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