Establishing the purpose, authority, and scope of the special inspector's duties in structural welding oversight under AWS D1.1 and the applicable building code.
Purpose and Authority of Welding Inspection
Structural welding inspection is not about catching workers doing something wrong. It is about providing independent verification that welded connections meet the design intent, the applicable standards, and the approved construction documents. That distinction matters because it shapes how an inspector approaches every interaction on site - not as an adversary to the contractor, but as the owner's representative responsible for confirming that the structural frame will perform as designed.
The applicable building code establishes the legal framework for special inspection. It requires that the owner engage a special inspector for welding on structures where the code mandates special inspection. AWS D1.1 Clause 8 further defines the inspector's authority, qualifications, and responsibilities. The inspector works under the direction of the engineer of record and reports to the building official through the statement of special inspections. Understanding this reporting chain is important - the inspector does not report to the contractor and cannot be directed by the contractor to approve work that does not conform.
AWS D1.1/D1.1M:2020 Clause 8 – Inspection; AWS D1.1 Clause 8.1 – General inspector requirements; AISC 360 Chapter N – Quality Assurance and Quality Control.
In practice, the relationship with the contractor's welding supervisor is one of the most important professional relationships on the job. Establishing clear expectations early - what you will be checking, when you need access, and what documentation you require - prevents friction later. Most experienced contractors appreciate a consistent inspector who communicates clearly rather than one who shows up unpredictably and surprises them with rejections.
New inspectors sometimes feel pressure from contractors to accept marginal work because of schedule concerns. It is essential to understand that accepting nonconforming work without proper authorization is a violation of the inspector's duty and can expose both the inspector and the project to significant liability. Decisions to accept nonconforming work belong to the engineer of record, not the inspector.
Pre-Construction Review and the Statement of Special Inspections
Before the first arc is struck, the inspector should have reviewed the approved construction documents, the structural drawings, the project specifications, and the approved welding procedure specifications. Arriving on site without this background is like showing up to referee a game you don't know the rules of. The pre-construction review allows the inspector to understand what connections are being made, what processes are approved, and what critical inspection points will require mandatory hold points.
The statement of special inspections is the document that defines what the inspector will observe and what tests will be performed. It identifies whether inspection is continuous or periodic for each type of welding on the project. Continuous inspection means the inspector is present for all welding operations. Periodic inspection means the inspector verifies at designated intervals. The distinction is significant - CJP groove welds in primary structural members typically require continuous inspection, while fillet welds for secondary connections may be periodic.
AWS D1.1/D1.1M:2020 Clause 8.1 – General inspector requirements; AWS D1.1 Clause 8.1.4 – Inspection of WPS and welder qualifications; AISC 360 Chapter N – Quality Assurance and Quality Control requirements for structural steel.
The structural drawings will typically include a welding notes block, often found on the general structural notes sheet or the connection detail sheets. This block identifies the weld quality standard (usually AWS D1.1), the electrode classifications permitted, and any connection-specific requirements. Connection details throughout the drawing set will show weld symbols that define the joint type, weld size, and any finish or inspection requirements. The inspector should mark up the drawings to identify all locations requiring inspection before starting field work.
Pre-construction inspection checklist: (1) Review approved structural drawings and confirm welding note location and content. (2) Confirm all WPS documents are project-approved and cover the joint configurations and positions required. (3) Verify welder qualification records are current and cover the processes and positions to be used. (4) Review the statement of special inspections to confirm inspection frequency for each weld type. (5) Identify mandatory hold points requiring notification before work proceeds. (6) Confirm access to preheat and interpass temperature measuring equipment.
Understanding how common structural welding processes work, what they produce, and the metallurgical basics that explain why specific requirements exist.
Common Structural Welding Processes
Shielded Metal Arc Welding, commonly called stick welding, is the most recognizable process on structural projects. The welder feeds a coated electrode into the arc manually. As the electrode burns, the coating generates shielding gas and slag that protect the molten weld pool from atmospheric contamination. SMAW is versatile and well-suited to field conditions, which is why it remains common in structural erection despite being slower than wire-fed processes.
Flux Cored Arc Welding is the dominant process on most contemporary structural steel projects. The electrode is a continuous wire with flux inside the core. Depending on the variant, external shielding gas may or may not be used. Self-shielded FCAW requires no gas cylinder, making it popular for open-air erection work, but it is more sensitive to technique and produces higher hydrogen levels than gas-shielded variants. Gas-shielded FCAW offers better weld quality but requires the gas supply to be maintained and protected from wind.
Submerged Arc Welding is almost exclusively a shop process. The arc is buried under a bed of granular flux, making it invisible to the naked eye. SAW deposits weld metal at high rates and produces excellent quality welds when properly set up, which is why it is used for fabricating heavy built-up members and primary structural components in the shop. An inspector visiting a fabrication facility will encounter SAW regularly. Verifying that the flux is dry, properly handled, and approved for the base metal is part of the shop inspection.
Being able to identify the welding process in use is fundamental. The electrode type, shielding gas setup, and equipment configuration tell you which WPS applies to that operation. An inspector who cannot identify whether a welder is running FCAW-G or FCAW-S cannot determine if the correct procedure is being followed. If you are uncertain, check the wire spool label and the electrode package documentation.
