7. Consumables, Shielding and Advanced Materials

Introduction and Context

In fusion welding, the joint is created not only by heat and mechanical manipulation but also by a carefully selected consumable and a controlled chemical environment. Electrodes, filler metals, fluxes, shielding gases, backing materials and surface treatments determine the composition, cleanliness, solidification behaviour, defect susceptibility and service performance of the weld. Their selection is therefore a materials-engineering decision rather than a simple process-setting exercise.

The importance of consumable selection becomes greater as materials become more demanding. High-strength steels may require hydrogen-controlled electrodes and controlled heat input. Stainless steels require attention to chromium loss, ferrite balance and sensitization. Aluminium alloys are sensitive to oxide films, hydrogen porosity and hot cracking. Titanium demands exceptionally pure shielding because small amounts of oxygen or nitrogen can embrittle the weld. Nickel alloys, composites and dissimilar joints introduce additional issues involving segregation, dilution, thermal expansion and intermetallic formation.

This chapter develops a systematic basis for selecting consumables and shielding systems for major engineering material groups. It also considers qualification, storage, automation, quality assurance and emerging developments in advanced filler materials.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain the functions of electrodes, filler metals, fluxes and shielding gases.

2. Relate consumable composition to weld-metal microstructure and performance.

3. Select suitable consumables for steels, stainless steels, aluminium, titanium and nickel alloys.

4. Identify the principal difficulties in composite and dissimilar-material welding.

5. Compare shielding gases and flux systems for different arc-welding processes.

6. Apply a structured procedure for consumable selection and qualification.

7. Diagnose common defects caused by unsuitable consumables, contamination or inadequate shielding.

8. Evaluate current developments in engineered, digital and application-specific consumables.

The Metallurgical Role of Welding Consumables

A welding consumable may be a continuously fed wire, a covered electrode, a flux-cored wire, a solid filler rod, a strip, a powder or a flux. Its immediate purpose is to supply material to the joint, but its deeper function is to establish a weld-metal chemistry and solidification path compatible with the parent materials and service conditions.

The final weld metal is commonly a mixture of filler metal and melted base metal. The proportion of base metal entering the weld is called dilution. If dilution is high, the nominal composition of the filler does not represent the actual weld composition. This is particularly important for stainless steels, nickel alloys, hardfacing alloys and dissimilar joints. A filler that is satisfactory in a low-dilution process may produce an unsuitable weld when used with high current, deep penetration or narrow joint preparation.

Consumables influence:

• tensile strength, yield strength and ductility;
• toughness at low or elevated temperature;
• corrosion, oxidation and wear resistance;
• hydrogen content and hydrogen-assisted cracking risk;
• solidification cracking and liquation cracking;
• arc stability, penetration and deposition rate;
• slag detachability and weld-bead shape; and
• residual stress and distortion through heat input and deposition efficiency.

The selection process must therefore begin with the required service properties, not with the convenient availability of a wire or electrode.

Electrodes and Filler Metals

An electrode may be consumable or non-consumable. In shielded metal arc welding, the covered electrode is consumed and its coating generates shielding gases and slag. In gas metal arc welding and submerged arc welding, a continuously supplied wire acts as both electrode and filler. In gas tungsten arc welding, the tungsten electrode is normally non-consumable and a separate filler rod may be added.

A solid wire offers a relatively predictable composition and high deposition efficiency. Flux-cored wire contains a metallic sheath and a powdered core that may provide alloying elements, deoxidizers, arc stabilizers, slag formers and gas-forming compounds. Metal-cored wire contains a largely metallic core and generally produces high deposition rates with lower slag volumes. Covered electrodes are versatile and suitable for site work, but they demand strict storage and handling, especially when low-hydrogen performance is required.

Filler-metal classification systems typically identify strength, composition, welding position, current type and usability. The engineer must not treat a classification number as a complete selection. The classification must be checked against the welding procedure specification, base-metal grade, heat-treatment condition, design code and service environment.

