API 510 Chapter 13

Prepare for the API 510 Pressure Vessel Inspector certification exam with this API 510 Chapter 13 API RP 577 Welding study guide and free practice test.

API Recommended Practice 577, Welding Processes, Inspection, and Metallurgy, is an important reference for API 510 candidates because pressure-vessel inspectors regularly encounter welding during fabrication, maintenance, repairs, alterations, and rerating activities.

This chapter introduces the fundamental welding processes, welding consumables, electrical characteristics, shielding methods, common welding variables, weld discontinuities, and inspection considerations that an API 510 inspector should understand.

After reviewing the study material, try the API RP 577 welding process familiarization questions to check your knowledge.

What Is API RP 577?

API RP 577 provides practical guidance for inspectors involved with welding, welding inspection, and metallurgy associated with pressure equipment and process-industry equipment.

For API 510 candidates, API RP 577 helps connect welding theory with practical inspection activities.

Important subjects include:

• Welding terminology

• Common welding processes

• Welding consumables

• Welding electrodes and filler metals

• Shielding gases

• Fluxes

• Welding current and polarity

• Welding variables

• Weld joint preparation

• Preheat

• Interpass temperature

• Postweld heat treatment

• Welding procedure qualification

• Welder qualification

• Weld inspection

• Common weld discontinuities

• Metallurgical effects of welding

• Weldability

• Carbon equivalency concepts

• Hardness

• Hydrogen cracking

• Nondestructive examination

The objective for an API 510 inspector is not to become a production welder.

The inspector should understand welding well enough to recognize whether welding activities are being performed using appropriate procedures, qualified personnel, suitable consumables, and appropriate inspection controls.

Why Is API RP 577 Important for API 510?

Pressure vessels frequently require welding during:

• Original fabrication

• Crack repairs

• Corrosion repairs

• Weld buildup

• Insert-plate repairs

• Nozzle replacement

• New nozzle installation

• Alterations

• Rerating modifications

• Attachment installation

An inappropriate welding procedure can introduce problems such as:

• Cracking

• Lack of fusion

• Incomplete penetration

• Excessive hardness

• Porosity

• Slag inclusion

• Undercut

• Distortion

• Residual stress

• Metallurgical degradation

The API 510 inspector should therefore understand the relationship between:

Welding process → Consumable → Procedure → Welder → Metallurgy → Inspection → Acceptance

Welding Process Fundamentals

A welding process creates coalescence between materials by using heat, pressure, or a combination of both.

For most pressure-vessel welding processes included in API 510 preparation, an electric arc provides the heat needed to melt the base material and filler metal.

The resulting molten weld pool solidifies and forms the welded joint.

Different welding processes use different combinations of:

• Electrode type

• Filler metal

• Flux

• Shielding gas

• Current

• Voltage

• Polarity

• Travel speed

• Heat input

Understanding these differences makes API RP 577 questions much easier.

Welding Processes Important for API 510

API RP 577 discusses several welding processes.

For API 510 exam preparation, candidates should pay particular attention to:

• Shielded Metal Arc Welding – SMAW

• Gas Tungsten Arc Welding – GTAW

• Gas Metal Arc Welding – GMAW

• Flux Cored Arc Welding – FCAW

• Submerged Arc Welding – SAW

The current API 510 Body of Knowledge limits detailed WPS/PQR/WPQ review questions to:

SMAW, GTAW, GMAW, and SAW.

However, API RP 577, as a reference, contains broader welding-process knowledge, so inspectors should also understand other common processes at a familiarization level.

Shielded Metal Arc Welding – SMAW

SMAW is commonly called:

• Stick welding

• Manual metal arc welding

• MMA

SMAW uses a consumable flux-coated electrode.

An electric arc forms between the electrode and workpiece.

The electrode core melts and becomes filler metal.

At the same time, the electrode coating provides shielding and produces slag that protects the molten and solidifying weld.