One frequent oversight is allowing welders to switch processes without verifying that the WPS and welder qualification cover the new process. A welder qualified for SMAW on a specific joint type is not automatically qualified to perform the same joint with FCAW. Each process requires separate qualification testing.
Heat Input, Preheat, and Metallurgical Basics
Preheat is one of the most misunderstood and most frequently ignored requirements in structural welding. The purpose is to slow the cooling rate of the base metal after welding. Steel that cools too rapidly after being heated by the welding arc can develop hard, brittle microstructures in the heat-affected zone that are prone to hydrogen-assisted cracking. This type of cracking is particularly insidious because it can occur hours or even days after welding is complete - long after the inspector has moved on.
The required preheat temperature depends on the base metal grade, the base metal thickness, the hydrogen level of the filler metal, and the heat input of the welding process. AWS D1.1 Table 5.8 provides minimum preheat and interpass temperature requirements for common structural steel grades. Inspectors must verify preheat before welding begins and monitor interpass temperature throughout the operation, because allowing the joint to cool excessively between passes can be as damaging as failing to preheat.
AWS D1.1/D1.1M:2020 Clause 7.6 – Preheat and interpass temperature requirements; AWS D1.1 Table 5.8 – Minimum preheat and interpass temperatures; AISC 360 Commentary on Chapter J – Discussion of heat-affected zone behavior.
Preheat verification procedure: (1) Identify the base metal specification and thickness from the drawings or mill certifications. (2) Determine the minimum required preheat from the applicable WPS and AWS D1.1 Table 5.8. (3) Measure the base metal temperature at a minimum of 3 inches from the joint in all directions using a contact pyrometer, infrared thermometer, or temperature-indicating crayon rated for accuracy. (4) Verify temperature is met before the arc is struck. (5) Monitor interpass temperature between passes - do not allow the joint to cool below the minimum preheat before the next pass. (6) Document preheat readings in the inspection record with time and location.
Temperature-indicating crayons are the most common tool used in the field for preheat verification. They melt at a specific temperature, giving a visible confirmation that the required minimum has been reached. Contact pyrometers are more accurate and should be used for critical members or when disputes arise. Cold weather work introduces significant risk - welding on steel below the minimum preheat temperature in ambient temperatures at or below freezing requires careful monitoring, because steel loses heat rapidly to the surrounding air.
Understanding WPS documents, how procedures are qualified, and what the inspector must verify about procedure compliance.
The Welding Procedure Specification
A Welding Procedure Specification is the document that defines how a weld must be made. It specifies the welding process, base metal specification, filler metal classification, joint configuration, position, preheat and interpass temperature range, electrical parameters, and post-weld heat treatment if required. The purpose is to provide welders with a repeatable, tested set of conditions that will produce a weld meeting the design requirements. Without a qualified WPS, there is no way to know whether the welding conditions being used have ever been demonstrated to produce acceptable results.
AWS D1.1 distinguishes between essential, supplementary essential, and nonessential variables within a WPS. Essential variables are those whose change invalidates the procedure qualification - if one of these changes, a new PQR is required. Supplementary essential variables apply when Charpy toughness requirements are invoked, which is the case for seismic and other high-demand applications. Nonessential variables may be changed without re-qualifying the procedure as long as the WPS is updated. Understanding which variables are essential matters because it determines when a contractor must requalify.
AWS D1.1/D1.1M:2020 Clause 5.4 – WPS content requirements; AWS D1.1 Table 6.5 – Essential variables for WPS qualification; AWS D1.1 Clause 5 – Prequalified WPS requirements and limitations.
The project specifications will typically reference which WPS documents are approved for the project. The drawings will show weld symbols that define the joint type and weld size - the inspector then confirms that an approved WPS covers that joint type, position, and base metal combination. If a contractor is making a joint that does not appear to be covered by any approved WPS, that is a nonconformance requiring immediate notification to the engineer of record.
When reviewing a WPS in the field, verify that the document has been approved or prequalified, that it covers the actual base metal being welded, and that the electrical parameters listed match what is being used on the machine. Many inspectors only check the cover page of a WPS and miss that the document may have multiple sheets covering different positions. If a welder is making a vertical weld but the WPS was only tested in the flat position, that is a significant problem that requires immediate attention.
Procedure Qualification Records and Prequalified Procedures
A Procedure Qualification Record documents the actual welding conditions used during a qualification test and the test results. The PQR supports the WPS by demonstrating that the combination of variables in the procedure has been tested and produced welds meeting the mechanical property requirements. A WPS without a supporting PQR - unless it meets the strict requirements for a prequalified procedure - is not an acceptable basis for production welding.
AWS D1.1 provides prequalified status to certain combinations of processes, base metals, joint designs, and filler metals that have a long history of producing acceptable welds. A prequalified WPS does not require PQR testing, but it must comply exactly with all the limitations listed in AWS D1.1 Clause 5. The limitations are specific - things like maximum fillet weld size in a single pass, minimum preheat for given thicknesses, and maximum heat input. A procedure that deviates from these limits, even in one variable, loses its prequalified status and must be qualified by test.