Fluxes

Fluxes perform several simultaneous functions. They may dissolve or float away oxides, absorb impurities, form a protective slag, stabilize the arc, control bead shape and introduce alloying elements. In submerged arc welding, the flux also determines how effectively the arc is enclosed and how the weld cools beneath the slag blanket.

Fluxes may be fused, agglomerated or ceramic. Fused fluxes are produced by melting and crushing a homogeneous mass; agglomerated fluxes bind powdered ingredients without complete melting; ceramic fluxes are designed to provide specific alloying or metallurgical effects. Basic fluxes generally provide improved toughness and lower diffusible hydrogen when properly dried, whereas acidic fluxes often provide smooth bead appearance and easy slag removal. The choice is a compromise between productivity, toughness, hydrogen control, alloy recovery and process stability.

Flux basicity is an important but not sufficient indicator of weld performance. A high-basicity flux can reduce oxygen content and improve toughness, but it may be more sensitive to moisture and may impose stricter storage requirements. Flux recycling in submerged arc welding must also be controlled because fine particles, slag contamination and moisture can alter its behaviour.

Shielding Gases

Shielding gas prevents atmospheric oxygen, nitrogen and moisture from reaching the molten pool. It also affects arc voltage, droplet transfer, penetration, bead profile, heat input and spatter.

Argon is chemically inert and provides easy arc starting and stable operation. Helium increases arc voltage and heat transfer, which can be useful for aluminium, copper and thick sections, although it is more expensive and may require higher flow rates. Carbon dioxide is reactive and economical; it provides deep penetration in steels but tends to increase oxidation and spatter. Small additions of oxygen or carbon dioxide to argon can improve wetting and arc stability in steel welding. Hydrogen may be added in carefully controlled quantities to shielding gases for some austenitic stainless-steel or nickel-alloy applications, but it is unsuitable where hydrogen cracking or porosity is a concern.

Gas selection must account for process, material thickness, joint geometry, welding position, surface condition and ventilation. Excessive flow is not necessarily beneficial: turbulence can entrain air and produce porosity. Gas hoses, regulators, torch seals and flow meters must be inspected because leakage and contamination may be mistaken for a metallurgical problem.

A Framework for Consumable Selection

A practical selection framework consists of six connected decisions.

1. Define the service requirement

Identify the required strength, toughness, fatigue resistance, corrosion resistance, wear resistance, operating temperature and expected life. A filler that matches tensile strength may still be unacceptable if it lacks impact toughness or resistance to a particular chemical environment.

2. Characterize the parent materials

Record grade, thickness, heat-treatment condition, carbon equivalent, surface coating and metallurgical sensitivity. For stainless steels and nickel alloys, chemistry is often more important than nominal strength. For aluminium, temper condition and alloy family strongly affect cracking and strength recovery.

3. Select the weld-metal chemistry

The weld metal may be designed to match the base metal, slightly overmatch it, or deliberately differ from it. Overmatching is common in high-strength steels, while austenitic stainless fillers are sometimes selected to tolerate dilution and reduce cracking risk. In dissimilar joints, the filler may be chosen for compatibility with both materials rather than for exact matching with either one.

4. Control dilution and heat input

Joint design, process choice, current, travel speed and electrode manipulation influence dilution. A consumable should be evaluated under the actual welding conditions, not only from catalogue data.

5. Control hydrogen and contamination

Low-hydrogen consumables, preheating, dry storage, clean joint preparation and suitable shielding are essential for susceptible steels. Aluminium requires removal of hydrated oxide and oil contamination. Titanium requires exceptional cleanliness and trailing or backing shields.

6. Verify through procedure qualification

A qualified welding procedure should demonstrate acceptable visual quality, radiographic or ultrasonic integrity where required, tensile and bend performance, toughness, hardness, corrosion behaviour or other specified properties. Production control must ensure that the qualified consumable, gas, polarity, flux condition and storage practice are actually used.

