Structural Steel QC Inspector Interview Questions: AWS D1.1 Guide

Structural steel QC inspectors are essential on oil and gas, power, and infrastructure projects. Interviewers test your knowledge of AWS D1.1, AISC 360, bolted connections, welding inspection, and NDT. This guide covers 40 questions with detailed, code-referenced answers.

---

AWS D1.1 Fundamentals

1. What is AWS D1.1, and what does it govern?

AWS D1.1 is the Structural Welding Code – Steel. It governs:

• Welder qualification — process, position, thickness
• WPS/PQR — procedure qualification
• Pre-heat and interpass temperature requirements
• Weld inspection — visual (VT) and NDT (MT, PT, UT, RT)
• Acceptance criteria — by weld category (A, B, C)
• Inspection tiers — Tier 1, 2, 3 based on structural importance

2. What are the AWS D1.1 inspection tiers?

Tier	Application	NDT Requirement
Tier 1	Static, non-critical	VT only
Tier 2	Static, critical	VT + MT/PT on percentage
Tier 3	Dynamic / fatigue	VT + UT or RT on 100%

The tier is determined by the engineer based on the connection's load type and importance.

3. What are the AWS D1.1 weld categories?

Category	Description	NDT
A	Non-critical, statically loaded	VT
B	Critical, statically loaded	VT + MT/PT
C	Dynamic / fatigue loaded	VT + UT/RT

4. What pre-heat is required for structural steel?

Pre-heat depends on the steel grade, thickness, and process. Per AWS D1.1 Table 3.2:

Thickness	Pre-Heat (A36, SMAW)
≤6 mm	None required
6–19 mm	0°C (32°F)
19–38 mm	10°C (50°F)
38–65 mm	66°C (150°F)
>65 mm	107°C (225°F)

Pre-heat prevents hydrogen-induced cracking — critical for thick sections and high-strength steels.

---

Welding Inspection

5. What do you check on a structural weld visually?

Check	Acceptance
Cracks	Not permitted (any size)
Undercut	≤0.25 mm depth, ≤1 mm long per 100 mm
Porosity	Limited per Table 6.1 (size and frequency)
Excess reinforcement	≤3 mm for ≤25 mm thick
Spatter	Acceptable (cosmetic)
Profile	Smooth transition, no sharp notches
Leg size	≥ specified (measured)
Convexity	≤3 mm

6. What is a WPS, and what essential variables does it include?

A WPS (Welding Procedure Specification) is the written instruction for the welder. Essential variables per AWS D1.1:

• Process (SMAW, GMAW, FCAW, SAW)
• Base metal (ASTM spec, group)
• Filler metal (classification, diameter)
• Pre-heat and interpass temperature
• Position (1G, 2G, 3G, 4G, etc.)
• Thickness range qualified
• Electrical parameters (amps, volts, travel speed)
• Shielding gas (if applicable)

A change to any essential variable requires a new PQR.

7. What is the difference between a fillet weld and a groove weld?

• Fillet weld: Triangular cross-section, joins two surfaces at an angle (T, lap, corner). Measured by leg size.
• Groove weld: Made in a prepared groove (V, U, J, bevel). Full or partial penetration. Measured by throat.

Groove welds are stronger but require more preparation and NDT.

---

Bolted Connections

8. What is the difference between A325 and A490 bolts?

Bolt	Tensile Strength	Use	Galvanizing
A325	120 ksi (827 MPa)	Common structural	Allowed
A490	150 ksi (1034 MPa)	Critical, high-load	Not allowed (hydrogen embrittlement)

A490 is stronger but cannot be galvanized — hydrogen embrittlement causes delayed failure.

