Chapter 4: Welding Quality Control

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🔍 4.1 Why Welding Quality Control Matters

Welding is widely used in pipelines, pressure vessels, steel structures, boilers, and refineries. A defective weld can cause:

Leakage of gases/fluids

Structural failure or collapse
Explosion or fire hazard
Massive financial and human loss

✅ Effective welding QA/QC ensures safety, reliability, and compliance with codes like ASME, API, AWS, and ISO.

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📘 4.2 Key Welding Documents in QA/QC

Document	Full Form	Purpose
WPS	Welding Procedure Specification	Describes how welding is to be performed
PQR	Procedure Qualification Record	Confirms WPS by testing weld sample
WPQ/WQTR	Welder Performance Qualification	Certifies welder's ability to produce sound welds

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🧪 4.3 Welding Inspection Stages

🔹 Pre-Welding Inspection

Review WPS and drawings

Check base materials and electrodes
Verify welder qualification
Joint preparation and fit-up
Preheat requirement check

🔹 During Welding Inspection

Monitor parameters: current, voltage, travel speed

Check interpass temperature
Ensure compliance with WPS
Check for welding sequence and technique

🔹 Post-Welding Inspection

Visual inspection (VT)

Non-destructive testing (UT, RT, MT, PT)
Dimensional check
Post weld heat treatment (if required)

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🧰 4.4 Common Welding Defects

Defect	Description	Cause
Porosity	Gas pockets in weld	Improper shielding gas
Cracks	Linear separations	High stress, poor technique
Undercut	Groove at weld toe	Excessive current
Lack of Fusion	No bond between layers	Low heat input or poor cleaning
Incomplete Penetration	Weld doesn't reach root	Poor joint design or low heat

🔍 These defects are identified via visual & NDT methods, and may require repair/rework.

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📏 4.5 Weld Size, Symbol & Inspection Tools

🛠 Tools:

Weld gauges (leg length, throat thickness)

Fillet weld gauge
Angle gauge
Visual inspection mirror
Measuring tape, marker, temperature crayon

🔣 Weld Symbols (per AWS A2.4):

➖ Fillet Weld

🞔 Groove Weld
⊥ Backing
⏐ Field weld
☑ All-around weld

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🧾 4.6 Weld Quality Records & Traceability

Weld Map: Identifies weld joints with welder ID, process used

NDT Reports: Record of RT/UT results for each joint
Welder Log: Tracks which welder did what joint
Heat Numbers: Trace material used in each weld to MTC

📌 These records are reviewed by client and third-party inspectors (TPI).

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🏭 4.7 Real-World Example: Welding QA/QC in Oil & Gas Pipeline

Project: 20 km oil pipeline welding
QA/QC Process:

1. WPS prepared and approved

2. Welders qualified (WPQ)

3. Fit-up checked and marked

4. Welding monitored and inspected

5. RT done on 10% of welds (as per ITP)

6. All welds mapped and logged

7. NDT reports submitted to client

8. Pressure test conducted successfully

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🧠 Summary

Welding QA/QC is essential for safe and reliable mechanical systems

Engineers must be fluent in WPS, PQR, WPQ, and NDT for welds
Effective weld documentation and inspection builds trust and prevents failure
Codes like ASME IX, API 1104, AWS D1.1 must be followed

Quiz: Welding Quality Control

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Q1. What does WPS stand for in welding?
A) Welding Pipe Schedule
B) Weld Procedure Specification
C) Welder Process Sheet
D) Welding Protocol Standard
🟩 Correct Answer: B

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Q2. Which document verifies that a welding procedure produces acceptable welds?
A) Welder Log
B) Work Instruction
C) Procedure Qualification Record (PQR)
D) Material Test Certificate (MTC)
🟩 Correct Answer: C

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Q3. What is the main purpose of a WPQ (WQTR)?
A) To specify welding machines
B) To certify the welder's performance
C) To inspect base material
D) To list welding defects
🟩 Correct Answer: B

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Q4. Which NDT method is best suited to detect internal weld defects?
A) Visual Testing
B) Dye Penetrant Test
C) Magnetic Particle Test
D) Radiographic Testing (RT)
🟩 Correct Answer: D

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Q5. What is a common cause of porosity in welds?
A) High preheat temperature
B) Contaminated electrode or base metal
C) Low voltage
D) Excessive weld bead size
🟩 Correct Answer: B

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Q6. Which of the following is not a welding defect?
A) Undercut
B) Crater crack
C) Full fusion
D) Incomplete penetration
🟩 Correct Answer: C

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Q7. In welding QA/QC, a weld map is used to:
A) Show pressure testing layout
B) Assign weld symbols to drawing
C) Identify each weld with welder ID and location
D) Indicate thickness of electrodes used
🟩 Correct Answer: C

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Q8. Which of the following is used to measure throat thickness of a fillet weld?
A) Vernier Caliper
B) Depth Gauge
C) Weld Gauge
D) Surface Plate
🟩 Correct Answer: C

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Q9. Which code deals with welding procedure and welder qualification in pressure vessel work?
A) ASME Section VIII
B) ASME Section V
C) ASME Section IX
D) ISO 9001
🟩 Correct Answer: C

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Q10. Post Weld Heat Treatment (PWHT) is usually done to:
A) Cool down the weld area
B) Increase fusion rate
C) Relieve residual stress and improve toughness
D) Make welding faster
🟩 Correct Answer: C