Welding Procedures and Personnel Qualification

Introduction

Welding quality is not produced by skill alone. It depends on a controlled relationship among joint design, base materials, welding consumables, equipment, thermal conditions, welding sequence, inspection, and the competence of the people performing and supervising the work. A qualified welding procedure converts engineering requirements into repeatable production instructions, while personnel qualification demonstrates that a welder or welding operator can apply those instructions successfully.

In industrial fabrication, procedure and personnel qualification are normally governed by a fabrication code, standard, contract specification, or regulatory requirement. Examples include ASME Section IX, AWS D1.1, ISO 15614, ISO 9606, and related standards. These documents are not interchangeable. The applicable project code determines which variables are essential, what test constitutes qualification, the range of applicability, and the acceptance criteria.

This chapter develops the principles needed to prepare Welding Procedure Specifications (WPSs), Welding Procedure Qualification Records (PQRs), and welder qualification records. It also explains essential variables, consumable control, preheating, interpass temperature, sequencing, inspection, acceptance criteria, and the responsibilities of engineering and quality personnel.

Learning Objectives

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

1. Explain the relationship among a code, WPS, PQR, and welder qualification record.
2. Identify essential, nonessential, and supplementary essential variables.
3. Prepare the technical content of a practical WPS.
4. Interpret procedure qualification test results and determine the qualified range.
5. Explain the effects of consumable storage, preheat, interpass temperature, and heat input.
6. Distinguish procedure qualification from personnel qualification.
7. Apply acceptance criteria to visual, mechanical, and nondestructive examination results.
8. Analyze a fabrication case and recommend technically defensible corrective action.

1. The Qualification System

A welding qualification system contains several connected documents and activities:

The WPS is prospective: it tells the production team what is permitted. The PQR is historical: it records what was actually used on a qualification test coupon and what results were obtained. The WPS must not claim a range broader than that allowed by the governing code and supported by the PQR. A welder qualification record demonstrates the capability of a person, not the suitability of a welding procedure.

Qualification is therefore a system of controlled evidence rather than a single test. A sound system answers four questions:

• Was the procedure suitable for the materials and service conditions?
• Were the actual test variables recorded accurately?
• Is the production welder qualified for the process, position, material, thickness, and joint type involved?
• Can the completed weld be traced to an approved procedure and qualified personnel?

2. Codes, Standards, and Responsibility

Before preparing a WPS, the responsible engineer identifies the governing requirements. This includes the construction code, material specification, design temperature, service fluid, joint category, inspection level, and contractual requirements. The code may specify toughness testing, hardness limits, post-weld heat treatment, allowable welding processes, or restrictions on repairs.

A code should be treated as a controlled technical document. Clauses may change between editions, and the same term may have different meanings in different standards. For example, a variable considered essential in one code may be nonessential in another. The engineer must therefore avoid copying a WPS from an unrelated project without confirming its applicability.

Typical responsibilities are divided as follows:

• Design engineering: defines loads, materials, joint details, service conditions, and required quality.
• Welding engineer or welding coordinator: selects processes, develops and qualifies procedures, and controls welding variables.
• Quality personnel: verify documentation, inspection, traceability, and conformity.
• Welding supervisor: ensures that production follows the approved WPS and that equipment and consumables are suitable.
• Welder or welding operator: applies the approved procedure and reports abnormal conditions.
• Inspection and testing personnel: conduct examinations using qualified methods and report results objectively.

A qualification record is not a substitute for engineering judgment. A procedure may pass a test and still be inappropriate if it does not address corrosion, fatigue, hydrogen cracking, distortion, service temperature, or access limitations.

3. Welding Procedure Specifications

A WPS should be sufficiently precise to control the variables that influence weld quality, but sufficiently practical for production use. It normally includes the following information.

3.1 Joint design

The WPS identifies the joint type, groove angle, root opening, root face, backing, backing material, and weld size. For fillet welds it may specify leg length, effective throat, joint configuration, and sequence. Joint preparation must be compatible with the available access and the selected process.

A nominal fillet weld leg length does not by itself guarantee the required effective throat. For an approximately equal-leg, right-angle fillet weld, the theoretical throat is:

where t is the theoretical throat and z is the equal leg length, both in the same units. This geometric relationship assumes a straight-line connection between the toes and an idealized right-triangle profile. Actual effective throat may be affected by convexity, concavity, penetration, and code provisions.

