AWS Certified Welding Inspector (CWI / SCWI) — Study Guide

AWS Certified Welding Inspector (CWI / SCWI) — Study Guide

Credentials: AWS Certified Welding Inspector (CWI); AWS Senior Certified Welding Inspector (SCWI) Issuing body: American Welding Society (AWS) Jurisdiction: USA (recognized internationally wherever North American welding codes govern) Renewal: 3 years for both — by documented work activity (no continuous inactivity > 2 of 3 years) + current visual-acuity record, or by retaking the Part B practical; 60-day administrative grace period

This is one guide with a progression structure: Part 1 covers the CWI (the working inspector's credential); Part 2 covers the SCWI endorsement pathway that sits on top of it. If you only need CWI, read Part 1 and the shared sections.

PART 1 — CWI (Certified Welding Inspector)

1. Header

Level: Inspector (entry/professional) Prerequisites: 3 years of verified welding-inspection experience; education can reduce the experience requirement (per AWS QC1/B5.1 — a relevant degree substitutes for a portion of the time) Exam: Three parts, each must be passed at 72%: Part A — Fundamentals (150 questions), Part B — Practical (46 questions), Part C — Code Book (46 questions)

2. Pathway

1. Document experience. 3 years of welding-inspection or closely related fabrication/QC experience, verified by employer(s). Relevant post-secondary education reduces the requirement.
2. Vision test. Near-vision acuity (Jaeger J2 or equivalent at 12+ inches, with or without correction) and color perception sufficient to distinguish weld-inspection color codes — documented before and at each renewal.
3. Sit the three-part exam. Part A tests welding fundamentals broadly; Part B is hands-on — you inspect actual weld specimens and replica discontinuities with gauges; Part C is open-code-book on the code you select (AWS D1.1 Structural Steel is the most common; API 1104 and ASME Section IX are other selectable books).
4. Earn the credential; renew every 3 years by work-activity documentation or by re-exam.

Exam format (verified per AWS QC1/B5.1 via AWS and third-party summaries):

• Part A: 150 multiple-choice questions, closed-book — welding processes, metallurgy, symbols, NDE, safety, QC math
• Part B: 46 questions, practical — measurement with weld gauges, discontinuity identification on real specimens, WPS/PQR review
• Part C: 46 questions, open-book — the selected code (D1.1, API 1104, or ASME IX); tests code navigation and clause application
• Pass mark: 72% on each part independently — a 95% on Part A does not rescue a 70% on Part B

3. Knowledge Domains

Domain A — Welding processes (Part A, heavy weight)

Know the process families at the level of what the inspector must verify: SMAW (stick — electrode classification E7018: E=electrode, 70=70 ksi tensile, 1=all-position, 8=low-hydrogen iron-powder coating; low-hydrogen handling — electrodes must be stored in holding ovens at ~250°F after opening, and exposure limits matter because moisture → hydrogen → cracking); GMAW (MIG — short-circuit vs spray vs pulsed transfer modes; shielding gas selection: 75/25 Ar/CO2 for short-circuit on steel, 98/2 for spray); FCAW (gas-shielded vs self-shielded; self-shielded wires for outdoor wind tolerance); GTAW (TIG — tungsten types: thoriated, ceriated, lanthanated; AC for aluminum, DCEN for steel; gas lens vs collet body); SAW (submerged arc — high deposition, flux handling/moisture control); OAW/OFW (limited structural relevance, still tested); plus brazing (filler melts above 840°F/450°C but below base-metal melting — the definition question) and thermal cutting/gouging (air-carbon-arc gouging as a weld-removal method).

Why it matters to inspection: each process has characteristic discontinuities — SMAW: slag inclusion and undercut; GMAW short-circuit: cold lap/lack of fusion; SAW: centerline cracking if parameters drift; GTAW: tungsten inclusions. The Part B specimens are chosen to show these.

Domain B — Welding metallurgy (Part A)

The heat-affected zone (HAZ). The region of base metal whose microstructure was altered by welding heat without melting. In carbon steels, the coarse-grained HAZ near the fusion line is the crack-susceptible region — grain growth plus hardening.

Hydrogen cracking (cold cracking). Requires three simultaneous conditions: susceptible microstructure (hardened/martensitic HAZ), hydrogen (from moisture, coatings, atmosphere), and tensile stress (residual welding stress) — plus time at near-ambient temperature (it is delayed cracking, appearing hours to days after welding). Prevention is the inspector's checklist: preheat (slows cooling, lets hydrogen diffuse out), low-hydrogen practice (dry electrodes, clean joints), interpass temperature control, and sometimes post-weld heat treatment.