Material-Specific Selection

Carbon and Low-Alloy Steels

For carbon and low-alloy steels, the principal concerns are strength matching, hydrogen-assisted cracking, heat-affected-zone hardening and toughness. Low-hydrogen basic electrodes and wires are preferred for many restrained structures, thick sections and higher-strength grades. Consumables must be stored in sealed packaging or heated holding ovens according to the manufacturer’s requirements. Reconditioning temperatures and exposure limits must not be assumed to be universal.

Preheat and interpass-temperature control reduce cooling rate and help hydrogen diffuse from the joint. However, excessive heat input may reduce toughness, promote grain coarsening or impair the properties of quenched-and-tempered steels. The selected filler must therefore be considered together with preheat, interpass temperature, bead sequence and post-weld heat treatment.

For weathering steels, the filler should provide suitable alloying elements and atmospheric-corrosion behaviour. For cryogenic applications, impact toughness at the design temperature becomes a dominant criterion. For high-temperature creep-resistant steels, consumable chemistry, post-weld heat treatment and long-term microstructural stability must be considered together.

Stainless Steels

Stainless-steel welding requires control of chromium, nickel, molybdenum, carbon, nitrogen and ferrite. Austenitic stainless welds generally require a controlled amount of delta ferrite to reduce susceptibility to solidification cracking. Too much ferrite, however, may impair toughness, corrosion resistance or high-temperature performance. Ferrite prediction diagrams and weld-metal ferrite measurements are useful tools, but they should be applied with awareness of their assumptions.

Low-carbon or stabilized grades reduce sensitization caused by chromium-carbide precipitation. Consumables for duplex stainless steels must provide an appropriate phase balance after welding; excessive ferrite can reduce toughness and corrosion resistance, while excessive austenite may affect strength and localized corrosion performance. Heat input, interpass temperature and shielding-gas nitrogen can influence the final phase balance.

Surface cleanliness is essential. Carbon-steel tools, iron contamination and inadequate post-weld cleaning can produce rust staining or initiate corrosion. Pickling, passivation, mechanical cleaning and dedicated stainless-steel brushes may be required. Gas mixtures containing oxygen or carbon dioxide should be selected cautiously because excessive oxidation can reduce corrosion resistance and alter the weld surface.

Aluminium and Its Alloys

Aluminium presents three major welding problems: a refractory oxide film, high thermal conductivity and hydrogen-related porosity. The oxide melts at a much higher temperature than aluminium itself. Effective cleaning, suitable polarity and adequate arc action are therefore necessary. Oils, moisture and hydrocarbon residues are especially dangerous because hydrogen dissolves readily in molten aluminium and is rejected during solidification.

Filler selection depends on alloy family, joint geometry, service temperature and cracking tendency. Silicon-containing fillers often provide good fluidity and reduced cracking in several aluminium alloys, while magnesium-containing fillers may be preferred where higher strength or improved corrosion performance is required. Exact selection must follow the alloy combination and applicable specification.

Heat-treatable aluminium alloys may lose strength in the heat-affected zone even when the weld metal is sound. A filler cannot fully restore a temper that has been overaged or solution-treated by welding. Designers must therefore consider joint efficiency, local reinforcement, post-weld heat treatment and the possibility of using a non-heat-treatable filler to improve crack resistance.

Argon is widely used for aluminium, while helium or argon–helium mixtures can increase heat transfer in thick sections. Shielding quality, gas purity and torch angle are critical. Excessive gas flow can cause turbulence, and inadequate pre-cleaning may result in lack of fusion or oxide inclusions.

Titanium

Titanium reacts strongly with oxygen, nitrogen and hydrogen at welding temperatures. Contamination produces a hard, brittle and discoloured weld or heat-affected zone. Conventional torch shielding is often insufficient because the hot metal remains reactive after it leaves the arc. High-purity argon, carefully designed trailing shields and back purging are commonly required.

