High-Cr Steel %Ni = 7,05 %Cr = 25,80 Medium-Ni Steel %Ni = 6,92 %Cr = 24,90 High-Ni Steel %Ni = 7,63 %Cr = 24,65 COMPONENT 2 BAR 3 DISC 5 toughness should be satisfactory even at lower temperatures. It implies the importance of the study of all those factors, which affect the material toughness. In particular, the chemical composition, the forging ratio and the heat treatment parameters play a key role in balancing the material properties. Moreover, it is established that any possible precipitation phenomenon occurring during the solution treatment or the service of the component is deleterious for the material toughness [4, 5, 6, 7]. A/F ratio = Austenite [%] / Ferrite [%] 1 2 3 1 1110°C - TQ INDUSTRIAL QUENCHING (COMPONENT) 1120°C IDEAL QUENCHING (SAMPLE) 1140°C IDEAL QUENCHING (SAMPLE) 1180°C IDEAL QUENCHING (SAMPLE) NO STANDARD TEMPERATURE STANDARD TEMPERATURE 750 MPa 520 MPa The A/F ratio in not the unique factor affecting the material impact toughness Cooling rate related to the component dimension 25% 45% INDUSTRIAL 2 3 237J@-46°C 78J@-46°C CRACK PATH CRACK PATH MICROSTRUCTURAL CONTRIBUTIONS 1 2 3 [1] ASTM A182/A182-16, “Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service”, ASTM International [2] M-630, NORSOK STANDARD, Material data sheets and element data sheets for piping, (2010) [3] ASTM A370-16, “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”, ASTM international [4] M. ROSSO, I. PETER, D. SUANI, About the heat treatment and properties of Duplex Stainless Steels, Journal of Achievements in Materials and Manufacturing Engineering, (2013), 59(2), p 26-36 [5] S. TOPOLSKA, J. LABANOWSKY, Effect of microstructure on impact toughness of duplex and superduplex stainless steels, Journal of Achievements in Materials and Manufacturing Engineering, (2009), 36(2), p 142-149 [6] M.A. DOMINGUEZ-AGUILAR, R.C. NEWMAN, Detection of deleterious phases in duplex stainless steels by weak galvanostatic polarization in alkaline solution, Corrosion Science, (2006), 48, p 2560-2576 [7] D. BRUCH, D. HENES, P. LEIBENGUTH, and C. HOLZAPFEL, Investigations on microstructure, mechanical properties and corrosion resistance of large thickness duplex stainless steel forgings, Stainless Steel World 2007 Conference, Maastricht (2007) time High-Ni steel Medium-Ni steel 5 min 60 min T = 980°C 9,90 °C/s 3,22 °C/s 1,91°C/s austenite amount 55% 55% 56% Test Temperature = -46°C A = 55,0% 7,89 °C/s A = 53,0% 2,00 °C/s A = 44,5% 3,14 °C/s A = 43,3% 7,00 °C/s = − , ∙ [ % ] − , ∙ [°C/s] − ° = , ∙ [ % ] + , ∙ [°C/s] >-46°C =-46°C <-46°C <45J =45J >45J EDXS ANALYSIS, wt. % Cr Mn Fe 31,1 0,72 53,6 Ni Mo Si 4,71 9,05 0,83
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Doctoral Programme in Mechanical Engineering
Characterization of metallic alloys for Oil & Gas applications
Doctoral Thesis of Francesca Tavasci - Supervisor: Prof. Barbara Rivolta XXX Cycle, Materials
Objectives
Investigated Material
Results
References
MeccPhD Doctoral Programme in Mechanical Engineering Programme Coordinator prof. Daniele Rocchi
Department of Mechanical Engineering Via La Masa 1 20156 Milano
info and contact [email protected]
Co
ncl
usi
on
s
Intr
od
uct
ion
Different Duplex Stainless Steel grades have been developed during the years and are, nowadays, available on the market. The most promising one in terms of tensile and toughness properties is the F55 grade [1], which is characterized by an amount of Chromium of 24-26% and Nickel of 6-8%. It stands out for the low temperature toughness, nowadays tested at -46°C, as the NORSOK standards [2] require: Charpy V-notch testing according to ASTM A370 [3] standard at -46°C, with minimum absorbed energy of 45J average and 35J single.
The actual trend of the Oil & Gas market is to exploit all the available natural resources, even aiming for Poles drilling. For reaching this goal, no limits from the material should come: the actual working condition of the F55 grade is outdated and the material
Forged bars with medium-Nickel content (7,00%) have been also investigated for comparing the toughness behavior of the high-Nickel (7,63%) F55 grade with the most spread condition available on the industrial market.
Influence of Nickel on the A/F ratio and on the mechanical properties of the high-Ni F55 steel in case of ideal quenching
Influence of the cooling rate during quenching on the impact toughness of the high-Ni F55 steel
Study of the high temperature precipitation phenomena of F55 steel
Crack path and fracture surface analysis of F55 grade
Q1st = 280 kJ mol-1
Q2nd= 201 kJ mol-1
High-Ni amounts in the chemical composition of the F55 grade are beneficial for the material, which has a good impact toughness even at -80°C, if the solution temperature is properly chosen (A/F ratio) and the cooling rate is sufficiently high for avoiding precipitation phenomena. Such result is industrially limited by the poor material conductivity, but a higher Nickel amount assures bigger margin on the material toughness requirements.