Carbon equivalent (CE). The weldability index: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 (IIW formula, weight %). Higher CE → higher hardenability → greater cracking risk → more preheat. Rule of thumb: CE above ~0.40–0.45 starts demanding preheat on restrained joints; above ~0.60 demands serious preheat and low-hydrogen discipline. The exam tests CE calculation and its use — it predicts HAZ hardness, not strength.

Preheat and interpass. Preheat slows the cooling rate through the martensite-transformation range; interpass maximum prevents excessive grain growth and, on quenched-and-tempered or precipitation-hardened materials, prevents softening/property loss. Both are WPS essential variables — the inspector verifies them with temperature-indicating crayons, contact pyrometers, or IR.

Solidification cracking (hot cracking). Occurs during weld-metal solidification — driven by low-melting constituents (sulfur, phosphorus) segregating to grain boundaries under shrinkage stress. Controlled by chemistry (low S/P), joint design (avoid highly restrained narrow grooves), and bead shape (avoid deep-narrow profiles).

Domain C — Welding symbols and drawings (Parts A and B)

AWS A2.4 symbols. The arrow side vs other side, the reference line, weld-all-around circle, field-weld flag, melt-through, backing, contour symbols, and — most tested — groove weld symbols: square, V, bevel, U, J, flare-V, flare-bevel, and the dimensions that go with them (groove angle, root opening, root face, depth of preparation S, effective throat E). Fillet weld: leg size on the left of the symbol, length and pitch (center-to-center) on the right; staggered vs chain intermittent.

Why it works this way: the symbol is a legal instruction — the welder builds what the symbol says, and the inspector accepts or rejects against it. Misreading the arrow side is the classic Part B trap: a weld placed on the wrong side of the joint is a rejectable defect even if the weld itself is sound.

WPS/PQR. The PQR (Procedure Qualification Record) documents the actual test weld and its mechanical-test results; the WPS (Welding Procedure Specification) is the production instruction written within the PQR's qualified ranges. Essential variables (process, base-metal P-number/group, filler F-number/A-number, preheat, PWHT, thickness/position qualified) — changing one re-qualifies the procedure. The inspector's job: verify production welding stays inside the WPS envelope (amperage, voltage, travel speed, preheat, interpass, gas flow).

Domain D — Discontinuities and acceptance criteria (Part B core)

Know the discontinuity vocabulary precisely — the exam distinguishes them: porosity (spherical gas voids; scattered vs clustered vs piping); slag inclusion (nonmetallic, elongated — distinguished from porosity by shape); incomplete fusion / lack of fusion (unfused interface — planar, the most structurally severe along with cracks); incomplete joint penetration (root not fused through); undercut (groove melted into base metal at the toe, left unfilled — a stress riser); overlap (weld metal rolling over unfused base metal); cracks — longitudinal, transverse, crater, toe, root, underbead (hydrogen), lamellar tearing (base-metal tearing parallel to the surface in rolled plate under through-thickness stress); arc strikes (rejectable — they're tiny hard spots/crack initiators outside the joint).

Acceptance criteria come from the code book (Part C): AWS D1.1 Table 6.1 (statically loaded) vs Table 8.1 (cyclically loaded) — cyclically loaded structures have far stricter limits on undercut, porosity, and discontinuities because fatigue, not static strength, governs. Cracks are rejectable, period — in every code, every service. Undercut depth limits, porosity size/sum limits, and reinforcement limits are the lookup questions.

Domain E — NDE methods (Parts A and B)

VT (visual) — the CWI's primary method; know lighting, magnification, and gauge use. PT (liquid penetrant — surface-breaking only; dwell and development times; visible vs fluorescent). MT (magnetic particle — ferromagnetic materials only; yoke vs prod technique; AC vs DC/half-wave; field direction must cross the expected discontinuity). RT (radiography — volumetric; IQI/penetrameter sensitivity; film density; geometric unsharpness; radiation safety — time/distance/shielding). UT (ultrasonics — volumetric; shear-wave angle-beam for welds; calibration with IIW block; DAC/TCG curves; couplant; near-surface dead zone). Know which method finds what: surface-breaking → PT/MT/VT; internal planar (lack of fusion, cracks) → RT/UT; UT sizes planar defects better than RT; RT gives a permanent film record.

Domain F — Destructive testing and qualification (Parts A and C)

Tensile, bend (face/root/side — which surface is in tension for each), Charpy impact (notch toughness, transition temperature), macro-etch (reveals penetration, fusion, HAZ, bead sequence), hardness traverses. Welder qualification (performance qualification — the welder's skill test) vs procedure qualification (the WPS's engineering test): a qualified welder does not make an unqualified procedure acceptable, and vice versa. Position qualification ranges (1G qualifies flat only; 3G/4G combos qualify all positions for plate; 6G qualifies all positions for pipe) are pure memorization — heavily tested.