Filler metals are selected to match the titanium grade or to achieve a specified strength and ductility. Joint surfaces must be chemically clean and free from fingerprints, grease, paint and embedded iron. The colour of the weld and adjacent heated metal can provide a useful process-control indication, although colour alone is not a substitute for mechanical or metallurgical verification. Titanium welding is consequently a discipline in which cleanliness, gas coverage and equipment integrity are as important as current and travel speed.

Nickel-Based Alloys

Nickel alloys are used where strength, oxidation resistance, corrosion resistance or high-temperature stability are required. Their welding difficulties include sluggish fluidity, segregation, hot cracking, liquation cracking and sensitivity to contamination by sulphur, lead, phosphorus and other low-melting constituents.

Filler metals may be matched to the alloy, selected to improve crack resistance or chosen to provide a transition between dissimilar materials. Narrow bead placement, controlled heat input and careful interpass cleaning are often beneficial. Excessive dilution can introduce elements from the base material that destabilize the weld microstructure or promote cracking. For corrosion-resistant nickel alloys, surface oxidation and iron contamination must be minimized, and post-weld cleaning may be necessary.

Composites and Metal-Matrix Materials

Many polymer-matrix composites cannot be fusion welded because their matrix decomposes before a conventional weld pool can form. Joining may instead use resistance welding, induction welding, ultrasonic welding, laser-assisted thermoplastic fusion or a separate metallic insert. Consumable selection in these processes concerns interlayers, meshes, films, adhesives and thermoplastic matrices rather than conventional electrodes.

Metal-matrix composites containing ceramic particles are difficult to weld because reinforcement may react with the matrix, segregate, fracture or alter heat flow. The preferred approach may be low-heat-input joining, brazing, friction-based processing or the use of a compatible interlayer. The engineer must distinguish between a material that can be welded by a modified fusion process and one for which a fundamentally different joining method is more appropriate.

Dissimilar-Material Joints

Dissimilar joints combine differences in melting point, thermal expansion, electrical conductivity, metallurgical compatibility and corrosion potential. A suitable filler may be selected to dilute acceptably with both materials, suppress brittle intermetallic compounds and provide a graded transition in properties.

Typical risks include hard or brittle reaction layers, galvanic corrosion, hot cracking, residual stress and reduced fatigue life. Buttering one or both members with a compatible alloy can reduce dilution. Intermediate layers, controlled heat input and modified joint geometry may also be used. In some aluminium–steel joints, direct fusion welding is avoided because brittle iron–aluminium intermetallic layers form readily; mechanical fastening, brazing, friction welding or a carefully engineered transition insert may be more reliable.

Applied Case Study: Stainless-Steel Pipeline Repair

Background

An illustrative process-plant repair involves joining a duplex stainless-steel pipe spool to a matching component in a restrained position. The joint must resist chloride-containing service and maintain adequate toughness. A previous repair had shown excessive ferrite and localized corrosion near the weld toe.

Problem Analysis

The investigation identified three interacting causes: an unsuitable filler with insufficient nickel balance, excessive interpass temperature and poor control of shielding gas. The high cooling and reheating history produced an unfavourable ferrite–austenite balance. Surface contamination and excessive oxidation further reduced corrosion performance.

Approach

The engineering team specified a duplex-compatible filler with chemistry designed to promote adequate austenite formation after welding. The procedure limited heat input and interpass temperature, used controlled bead sizes and required interpass cleaning. High-purity shielding gas and an effective root purge were specified. Consumables were stored in sealed, controlled conditions, and the procedure qualification included ferrite measurement, visual examination, radiography, bend testing and corrosion-related metallurgical examination.

Outcome

The qualified procedure produced a more balanced weld microstructure and eliminated the visible oxidation associated with the earlier repair. Production inspection confirmed consistent gas coverage and consumable control. The repair was accepted after satisfying the specified mechanical and metallurgical requirements.

