Summary: The Basics of Weld Validation

Welding is permanent—you can’t just unbolt, unclamp, or reglue something if the weld is bad. That’s why validating a weld is so important when it serves a functional purpose (not just aesthetics).

If your weld needs to be structurally sound, follow this simple process:

1. Use a Weld Process Specification (WPS). This document defines how the weld should be performed, including material type, thickness, heat input, and other parameters.
2. Perform a Weld Procedure Qualification Record (WPQR). This is your proof that the WPS works. It includes evidence like pull tests, bend tests, or non-destructive testing (NDT).
3. Qualify the Welder (WQR). The person welding must be tested to ensure they can execute the WPS correctly.
4. Inspect the Weld. Start with a heavy inspection process, especially in the first few batches. Over time, you can scale it back based on performance.

If welding isn’t a primary part of your business but you need to qualify a weld, this guide will break it down in a practical way.

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Step 1: Establish the Weld Process Specification (WPS)

A Weld Process Specification (WPS) is a document that defines the exact welding process needed to produce a good weld. This includes:

• Material type & thickness – Different metals require different welding settings and filler materials.
• Joint design – Whether it’s a butt joint, lap joint, or fillet weld.
• Welding process – Stick, MIG, TIG, or another method.
• Weld penetration – Whether full penetration is required for maximum strength.
• Heat & voltage settings – Overheating can weaken the metal, while too little heat can cause a weak weld.
• Preheat & post-weld treatment – Some metals require preheating, while others need stress relief after welding.
• Testing requirements – Specifies how the weld will be inspected and validated.

Where to Find Prewritten WPS Documents

If you’re lucky, an existing WPS might already fit your needs. Here’s where to find them:

• AWS (American Welding Society) Prequalified WPSs – AWS provides pre-approved WPSs for common materials and joint designs. These are widely accepted and can save time and effort. Available through AWS for a fee.
• ASME Boiler & Pressure Vessel Code (BPVC) Section IX – Contains standard WPS documents for industrial applications. Often required in regulated industries.
• Manufacturer WPSs – Some welding equipment manufacturers provide WPS templates for their machines and consumables.
• Industry-Specific Standards (e.g., API, ISO 15614, EN 287) – These may apply if you’re in an industry like pipeline welding, aerospace, or structural fabrication.
• Consulting with a Certified Welding Inspector (CWI) – If no prewritten WPS fits your exact needs, a CWI can help create one.

Cost Considerations

• Prequalified WPSs from AWS typically range from $50 to $200 per specification.
• Custom WPS development and testing can cost $1,000–$5,000 depending on complexity.
• If a regulatory body requires a specific WPS, expect additional certification costs.

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Step 2: Validate the Weld (WPQR – Weld Procedure Qualification Record)

Once you have a WPS, you need to prove that it works. This is where the Weld Procedure Qualification Record (WPQR) comes in. The WPQR is just a record of the evidence that the weld meets the required performance criteria.

Weld Testing Methods (What to Expect)

Validating a weld means testing it to ensure it meets structural, mechanical, and safety requirements. There are two main categories of tests:

Non-Destructive Testing (NDT) – Examines the weld without damaging it.

1. Visual Inspection – Checks for pinholes, cracks, spatter, and heat discoloration.
2. Dye Penetrant Testing (PT) – Uses a dye to reveal surface defects.
3. Magnetic Particle Testing (MT) – Uses a magnetic field to detect near-surface cracks.
4. Ultrasonic Testing (UT) – Uses sound waves to find hidden cracks inside the weld.
5. X-ray Radiographic Testing (RT) – Provides an internal view of the weld to detect voids, inclusions, and porosity.

Acceptance Criteria:

• No surface cracks or pinholes exceeding 1/32 inch (AWS D1.1).
• No internal cracks exceeding 10% of the weld thickness.
• Porosity should not exceed 0.5 inches per linear inch of weld.

Destructive Testing – Physically stresses or breaks the weld.

1. Bend Test – The weld is bent to check for cracking.
2. Pull Test (Tensile Test) – Measures the force needed to break the weld.
   • Safety Factor Rule of Thumb: Weld should hold at least 1.5x the expected load in real-world conditions.
3. Charpy Impact Test – Measures how much energy the weld can absorb before breaking.
4. Hardness Test – Determines if the weld is too brittle or too soft.

Acceptance Criteria for Destructive Testing:

• A properly welded joint should not break at the weld itself. If it does, the weld is the weakest point.
• Bend Test Standard: The weld must bend without cracks over 1/8 inch (AWS D1.1).

If the weld fails, adjust the WPS parameters (heat, filler material, technique) and retest.

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Step 3: Qualify the Welder (WQR – Welder Qualification Record)

Even with a perfect WPS, the welder must be able to execute it correctly.

How a Welder is Qualified

• They weld a test piece following the WPS.
• The weld is tested using NDT or destructive testing.
• If the weld meets standards, the welder receives a Welder Qualification Record (WQR).

Can a Welder and a WPS be Qualified Together?

Yes. If you’re setting up a new welding procedure, you can qualify both the WPS and the welder at the same time by running the same test weld.

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Step 4: Inspect the Weld

Best Practices for Weld Inspection

• For small batches (fewer than 10 welds): Inspect every weld.
• For production runs: Start with 100% inspection for the first 5-10 batches.
• If defect rate is under 1%: Switch to random sampling (1 out of 10 welds).
• If defect rate is above 1%: Continue 100% inspection until improvement.

Acceptance Rates for Common Defects:

• Porosity: No more than 5% of weld area.
• Undercut: Not exceeding 1/32 inch depth.
• Cracks:Not acceptable in structural welds.

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