SMAW Characteristics

SMAW is:

• Portable

• Versatile

• Suitable for field work

• Useful for maintenance and repair

• Capable of welding in multiple positions

• Widely used on carbon and low-alloy steels

Because the electrodes are relatively short, welding must stop periodically so the welder can replace the consumed electrode.

Slag must generally be removed between weld passes.

SMAW Consumables

SMAW electrodes are classified according to applicable AWS filler-metal specifications.

A common example is:

E7018

Although candidates should use the applicable specification for detailed classification, understanding the basic designation is useful.

In a simplified E7018 example:

E = electrode

70 = minimum tensile-strength classification

1 = suitable for applicable all-position welding

8 = identifies characteristics associated with coating, current, and usability classification

Another commonly recognized electrode is:

E6010

Different electrodes have different:

• Coatings

• Penetration characteristics

• Hydrogen levels

• Positions

• Current/polarity requirements

• Mechanical properties

Therefore, electrodes should not be substituted casually.

Low-Hydrogen SMAW Electrodes

Low-hydrogen electrodes are especially important when welding steels susceptible to hydrogen-assisted cracking.

Examples include certain E7018-type electrodes.

Moisture in electrode coatings can introduce hydrogen into the weld.

Therefore, low-hydrogen electrode control can involve:

• Correct storage

• Heated holding ovens

• Exposure-time limits

• Proper handling

• Reconditioning where permitted

An electrode labeled “low hydrogen” will not remain low hydrogen if it is improperly stored and absorbs moisture.

SMAW Advantages

SMAW is popular for repair work because it offers:

• Portable equipment

• Simple setup

• Good accessibility

• Multiple welding positions

• Wide range of available electrodes

• Suitability for field conditions

SMAW Limitations

Limitations can include:

• Lower productivity than continuous-wire processes

• Frequent electrode changes

• Slag removal

• Potential slag inclusions

• Greater dependence on welder skill

• Electrode moisture-control requirements

Gas Tungsten Arc Welding – GTAW

GTAW is also commonly called:

TIG – Tungsten Inert Gas welding

GTAW uses a nonconsumable tungsten electrode.

The tungsten creates the arc but normally does not become the filler metal.

Filler metal, when required, is supplied separately.

The weld pool is protected by shielding gas.

Common shielding gases include:

• Argon

• Helium

• Mixtures appropriate to the application

GTAW Characteristics

GTAW is well known for:

• Excellent weld quality

• Precise heat control

• Clean weld deposits

• Good root-pass control

• No flux slag

• Ability to weld thin materials

• Suitability for stainless and alloy materials

It is frequently used for high-quality root passes in pressure equipment and piping.

GTAW Filler Metal

GTAW commonly uses bare filler-metal rods classified with designations beginning with:

ER

Examples used in industry can include classifications such as:

• ER70S-2

• ER70S-6

• Stainless-steel filler classifications

The correct filler metal depends on:

• Base material

• Mechanical-property requirements

• Service

• Welding procedure

GTAW Tungsten Electrode

A critical exam concept is:

The tungsten electrode is normally nonconsumable.

The tungsten produces the arc.

It is not the same thing as the filler metal.

Contamination or accidental contact between the tungsten and molten weld pool can create welding problems.

Tungsten Inclusion

If tungsten becomes transferred into the weld metal, it may create a tungsten inclusion.

Because tungsten is much denser than steel, a tungsten inclusion can appear relatively light on a radiographic image.

This is a useful API 510/NDE crossover concept.

GTAW Shielding Gas

GTAW depends on adequate shielding-gas coverage.

Loss of shielding can result in:

• Oxidation

• Porosity

• Contaminated weld metal

• Poor weld appearance

Wind or drafts can therefore be particularly important during field GTAW.

GTAW Advantages

Advantages include:

• High-quality welds

• Excellent control

• No slag

• Low spatter

• Precise heat input

• Excellent root-pass capability

GTAW Limitations

Limitations include:

• Relatively slow deposition

• Greater operator skill requirement

• Sensitivity to contamination

• Sensitivity to wind

• Lower productivity for large weld deposits

Gas Metal Arc Welding – GMAW

GMAW is commonly known as:

MIG/MAG welding

GMAW uses a continuously fed consumable wire electrode.