9. How do you verify bolt torque on a structural connection?

Per AISC 360 and the RCSC Specification:

1. Check the bolt lot — correct grade (A325, A490), calibrated
2. Verify the torque value from the project spec or RCSC table
3. Use a calibrated torque wrench — calibration certificate valid
4. Torque pattern — star/cross pattern on flanges, diagonal on plates
5. Mark and record — mark each bolt after torquing
6. Witness torque check — 10% of bolts re-checked by QC

10. What is a slip-critical connection, and how is it inspected?

A slip-critical connection resists load by friction between faying surfaces (not bolt shear). Inspection:

• Faying surface — clean, uncoated, or with approved slip-resistant coating
• Bolt tension — verified by torque or bolt tension calibrator (DTI)
• Slip coefficient — tested per RCSC (Class A, B, or C)
• Torque — higher than bearing connections

Slip-critical connections are used in fatigue and dynamic applications.

---

NDT for Structural Steel

11. What NDT methods are used on structural steel?

Method	What It Finds	Typical Use
VT	Surface defects	All welds — first line of defense
MT	Surface/near-surface (ferromagnetic)	Carbon steel surface defects
PT	Surface-breaking (any metal)	Stainless, non-ferrous surface defects
UT	Internal (cracks, lack of fusion)	Thick welds, Tier 3
RT	Internal (porosity, slag)	Critical welds, when specified

12. What is the difference between MT and PT?

• MT (Magnetic Particle): Uses a magnetic field and iron particles. Finds surface and near-surface defects on ferromagnetic materials only (carbon steel).
• PT (Penetrant Testing): Uses a dye that penetrates surface-breaking defects. Finds surface-only defects on any metal (stainless, aluminum).

MT is faster and finds sub-surface defects; PT is for non-magnetic materials.

---

Fabrication and Fit-Up

13. What do you check during a structural steel fit-up inspection?

1. Dimensions — matches the shop drawing (tolerance per AISC 360)
2. Joint geometry — bevel angle, root gap, land per WPS
3. Alignment — hi-lo (misalignment) within tolerance
4. Tack welds — sound, no cracks, spaced evenly
5. Cleanliness — no oil, rust, moisture in the groove
6. Backing bars — if used, properly fitted
7. Pre-heat — if required, verified before welding starts

14. What is camber, and why is it built into structural beams?

Camber is a slight upward curve built into a beam to offset deflection under load. Required on:

• Long-span beams (>6 m)
• Cantilevers
• Composite beams

Typical camber: L/250 to L/300 of the span. Without camber, the beam sags and appears non-level after loading.

---

Scenario-Based Questions

15. You find a crack in a structural weld. What do you do?

1. Stop the work immediately
2. Raise an NCR
3. Mark and photograph the crack
4. Determine the extent — MT or UT to find the full length
5. Gouge out the crack — grind or air-arc to sound metal
6. Verify removal — MT to confirm the crack is gone
7. Re-weld per the WPS (with pre-heat if required)
8. Re-inspect — MT or UT to confirm the repair is sound
9. Document — NCR, repair record, new NDT report

16. A welder is welding in the wrong position (not qualified). What do you do?

1. Stop the work immediately
2. Raise an NCR
3. Verify the welder's qualification — check the position on the cert
4. Do not allow resumption until the welder is qualified for the position (re-test required)
5. Inspect the completed welds — they may need cut-out and re-welding by a qualified welder
6. Document — the NCR and the corrective action

---

Final Tips for Structural Steel QC Interviews

1. Know AWS D1.1 — tiers, categories, acceptance criteria
2. Understand bolted connections — A325 vs A490, torque, slip-critical
3. Practice weld defect identification — VT, MT, PT
4. Mention AISC 360 — the companion code for steel construction
5. Carry your AWS CWI or CSWIP certificate
6. Be ready for NCR scenarios — they test your judgment

---

Practice Structural Steel QC Questions with SkillJet.co

SkillJet.co's QC Inspector Simulator includes:

• ✅ Civil & Structural discipline with 200+ code-based scenarios
• ✅ Visual weld defect identification drills
• ✅ Aramco SAES-C-001 and ADNOC AGES-CV-01 overlays
• ✅ Real-time readiness scoring

Start your free QC diagnostic →