AWS D1.1/D1.1M:2020 Clause 6.9 – Procedure qualification by testing; AWS D1.1 Clause 6.9.1 – Required tests for CJP groove weld qualification; AWS D1.1 Annex Q – Example forms for WPS and PQR documentation.
A common situation inspectors encounter is a contractor presenting a WPS that references a PQR from a previous project or from the fabricator's general qualification library. The inspector's responsibility is to verify that the PQR actually supports the WPS - that the variables tested fall within the range specified in the procedure. Some contractors maintain PQR files that are not organized in a way that makes verification easy. Request the full documentation package before work begins, not during.
The WPS is the instruction document - it tells the welder what to do. The PQR is the test record - it proves that following those instructions produces acceptable welds. Both documents must be available for inspector review. The WPS is used daily in the field; the PQR is the technical basis that justifies the WPS.
How welders are qualified, what records must be maintained, and how to verify that the right welder is performing the right work.
Welder Qualification Testing and Continuity
Welder qualification is separate from procedure qualification. Where procedure qualification demonstrates that a set of welding conditions will produce acceptable welds, welder qualification demonstrates that a specific individual has the skill to make acceptable welds using those conditions. A qualified welder working outside the scope of their qualification test is not a qualified welder for that application, regardless of their years of experience.
The scope of a welder's qualification depends on the test conditions - the process used, the test position, the base metal group, and the type of weld made. A welder who tests in the flat position is qualified only for flat position work. Testing in the overhead position qualifies for overhead, vertical, and flat. AWS D1.1 Clause 6 specifies which positions and joint types are qualified by each test. Understanding these ranges is essential for verifying that the people performing work on your project are actually qualified to do so.
Welder qualification does not last indefinitely without active use. AWS D1.1 requires that welders maintain continuity by using the qualified process at least once every six months. If a welder has not used a particular process within that period, their qualification for that process lapses and they must re-qualify. The contractor is responsible for tracking continuity, but the inspector should verify current qualification records before allowing welders to begin work.
Welder verification procedure: (1) Request the welder qualification test records (WQR) for each welder assigned to the project. (2) Verify the qualification test date is within the six-month continuity window or that documented continuity has been maintained. (3) Confirm the process, position, and joint type tested covers the work being assigned. (4) Record each welder's ID or stamp number and qualification scope in your inspection log. (5) If a welder's qualification is questionable, require additional documentation or testing before allowing them to proceed.
Inspectors sometimes check welder qualification records only at the start of a project and never revisit them. Six months can pass quickly on a long project, and welders rotate on and off crews regularly. Establish a schedule to re-verify qualification continuity throughout the project, especially after construction breaks or periods when specific processes were not in use.
Essential Variables and Re-Qualification Requirements
A welder's qualification is process-specific, position-specific, and base metal group-specific. When any essential variable changes, the qualification for the original combination does not transfer. AWS D1.1 Table 4.12 lists the essential variables for performance qualification. Changes that trigger re-qualification include: change of welding process (SMAW to FCAW), addition of a position not previously qualified, and certain changes in electrode or filler metal classification.
Common essential variable changes requiring re-qualification (D1.1 Table 4.12): Change of welding process - yes. Addition of welding position beyond those tested - yes. Change from single pass to multi-pass or vice versa for fillet welds - yes. Change in backing (with to without) for groove welds - yes. Change of base metal group per Table 3.1 - yes if outside tested group limits.
AWS D1.1 Table 4.12; AWS D1.1 Section 4.2; AWS D1.1 Section 4.3.4.
Allowing a welder qualified only in the flat position (1G/1F) to weld in the vertical or overhead position. Position limitations are strict: qualification in 3G includes 1G and 2G, but qualification in 1G covers only 1G. The inspector must verify the welder's certification card lists the positions being used on the project.
Continuity of Qualification and Welder Record Review
AWS D1.1 Section 4.3.4 requires that a welder who has not used a welding process for a period exceeding 6 months is no longer considered qualified for that process. The inspector must verify continuity records at project start by reviewing the welder's certification card and employment records confirming the process has been used within the past 6 months. Welders returning from extended leave or process changes need re-qualification before production welding.
At project mobilization: Step 1 - Collect qualification cards and continuity logs for all welders. Step 2 - Verify each card shows a qualification date within the past 6 months for the processes to be used. Step 3 - If continuity is in question, require the contractor to document continuous employment on that process or schedule re-qualification. Step 4 - Record all verified welder qualifications in the project inspection log.
Continuity logs from the contractor's payroll or work records can substitute for formal re-testing when they document the welder has been using the qualified process continuously. The inspector should request original records, not summaries. Photocopies are acceptable; verbal confirmation is not.
AWS D1.1 Section 4.3.4; AWS D1.1 Section 4.28; IBC Section 1705.12.
Understanding weld types, joint configurations, and the geometric requirements that determine acceptable weld quality.
