Welding for Challenging Environments

Proceedings of the International Conference on Welding for Challenging Environments, Toronto, Ontario, Canada, 15–17 October 1985

Sam Stuart

• Publisher: Pergamon
• Year: 2014
• Print ISBN: 9780080318660
• eBook ISBN: 9781483279114
• Topic: Tecnologia e ingegneria
• Subtopic: Meccanica dei fluidi

Welding for Challenging Environments documents the proceedings of the International Conference on Welding for Challenging Environments held in Ontario, Canada on October 15-17, 1985. This compilation provides a unique reference to the state of technological development, research, and application of welded fabrications in challenging environments. This book discusses the developments in pulsed gas metal arc welding; pulsed FM-GMA welding; and narrow gap welding of pressure vessels. The fracture toughness considerations for offshore structures; microcomputer method for predicting preheat temperatures; and submerged arc welding of high yield strength steel are also elaborated. This text likewise covers the influence of nitrogen content on deposited weld metal notch toughness gas-metal-slag interactions of binary fluxes containing CaF2 and evaluation of susceptibility of welds made with a stable austenitic welding wire to hot cracking. This publication is a good source for welders and metallurgists, as well as students interested in welded fabrications in challenging environments.

RECENT DEVELOPMENTS IN PULSED GAS METAL ARC WELDING

C.J. Allum, GEC Industrial Controls Limited, Rugby, England

ABSTRACT

Gas metal arc welding (GMAW) is currently attracting much interest on account of significant developments in process control over the past few years. These developments are largely associated with benefits gained from the application of modern solid state power devices to welding power supplies. In this paper pulsed current GMAW is considered with emphasis on interactions between pulse parameters, parameter selection, fusion characteristics and process control.

KEYWORDS

Pulsed current gas metal arc welding

metal transfer

power sources

process control

INTRODUCTION

GMAW is arguably the most versatile of all welding processes being capable of joining in any position a wide range of materials, using manual or mechanised techniques on thin sheet or sections hundreds of millimeters thick. Process productivity is potentially high since filler metal is continuously deposited, with little slag, at high deposition rates (associated with efficient wire melting) and suitable for use in narrow gap weld preparations. Good toughness with very low deposited hydrogen levels are achievable meeting the requirements of many demanding applications. Furthermore GMAW allows close control of plate dilution and finds applications besides welding in cladding and brazing.

GMAW has however, yet to achieve the potential outlined above. Historically, two process weaknesses (metal transfer and fusion characteristics) and a number of equipment related short comings have limited the application of GMAW.

Metal may be transferred in a variety of modes. At very low currents short circuiting (dip transfer) is required and not all materials are weldable in this mode. The explosive nature of such transfers gives rise to spatter and intermittent arcing produces a susceptability to lack of fusion defects. At higher currents transfer becomes globular and non projected. Further increases in current result in a spray of small droplets, typically of wire diameter projected across the arc gap.

Synergy is a control technique used in pulsed current MIG welding (Ref 1) where mean current is determined by wire feed speed such that stable wire melting and drop transfer occur. The outcome of this technique is simplified process operation with nominally one knob control. A wide range of methods exist for achieving the above characteristics but only two basic approaches are considered here (see Ref 8). One technique consists of driving the power supply in response to a wire feed speed control signal. This might for instance be used to increase pulse frequency proportionally to wire feed speed demand. Metal transfer can then be controlled by predetermined unit pulses of current (of specified Ip and Tp) while frequency control simply changes the time spacing between pulses with the effect of altering mean current. With this control scheme droplets of uniform size are detached at every mean current (i.e. W/F in constant) and mean current increases approximately in proportion to wire feed rate when low background currents are employed. Process control is then achieved directly from wire feed rate. For this type of control no arc length self adjustment exists i.e. when the torch is withdrawn from the work arc length increases with fixed wire extension.

Arc length self adjustment may also be achieved by incorporating voltage control. Here a voltage error signal is generated (difference between reference voltage and measured voltage) which in effect modifies the wire feed to pulse frequency ratio to achieve the desired arc voltage. Features of conventional self adjusting GMAW are thereby regained. A second so called synergic technique relies entirely on voltage control to produce frequency modulation without...