4. Key Equations (with units and assumptions)

• Heat input: HI (kJ/in) = (V × A × 60) ÷ (travel speed in/min × 1000). Assumption: arc efficiency not included (true heat input multiplies by process efficiency: ~0.8 SMAW, ~0.9 SAW). Controls cooling rate → HAZ hardness.
• Carbon equivalent (IIW): CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15, weight %. Predicts hardenability/cracking risk, not strength.
• Fillet weld strength: nominal strength = 0.6 × F_EXX × throat area; throat = 0.707 × leg size (equal-leg fillet), area in in², strength in lb. Assumption: transverse loading per AWS D1.1; directional strength increase for longitudinal loading.
• Preheat estimation: no single code equation — CE-based methods (e.g., AWS D1.1 Annex H) combine CE, hydrogen level, and restraint. Know the inputs, not a formula.
• RT geometric unsharpness: Ug = (source size × object-to-film distance) ÷ source-to-object distance, same length units. Smaller Ug = sharper image; codes limit it.

5. Worked Examples

Example 1 — Heat input. A GMAW weld runs at 27 V, 240 A, travel speed 12 in/min. Step-by-step: HI = (27 × 240 × 60) ÷ (12 × 1000) = 388,800 ÷ 12,000 = 32.4 kJ/in. Inspector's use: compare against the WPS range (say 25–40 kJ/in) — in range. If travel speed had been 20 in/min, HI = 19.4 kJ/in — out of range on the low side, risking lack of fusion and excessive hardness.

Example 2 — Carbon equivalent. A plate chemistry: C 0.18%, Mn 1.2%, Cr 0.10%, Ni 0.15%, Mo 0.05%, V 0.02%, Cu 0.10%. Step-by-step: CE = 0.18 + 1.2/6 + (0.10+0.05+0.02)/5 + (0.15+0.10)/15 = 0.18 + 0.20 + 0.034 + 0.0167 = 0.43. Inspector's use: above ~0.40 — preheat required per the WPS; on a restrained joint, expect minimum preheat in the 150–250°F band (exact value from the code's preheat tables, not from CE alone).

Example 3 — Fillet weld strength. A 1/4-in fillet, E70 electrode, 6 in long, loaded transversely. Step-by-step: Throat = 0.707 × 0.25 = 0.177 in. Area = 0.177 × 6 = 1.061 in². Nominal strength = 0.6 × 70 ksi × 1.061 = 44.6 kips (LRFD/ASD factors applied per the design code). Lesson: strength scales with throat, not leg — a convex oversized weld wastes metal without proportional gain.

Example 4 — Part B gauge reading. A fillet weld gauge shows the leg at 5/16 in against a specified 1/4-in fillet, with 1/32-in undercut at the toe on a statically loaded D1.1 structure. Step-by-step: Oversize fillet is acceptable (no maximum in D1.1 for static, though economy suffers). Undercut: D1.1 Table 6.1 allows undercut ≤ 1/32 in for certain cases but the general static limit is 1/16 in max depth with cumulative limits — 1/32 in is within the static allowance. Lesson: the same undercut on a cyclically loaded structure (Table 8.1) would likely reject — always check which table governs.

Example 5 — Welder qualification range. A welder qualified on 3/8-in plate in 3G (vertical) with SMAW. Step-by-step: Per AWS D1.1 Table 4.10/4.11 logic: 3G qualifies vertical and flat positions (not overhead — that needs 4G); thickness qualified is 1/8 in to 3/4 in (2T rule for the test thickness range). A 1-in-thick overhead weld is outside qualification — reject the assignment, not the welder.

6. Standards/Regulations Cross-Reference

• AWS D1.1/D1.1M Structural Welding Code — Steel (2025 is the 23rd edition; prequalified WPSs in Clause 5): the default Part C code book. Know: prequalified joint details, welder qualification (Clause 4), fabrication (Clause 5/7), inspection (Clause 6 — Tables 6.1/8.1 acceptance criteria), stud welding (Clause 9).
• ASME Section IX: welding/brazing qualifications — P-numbers, F-numbers, A-numbers, essential/nonessential/supplementary-essential variables. The Part C option for pressure-equipment inspectors; pairs with ASME BPVC Section VIII (vessel construction) and B31.1/B31.3 (piping) as the construction codes the qualifications serve.
• API 1104: pipeline welding — the Part C option for pipeline inspectors; distinct acceptance criteria and a different qualification philosophy (more procedure-specific).
• AWS A2.4 (symbols), A3.0 (terms and definitions), B1.10/B1.11 (NDE guides): the reference backbone behind Parts A and B.
• OSHA 29 CFR 1910 Subpart Q / 1926 Subpart J: welding/cutting/hot-work safety — fire watch, confined spaces, ventilation. Part A safety questions draw here.
• CSWIP 3.1 (TWI, UK): the international counterpart credential — 5-year validity; know it exists for cross-border work (covered in the good-to-know guide).