Weld Types and Joint Configurations
Structural connections rely primarily on two weld types: fillet welds and groove welds. Fillet welds are triangular in cross-section and join surfaces that meet at approximately right angles. They are the most common weld type in structural steel fabrication and erection. Groove welds fill a prepared gap between members and are used where full cross-sectional strength must be transferred. Complete Joint Penetration groove welds, called CJP welds, extend through the full thickness of the joint and are used in the most heavily loaded connections, including moment connections and column splices.
Joint preparation is one of the most critical pre-weld inspection points. For groove welds, the joint geometry - root opening, included angle, and root face dimension - must match the WPS. Deviations that widen the root opening require more filler metal and may affect the mechanical properties of the completed weld. Deviations that narrow it may prevent the welder from achieving the root fusion required. The inspector should check joint geometry with a weld gauge before welding begins and document the measurements.
AWS D1.1/D1.1M:2020 Figures 5.1 and 5.2 – Prequalified CJP and PJP groove weld joint details; AWS D1.1 Clause 4.9.1.2 – Minimum fillet weld size; AWS D1.1 Clause 4.9.1.1 – Maximum fillet weld size in a single pass.
The weld symbol on a structural drawing is a standardized notation that conveys the weld type, size, location, and any special requirements in a compact format. The reference line runs horizontally with the arrow pointing to the joint. Weld information below the reference line applies to the arrow side; information above applies to the other side. The tail of the symbol may reference the applicable WPS. Common structural inspectors must be able to read basic weld symbols fluently - the symbol for a 5/16-inch fillet weld on the arrow side should be immediately recognizable, as should the symbol for a CJP groove weld with backing.
Before any groove weld begins, check that the backing bar, if required, is fully seal-welded to the member with no gaps. A gap between the backing and the base metal at the root can prevent fusion at the most critical location in the joint. This is a common setup deficiency that is easy to miss and difficult to correct after welding begins.
Weld Sizing and Effective Throat
The size of a fillet weld is defined by the leg length - the dimension from the root to the toe along each fused face. The effective throat is the perpendicular distance from the root to the theoretical face of the weld, and it is the dimension used to calculate weld strength. For a flat-face fillet weld, the effective throat equals approximately 0.707 times the leg size. For welds with convex or concave profiles, the relationship changes. Undersized fillet welds are a direct strength deficiency; the inspector must verify size on completed welds using a weld gauge designed for that measurement.
A variety of weld gauges are available for measuring fillet weld size. The most common are the adjustable fillet weld gauge and the AWS weld gauge. The adjustable gauge directly measures the leg length. The inspector should take multiple measurements along the length of the weld and document both the minimum and the representative size. A weld that meets size requirements over most of its length but falls short over a significant portion still has a deficiency that must be addressed.
Fillet weld size measurement procedure: (1) Allow the weld to cool sufficiently to handle safely without burns. (2) Remove slag from the completed weld surface before measurement. (3) Place the appropriate leg of the fillet weld gauge against the weld face and read the size. (4) Take measurements at intervals - every few feet for long welds, and at each end for short welds. (5) Note any locations where the weld falls below the required size. (6) Document required size, measured sizes, and locations in the inspection report.
Fillet weld strength is proportional to the effective throat. An undersized weld is weaker in proportion to how much undersized it is. A weld that is consistently 1/16 inch under the required size has meaningfully less capacity than designed. Weld size verification is not a bureaucratic exercise - it is a direct confirmation of structural adequacy.
Recognizing weld discontinuities, understanding the difference between a discontinuity and a defect, and applying AWS D1.1 acceptance criteria.
Types of Weld Discontinuities
A discontinuity is an interruption in the physical structure of a weld. Not every discontinuity is a defect - a defect is a discontinuity whose size, shape, or location exceeds the acceptance criteria of the applicable standard. Understanding this distinction keeps inspectors from over-rejecting welds with minor imperfections that have no structural significance, and from under-rejecting welds with subtle flaws that matter greatly. The most critical discontinuities in structural welding are cracks, incomplete fusion, and incomplete joint penetration, because these directly affect the load-carrying capacity of the connection.
Cracks are the most serious weld discontinuity. Transverse cracks run perpendicular to the weld axis and are particularly dangerous because they propagate in the direction of the primary structural load. Longitudinal cracks run parallel to the weld axis. Toe cracks initiate at the weld toe, where stress concentrations are highest. Underbead cracks occur in the heat-affected zone below the weld and are associated with hydrogen embrittlement. Any crack in a structural weld is cause for immediate rejection - AWS D1.1 has no acceptance tolerance for cracks.
Porosity consists of gas pockets trapped in the solidified weld metal. It results from contamination of the weld pool by moisture, mill scale, or shielding gas disruption. Individual pores are usually less critical than cluster or linear porosity, but all porosity must be evaluated against the AWS D1.1 acceptance limits. Slag inclusions are non-metallic particles trapped in the weld metal, typically from incomplete slag removal between passes. They reduce the effective cross-section of the weld and can act as stress concentrators.