The wire serves as both:

• Electrode

and

• Filler metal

An externally supplied shielding gas protects the molten weld pool.

GMAW Shielding Gases

Depending on the application, shielding gases can include:

• Argon

• Carbon dioxide

• Argon/CO₂ mixtures

• Other appropriate gas combinations

Gas selection affects:

• Arc characteristics

• Penetration

• Spatter

• Transfer mode

• Weld profile

GMAW Metal Transfer Modes

Candidates should recognize the major transfer concepts.

Short-Circuiting Transfer

The wire repeatedly contacts the weld pool, creating rapid short circuits that transfer molten metal.

Characteristics can include:

• Relatively low heat input

• Suitability for thinner materials

• Out-of-position capability

• Risk of lack of fusion if improperly applied

Globular Transfer

Larger droplets transfer across the arc.

It can produce:

• Greater spatter

• Less stable transfer than spray

• Particular positional limitations depending on conditions

Spray Transfer

Small droplets transfer across the arc in a stable stream.

Spray transfer typically provides:

• High deposition

• Good fusion

• Relatively high heat input

It is generally more suited to suitable flat/horizontal applications than some low-energy transfer modes.

Pulsed Spray

Current alternates between background and peak levels to achieve controlled droplet transfer.

This can provide spray-type transfer with reduced average heat input.

GMAW Consumables

A common carbon-steel GMAW wire example is:

ER70S-6

The filler metal is continuously supplied from a spool or similar feeding system.

Candidates should understand that GMAW generally uses:

Continuous solid wire + external shielding gas

GMAW Advantages

Advantages can include:

• High productivity

• Continuous electrode feeding

• No slag in conventional solid-wire GMAW

• High deposition rates

• Easy automation

• Reduced electrode-change downtime

GMAW Limitations

Possible limitations include:

• Wind sensitivity

• More complex equipment than SMAW

• Potential lack of fusion with inappropriate parameters

• Need for shielding gas

• Transfer-mode limitations

Flux Cored Arc Welding – FCAW

FCAW uses a continuously fed tubular electrode containing flux ingredients inside the wire.

This is an easy point to remember:

SMAW → Flux outside the electrode

FCAW → Flux inside the tubular wire

FCAW Types

Two broad forms are:

Gas-Shielded FCAW

Uses:

Flux-cored wire + external shielding gas

Self-Shielded FCAW

Relies on the consumable’s flux system and does not require external shielding gas.

This can make some self-shielded FCAW applications useful in field conditions where wind would make external gas shielding difficult.

FCAW Advantages

Possible advantages include:

• High deposition

• Continuous-wire operation

• Good productivity

• Useful positional capability with suitable consumables

• Strong field applications

FCAW Limitations

Limitations can include:

• Slag removal

• Potential slag inclusions

• Fume generation

• Consumable-control requirements

• Process-specific usability considerations

Submerged Arc Welding – SAW

SAW uses:

• Continuously fed consumable electrode wire

• Granular flux covering the arc

The arc is literally submerged beneath the granular flux.

Because the arc is covered, there is normally little visible arc radiation during welding.

SAW Characteristics

SAW is especially suitable for:

• Long weld seams

• Thick materials

• Shop fabrication

• High-deposition welding

• Mechanized or automated welding

Pressure-vessel longitudinal and circumferential seams can be produced using SAW.

SAW Consumables

SAW uses a combination of:

Electrode wire + granular flux

Unlike SMAW, the flux is not coated around an individual stick electrode.

Unlike GMAW, an external shielding-gas cylinder is generally not used to provide primary arc shielding.

The flux system protects the arc and molten weld pool.