7. Pitfalls & Trap Patterns

1. The 72% is per part. Banking 95% on Part A buys nothing on Part B. Study time should skew toward your weakest part, which for most candidates is Part B (practical) or Part C (code navigation).
2. Arrow side vs other side. The single most-tested symbol skill. Slow down on every symbol question and mark the arrow first.
3. Static vs cyclic acceptance tables. D1.1 Table 6.1 vs 8.1 — the question always tells you the loading; the wrong table gives the wrong answer.
4. Cracks are never acceptable. Any answer choice that accepts a crack is wrong, in any code, any service.
5. Essential variables. If a WPS change touches an essential variable, the procedure must be requalified — "the welder is experienced" is not a requalification.
6. Part C is a navigation test. You get the code book; the exam measures whether you can find the clause in time. Practice with the actual edition you'll test on.
7. Hydrogen cracking needs all three legs (susceptible microstructure + hydrogen + stress). Questions offering "eliminate any one" as prevention are testing this model.

Exam strategy: Part A rewards breadth — don't over-study one process. Part B rewards gauge fluency — practice measuring fillets, reinforcement, undercut, and misalignment until it's automatic, and learn the specimen-discontinuity vocabulary (porosity vs slag vs LOF by appearance). Part C rewards tabbing your code book before exam day. Time management: Part A is 150 questions — roughly 2 minutes each; flag calculation questions and return.

8. Practice Problems

1. Compute heat input for 24 V, 180 A, 10 in/min. Is it within a WPS range of 20–30 kJ/in? Answer: (24 × 180 × 60)/(10 × 1000) = 25.9 kJ/in — in range.

2. A steel has CE = 0.55 and the joint is highly restrained. What is the inspector's primary concern and the standard mitigation? Answer: Hydrogen (cold) cracking in the HAZ. Mitigation: preheat + low-hydrogen practice + interpass control; verify against the WPS/code preheat tables.

3. A WPS qualified with E7018 SMAW is used in production with E6010 for the root pass. Acceptable? Answer: No — electrode F-number/classification is an essential variable; changing from low-hydrogen E7018 to cellulosic E6010 re-qualifies the procedure.

4. Name the discontinuity: elongated nonmetallic material trapped between weld passes, visible on a macro-etch as dark stringers. Answer: Slag inclusion (interpass). Distinguish from porosity (spherical) and lack of fusion (planar, at the interface).

5. A welder qualified 6G on 2-in. pipe welds a 1/2-in. plate groove in the flat position. Within qualification? Answer: Yes — 6G pipe qualifies all positions; thickness range from the 2-in. test coupon covers 3/16 in. to 4 in. (per D1.1 Table 4.11 logic), which includes 1/2-in. plate (pipe-to-plate position qualification transfers for groove welds within the code's rules).

6. Why is an arc strike outside the weld joint rejectable? Answer: It creates a tiny hardened, potentially micro-cracked spot — a crack initiation site — in base metal that was never intended to be thermally affected. Grind, inspect (MT/PT), and document.

7. D1.1 cyclically loaded structure: 1/16-in. undercut found at a transverse groove weld toe. Accept or reject? Answer: Reject — Table 8.1 (cyclically loaded) limits are far stricter than Table 6.1; transverse undercut in cyclic service is essentially zero-tolerance beyond minimal depth. (Verify exact value in the edition's table — the principle is what the exam tests.)

PART 2 — SCWI (Senior Certified Welding Inspector)

1. Header

Level: Inspector (senior) Issuing body: AWS Prerequisites: Hold CWI for at least 6 of the past 8 years; 15 years of welding-related work experience Pathway change (April 1, 2025): the single SCWI exam was retired and replaced by an endorsement pathway — candidates must earn four CWI endorsements: the Welder Performance Qualifier endorsement, the Welding Procedure Qualifier endorsement, plus two elective endorsements. Cross-check current endorsement offerings against AWS QC1 before relying on specifics — the program is young and AWS refines the list. Renewal: 3 years, same framework as CWI

2. What changes at the senior level

The CWI verifies conformance — does this weld meet the code? The SCWI demonstrates authority over the welding program: qualifying welders (performance qualification — running the test booth, evaluating bend specimens, documenting ranges qualified), qualifying procedures (PQR development — designing the test matrix, witnessing mechanical testing, writing WPSs inside qualified envelopes), and owning quality systems (audit, NCR disposition, code interpretation disputes).

