Chapter 15: Welding Inspection & Non-Destructive Testing (NDT)
Essential for Mechanical QA/QC Engineers, Fabrication Inspectors, Site Engineers
🔧 1. Importance of Welding Inspection
Welding is a critical joint process in mechanical structures, pipelines, pressure vessels, etc.
Improper welding can cause:
Cracks, porosity, weak joints
Catastrophic failuresRework and financial loss
🔍 Inspection ensures:
Structural integrity
Safety compliance (ASME, API, AWS codes)
Code conformance
Better lifecycle performance
🔩 2. Key Welding Inspection Stages
Stage | Checks Involved |
---|---|
Pre-weld Inspection | Material type, electrode type, WPS review |
In-process | Arc length, temperature, technique, cleaning |
Post-weld | Dimensions, defects, NDT testing, reports |
📜 3. Welding Procedure Specification (WPS)
WPS is a written, qualified document that provides:
Welding parameters (current, voltage, technique)
Material & filler metalPosition, preheat/postheat temp
Backing, joint design, etc.
📌 PQR (Procedure Qualification Record): Actual test record proving WPS meets code.
📐 4. Visual Inspection (VT)
First line of defense in weld QA.
Checks:
Cracks, undercut, overlap, porosity
Weld bead size, throat thicknessSpatter, arc strike, root fusion
🛠 Tools: Weld gauges, magnifying glass, mirror, flashlight
🧪 5. Non-Destructive Testing (NDT) Techniques
NDT Method | Description | Application |
---|---|---|
RT (Radiography) | X-ray or gamma rays detect internal defects | Critical pressure vessels, pipelines |
UT (Ultrasonic Testing) | Sound waves detect internal flaws | Thick welds, castings |
MT (Magnetic Particle) | Magnetic field highlights surface/subsurface cracks | Ferrous materials |
PT (Penetrant Testing) | Dye penetrant shows surface-breaking defects | All metals (except porous) |
ET (Eddy Current) | Electromagnetic testing for surface/near-surface flaws | Aerospace, thin welds |
🏗️ 6. Real-World Application Example
Project: Boiler drum in a thermal plant
Welded by semi-automatic process
RT revealed slag inclusionSection failed hydrotest
Cost of failure: ₹20 lakh (including delay and repair)
🔧 Lesson: Early UT & RT could have avoided total rework.
📋 7. Welding Defects & Causes
Defect | Cause |
---|---|
Porosity | Gas entrapment, wet electrodes |
Undercut | High heat, poor technique |
Incomplete Penetration | Low current, poor joint prep |
Slag Inclusion | Inadequate cleaning, wrong angle |
🔒 8. Safety in NDT
RT: Radiation safety, PPE, warning signs
PT/MT: Handle chemicals with gloves, use ventilationUT: Wear ear protection in high-decibel environments
🧰 9. Field Application Tips
Always verify WPS and welder qualification (as per ASME Sec IX)
Ensure surface cleaning before PT/MTUse calibrated UT/RT machines
Maintain NDT logs and weld maps
Cross-check repairs before final clearance
🧪 Welding/NDT Reports Must Include:
Welder ID & WPS used
Joint numberType of test (UT, RT, etc.)
Results and acceptance status
Inspector signature and date
Quiz: Welding Inspection & NDT
Q1. What is the primary purpose of Non-Destructive Testing (NDT)?
A) To destroy the weld sample
B) To clean the surface of metal
C) To inspect for defects without damaging the component
D) To improve welding speed
🟩 Correct Answer: C
Q2. Which NDT method uses X-rays or gamma rays?
A) Ultrasonic Testing
B) Magnetic Particle Testing
C) Radiographic Testing
D) Penetrant Testing
🟩 Correct Answer: C
Q3. What does a WPS (Welding Procedure Specification) provide?
A) Storage location of welding rods
B) Salary structure of welders
C) Approved parameters and process for welding
D) Testing method for final product only
🟩 Correct Answer: C
Q4. Which of the following is not a surface defect?
A) Porosity
B) Undercut
C) Slag inclusion
D) Arc strike
🟩 Correct Answer: C
Q5. Which NDT method is suitable for detecting sub-surface cracks in ferrous materials only?
A) Penetrant Testing
B) Eddy Current Testing
C) Magnetic Particle Testing
D) Ultrasonic Testing
🟩 Correct Answer: C
Q6. A common reason for porosity in a weld is:
A) Low voltage
B) Wet electrode or contamination
C) Overlapping
D) Incorrect NDT method
🟩 Correct Answer: B
Q7. What kind of information does a Radiographic Test Report contain?
A) Welder’s height
B) X-ray images and defect analysis
C) Electrical power used
D) Paint color used
🟩 Correct Answer: B
Q8. What does “PQR” stand for in welding QA?
A) Product Quality Ratio
B) Procedure Qualification Record
C) Professional Quality Report
D) Primary Quality Rank
🟩 Correct Answer: B
Q9. Which method is best for detecting internal flaws in thick welds?
A) Magnetic Particle Test
B) Visual Inspection
C) Ultrasonic Testing
D) Penetrant Testing
🟩 Correct Answer: C
Q10. What is the first step in visual weld inspection?
A) Apply dye penetrant
B) Check calibration
C) Surface cleaning and lighting
D) Turn off welding machine
🟩 Correct Answer: C