SAW Advantages

Advantages include:

• Very high deposition rates

• High productivity

• Deep penetration

• Good weld appearance

• Excellent suitability for automation

• Minimal spatter

• Limited visible arc

SAW Limitations

Limitations include:

• Restricted positional capability

• Flux handling

• Slag removal

• Limited suitability for complex field repairs

• Greater equipment setup requirements

Welding Process Comparison

Process	Electrode	Shielding	Slag	Typical Strength
SMAW	Consumable stick electrode	Electrode coating	Yes	Portable repair welding
GTAW	Nonconsumable tungsten	External gas	No	Precise, high-quality welding
GMAW	Continuous consumable solid wire	External gas	No	High productivity
FCAW	Continuous consumable tubular wire	Flux and sometimes gas	Usually yes	High deposition/field fabrication
SAW	Continuous consumable wire	Granular flux	Yes	Automated high-deposition welding

This comparison is extremely useful for API RP 577 familiarization.

Consumable vs Nonconsumable Electrodes

This is a basic but important exam concept.

Consumable Electrode

The electrode melts and becomes part of the weld.

Examples include:

• SMAW

• GMAW

• FCAW

• SAW

Nonconsumable Electrode

The electrode primarily creates the arc and normally does not become part of the weld.

The major example is:

GTAW tungsten electrode

Filler metal can be added separately.

Flux vs Shielding Gas

A weld pool must be protected from harmful atmospheric contamination.

Different processes accomplish this differently.

Flux-Based Protection

Examples:

• SMAW

• FCAW

• SAW

Flux can provide:

• Shielding gases

• Slag

• Deoxidizers

• Arc stabilization

• Alloying ingredients depending on consumable design

Gas-Based Protection

Examples:

• GTAW

• GMAW

• Gas-shielded FCAW

Common gases include:

• Argon

• Helium

• CO₂

• Mixtures

Why Shielding Matters

Atmospheric gases such as:

• Oxygen

• Nitrogen

• Hydrogen-containing moisture

can adversely affect molten weld metal.

Poor shielding can contribute to:

• Porosity

• Oxidation

• Poor mechanical properties

• Surface contamination

• Weld defects

Welding Current

Welding-current type affects arc behavior and electrode performance.

The two major forms are:

DC – Direct Current

AC – Alternating Current

Process and electrode requirements determine which current is appropriate.

Welding Polarity

For DC welding, polarity describes which terminal is connected to the electrode.

DCEP

Direct Current Electrode Positive

Also commonly called reverse polarity.

DCEN

Direct Current Electrode Negative

Also commonly called straight polarity.

Polarity can affect:

• Penetration

• Electrode melting

• Arc stability

• Cleaning action

• Heat distribution

Candidates should use the consumable and procedure requirements rather than assuming one polarity is correct for every process.

Welding Voltage

Arc voltage is related to arc length and electrical potential across the welding arc.

Changing voltage can influence:

• Arc length

• Weld bead width

• Weld profile

• Transfer characteristics

It is one of the important welding variables inspectors encounter when reviewing welding procedures.

Amperage

Current strongly influences the amount of heat produced by the arc.

Increasing amperage can generally increase:

• Penetration

• Electrode melting rate

• Deposition

Excessive current can contribute to:

• Undercut

• Excessive penetration

• Poor bead profile

• Excessive heat input

Too little current can contribute to:

• Poor fusion

• Unstable arc

• Insufficient penetration

Travel Speed

Travel speed affects how long heat is applied to a particular area.

Excessively fast travel can contribute to:

• Incomplete fusion

• Undercut

• Narrow weld bead

Excessively slow travel can produce:

• Excessive heat input

• Wide bead

• Excessive reinforcement

• Distortion

Heat Input

Heat input is an important welding and metallurgy concept.

It is influenced by:

• Voltage

• Current

• Travel speed

In general:

Higher current/voltage or slower travel → greater heat input

Lower current/voltage or faster travel → lower heat input

Heat input affects:

• Cooling rate

• HAZ width

• Microstructure

• Hardness

• Distortion

• Mechanical properties

Welding Positions

Candidates should recognize common welding positions.

For plate, these include positions such as:

• Flat

• Horizontal

• Vertical

• Overhead

For piping or tubular work, positions can include:

• 1G

• 2G

• 5G

• 6G

Welder qualification range depends on the position and applicable ASME Section IX requirements.