3.2 Base metal

The WPS identifies the material specification, grade, product form, thickness range, and material grouping system used by the governing code. Material identification is essential because carbon equivalent, hardenability, strength, toughness, and chemical composition influence welding behavior.

For carbon and low-alloy steels, a commonly used carbon-equivalent expression is the IIW formula:

The symbols represent mass percentages of carbon, manganese, chromium, molybdenum, vanadium, nickel, and copper. The expression is an empirical indicator of hardenability and cracking susceptibility, not a complete welding procedure. It is most useful when applied with thickness, hydrogen level, restraint, heat input, and preheat considerations. Different standards use different carbon-equivalent formulas, so the applicable specification must be consulted.

3.3 Welding process and equipment

The WPS states the process, mode of transfer where relevant, polarity, current type, equipment limitations, and whether welding is manual, semiautomatic, mechanized, or automatic. Examples include shielded metal arc welding, gas metal arc welding, gas tungsten arc welding, flux-cored arc welding, submerged arc welding, and resistance welding.

Equipment should be calibrated or verified where the code or quality system requires it. An amperage display that has not been checked may provide false confidence. The WPS should also identify shielding gas composition and flow range when gas shielding is used.

3.4 Filler metal and shielding medium

Consumables are specified by classification, trade designation when necessary, diameter or size, flux type, and storage requirements. For example, an electrode classification may indicate minimum tensile strength, welding position, coating type, and diffusible-hydrogen category. Classification alone does not eliminate the need for proper storage and issue control.

Shielding gas purity, composition, flow, and delivery-system condition influence porosity, oxidation, arc stability, penetration, and weld-metal chemistry. Excessive gas flow can cause turbulence and entrain air; insufficient flow can permit atmospheric contamination.

3.5 Electrical and travel variables

Current, voltage, wire-feed speed, travel speed, electrode extension, and polarity are specified as applicable. For constant-voltage wire processes, wire-feed speed is closely related to current, but the relationship depends on electrode type, diameter, polarity, and equipment. It should not be treated as a universal conversion.

Heat input is a useful thermal-control parameter. For many arc-welding processes, a nominal arc-energy expression is:

where H is heat input in kJ/mm, η is arc efficiency, V is arc voltage in volts, I is current in amperes, and v is travel speed in mm/s. If travel speed is expressed in mm/min, the equivalent form is:

The factor η accounts for the fraction of electrical energy transferred effectively to the workpiece. These equations assume a reasonably steady arc and are estimates, not direct measurements of weld thermal history. They are useful for comparing conditions and controlling a qualified range. Excessive heat input can reduce cooling rate, increase distortion, enlarge the heat-affected zone, and impair toughness; insufficient heat input can cause lack of fusion, inadequate penetration, or excessive hardness.

Worked Example: Nominal Heat Input

A welding operation uses 24 V, 180 A, a travel speed of 5 mm/s, and an assumed efficiency of 0.80. The nominal heat input is:

H = (0.80 × 24 × 180)/(1000 × 5)

H = 0.6912 kJ/mm, or approximately 0.69 kJ/mm.

This result is valid only for the stated assumptions and unit convention. It does not by itself establish an acceptable production range; that range must be supported by the governing code, procedure qualification, and service requirements.

3.6 Preheat and interpass temperature

Preheat is the temperature of the base metal in the region surrounding the weld immediately before welding begins. It reduces the cooling rate, helps hydrogen diffuse from the weld area, and lowers the risk of delayed hydrogen cracking. Interpass temperature is the temperature of the weld and adjacent base metal immediately before depositing the next pass.

A WPS should state minimum preheat and maximum interpass temperature where relevant. Measurement should be made at a location and distance specified by the applicable code or procedure. Temperature crayons, contact thermometers, thermocouples, or infrared instruments may be used, but surface condition and emissivity affect infrared readings.

Preheat is not a universal cure. Excessive preheat can produce undesirable microstructures, reduce productivity, increase distortion, and damage heat-sensitive materials. Hydrogen control also requires clean surfaces, low-hydrogen consumables, proper storage, adequate arc energy, and appropriate post-weld treatment where required.

