Low Carbon HTP Structural Steel : A Paradigm Shift CHA...Low Carbon HTP Structural Steel : A Paradigm Shift by ... API PSL2/ISO 3183/GB/T 9711 0.12 ... ISO 10025-4 355/460 TMCP 0.16

Low Carbon HTP Structural Steel : A Paradigm Shift

by

J. Malcolm Gray and P. R. Kirkwood

Presented at the Charles Hatchett Seminar, London, UK

Perspective & Summary The technology and application of microalloyed steels has

developed rapidly over the past half century. Metallurgical

developments have been very rapid in linepipe steels and

automotive grades and much slower for structural steels.

Yield strengths above 100-120 ksi are available for

automotive and linepipe applications, but until recently

structural steels rarely exceeded 60 ksi. There are signs,

particularly in China, where linepipe technology and related

specifications are being utilized in impressive construction

projects, (airports, stadiums and very tall buildings).

What is HTP* Steel? (* High Temperature Processed)

• Conventional Steel 0.04%Nb FRT 710-830°C

• HTP Steel 0.10%Nb FRT 840-910°C

RETARDATION OF RECRYSTALLIZATION BY MICROALLOYING ELEMENTS

1993--X60

1998--X65

2000--X70

2003—X80

2005—X100

2007—X120

Huoerguosi

Lunnan

Guangzhou

Shanghai

Beijing

Hongkong

1st West-east

1016mm,10MPa,

3856km X70

2nd Shanxi— Beijing

1016mm,10MPa,

851km X70

2nd West-east

1219mm,12MPa,

4913km X80

1st Shanxi— Beijing

660mm,6.4MPa,

918km X60

Ji-ning

1016mm,10MPa,

912km X70 (7.9km X80)

PROGRESS OF LINEPIPE DEVELOPMENT SHOWING SIMULTANEOUS INCREASE IN TOUGHNESS WITH STRENGTH

AND PASSAGE OF TIME

Changes in maximum niobium and carbon contents with time (and strength increase) for linepipe steel.

Change in Niobium Level in the Production of C-Si-Mn-Nb-Al Steels

Austenite Grain Coarsening Behaviour for steels reheated to 1200°C for 1 hr and water quenched.

Carbon & Niobium Restrictions for TMCP Welded X70 PIPE

Specification C% Nb% Nb+V+Ti %

API PSL2/ISO 3183/GB/T 9711 0.12 - ≤ 0.15

API PSL2 Annex G (pipe resistant to ductile fracture)

0.10 0.08 ≤ 0.15

API PSL2 Annex H (Pipe for sour service)

0.10 0.08 ≤ 0.15

API PSL2 Annex J (Pipe for offshore service)

0.12 0.08 ≤ 0.15

DNV-OS-F101 (Pipe for offshore service)

0.12 0.08 ≤ 0.15

CSA Z 245 0.26 0.11 -

CNPC 0.09 0.11 ≤ 0.15

Carbon & Niobium Restrictions in Structural Steel Specifications

Specification C% Nb% Nb+V+Ti %

ISO 10025-3 355/460 N/R 0.20 0.06

ISO 10025-4 355/460 TMCP 0.16 0.06

ISO 10025-6 ≥ 460 Q&T 0.20 0.07

ISO 4950-2 (E) 355/460 0.18 0.06

ASTM/SA 841- Type F G7 0.10 0.11

CSA G40.21-04 350/480 0.20 Nb+V ≤ 0.1 or 0.12

GB/T 5191 -2004 345 to 690 0.20 0.06 ≤ 0.15

GB/T 5191- 2008 345/420 0.18/0.20 0.07 ≤0.22

GB/T 5191-2008 460/690 0.18/0.20 0.11 ≤0.22

Carbon & Niobium Restrictions in Offshore Structural Steel Specifications (≈ 40mm plates)

Specification C% Nb%

ISO 10025 - S355 G2+ N 0.18 0.06

ISO 10025 - S355 G6+M (TMCP) 0.14 0.06

ISO 10025- S355 G9+M (TMCP) 0.12 0.03

API 2H & 2Y 0.18 0.05

API 2W (50T) TMCP 0.16 0.03

Mobile structures E36/EH36 0.18 0.05

CLEARLY INTERNATIONAL SPECIFICATIONS MUST BE

RATIONALISED AND BROUGHT INTO THE 21ST CENTURY.

Conclusions There are exciting possibilities for rapidly constructing huge

structures with novel designs. Linepipe metallurgy, using low

carbon, low sulfur, calcium treated steel, transferred to the

structural steel arena results in steels with strengths up to

690 MPa, excellent weldability and remarkable Z direction

properties. Opportunities exist to utilize hot rolled steels in

industries and applications which traditionally use normalized

or Q&T grades of steel.