Groove Welds and Fillet Welds

Groove Weld

A groove weld is deposited in a prepared groove between components.

Groove welds can provide:

• Full penetration

• Partial penetration

depending on design and execution.

Fillet Weld

A fillet weld generally has an approximately triangular cross-section joining surfaces that are approximately perpendicular or overlapping.

Candidates should understand basic terms such as:

• Leg

• Throat

• Face

• Toe

• Root

These terms are important when interpreting ASME VIII attachment-weld requirements.

Weld Joint Preparation

Before welding, the joint may require preparation such as:

• Beveling

• Cleaning

• Alignment

• Root-gap control

• Tack welding

Incorrect joint preparation can contribute to:

• Incomplete penetration

• Lack of fusion

• Excessive weld metal

• Distortion

• Misalignment

The welding inspector should verify the joint condition before welding begins.

Preheat

Preheat means heating the base metal before welding.

Important reasons can include:

• Slowing the cooling rate

• Reducing hardness

• Allowing hydrogen to diffuse

• Reducing hydrogen-cracking susceptibility

• Controlling thermal gradients

Preheat requirements can depend on:

• Material

• Thickness

• Carbon equivalent

• Hydrogen level

• Welding process

• Service

Interpass Temperature

Interpass temperature is the temperature of the weld area before depositing the next weld pass.

Both minimum and maximum interpass temperatures may be important.

If temperature is too low:

• Hydrogen-cracking concerns may increase in susceptible materials.

If temperature is too high:

• Excessive heat input

• Microstructural changes

• Mechanical-property degradation

may occur.

Postweld Heat Treatment

PWHT occurs after welding and was covered in detail in Chapter 11.

It can be required to:

• Reduce residual stresses

• Temper hardened HAZ regions

• Control hardness

• Meet material/service requirements

Preheat and PWHT are not interchangeable.

Welding Procedure Specification – WPS

A WPS tells the welder how production welding should be performed.

It contains the applicable welding variables, such as:

• Welding process

• Base material

• Filler metal

• Electrical characteristics

• Position

• Preheat

• PWHT

• Technique

Think of the WPS as:

The approved welding instructions.

Procedure Qualification Record – PQR

A PQR records the actual variables used to make a procedure-qualification test coupon and the results of required mechanical testing.

It provides evidence supporting the WPS.

A useful memory aid is:

WPS = instructions

PQR = evidence that the procedure can produce acceptable properties

Welder Performance Qualification – WPQ

A WPQ demonstrates that a welder or welding operator can produce an acceptable weld using an applicable qualified welding procedure.

Therefore:

WPS qualifies the method.

WPQ qualifies the person.

Common Welding Discontinuities

API RP 577 candidates should recognize common weld imperfections and their likely causes.

Porosity

Porosity results from gas trapped during weld solidification.

Possible causes include:

• Moisture

• Contamination

• Poor shielding

• Dirty material

• Incorrect technique

Radiographically, porosity often appears as rounded dark indications.

Slag Inclusion

Slag can become trapped within the weld metal, especially in flux-based welding processes.

Possible causes include:

• Poor slag removal

• Incorrect electrode angle

• Improper bead placement

• Low heat input

• Poor joint geometry

Lack of Fusion

Lack of fusion occurs when weld metal fails to fuse properly with:

• Base metal

or

• Previous weld passes

Possible causes include:

• Low heat input

• High travel speed

• Poor technique

• Surface contamination

• Incorrect electrode manipulation

Lack of fusion is a planar discontinuity and can be particularly significant.

Incomplete Penetration

Incomplete penetration occurs when weld metal does not completely penetrate the intended joint root.

Possible causes include:

• Insufficient root gap

• Incorrect groove angle

• Low heat

• Large root face

• Poor technique

Undercut

Undercut is a groove melted into the base metal adjacent to the weld toe or root and left insufficiently filled with weld metal.

Possible causes include:

• Excessive current

• Excessive travel speed

• Incorrect electrode angle

Cracking

Cracks are among the most serious welding discontinuities.