3.7 Welding position and progression

Position affects access, molten-metal control, deposition rate, and defect risk. The WPS specifies positions such as flat, horizontal, vertical, overhead, or pipe orientations. Vertical-up and vertical-down welding are not automatically interchangeable because penetration, heat control, and operator technique differ.

The direction of progression, bead sequence, layer arrangement, and manipulation pattern may be important for distortion control and defect avoidance. A procedure for a thick restrained joint may require balanced deposition, back-step welding, skip welding, or a specified multipass sequence.

3.8 Post-weld heat treatment

Post-weld heat treatment may be required to reduce residual stress, temper hard microstructures, reduce hydrogen cracking risk, or satisfy service requirements. A WPS should specify heating rate where controlled, holding temperature, holding time, cooling method, furnace conditions, and thermocouple arrangement as required by the code.

The holding time is code-dependent and may be based on thickness or material group. It must not be invented from a general rule of thumb. Uniform temperature is essential; a component that appears heated externally may still contain substantial internal temperature gradients.

4. Essential Variables and the Qualified Range

An essential variable is a change that can affect the mechanical properties or soundness of the weld sufficiently that requalification may be required. Examples may include a change in base-metal group, welding process, filler-metal classification, thickness range, position, polarity, heat input, preheat, interpass temperature, shielding gas, or post-weld heat treatment. The exact list is defined by the governing code.

A nonessential variable may be changed without requalifying the procedure, but the WPS must be revised when the change affects production instructions. A supplementary essential variable becomes essential when impact toughness or another special property is required.

The qualified range is not simply the range observed by the welder. It is the range permitted by the code based on the test coupon and the recorded variables. A PQR that records 10 mm plate does not automatically qualify every thickness. The code may permit a range above and below the test thickness, or may require additional tests for greater thickness or toughness.

The engineer should create a variable-control matrix before approving a WPS:

This matrix prevents an important variable from being omitted merely because it seems operationally convenient.

5. Procedure Qualification Records

The PQR records the actual test conditions, not the intended settings. It should identify the test organization, date, welder, material certificates, consumable batch, joint configuration, process, electrical parameters, preheat, interpass temperature, shielding gas, welding position, pass sequence, and post-weld treatment.

Test results may include visual examination, radiography or ultrasonic testing, tensile tests, guided bends, macroexamination, impact tests, hardness tests, and other examinations required by the code. The report should identify specimen dimensions, test temperature where relevant, failure location, measured strength, bend condition, and any discontinuities.

A PQR must be traceable. The test coupon should be linked to material certificates, consumable certificates, laboratory reports, and the signed record. Unclear or reconstructed data weaken the validity of the qualification. If actual variables were not recorded, the record should not be presented as though they were known.

Acceptance criteria

Acceptance criteria are code-specific. Visual acceptance may address cracks, crater cracks, incomplete fusion visible at the surface, unacceptable undercut, overlap, arc strikes, weld size, profile, and surface porosity. Radiographic or ultrasonic criteria may address planar indications, volumetric indications, length, spacing, and location. Mechanical tests may specify minimum tensile strength, bend-test soundness, impact energy, or hardness limits.

A weld can be acceptable under one criterion and unacceptable under another. For example, a weld may pass visual examination but fail a bend test because of internal lack of fusion. Conversely, a minor surface indication may be repairable under a particular code but unacceptable in a critical service.

Inspection results must be interpreted using the correct edition and acceptance clause. General statements such as “no defects permitted” are usually technically inadequate because codes distinguish between discontinuities, defects, dimensions, and service categories.

6. Welder and Welding Operator Qualification

Welder qualification addresses the capability of an individual to produce an acceptable weld using a specified process and test arrangement. It does not qualify the WPS, and passing a procedure qualification does not qualify every welder to use it.

The qualification record normally identifies:

• process and mode of operation;
• base-metal and filler-metal ranges;
• plate or pipe diameter and thickness range;
• welding position and progression;
• backing or open-root condition;
• joint type and test coupon;
• examination method and results; and
• continuity or maintenance requirements.

A welder who qualifies on a backed groove weld may not automatically be qualified for an open-root pipe weld. Similarly, qualification in one process does not necessarily qualify the person for a different process. The code establishes the permitted range.