Incomplete fusion occurs when the weld metal fails to fuse with the base metal or a previous weld pass. It can occur at the sidewall of a groove weld, at the root, or between passes. This is one of the most structurally significant discontinuities because it creates a planar void that acts as a built-in crack. Incomplete joint penetration in a CJP groove weld means the weld does not extend through the full thickness of the joint - a direct failure to meet the design intent. Both discontinuities are almost impossible to detect visually on a completed weld and typically require UT or RT for reliable detection.
Many discontinuities that appear serious on the weld surface turn out to be minor upon thorough evaluation. Conversely, a weld with an acceptable surface appearance may have significant internal defects. This is why visual inspection alone is insufficient for CJP groove welds in critical connections - volumetric NDT is required precisely because the most dangerous flaws cannot be seen from the outside.
Applying Acceptance Criteria
AWS D1.1 Table 8.1 provides acceptance criteria for visual inspection of structural welds. These criteria address weld size, weld profile (convexity, concavity, and undercut), surface porosity, and cracks. The criteria for statically loaded structures differ from those for cyclically loaded structures, where fatigue considerations make the acceptance limits stricter. The inspector must know which loading category applies to the structure being inspected - the structural engineer's drawings and specifications should make this clear.
Undercut is a groove melted into the base metal at the weld toe that is not filled by the weld metal. It appears as a notch running along the edge of the weld bead and creates a stress concentration that can initiate fatigue cracking under cyclic loading. AWS D1.1 limits undercut to 1/32 inch for most applications on the tension face of cyclically loaded members. The depth of undercut should be measured with a notch gauge or weld profile gauge, not estimated visually.
AWS D1.1/D1.1M:2020 Table 8.1 – Visual inspection acceptance criteria; AWS D1.1 Clause 8.15 – Weld acceptance/rejection criteria; AWS D1.1 Table 8.2 – UT acceptance/rejection criteria for CJP groove welds.
When a visual examination reveals a potential defect, the inspector must document the finding precisely - location, size, and character of the discontinuity. The decision to reject is based on comparing the measured discontinuity against the applicable table values, not on a general sense that the weld looks bad. An inspector who rejects welds without being able to cite the specific acceptance criterion being violated will quickly lose credibility and may face justified pushback. Know the criteria and apply them objectively.
Confusing workmanship with structural adequacy is a frequent mistake. A weld with rough surface appearance but no measurable discontinuities beyond the acceptance limits is an acceptable weld, even if it looks poor to an untrained eye. Conversely, a smooth, shiny weld surface does not guarantee internal soundness. Discipline in applying the written criteria consistently is what separates reliable inspection from subjective guessing.
Conducting thorough visual inspection, using the right tools, and documenting findings correctly.
Visual Inspection Techniques and Equipment
Visual inspection is the primary inspection method for all structural welds, required before any other NDT method is applied. It is also the method that experienced inspectors rely on most, because a thorough visual examination by a knowledgeable eye catches a wide range of surface and near-surface discontinuities efficiently. The effectiveness of visual inspection depends entirely on lighting conditions, access, eye condition of the inspector, and the systematic method used. AWS D1.1 sets minimum lighting requirements for visual examination that inspectors must meet.
The basic visual inspection toolkit includes a weld gauge set, a flashlight or inspection lamp capable of illuminating recessed areas, a 10x magnifying glass for close examination of suspect areas, a steel rule for measuring, a notch gauge for undercut measurement, and a straight edge for checking weld profile linearity. The inspector should also have the approved WPS and acceptance criteria tables accessible for reference during the examination.
Visual weld inspection sequence: (1) Confirm all slag has been completely removed from the weld surface - slag remaining masks the weld profile and any underlying discontinuities. (2) Examine the weld over its full length under adequate lighting at an angle that allows both the weld face and the toes to be seen. (3) Measure weld size using the appropriate gauge. (4) Check the weld profile for excessive convexity or concavity. (5) Examine both toes for undercut using a notch gauge at suspect locations. (6) Inspect for surface porosity and cracks. (7) Document all measurements and findings before moving to the next weld.
Access is a persistent challenge in structural welding inspection. Welds are often located in positions that require awkward positioning to see properly - inside the web of a beam, at the bottom flange of an elevated connection, or inside a column-to-base plate junction. Request access equipment in advance and do not accept 'you'll have to trust us on that one' from contractors. Welding that cannot be inspected during installation may require removal or be subject to volumetric NDT, which is far more disruptive and expensive after the fact.
The VT Sequence - Before, During, and After Welding
Effective visual inspection requires presence at three stages: pre-weld (verify fit-up, preheat, WPS compliance), in-process (verify interpass cleaning, interpass temperature, bead sequencing), and post-weld (verify final weld size, profile, and surface condition). D1.1 Section 6.9 assigns specific inspector responsibilities at each stage. Post-weld VT cannot compensate for skipped pre-weld inspection - many critical attributes are inaccessible after welding is complete.
Pre-weld: verify joint geometry, root opening, base metal cleanliness, preheat, and WPS identity on the welder's card. In-process: check interpass temperature with contact pyrometer, visually confirm each pass is slag-cleaned before the next. Post-weld: measure weld size with fillet gage and undercut gage, inspect for cracks, porosity clusters, and incomplete fusion at toes. Document hold points met and any deviations found at each stage.
