ASME B31.3: Inspection, Examination & Testing

ASME B31.3: The Lifecycle of Quality

Inspection, Examination & Testing (Chapter VI)

Who is Responsible for Quality?

ASME B31.3 defines two distinct but parallel quality functions. "Inspection" is the verification work performed by the Owner, while "Examination" is the quality control work performed by the fabricator or erector.

Owner's Responsibility

Verifies Code compliance through...

Owner's Inspector

(Performs Inspection)

↓

→

Fabricator/Erector's Responsibility

Applies quality control procedures...

Examiner (e.g., NDE Tech)

(Performs Examination)

The Foundation: Visual Examination (VT)

Before any other NDE or testing, all fabrication and erection must be visually examined. This is the most fundamental check for quality and conformance to the design.

100%

Visual Examination Required

Visual Examination forms the baseline for 100% of the work, supplemented by other NDE methods as required by the fluid service.

How Much to Examine? NDE Extent

The required percentage of Nondestructive Examination (specifically RT or UT) for welds is not one-size-fits-all. It depends directly on the system's "Fluid Service" classification, which is based on risk.

This chart shows the minimum required percentage of circumferential butt welds that must be examined by RT or UT for different service categories. Category D often allows an Initial Service Leak Test in lieu of % NDE.

Looking Deeper: NDE Methods

When VT isn't enough, NDE methods are used to find defects below the surface or too small to see. They are broadly categorized by whether they find surface or volumetric (internal) flaws.

Radiography (RT)

Volumetric

Uses X-rays or gamma rays to create an image of the weld's internal structure. Good for finding porosity and inclusions.

Ultrasonic (UT)

Volumetric

Uses high-frequency sound waves to detect internal flaws. Very effective for finding cracks and lack of fusion.

Magnetic Particle (MT)

Surface

Finds surface and near-surface defects in ferromagnetic materials by applying magnetic particles and a magnetic field.

Liquid Penetrant (PT)

Surface

Uses a liquid dye to bleed out of surface-breaking defects, making them visible. Works on non-porous materials.

Progressive Examination

What happens when a defect is found in the 5% random check for Normal Service? The Code requires "progressive" examination to ensure it wasn't a single bad weld.

Start: Test 1 Spot (from 5% batch)

Defect Found?

YES

Test 2 Additional Spots (from same lot)

Defects Found?

Test 100% of Lot

Batch Cleared

Key Acceptance Criteria (VT)

A summary of the most critical acceptance criteria for Visual Examination (per Table 341.3.2A). Finding any of these requires repair.

❌
Cracks: Not permitted (Zero tolerance).
❌
Lack of Fusion: Not permitted.
❌
Incomplete Penetration: Not permitted (for most welds).
⚠️
Undercutting: Permitted only if depth is ≤ 0.8 mm (1/32 in).
⚠️
Weld Reinforcement: Must be within specified height limits.

The Final Proof: Leak Testing

After all examination and inspection, the entire piping system must undergo a final leak test to prove its integrity under pressure. The Hydrostatic test is the most common method.

The chart compares the required test pressures relative to the system's Design Pressure (DP). A Hydrostatic test is performed at 1.5x DP, while a Pneumatic (air/gas) test is lower at 1.1x DP due to the higher stored energy and risk.

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