Continuity is important because welding competence can deteriorate when a process is not used for a specified period. Employers should maintain continuity logs showing the date, process, and relevant work performed. Continuity records should be accurate and auditable, not signed retrospectively without evidence.

Qualification testing should be conducted under representative conditions. A test designed only to make success easy may fail to demonstrate production capability. Conversely, an unnecessarily severe test may exclude competent personnel without improving product reliability. The correct test is the one required by the governing code and representative of the intended work.

7. Consumable and Hydrogen Control

Consumables must be received, identified, stored, issued, and returned under a controlled system. Important controls include:

• maintaining package identification and batch traceability;
• protecting electrodes and fluxes from moisture;
• using holding ovens at specified temperatures;
• controlling exposure time after removal from storage;
• preventing contamination of wire, rods, and flux;
• recording rebaking or reconditioning where permitted; and
• separating consumables with different classifications.

Low-hydrogen electrodes are effective only when handled correctly. A damp electrode can introduce hydrogen even when its classification is nominally low hydrogen. Hydrogen cracking risk is also influenced by restraint, steel hardenability, thickness, cooling rate, and residual stress.

Surface preparation is equally important. Oil, paint, rust, moisture, cutting residues, and zinc coatings can generate porosity, hydrogen, toxic fumes, or lack of fusion. Cleaning requirements should be included in the WPS or associated work instruction.

8. Welding Sequence, Distortion, and Residual Stress

Welding produces localized heating and cooling. Uneven thermal expansion and contraction generate distortion and residual stress. Procedure qualification should therefore consider not only test strength but also production geometry and restraint.

Practical controls include:

• accurate fit-up and controlled tack welding;
• balanced welding about the neutral axis;
• skip or back-step sequences where appropriate;
• minimizing unnecessary weld volume;
• using presetting or strongbacks with engineering approval;
• controlling interpass temperature; and
• allowing suitable access for inspection and repair.

A sequence that reduces distortion may increase restraint and cracking risk. For this reason, distortion control cannot be separated from metallurgy and joint design. Heavy restraint should be evaluated before production, especially for high-strength steels, thick sections, and low-temperature service.

9. Qualification Workflow

A robust qualification workflow is:

1. Review drawings, material certificates, service conditions, and governing code.
2. Define joint details, process, consumables, thermal controls, and examination requirements.
3. Draft a preliminary WPS.
4. Identify essential and supplementary essential variables.
5. Weld a representative test coupon while recording actual conditions.
6. Perform required visual, nondestructive, and mechanical tests.
7. Complete and approve the PQR.
8. Prepare the production WPS within the qualified range.
9. Qualify welders for the required processes, positions, materials, and joint conditions.
10. Implement production controls, inspection, traceability, and continuity monitoring.
11. Review deviations, repairs, and nonconformities through an approved control process.

The workflow is iterative. If a test fails, the correct response is not automatically to repeat it until it passes. The failure should be analyzed: Was the joint contaminated? Was the heat input unsuitable? Was the consumable damp? Was the test method valid? Was the material correctly identified? Corrective action should address the cause.

10. Illustrative Case Study: Cracking in a Restrained Low-Alloy Steel Joint

Background

A fabrication company is preparing a procedure for a 25 mm low-alloy steel pressure-component attachment. The joint is highly restrained, service temperature is below ambient, and the weld will be made using a low-hydrogen flux-cored process. The first trial weld develops delayed toe cracking approximately 36 hours after completion.

Problem analysis

The initial WPS specified a minimum preheat of 50 °C, but the material certificate indicated a relatively high carbon equivalent. The consumable storage log was incomplete, the joint had been exposed to condensation, and the interpass temperature was not recorded. The fit-up also created a narrow root opening that encouraged rapid travel and low heat input.

The cracking pattern and delay suggested hydrogen-assisted cracking as a leading possibility, although final diagnosis would require metallurgical examination and review of all evidence. The combination of hardenability, hydrogen, restraint, and rapid cooling was more significant than any single variable.

Approach and solution

The welding engineer took the following actions:

• verified the steel grade and material grouping;
• reviewed the applicable code and toughness requirements;
• established a controlled consumable storage and issue system;
• increased and verified preheat based on material and restraint assessment;
• specified a maximum interpass temperature and recorded it with contact thermometers;
• required cleaning and drying of the joint before welding;
• revised the root detail to permit reliable fusion;
• introduced a controlled cooling and delayed inspection period where required;
• qualified a revised procedure using representative restraint and thickness; and
• requalified welders on the actual process and position.