Pre-heat verification is often skipped under schedule pressure. Without documented preheat the inspector cannot certify the weld per D1.1 requirements. If preheat was not verified, that hold point must be documented as missed and the Engineer of Record notified for disposition - do not accept the weld silently.
AWS D1.1 Section 6.9; AWS D1.1 Section 6.5 (preheat); IBC Section 1705.12.2.
Weld Gage Selection and Measurement Techniques
The bridge cam gage is the standard multi-function tool for structural weld inspection. It measures fillet weld leg size, weld throat, convexity, concavity, undercut depth, and groove weld reinforcement height. The appropriate measurement for the drawing specification must be used: drawings specifying fillet weld size refer to the leg, not the throat. For 45-degree fillet welds, throat = 0.707 x leg. For skewed joints (weld angle other than 45 degrees), effective throat must be calculated from actual geometry - leg measurement alone is not sufficient.
Fillet gage: place flush-side against base metal, read scale at weld toe - measures leg. Undercut gage: place probe tip in undercut groove and read depth in 0.01-inch increments. Convexity: bridge cam measures height above base metal line - D1.1 limits to 0.06 + 0.12 x weld size (max 3/16 in.). Throat measurement: bridge cam 'throat' setting provides direct reading for 45-degree joints.
Measuring the weld leg on a skewed joint and calling it compliant with a throat-based specification. When the dihedral angle departs from 90 degrees, effective throat changes. The inspector must calculate or check a table for the relationship. Underreporting undercut by using visual estimation rather than a gage reading - D1.1 Table 6.1 has numerical limits that require measurement.
AWS D1.1 Table 6.1; AWS D1.1 Section 6.9.1; AWS D1.1 Annex A (effective throat tables).
The NDT methods used to evaluate structural welds beyond visual inspection, when each is required, and what the inspector must understand about their application.
Magnetic Particle and Penetrant Testing
Magnetic Particle Testing is a surface and near-surface method used on ferromagnetic materials - which includes structural steel. The method works by inducing a magnetic field in the part and applying magnetic particles to the surface. Where a discontinuity disrupts the magnetic field, the particles accumulate and form an indication. MT is sensitive to surface-breaking and near-surface discontinuities including tight cracks that might not be visible by eye alone. It is commonly used on CJP groove welds at connection points where UT is also required, as a supplement to confirm surface integrity.
Liquid Penetrant Testing works by applying a dye penetrant to the clean weld surface, allowing it to enter any surface-opening discontinuity by capillary action, and then developing the indication with a contrasting developer. PT can detect tighter surface cracks than visual inspection alone, including tight hydrogen cracks that may not be visible without it. PT works on any non-porous material and is often used on non-magnetic materials where MT is not applicable, but it is also used on structural steel welds. Its limitation is that it detects only surface-open discontinuities - it cannot find subsurface flaws.
AWS D1.1/D1.1M:2020 Clause 8 – Inspection requirements and method references; ASTM E709 – Standard guide for magnetic particle examination; ASTM E165 – Standard practice for liquid penetrant examination; AWS D1.1 Clause 9 – Tubular structures (T-, Y-, and K-connections).
MT and PT require clean, bare metal surfaces. Paint, galvanizing, and heavy mill scale must be removed before testing. This is particularly relevant on painted structural members where spot testing after erection requires proper surface preparation. The inspector should verify that the testing technician is qualified and that the materials and equipment being used meet the requirements of the applicable standard.
Ultrasonic and Radiographic Testing
Ultrasonic Testing is the primary volumetric inspection method for structural CJP groove welds. High-frequency sound waves are introduced into the weld through a transducer placed on the base metal surface. Discontinuities within the weld reflect the sound back to the transducer, creating signals on the display that the UT technician evaluates. Phased array UT and time-of-flight diffraction methods have become increasingly common and provide more detailed information than conventional single-channel UT. Regardless of the technique used, UT must be performed by a qualified technician, typically ASNT Level II certified in UT.
Radiographic Testing uses X-ray or gamma radiation to expose a film or digital detector placed on the opposite side of the weld. Discontinuities appear as variations in density on the radiographic image. RT provides a permanent, interpretable record that can be reviewed by multiple evaluators. Its limitations include radiation safety requirements, the need for site clearance during exposure, and difficulty evaluating planar discontinuities oriented parallel to the beam. For structural steel CJP welds, UT is generally preferred, but RT may be specified for certain applications or as a second check.
AWS D1.1/D1.1M:2020 Clause 8.13 – Ultrasonic testing of groove welds; AWS D1.1 Table 8.2 – UT acceptance/rejection criteria; ASNT SNT-TC-1A – Personnel qualification standard for NDT; AWS D1.1 Clause 8.14 – Radiographic testing of groove welds.
The special inspector's role with respect to NDT is primarily coordinative and evaluative rather than technical. The inspector confirms that NDT is being performed by qualified technicians using approved procedures, that the correct welds are being tested at the required frequency, and that the NDT reports are properly documented and any rejections are addressed. The inspector does not typically perform UT but must be able to review a UT report and understand what the findings mean.
