lesson 1 cr mo steels history
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Lesson 1 Cr Mo Steels HistoryTRANSCRIPT
IIW-AWS
Technical Lectures
The Cr-Mo Steels
January/February 2006
J. F. Henry
The Cr-Mo SteelsA Cornerstone of the Modern Power and
Petrochemical Industries
Lesson 1IIW-AWS
January/February 2006
Topics of Discussion
• History of the Cr-Mo Steels – Lesson 1• Basic Metallurgy of the Cr-Mo Steels – Lesson 2• Welding Issues – Lesson 2• Temper Embrittlement – Lesson 3• Weld-Related Failures – Lesson 4• The “New” Generation of Creep Strength-Enhanced
Ferritic Steels – Lesson 5• Issues of Concern Regarding Control of the “Advanced”
Alloys – Lesson 6
Lesson 1IIW-AWS
January/February 2006
History: 80 Years of Critical Industrial Service
“Oil is King!”Texas Newspaper - 1922
Tosco, Martinez oil refinery
Lesson 1IIW-AWS
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History of Development
• Serious development of alloy steels began in early 1920s
• Development driven by changes in refinery practice
Lesson 1IIW-AWS
January/February 2006
Changes in Refining Requirements
• Increasing demand for gasoline, spurred by mass production of automobiles
• Higher temperatures required for cracking process used to produce gasoline
• Refining temperatures began to exceed the capabilities of carbon steels in terms of both mechanical strength (i.e., creep strength) and corrosion resistance
Lesson 1IIW-AWS
January/February 2006
Corrosion Resistance
• Increasing use of West Texas “Sour” crudes• Excessive corrosion of carbon steels• Initial use of 12Cr & 18Cr/8Ni stainless steels to combat
more aggressive feed stocks• Desire for cheaper materials led to development of 5%Cr
steel in 1928
Lesson 1IIW-AWS
January/February 2006
Elevated Temperature Strength
• At higher processing temperatures required for new cracking operations, carbon steel inadequate
• Discovery that additions of molybdenum (Mo) or tungsten (W) substantially improved elevated temperature performance
• Addition of Mo and/or W to 5Cr steel offered better elevated temperature strength (compared to CS) in an alloy that was more resistant to sulfur-based corrosion than CS
• Mo became the alloy addition of choice – lower cost and improved resistance to temper embrittlement
Lesson 1IIW-AWS
January/February 2006
Milestones In Alloy Development
Lesson 1IIW-AWS
January/February 2006
Developing New Alloys
• Variations in the composition of refinery feed stock, particularly sulfur content of crude, led to demand for alloy “tailoring”
• For “sweet” crudes (lower S), lower Cr content needed for corrosion resistance, and improved creep strength obtained through additions of Mo and, in some cases, vanadium (V). This led to development of “leaner” alloys:a) 1-3%Cr with Mo or Wb) 2Cr-1/2Mo for resistance to graphitization
Lesson 1IIW-AWS
January/February 2006
By the mid 1930’s the
basic group of Cr-Mo steels
had been approved by
ASTM/ASME
Lesson 1IIW-AWS
January/February 2006
Evolution of Alloy Development
Piercing Mill Making A Seamless Tube Of 7%Cr Steel
(Timken Roller Bearing Co.)
Lesson 1IIW-AWS
January/February 2006
Evolution of Alloy Development
• Refining of increasing amounts of “sour” crude led to experimentation with Cr contents >5%, but <12% needed for stainless steels
• 7-9% Cr-Mo steels developed• For refining applications improvement in corrosion
resistance was significant:5Cr steels 4-10X more corrosion resistant than CS7Cr steels 2X more corrosion resistant than 5Cr steels9Cr steels 4X more corrosion resistant than 5Cr steels
Lesson 1IIW-AWS
January/February 2006
Evolution of Alloy Development
• For critical bolting applications at lower temperatures, high tensile strength desired
• Materials such as 4140 – CrMo alloy with 0.40% C – were developed to facilitate through hardening
Lesson 1IIW-AWS
January/February 2006
Cr-Mo Steels - Carbon Content
• For many of the most widely-used Cr-Mo alloys, the carbon content is maintained < 0.15% (weight)
• Higher C adversely affects weldability• Higher C does not substantially improve creep strength• Higher C can reduce corrosion resistance through excess
carbide formation
Lesson 1IIW-AWS
January/February 2006
Cr-Mo Steels in the Power Industry
In the Power Industry, the introduction of welding for major pressure parts spurred rapid increase in
steam temperatures and pressures
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January/February 2006
• At steam outlet temperatures >400°C (750°F) there was a need for alloys with higher creep strength and improved oxidation resistance
• The Cr-Mo steels developed for the petrochemical industry proved to be a good fit
Cr-Mo Steels in the Power Industry
Lesson 1IIW-AWS
January/February 2006
Development of “Advanced” Ferritic Steels
• Work in the 1930s and 1940s had demonstrated the potent strengthening effect of small additions of V, Ti, Cb, and other carbide forming alloy additions
• The successful introduction of X20CrMoV, a higher carbon vanadium fortified 12Cr alloy, in Europe in the early 1960s was an early result of these efforts
• Further advances were made in support of the nuclear industry’s fast breeder reactor programs beginning in the early 1970s
• These efforts culminated in the development of the modified 9Cr-1Mo alloy, now known as Grade 91
Lesson 1IIW-AWS
January/February 2006
Creep Rupture Strength
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January/February 2006
Creep Strength Enhanced Alloys
• Following cancellation of the fast breeder programs in the late 1970s, application of Grade 91 and later variants (i.e., Grades 92, 911, 122, 23, etc.) shifted to the fossil power industry
• Favored by designers for improved performance in cyclic service (conventional boilers and HRSGs)
• An essential component of the materials strategy for ultra-supercritical boilers
Lesson 1IIW-AWS
January/February 2006
0
5
10
15
20
25
800 850 900 950 1000 1050 1100 1150
Temperature (F)
Allo
wab
le S
tress
(ksi
)
P22
P91
• Design Codes do not penalize for increased thickness.• Thermal stress varies with square of thickness.• Fatigue life varies with cube of stress.
• High creep-strength materials (e.g.,P91) reduce wall thickness in high temperature areas, which improves cycling capability.
• P91 gives 40% thickness reduction for same creep life and 12 times the fatigue life.
Design Interest In CSEF Steels