Types can include:

• Hot cracks

• Cold cracks

• Crater cracks

• Hydrogen-assisted cracks

• HAZ cracks

Cracking should lead to evaluation of the underlying cause rather than merely cosmetic repair.

Hydrogen-Assisted Cracking

Hydrogen-assisted cracking is an important welding-metallurgy topic.

The main contributing factors are commonly:

Hydrogen

Susceptible microstructure

Tensile stress

Control methods can include:

• Low-hydrogen consumables

• Proper electrode storage

• Preheat

• Heat-input control

• Suitable material/welding procedure

• PWHT where required

Hot Cracking

Hot cracking develops during or near weld-metal solidification at high temperature.

Factors can include:

• Weld-metal chemistry

• Joint restraint

• Bead shape

• Solidification characteristics

It is different from delayed hydrogen cracking, which generally occurs after the weld has cooled.

Arc Strikes

An arc strike occurs when an arc is unintentionally initiated outside the intended weld area.

Arc strikes can create:

• Local hardening

• Cracking

• Metallurgical damage

• Surface imperfections

They should therefore be evaluated and removed/repaired where required by applicable procedures.

Distortion

Welding produces localized heating and contraction.

This can create:

• Angular distortion

• Shrinkage

• Misalignment

• Residual stress

Methods used to control distortion can include:

• Welding sequence

• Fixtures

• Balanced welding

• Heat-input control

• Joint design

Welding Inspection Stages

A good welding inspection program does not begin after the weld is completed.

Before Welding

Check:

• Material

• Joint preparation

• Fit-up

• WPS

• Welder qualification

• Consumables

• Preheat

• Welding equipment

During Welding

Monitor:

• Process

• Consumable

• Electrical variables

• Preheat/interpass temperature

• Technique

• Cleaning between passes

• Weld sequence

After Welding

Inspect:

• Final weld profile

• Dimensions

• Surface condition

• Discontinuities

• NDE results

• PWHT where required

• Repair documentation

13.4 Welding Process Familiarization Questions

Now try the API RP 577 welding process familiarization questions.

Before beginning, make sure you can answer:

• Which process uses a flux-coated stick electrode?

• Which process uses a nonconsumable tungsten electrode?

• Which process uses continuous solid wire with external gas shielding?

• Which process uses a tubular flux-cored wire?

• Which process operates beneath granular flux?

• Which processes normally produce slag?

• Which processes require external shielding gas?

• What is a consumable electrode?

• What is a nonconsumable electrode?

• What is the purpose of shielding gas?

• What is the purpose of flux?

• What does DCEP mean?

• What does DCEN mean?

• What is heat input?

• What is preheat?

• What is interpass temperature?

• What is the difference between WPS, PQR and WPQ?

• What causes porosity?

• What causes slag inclusion?

• What is lack of fusion?

• Why are low-hydrogen electrodes controlled?

If these concepts are clear, you are ready for the Chapter 13 practice questions.

Welding Process Quick-Revision Table

Feature	SMAW	GTAW	GMAW	FCAW	SAW
Electrode	Consumable stick	Nonconsumable tungsten	Consumable wire	Consumable tubular wire	Consumable wire
Filler	Electrode	Separate if required	Wire electrode	Wire electrode	Wire electrode
Shielding	Flux coating	External gas	External gas	Flux/gas or self-shielded	Granular flux
Slag	Yes	No	No	Usually yes	Yes
Feed	Manual sticks	Separate filler	Continuous	Continuous	Continuous
Productivity	Moderate	Lower	High	High	Very high
Field repair use	Excellent	Good for precision work	More environment-sensitive	Good	Mainly fabrication/shop
Root-quality control	Good	Excellent	Process-dependent	Process-dependent	Limited by application

Use this table as a revision aid rather than as a substitute for studying API RP 577.

Common API RP 577 Exam Mistakes

Calling GTAW Tungsten a Filler Metal

Tungsten is normally a nonconsumable electrode.

Filler metal is added separately when required.