Each NDT method has a different detection capability. VT detects surface flaws. MT and PT detect surface and near-surface flaws. UT and RT detect subsurface volumetric flaws. For CJP groove welds in moment connections and other high-demand locations, both visual and ultrasonic examination are typically required. The sequence matters - visual inspection and surface cleaning should precede UT, because slag and rough surfaces can interfere with probe coupling.
Interpreting welding symbols per AWS A2.4 - reference line anatomy, basic and supplementary weld symbols, dimension placement, and verifying symbol requirements in the field.
Welding Symbols and Connection Details
The AWS A2.4 welding symbol standard defines a standardized graphical language for conveying weld requirements on engineering drawings. Every structural inspector must be fluent in reading this notation. The reference line, arrow, and weld symbol together define the joint and weld type. The numbers above and below the reference line specify weld size, length, and pitch. The finish and contour symbols indicate how the weld surface should be treated. Supplementary symbols indicate backing, spacers, and field weld requirements.
AWS A2.4 defines distinct symbols for each weld type. The most common are the fillet weld triangle and the various groove weld symbols - V, bevel, U, J, flare-V, and flare-bevel. Each groove symbol represents a different edge preparation geometry. The fillet symbol is a right triangle placed against the reference line. Groove symbols show the profile shape of the groove opening. Knowing these by sight is essential - the S2C exam expects you to identify weld types from their symbols quickly.
Supplementary symbols modify or add information to the basic weld symbol. The field weld flag (a triangle at the arrow-reference line junction) indicates the weld must be made on site. The weld-all-around circle means the weld extends continuously around the entire joint perimeter. Contour symbols - flush (straight line), convex (arc curving away), and concave (arc curving inward) - specify the final surface profile. A finish method letter (G for grinding, M for machining, C for chipping) tells how the contour is achieved.
Dimensions on welding symbols follow strict placement rules. Weld size (leg size for fillets, depth of preparation for grooves) goes to the LEFT of the basic weld symbol. Weld length goes to the RIGHT. For intermittent welds, the length and pitch are shown as length-pitch (e.g., 3-10 means 3-inch welds at 10-inch center-to-center spacing). Groove angles are shown inside the groove symbol opening. For PJP groove welds, the effective throat appears in parentheses next to the depth of preparation. Understanding these placements is tested heavily on the S2C exam.
Connection details on structural drawings are typically found on separate detail sheets, referenced from the framing plans by a detail number and sheet reference. A moment connection detail will show the beam-to-column interface, the location and type of welds, any backing bars, access holes, and the relationship between bolted and welded elements. The inspector must reconcile what is shown on the detail with the weld symbols on the plan views to confirm the complete connection requirements. When there is a conflict between plan notes and detail sheets, the engineer of record must clarify before work proceeds.
The flag symbol attached to the weld symbol indicates a field weld - a weld to be made at the jobsite rather than in the fabrication shop. This distinction is critical for inspection scheduling. Field welds require the special inspector's presence or verification on site. Shop welds are made under the quality control program of the fabricator and may be verified during a shop inspection visit rather than during erection.
In practice, carrying the full drawing set during structural steel inspection is impractical. The inspector should prepare a marked-up set of connection details showing which welds require special inspection, the required weld size and type at each location, and any specific requirements noted on the drawings. This field inspection guide becomes the working document during inspection and the basis for the inspection report.
A steel erection crew is installing beam-to-column moment connections. The connection detail shows a CJP groove weld at the beam top flange and a fillet weld at the bottom flange seat angle. During inspection, the inspector notices the crew is making a fillet weld at the top flange rather than a groove weld. Reviewing the drawing confirms the CJP requirement. The inspector stops the work and notifies the foreman. The crew explains that they do not have the backing bar and access hole configuration required for the groove weld. This is a pre-construction coordination failure - the fabrication drawings should have been checked before erection began. The engineer of record must approve any modification.
Reading the Reference Line - Arrow Side, Other Side, and Tail
Every welding symbol is built on a reference line with an arrow at one end and an optional tail at the other. Weld information placed below the reference line applies to the arrow side of the joint; information above the reference line applies to the other side. The tail identifies the applicable WPS, code, or specification. The flag symbol on the reference line indicates field welding. The circle at the reference line-arrow junction indicates all-around welding. These conventions apply universally across AWS A2.4 and must be interpreted correctly before any weld is made.
Example: A symbol showing a 5/16 fillet below the reference line at a W8x column flange means the fillet weld is on the near (arrow) side. If the same 5/16 symbol appears both above and below, welds are required on both sides. A CJP groove symbol with a backing bar (rectangle below the groove symbol) and no root opening dimension means the joint must be detailed on the drawing or per WPS. Always check the tail for a WPS or standard reference before accepting a verbal interpretation.
Placing a fillet weld on the wrong side of the joint by misreading above/below reference line position. On column-to-beam connections with angle clips, the arrow side changes based on which direction the arrow points - the connection between reference line and arrow is specific to the joint being indicated, not the page orientation.