Learning Points

The case demonstrates that filler selection alone cannot guarantee performance. Consumable chemistry, heat input, interpass temperature, gas purity, purge quality, surface preparation and inspection form one integrated welding system. It also shows why a procedure that appears visually acceptable may still be unsuitable for corrosion-critical service.

Common Failure Modes and Quality Controls

Porosity is commonly associated with moisture, oil, inadequate shielding, excessive gas flow, dirty surfaces or hydrogen pickup. Cracking may result from unsuitable weld-metal chemistry, excessive restraint, high dilution, rapid cooling or incorrect filler selection. Lack of fusion is often a process and joint-preparation problem, but poor arc characteristics and inappropriate shielding can contribute. Slag inclusions arise from inadequate cleaning, incorrect electrode angle, poor manipulation or unsuitable flux behaviour.

Consumables should be controlled through identification, batch traceability, storage records, issue control and exposure monitoring. Fluxes must be protected from moisture and contamination. Gas cylinders should be correctly identified, segregated and connected with clean equipment. Filler wires should be protected from rust, oil and abrasive dust. In automated systems, wire straightness, feeding force, liner condition and contact-tip wear directly influence deposition consistency.

A common mistake is to select a consumable solely by tensile strength. Other frequent errors include ignoring dilution, using damp low-hydrogen electrodes, assuming that more shielding gas is always better, mixing incompatible filler batches, failing to account for post-weld heat treatment, and transferring a procedure from one thickness or joint geometry to another without qualification.

Digital and Emerging Developments

Modern welding production increasingly combines consumable control with digital process monitoring. Wire-feed speed, current, voltage, travel speed, gas flow and heat input can be recorded for each weld. Deviations can trigger alerts before a defect becomes embedded in a large structure. Machine-learning systems are being investigated for arc-signal classification, porosity prediction and adaptive control, although their reliability depends on representative training data and independent validation.

Engineered consumables are also developing rapidly. Metal-cored wires, nanoparticle-modified fluxes, metal-powder additions and tailored alloy wires can improve deposition rate, refine microstructure or reduce spatter. Additive manufacturing uses wire or powder consumables whose chemistry must be controlled across many thermal cycles; consequently, interlayer bonding, anisotropy, residual stress and powder or wire quality become central concerns.

Sustainability considerations include reducing spatter and discarded wire, improving deposition efficiency, selecting gases with lower environmental impact where technically feasible, and using digital traceability to reduce rework. These developments do not remove the need for metallurgical understanding. Rather, they increase the value of sound materials selection and validated process control.

Professional and Regulatory Considerations

Consumable selection must comply with the governing design code, project specification and qualification standard. Welding engineers should verify classification, manufacturer certificates, batch identity, storage conditions and compatibility with the qualified procedure. Safety considerations include gas-cylinder handling, ventilation, ultraviolet radiation, fumes from fluxes or coatings, and the possibility of hazardous decomposition products.

Ethically, consumable substitution should never be made informally when it can affect weld chemistry or service performance. A cheaper or more readily available filler may be technically acceptable only after engineering review and, where required, procedure requalification. Traceability is particularly important in pressure equipment, aerospace structures, nuclear components, offshore facilities and safety-critical transportation systems.

Best-Practice Selection Checklist

Before production welding, the engineer should confirm that:

• the base-metal grades and service requirements are known;
• the filler chemistry and classification are appropriate;
• dilution and heat input have been considered;
• hydrogen control and consumable storage are adequate;
• shielding gas purity, flow and purge arrangements are validated;
• flux condition and recycling practice are controlled;
• surface preparation is suitable for the material;
• the procedure has been qualified for the actual joint and thickness;
• inspection and acceptance criteria are defined; and
• substitutions are controlled through documented technical approval.