Confusing GMAW and FCAW

GMAW generally uses solid continuous wire.

FCAW uses tubular wire containing flux.

Confusing SMAW and SAW

SMAW uses individual flux-coated electrodes.

SAW uses continuous wire beneath granular flux.

Assuming Every Welding Process Produces Slag

GTAW and conventional solid-wire GMAW do not normally produce flux slag.

Ignoring Consumable Storage

Moisture control can be critical for low-hydrogen consumables.

Confusing Preheat and PWHT

Preheat occurs before/during welding.

PWHT occurs after welding.

Confusing WPS and PQR

WPS provides production-welding instructions.

PQR documents procedure-qualification variables and test results.

Confusing Procedure and Welder Qualification

A qualified procedure does not automatically qualify a welder.

The production welder must have the applicable performance qualification.

How to Study API 577 Welding Processes

A very effective revision method is to learn each process using six questions.

1. What electrode does it use?

Consumable or nonconsumable?

2. How is the weld protected?

Flux, gas, or both?

3. How is filler metal supplied?

Stick, rod, solid wire, or tubular wire?

4. Does it produce slag?

Yes or no?

5. What are its main advantages?

Quality, portability, deposition rate, automation?

6. What common problems should the inspector watch for?

Porosity, slag inclusion, lack of fusion, contamination, hydrogen, etc.

A useful memory sequence is:

Process → Electrode → Filler → Shielding → Slag → Application → Defects

Take the Free API 510 Chapter 13 Practice Test

Take this free API 510 Chapter 13 API RP 577 Welding Practice Test and evaluate your understanding of welding processes and consumables.

Practice questions can cover:

• SMAW

• GTAW

• GMAW

• FCAW

• SAW

• Electrodes

• Filler metals

• Flux

• Shielding gases

• Current

• Polarity

• Transfer modes

• Preheat

• Interpass temperature

• PWHT

• Welding discontinuities

• WPS

• PQR

• WPQ

Attempt every question before checking the correct answer and explanation.

When you answer incorrectly, identify exactly which characteristic caused the confusion.

For example:

GTAW → tungsten → nonconsumable → gas shielded → no slag

or

SAW → continuous wire → granular flux → slag → high deposition

Repeated comparison is one of the fastest ways to learn welding processes.

Current API RP 577 Reference for API 510 Candidates

For the September 2026, January 2027, and May 2027 API 510 exam cycle, the applicable reference is:

API Recommended Practice 577
Welding Processes, Inspection, and Metallurgy
3rd Edition, October 2020
Errata 1, September 2025

The current API 510 Body of Knowledge requires candidates to be familiar with API RP 577.

For detailed WPS, PQR, and WPQ review questions, the current exam limits the processes to:

• SMAW

• GTAW

• GMAW

• SAW

Candidates should always confirm the official Publications Effectivity Sheet applicable to their own examination date because reference editions can change.

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Topics include:

• API 510 fundamentals

• API RP 577

• Welding processes

• SMAW

• GTAW

• GMAW

• FCAW

• SAW

• Welding consumables

• WPS

• PQR

• WPQ

• ASME Section IX

• Welding metallurgy

• Heat treatment

• NDE

• Pressure-vessel inspection

• Corrosion rates

• Remaining life

• MAWP

• Inspection intervals

• API RP 571

• API RP 572

• API RP 576

• Repairs

• Alterations

• Rerating

• Pressure testing

• ASME VIII calculations

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Continue Your API 510 Exam Preparation

After completing the API 510 Chapter 13 API RP 577 Welding Practice Test, review every incorrect answer by comparing the welding processes.

For every process, ask:

What electrode is used?

Is it consumable or nonconsumable?

How is filler metal supplied?

How is the weld shielded?

Does the process produce slag?

What are its common applications?

What defects or problems should the inspector watch for?

A strong revision sequence is:

Process → Electrode → Consumable → Shielding → Current → Application → Advantages → Limitations → Discontinuities

Once you can distinguish the welding processes using these characteristics, API RP 577 familiarization questions become considerably easier.

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