The revised PQR included complete electrical data, preheat, interpass measurements, consumable batch identification, and test results. The production WPS was then issued only within the range supported by the revised qualification.

Outcome

The revised procedure produced sound test welds with acceptable nondestructive and mechanical examination results. Production welds showed no delayed cracking during the specified inspection period. The company also improved continuity records and consumable traceability, reducing the likelihood of recurrence.

Learning points

The case demonstrates that qualification is not merely paperwork. A procedure can fail because thermal control, consumable control, joint preparation, or restraint was inadequately considered. It also shows why delayed inspection may be important for hydrogen-sensitive materials and why a welder qualification cannot compensate for a defective WPS.

11. Quality, Ethics, and Contemporary Practice

Welding records are safety-critical evidence. Falsifying a parameter, signing for an unperformed inspection, or using an unqualified welder can expose workers, the public, and the environment to serious harm. Professional ethics require accurate records, transparent reporting of deviations, and escalation when a condition is outside the approved procedure.

Digital welding systems increasingly record current, voltage, wire-feed speed, travel speed, temperature, and operator identity. These systems can improve traceability and detect deviations, but they do not replace engineering judgment. Sensor errors, incorrect calibration, poor data mapping, and unauthorized parameter changes remain possible.

Artificial intelligence may assist with weld-image classification, parameter monitoring, defect prediction, and document review. However, AI outputs require validation against qualified inspection methods and competent human oversight. An algorithm should not independently overrule a governing code or accept a weld outside approved criteria.

Best practice is to combine:

• code compliance;
• competent welding engineering;
• qualified personnel;
• calibrated equipment;
• controlled consumables;
• representative procedure tests;
• independent inspection; and
• complete, truthful records.

Chapter Summary

Welding procedure and personnel qualification establish controlled evidence that welding can be performed consistently and safely. The WPS provides production instructions; the PQR records actual qualification variables and test results; and the welder qualification record demonstrates an individual’s ability within a code-defined range. Essential variables determine when requalification is required, while supplementary essential variables become especially important when impact toughness or other special properties are specified.

A technically adequate WPS addresses joint design, base materials, process, consumables, electrical variables, shielding, preheat, interpass temperature, position, sequence, and post-weld heat treatment. Heat input can be estimated using H = ηVI/(1000v) when consistent units and stated assumptions are used, but qualification and service requirements—not a calculation alone—establish acceptable conditions.

Consumable moisture control, surface preparation, hydrogen management, restraint, distortion, inspection, acceptance criteria, and traceability are integral parts of welding quality. Qualification testing must be representative, records must reflect actual conditions, and deviations must be managed through an approved technical process. Digital monitoring and AI can support quality assurance, but neither replaces competent engineering judgment or the governing code.

Key Terms

Welding Procedure Specification (WPS): An approved instruction defining permitted production welding variables.

Procedure Qualification Record (PQR): A record of actual variables and test results used to qualify a welding procedure.

Welder Performance Qualification (WPQ): Evidence that an individual can produce an acceptable weld within a specified range.

Essential variable: A variable whose change may require procedure requalification.

Supplementary essential variable: An essential variable applied when special properties, such as toughness, are required.

Nonessential variable: A variable that may be changed without requalification but must be controlled on the WPS.

Preheat: Temperature of the base metal before welding begins.

Interpass temperature: Temperature of the weld area immediately before depositing the next pass.

Heat input: Estimated thermal energy transferred to the workpiece per unit length of weld.

Carbon equivalent: An empirical indicator of steel hardenability and cracking susceptibility.

Backing: Material or weld deposit supporting the root of a joint.

Consumable: Electrode, wire, rod, flux, or other material consumed during welding.

Hydrogen-assisted cracking: Delayed cracking promoted by hydrogen, susceptible microstructure, stress, and cooling conditions.

Interpass: The region or interval between successive weld passes.

Traceability: Ability to link materials, consumables, personnel, procedures, and inspections to a completed weld.

Acceptance criterion: A specified rule used to determine whether an indication or test result is acceptable.