Table of contents

• Cover image
• Title page
• Table of Contents
• Pergamon Titles of Related Interest
• Copyright
• FOREWORD
• Chapter 1: RECENT DEVELOPMENTS IN PULSED GAS METAL ARC WELDING
• Chapter 2: SYNERGIC PULSED GMAW – IN PERSPECTIVE
• Chapter 3: PULSED FM-GMA WELDING
• Chapter 4: NEW DEVELOPMENTS IN HIGH POWER LASER WELDING
• Chapter 5: TEMPERATURE MEASUREMENTS OF MOLTEN WELD POOL ALONG THE KEYHOLE IN LASER BEAM WELDING
• Chapter 6: ALL-POSITION MECHANIZED AND AUTOMATIC FCAW SYSTEMS FOR THE FABRICATION OF OFFSHORE STRUCTURES AND ARCTIC VESSELS
• Chapter 7: HEAVY SECTION WELDMENTS WITH A GMAW NARROW GAP WELDING PROCESS
• Chapter 8: EXTRA HEAVY STEEL PLATES PRODUCED BY THERMO-MECHANICAL PROCESS FOR ARCTIC OFFSHORE STRUCTURES AND SHIPS IN ICY SEA AREAS
• Chapter 9: THE DEVELOPMENT OF WELDING PROCEDURES FOR ARCTIC STRUCTURES AND OFFSHORE PLATFORMS USING TMCP (THERMO-MECHANICAL CONTROLLED PROCESS) STEEL PLATES
• Chapter 10: SOME FACTORS AFFECTING THE MECHANICAL PROPERTIES OF SUBMERGED ARC NARROW GAP WELDS
• Chapter 11: NARROW GAP WELDING OF PRESSURE VESSELS – a manufacturer’s view –
• Chapter 12: NARROW GAP WELDING OF 2′ HY-100 PLATE USING CLOSED LOOP, ADAPTIVE-FEEDBACK, THROUGH-THE-ARC TRACKING TECHNOLOGY
• Chapter 13: FRACTURE TOUGHNESS CONSIDERATIONS FOR OFFSHORE STRUCTURES IN UK WATERS
• Chapter 14: THE EFFECTS OF PWHT ON THE TOUGHNESS OF SHIELDED METAL ARC WELD METALS FOR USE IN CANADIAN OFFSHORE STRUCTURE FABRICATION
• Chapter 15: THE RELEVANCE OF CTOD IN CROSS WELDED JOINTS WITH WELD METAL OVERMATCHING IN STRENGTH
• Chapter 16: FIRST REPORT OF HAZ STUDY
• Chapter 17: TECHNOLOGICAL CHALLENGES IN WELDING FOR CANADIAN OFFSHORE ENVIRONMENTS
• Chapter 18: TESTING OF 125 MM AND 200 MM THICK LOW-STRENGTH LOW-CARBON STEEL FOR THE CONSTRUCTION OF A TRIPOD TOWER PLATFORM (TTP)
• Chapter 19: THE BEHAVIOR OF LONGITUDINAL HIGH FREQUENCY INDUCTION WELDED PIPES IN THE H2S ENVIRONMENT
• Chapter 20: ESTIMATION OF MAXIMUM HARDNESSES AND CRACKING SUSCEPTIBILITY OF HEAT-AFFECTED ZONES IN UNDERWATER WET WELDING OF STEELS
• Chapter 21: PREDICTION OF THERMAL HISTORY OF REPAIR WELDS
• Chapter 22: A MICROCOMPUTER METHOD FOR PREDICTING PREHEAT TEMPERATURES
• Chapter 23: RELATIONSHIP BETWEEN WIRE FEED SPEED AND SUBMERGED-ARC-WELDING PARAMETERS
• Chapter 24: INFLUENCE OF THE HOLE-SIDE PLASTIC DEFORMATION AS A RESULT OF THE STRESS CONCENTRATION ON THE ACCURACY OF RESIDUAL WELDING STRESS MEASUREMENT BY SMALL BLIND HOLE RELAXATION METHOD AND ITS MODIFICATION
• Chapter 25: THE EFFECT OF HEAT TREATMENT ON THE MICROSTRUCTURE AND PROPERTIES OF STRUCTURAL STEEL WELD DEPOSITS
• Chapter 26: 2 1/4 CR-1 MO-FILLER METALS WITH HIGH TOUGHNESS PROPERTIES AFTER STEP COOLING
• Chapter 27: SUBMERGED ARC WELDING OF HIGH YIELD STRENGTH STEEL
• Chapter 28: INFLUENCE OF NITROGEN CONTENT ON DEPOSITED WELD METAL NOTCH TOUGHNESS
• Chapter 29: EFFECT OF AMBIENT PRESSURE AND SHIELDING GAS FLOW ON HYDROGEN AND NITROGEN CONTAMINATION OF HYPERBARIC TIG AND GMA WELDS
• Chapter 30: HIGH-STRENGTH, HIGH-FRACTURE TOUGHNESS SUBMERGED-ARC WELD FOR ARCTIC LINE PIPE
• Chapter 31: GAS-METAL-SLAG INTERACTIONS OF BINARY FLUXES CONTAINING CaF2
• Chapter 32: EVALUATION OF SUSCEPTIBILITY OF WELDS MADE WITH A STABLE AUSTENITIC WELDING WIRE TO HOT CRACKING
• CONFERENCE DISCUSSION
• SUBJECT INDEX
• AUTHOR INDEX