Endorsement 1 — Welder Performance Qualifier. Deep competence in AWS B5.1/qualification rules: test coupon design, position/thickness/diameter ranges qualified by each test, bend-test evaluation (what counts as a discontinuity vs an acceptable indication — e.g., corner cracks from specimen preparation are discounted), and the paperwork chain that makes a qualification legally defensible.

Endorsement 2 — Welding Procedure Qualifier. PQR design: selecting essential variables to bracket production, mechanical-test selection (tension, bends, Charpy where required, hardness), interpreting results against code minima, and authoring WPSs that production can actually follow. Senior-level trap: a PQR that qualifies a range nobody needs is wasted money; a PQR that doesn't cover the production envelope is a nonconformance.

Elective endorsements (two). Chosen from AWS's endorsement menu to match the candidate's industry — the structure rewards demonstrated breadth beyond inspection (e.g., code-specific or technique-specific endorsements). Verify the current menu at AWS; do not assume legacy endorsement names.

3. Senior-level knowledge emphasis

• Code interpretation as a discipline. At SCWI level you are the person two CWIs argue in front of. This means knowing why clauses exist (the engineering intent behind preheat tables, the fracture-mechanics basis of cyclic acceptance criteria) so you can rule on cases the code doesn't explicitly cover — and knowing when to say "the code is silent; here's the conservative engineering position, documented."
• Quality systems. NCR (nonconformance report) lifecycle: identification, segregation/hold, disposition (use-as-is with engineering approval, repair, scrap), root-cause corrective action. Audit: procedure audits vs product audits. The SCWI owns the written practice the way an ASNT Level III owns the NDE written practice.
• Welding economics and planning. Deposition rates by process (SAW > FCAW > GMAW > SMAW > GTAW, roughly), the cost of rework (a repair costs multiples of first-time quality — the business case for inspection), sequencing to minimize distortion and residual stress.
• Metallurgy at the advisory level. Advising on filler selection for dissimilar joints, PWHT decisions, and failure analysis triage (when to call the metallurgist vs the NDE crew).

4. Pitfalls & strategy

1. Endorsement sequencing. You need all four endorsements plus the experience clock — plan the endorsement exams around work assignments that generate the required evidence.
2. The 2025 pathway is new. Third-party prep material lags; the authoritative source is AWS QC1 and AWS's current endorsement pages. Anything in a prep book about "the SCWI exam" describing a single test is outdated.
3. Senior ≠ harder CWI. The endorsements test program ownership, not harder discontinuity ID. Candidates who re-study Part B instead of learning qualification rules misallocate effort.
4. Documentation is the deliverable. At senior level, the weld is the welder's product; the record package (PQR/WPS/qualifications/NCRs) is yours. Exams test whether you know what a complete package contains.

5. Practice problems (SCWI level)

1. A PQR was qualified on 1-in. plate with PWHT. Production needs 1/2-in. plate without PWHT on the same P-number. Can the existing PQR support a WPS for production? Answer: No. PWHT is a supplementary essential variable where notch toughness matters, and thickness qualified has limits (generally 1/16 in. to 2T, i.e., up to 2 in. — the 1/2-in. thickness is covered) — but removing PWHT where the PQR included it changes a supplementary essential variable. A new PQR (or additional test coupon) is required.

2. A welder's 6G test shows a 1/8-in. corner crack on one face-bend specimen, clearly originating at the specimen's machined edge. Disposition? Answer: Per D1.1 bend-test acceptance, corner cracks occurring at the specimen edge without evidence of weld defects are discounted (the specimen is retested or the indication disregarded per the code's retest rules) — but document the observation and the code clause cited. Do not silently discard.

3. An NCR reports undercut exceeding Table 8.1 on a cyclically loaded bridge girder. List the disposition options and who approves each. Answer: Repair (grind/weld per an approved repair WPS — CWI/SCWI approves the repair procedure and re-inspects), use-as-is (requires engineering evaluation and documented approval — the inspector cannot approve this alone), or scrap/replace. The SCWI's role: ensure the disposition path is code-compliant and fully documented.

4. Why does SCWI require the Welder Performance Qualifier endorsement rather than just more inspection experience? Answer: Because senior authority includes granting qualification — deciding who is legally permitted to weld. That requires owning the qualification rules (ranges, retest logic, documentation), not just recognizing good welds.

Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.