Continuity: Documented evidence that a qualified welder has continued to use a process within the permitted period.

Post-weld heat treatment: Controlled heating after welding to modify metallurgical or residual-stress conditions.

Welding coordinator: Competent person responsible for coordinating welding activities and technical controls.

Review Questions

Short Answer Questions

1. What is the principal difference between a WPS and a PQR?
2. Why are essential variables important in procedure qualification?
3. Define preheat and interpass temperature.
4. State two purposes of consumable storage control.
5. Why does a welder qualification not qualify a welding procedure?

Long Answer Questions

1. Explain the complete relationship among the governing code, WPS, PQR, and welder qualification record.
2. Describe the technical information that should appear in a WPS for a multipass steel weld.
3. Explain how hydrogen, hardenability, restraint, and cooling rate interact to produce delayed cracking.
4. Discuss the purposes and limitations of heat-input control.
5. Explain how inspection and acceptance criteria should be selected and applied during qualification.

Analytical / Application Questions

1. A proposed production weld uses a different filler-metal classification, lower preheat, and a different welding position from the qualified test. Identify which changes may require review or requalification and explain why.
2. A welder passes a backed plate test but is assigned to weld an open-root pipe joint in the overhead position. Analyze whether the assignment is automatically permitted and identify the records that must be checked.
3. A qualified weld passes visual inspection but fails a guided bend test because of internal lack of fusion. Analyze possible causes and propose corrective actions involving joint preparation, parameters, technique, and procedure control.

Multiple Choice Questions with Answers

Question 1

Which document records the actual welding variables and test results used to qualify a procedure?

A. Welding Procedure Specification

B. Procedure Qualification Record

C. Welder continuity log

D. Material requisition

Correct Answer: B. Procedure Qualification Record

Question 2

Which variable most directly represents the thermal energy transferred per unit weld length?

A. Electrode diameter

B. Joint angle

C. Heat input

D. Shielding-gas purity

Correct Answer: C. Heat input

Question 3

A change in an essential variable generally requires what action?

A. No documentation

B. Automatic acceptance

C. Procedure review and possible requalification

D. Only a change to the weld map

Correct Answer: C. Procedure review and possible requalification

Question 4

What is a primary purpose of preheating susceptible steel?

A. To eliminate all residual stress

B. To reduce cooling rate and cracking risk

C. To increase shielding-gas flow

D. To replace consumable drying

Correct Answer: B. To reduce cooling rate and cracking risk

Question 5

Using H = ηVI/(1000v), what is the heat input when η = 0.80, V = 24 V, I = 180 A, and v = 5 mm/s?

A. 0.069 kJ/mm

B. 0.691 kJ/mm

C. 6.912 kJ/mm

D. 69.12 kJ/mm

Correct Answer: B. 0.691 kJ/mm

Question 6

Which statement correctly distinguishes welder qualification from procedure qualification?

A. Welder qualification proves the code is unnecessary

B. Procedure qualification proves every welder is qualified

C. Welder qualification demonstrates an individual's ability within a defined range

D. They are two names for the same record

Correct Answer: C. Welder qualification demonstrates an individual's ability within a defined range

Question 7

Why must low-hydrogen electrodes be stored and issued under control?

A. Moisture can increase hydrogen-related cracking risk

B. Storage changes the base-metal grade

C. Dry electrodes always increase distortion

D. Storage determines welding position

Correct Answer: A. Moisture can increase hydrogen-related cracking risk

Question 8

What is the likely consequence of using a WPS outside its qualified range?

A. The weld is automatically stronger

B. The work may be nonconforming and require technical review

C. The welder becomes newly qualified

D. Inspection is no longer required

Correct Answer: B. The work may be nonconforming and require technical review

Question 9

Which record best demonstrates that a qualified welder has continued using a process?

A. Continuity log

B. Material certificate

C. Joint design sketch

D. Shielding-gas invoice

Correct Answer: A. Continuity log

Question 10

Why is acceptance criteria applied using the governing code rather than a general statement such as 'no defects'?

A. Codes distinguish discontinuity types, sizes, locations, and service requirements

B. Codes permit every visible indication

C. General statements are always stricter than codes

D. Acceptance criteria are determined only by the welder

Correct Answer: A. Codes distinguish discontinuity types, sizes, locations, and service requirements