The precipitation of secondary phases during isothermal aging at 980°C starts within 5 minutes. After 10 minutes soaking at 980°C, σ-phase (280 kJ mol-1) is present in the microstructure of both high and medium Ni F55 steels.
Finally, from the analysis performed on the tested Charpy specimens, the intra ferritic contribution is the main one on the total crack path, and it is in the range from 70 to 80%. The fact that the crack predominantly propagates in the ferritic matrix, despite of the almost perfect equilibrium between the two phases (A/F ratio close to 1), suggests that the material toughness is mainly determined by the ferrite behavior.
Objectives
The major target of this experimental research is the improvement of the F55 grade toughness for extending its low temperature applicability field until -80°C, without worsening its tensile properties, by optimizing the heat treatment parameters of a high-Ni (7,63%) F55 alloy.
Because of the pronounced tendency of the F55 grade to precipitation, the main high temperature precipitation phenomena have been studied as minor research target, not only by traditional aging treatments in the laboratory furnace, but also by dilatometry.
Analysis of the tested Charpy specimens: crack path and fracture surface.
Medium-Ni_ High-Cr Steel
%Ni = 7,05 %Cr = 25,80
Medium-Ni Steel %Ni = 6,92
%Cr = 24,90
High-Ni Steel %Ni = 7,63
%Cr = 24,65
COMPONENT 2 BAR 3
DISC 5
toughness should be satisfactory even at lower temperatures. It implies the importance of the study of all those factors, which affect the material toughness. In particular, the chemical composition, the forging ratio and the heat treatment parameters play a key role in balancing the material properties. Moreover, it is established that any possible precipitation phenomenon occurring during the solution treatment or the service of the component is deleterious for the material toughness [4, 5, 6, 7].
A/F
ratio
= A
uste
nite
[%] /
Fer
rite
[%]
1
2
3
1
1110°C - TQ INDUSTRIAL QUENCHING
(COMPONENT)
1120°C IDEAL QUENCHING
(SAMPLE)
1140°C IDEAL QUENCHING
(SAMPLE)
1180°C IDEAL QUENCHING
(SAMPLE)
NO STANDARD TEMPERATURE
STANDARD TEMPERATURE
750 MPa
520 MPa
The A/F ratio in not the unique factor affecting the material
impact toughness
Cooling rate related to the component dimension
25%
45%
INDU
STRI
AL
2
3
237J@-46°C
78J@-46°C
CRAC
K PA
TH
CRACK PATH MICROSTRUCTURAL CONTRIBUTIONS
1
2
3
[1] ASTM A182/A182-16, “Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service”, ASTM International [2] M-630, NORSOK STANDARD, Material data sheets and element data sheets for piping, (2010) [3] ASTM A370-16, “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”, ASTM international
[4] M. ROSSO, I. PETER, D. SUANI, About the heat treatment and properties of Duplex Stainless Steels, Journal of Achievements in Materials and Manufacturing Engineering, (2013), 59(2), p 26-36[5] S. TOPOLSKA, J. LABANOWSKY, Effect of microstructure on impact toughness of duplex and superduplex stainless steels, Journal of Achievements in Materials and Manufacturing Engineering, (2009), 36(2), p 142-149 [6] M.A. DOMINGUEZ-AGUILAR, R.C. NEWMAN, Detection of deleterious phases in duplex stainless steels by weak galvanostatic polarization in alkaline solution, Corrosion Science, (2006), 48, p 2560-2576 [7] D. BRUCH, D. HENES, P. LEIBENGUTH, and C. HOLZAPFEL, Investigations on microstructure, mechanical properties and corrosion resistance of large thickness duplex stainless steel forgings, Stainless Steel World 2007 Conference, Maastricht (2007)
time
High-Ni steel
Medium-Ni steel
5 min 60 min
T = 980°C
9,90 °C/s
3,22 °C/s 1,91°C/s
austenite amount 55% 55% 56%
Test
Tem
pera
ture
= -4
6°C
A = 55,0% 7,89 °C/s
A = 53,0% 2,00 °C/s
A = 44,5% 3,14 °C/s
A = 43,3% 7,00 °C/s
𝑻𝑻𝟒𝟒𝟒𝟒𝟒𝟒 = − 𝟎𝟎,𝟖𝟖𝟖𝟖𝟒𝟒 ∙ 𝑨𝑨[%] − 𝟔𝟔,𝟖𝟖𝟔𝟔𝟖𝟖 ∙ 𝒗𝒗 [°C/s]
𝑲𝑲𝑲𝑲−𝟒𝟒𝟔𝟔°𝑪𝑪 = 𝟎𝟎,𝟒𝟒𝟒𝟒𝟖𝟖 ∙ 𝑨𝑨[%] + 𝟖𝟖𝟖𝟖,𝟒𝟒𝟒𝟒𝟒𝟒 ∙ 𝒗𝒗 [°C/s]
>-46°C
=-46°C
<-46°C
<45J
=45J
>45J
EDXS ANALYSIS, wt. % Cr Mn Fe
31,1 0,72 53,6 Ni Mo Si
4,71 9,05 0,83