AWS A2.4 Section 3; AWS A2.4 Figure 3.1; AWS D1.1 Section 2.3 (WPS applicability).
NDT and Finishing Symbols in Welding Notation
AWS A2.4 includes standardized symbols for nondestructive testing requirements and weld finish methods. NDT symbols are placed adjacent to the weld symbol and identify the required method (UT, RT, MT, PT) and inspection coverage (100%, spot, or specific locations). Finish symbols (G = ground, M = machined, C = chipped, U = unspecified) indicate the surface finish required for fit-up or fatigue design purposes. The inspector must verify that all NDT called out on the drawing is performed at the specified coverage level.
NDT symbol placement: typically placed on the tail of the welding symbol or as a note block near the detail. 'UT' with a percentage (e.g., 100%) means 100 percent ultrasonic testing of that weld. Finish designators: G (ground flush) is the most common for connections requiring close fit-up; U (unspecified) allows any method to achieve the required condition. Without a finish symbol, no specific surface treatment is required beyond D1.1 profile requirements.
AWS A2.4 Section 8 (examination symbols); AWS A2.4 Section 4 (finish designators); AWS D1.1 Table 6.11 (UT weld categories).
Ignoring NDT symbols on drawings because the inspector's scope only includes visual inspection. If the drawings call for UT or RT, the inspector must verify the contractor has scheduled the correct NDT and that results are received and reviewed by the EOR before the connection is encased or loaded.
Recording inspection activities correctly, managing nonconformances, and delivering the final documentation package.
Inspection Reports and Daily Logs
The inspection report is the inspector's permanent record of what was verified on a given day. It must be detailed enough that someone reviewing it months or years later can determine exactly what was inspected, what was found, and what action was taken. Vague entries like 'welding inspected, acceptable' are professionally inadequate. A proper entry identifies the connection location or member mark, the weld type and size, the inspection method used, the results of the inspection, and any nonconformances noted.
The statement of special inspections typically requires the inspector to submit periodic reports to the building official and the engineer of record during construction, and a final report upon completion. The final report must state that all required special inspection has been performed and that all work inspected was found to comply with the approved construction documents and applicable standards - or note any accepted nonconformances and the basis for acceptance.
AWS D1.1/D1.1M:2020 Clause 8.1 – Inspector requirements and reporting responsibilities; AWS D1.1 Clause 8.4 – Verification inspection; AISC 360 Chapter N – Quality Assurance documentation requirements.
Daily inspection report entries should include: (1) Date, weather conditions, and temperature if relevant to welding requirements. (2) Names of welders observed and their qualification stamp numbers. (3) Areas of the structure or specific connections inspected. (4) Welding processes and WPS documents verified in use. (5) Preheat measurements taken, locations, and temperatures recorded. (6) Visual inspection results for each connection examined. (7) NDT performed, reference numbers, and results. (8) Any nonconformances noted, notifications made, and corrective actions observed or required. (9) Inspector's signature and certification number.
Nonconformance Management and Project Close-Out
When the inspector identifies work that does not meet the requirements, the immediate steps are to document the nonconformance in writing, notify the contractor's responsible party, and notify the engineer of record if the nonconformance is structural in nature. The inspector does not determine the disposition of rejected work - that is the engineer's role. The engineer may require repair, removal and replacement, or may accept the work as-is with a documented engineering evaluation. The inspector records the engineer's decision and verifies that any required repair or additional testing is performed.
Weld repairs require as much attention as original welding, sometimes more. A repair weld is being made into a joint that has already experienced thermal cycling, may contain brittle microstructure from the original welding, and requires complete removal of the defective area before the repair can begin. The inspector must verify that the defect has been fully removed - often by MT or PT of the excavated area - and that the repair is being made in accordance with an approved repair WPS. Repair welds require preheat regardless of whether the original weld did.
Project close-out for welding inspection involves compiling all inspection reports, NDT reports, welder qualification records, WPS and PQR documentation, and the record of any nonconformances and their dispositions into a final documentation package. This package supports the final report to the building official and becomes part of the permanent project record. Some jurisdictions require submission of the original documentation; others accept a letter of compliance referencing the documentation package maintained by the inspection agency.
The signed final inspection report is the inspector's professional certification that the specified work was performed and verified. It is not a generic form letter - it is a professional statement with legal implications. Before signing, the inspector must be satisfied that all required inspections were actually performed, that all nonconformances were properly resolved, and that no outstanding issues remain. An inspector who signs off on a project knowing that required inspections were missed or deficiencies were left unresolved is exposing themselves to serious professional and legal consequences.
During UT of a beam top flange CJP groove weld at a moment connection, the technician identifies a large lack-of-fusion indication extending approximately 40% of the weld length. The inspector documents the finding, marks the weld location on the structure, and notifies both the contractor and the structural engineer. The engineer evaluates the connection and determines that the weld must be repaired. The contractor develops a repair procedure, which is reviewed and approved by the engineer. The inspector observes the repair, which includes MT verification of complete defect removal and UT of the completed repair weld. All documentation - the original UT report, the nonconformance record, the repair procedure, the repair UT report - becomes part of the project record.