WELDABILITY AND METALLURGY OF
WB-36
CONTENTS
1 A brief introduction
2 History and Evolution
3 Need of WB36
4 Mechanical properties and Metallurgy
5 Welding cycle for WB36
6 Practical problems with WB36
INTRODUCTION TO WB36 MATERIAL
Low-alloy ,heat-resistant steel 15 NiCu-MoNb 5 (WB 36)
Feed water piping systems with operating temperaturesof 340C maximum and but more typically ~250C.
Operating temperature in conventional power plants450C
German nuclear power plants use the material mainlybelow 300C and in some rare cases in pressure vesselsup to 340C.
HISTORY AND EVOLUTION OF WB36
Work was initiated to develop these steels in 1930s.
Initially problem was faced in reaching to final mix of this alloy as there was a tendency of hot shortness.
Finally this problem was overcome by doubling the amount of nickel in the alloy along with additions of Mo, Mn and Nb which also contributed in increase in strength.
HISTORY AND EVOLUTION OF WB36
1960 Development & Optimization of the grade in Germany
1970 First deliveries of pipes in WB 36 for conventional boilers
1980 First deliveries for nuclear boilers
2001 Introduction of Code case 2353 in ASME
2002 Introduction of 15NiCuMoNb 5 in EN 10216
2005 Introduction of T/P36 in ASTM A213/A335
WHY WB36?
Yield strength comparison at various temperatures
WHY WB36?
Minimum wall thickness pipe that could be used for an application at 320C(610F) and 370bar with an internal diameter of 480mm
Carbon
Min:0.10
Max:0.17 Ni
Min:1.0
Max:1.30
Cu
Min:0.50
Max:0.80
Mn
Min:0.80
Max:1.20
Mo
Min:0.25
Max:0.50
Cr
Max:0.30
Nb
Min:0.015
Max:0.045
N
Max:0.020
Si
Min:0.25
Max:0.50
S
Max:0.025
P
Max:0.030
Chemical
Composition
Of WB36
CCT DIAGRAM FOR WB36
MICROSTRUCTURE FOR WB36
The Chemistry of P36 combined with an optimized heat treatment provides a finegrain microstructure composed of bainite + ferrite and Cu hardening precipitation
HEAT TREATMENT AND MECHANICAL PROPERTY REQUIREMENTS FOR WB36
MECHANICAL PROPERTIES OF WB36
Co-efficient of linear expansion
MECHANICAL PROPERTIES OF WB36
MECHANICAL PROPERTIES OF WB36
Creep rupture tests on WB36
PRECIPITATION IN WB36
The strength of WB36 is based on Copper hardening precipitation.
Precipitation is formation of extremely small uniformly dispersed particles of a second phase within the original phase matrix.
Copper precipitated partly in initial state.
The other part is still in solution and can be precipitated during long-term operation at temperatures above 320350C.
Increase in strength is caused by pinning of dislocations by precipitates.
SOLUBILITY AND PRECIPITATION
WELDING CYCLE FOR WB36
PURGING
PRE-HEAT & INTERPASS
15mm thick 80150C 15-30mm thick 100180C30-50mm thick 120220C >50mm thick 120250C
DHTPWHTASTM A182/ASME B31.1 595-650C for Class 1 material and 540-620C for Class 2 material with soaking of 1hr/inch + 15 min on additional inch.
PRACTICAL PROBLEMS WITH WB36
The service-induced
hardening and
decrease in
toughness
Increase in DBTT
PRACTICAL PROBLEMS WITH WB36
PRACTICAL CASES
Following long hours of operation (90 000160000Hr) some damage was seen in piping systems and in one pressure vessel of conventional power plants during 19871992 which occurred during operation and in one case during in service hydro-testing.
In all damage situations, the operating temperature was between 320 and 350C.
An operation-induced hardening associated with a decrease in toughness was seen in all cases.
Thank you
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