Chapter Summary

Consumables and shielding systems govern the chemical, metallurgical and operational behaviour of a weld. Electrode and filler selection must be based on service requirements, parent-metal chemistry, dilution, heat input, hydrogen control and qualification evidence. Fluxes influence shielding, slag formation, alloy recovery, toughness and arc behaviour, while gases affect transfer mode, penetration, oxidation and porosity.

Carbon and low-alloy steels require particular attention to hydrogen and toughness. Stainless steels demand control of ferrite, sensitization, contamination and corrosion performance. Aluminium requires oxide removal and hydrogen-porosity control; titanium requires exceptionally pure and extended shielding; nickel alloys require control of segregation, cracking and contamination. Composites may require non-fusion joining methods, and dissimilar materials often need transition fillers, buttering, interlayers or alternative processes.

Reliable welding results from treating consumables, equipment, procedure parameters, storage and inspection as one integrated system. Digital monitoring and engineered consumables are expanding process capability, but they must be supported by metallurgical knowledge, qualification and professional responsibility.

Key Terms

Consumable: A material intentionally consumed during welding to provide an electrode, filler, shielding or flux function.

Filler metal: Metal added to a joint to form part or all of the weld zone.

Dilution: The proportion of melted base metal incorporated into the weld metal.

Flux: A chemical or mineral material that protects, cleans, stabilizes or modifies the weld pool.

Basic flux: A flux formulated to reduce weld-metal oxygen and often improve toughness and hydrogen control.

Shielding gas: Gas supplied to exclude atmospheric contamination from the arc and molten pool.

Low-hydrogen electrode: An electrode designed and handled to produce low diffusible hydrogen in the weld.

Metal-cored wire: A tubular electrode with a predominantly metallic core used for high deposition welding.

Solidification cracking: Cracking occurring as weld metal solidifies through a vulnerable temperature range.

Liquation cracking: Cracking caused by localized melting in the heat-affected zone or partially melted region.

Sensitization: Loss of stainless-steel corrosion resistance due to chromium-carbide precipitation at grain boundaries.

Ferrite: A body-centred cubic phase that may occur in stainless-steel weld metal and influence cracking and corrosion behaviour.

Hydrogen porosity: Gas cavities formed when dissolved hydrogen becomes insoluble during solidification.

Intermetallic compound: A distinct compound formed between metallic elements, often brittle in dissimilar joints.

Buttering: Depositing a compatible weld layer on a base material before completing the joint.

Heat input: Thermal energy supplied per unit length of weld, commonly related to current, voltage and travel speed.

Trailing shield: Additional shielding that protects hot metal behind the welding arc.

Consumable traceability: The ability to identify and document the origin, batch and use of a welding consumable.

Procedure qualification: Demonstration that a defined welding procedure produces a joint meeting specified requirements.

Review Questions

Short Answer Questions

1. What is dilution, and why is it important in stainless-steel and nickel-alloy welding?

2. State two functions of a welding flux.

3. Why is hydrogen control important when welding high-strength steels?

4. Identify two causes of porosity in aluminium welds.

5. Why does titanium require trailing or extended shielding?

Long Answer Questions

1. Explain the systematic procedure for selecting a filler metal for a safety-critical welded joint.

2. Discuss the influence of shielding gases on arc behaviour, penetration and weld quality.

3. Compare consumable-selection issues for carbon steel, stainless steel and aluminium.

4. Explain the metallurgical difficulties associated with nickel-alloy welding and suitable control measures.

5. Discuss why dissimilar-material joints may require buttering, interlayers or alternative joining processes.

Analytical / Application Questions

1. A restrained high-strength steel joint develops hydrogen-assisted cracks several hours after welding. Analyse the likely causes and propose a revised consumable and process-control plan.

2. A duplex stainless-steel weld has excessive ferrite and poor corrosion performance. Determine which consumable, shielding, heat-input and inspection factors should be reviewed.

3. An aluminium–steel joint repeatedly develops a brittle interface. Evaluate whether a modified filler, interlayer, buttering operation or non-fusion process would provide the most technically defensible solution.

22. Multiple Choice Questions with Answers

Question 1

Which factor most directly explains why a filler-metal classification alone is insufficient for selecting a consumable?

A. The classification never identifies the electrode diameter

B. The final weld chemistry is affected by dilution and welding conditions

C. All classifications apply only to manual welding

D. Filler metals have no influence on weld microstructure

Correct Answer: B. The final weld chemistry is affected by dilution and welding conditions

Question 2

What is the principal metallurgical reason for using low-hydrogen consumables in restrained high-strength steel joints?

A. To increase aluminium oxide removal

B. To prevent chromium-carbide precipitation

C. To reduce the risk of hydrogen-assisted cracking

D. To increase weld-metal electrical resistance

Correct Answer: C. To reduce the risk of hydrogen-assisted cracking

Question 3

Why can excessive shielding-gas flow cause porosity?

A. It may create turbulence that entrains atmospheric air

B. It always reduces arc voltage to zero

C. It converts argon into hydrogen

D. It prevents the electrode from melting

Correct Answer: A. It may create turbulence that entrains atmospheric air

Question 4

Which combination is most important when welding titanium?

A. High oxygen shielding and rapid exposure to air

B. Low-purity gas and carbon-steel cleaning tools

C. High-purity shielding, trailing protection and exceptional cleanliness

D. Wet flux and unrestricted interpass contamination

Correct Answer: C. High-purity shielding, trailing protection and exceptional cleanliness

Question 5

A heat-treatable aluminium alloy weld is sound but the adjacent heat-affected zone is weaker. What is the most appropriate interpretation?

A. The filler necessarily failed to melt

B. Welding may have altered the alloy temper in the heat-affected zone

C. The shielding gas must have contained nitrogen only

D. Aluminium alloys cannot be welded under any conditions

Correct Answer: B. Welding may have altered the alloy temper in the heat-affected zone

Question 6

What is the principal purpose of controlled ferrite in many austenitic stainless-steel weld metals?

A. To eliminate all corrosion resistance

B. To reduce susceptibility to solidification cracking

C. To ensure that the weld becomes fully martensitic

D. To increase hydrogen absorption

Correct Answer: B. To reduce susceptibility to solidification cracking

Question 7

Which situation most strongly justifies considering buttering in a dissimilar-material joint?

A. The joint has identical materials and no dilution

B. A deposited transition layer can reduce harmful dilution between incompatible materials

C. The process requires no filler metal

D. The base metals have exactly the same thermal expansion

Correct Answer: B. A deposited transition layer can reduce harmful dilution between incompatible materials

Question 8

Why are nickel alloys particularly sensitive to careful surface preparation?

A. Sulphur, lead and similar contaminants can promote cracking

B. Cleaning increases the alloy melting point indefinitely

C. Nickel alloys cannot conduct heat

D. Surface preparation controls only electrode polarity

Correct Answer: A. Sulphur, lead and similar contaminants can promote cracking

Question 9

Which practice best supports consumable traceability in safety-critical production?

A. Removing all batch labels before use

B. Mixing opened filler batches in one unmarked container

C. Recording batch identity, storage condition and use in the qualified procedure

D. Substituting any visually similar wire without review

Correct Answer: C. Recording batch identity, storage condition and use in the qualified procedure

Question 10

A duplex stainless-steel repair shows excessive ferrite after welding. Which corrective strategy is most technically relevant?

A. Increase contamination and remove the root purge

B. Review filler chemistry, heat input, interpass temperature and shielding conditions

C. Use a damp low-hydrogen electrode without qualification

D. Ignore microstructure because visual appearance is sufficient

Correct Answer: B. Review filler chemistry, heat input, interpass temperature and shielding conditions