How to Determine if a Pressure Vessel Has Cracks?

I. Visual Inspection – Initial Detection of Crack Signs
Before professional testing, a preliminary inspection can be conducted using the naked eye or simple tools. This is suitable for identifying obvious surface cracks.

1. Visual Inspection: Observe the vessel surface with the naked eye or a 5-10x magnifying glass, focusing on stress concentration areas such as welds, heat-affected zones, nozzles, and end cap transition areas.

Cracks often appear as thin, linear marks and may be accompanied by rust, leakage marks, or localized discoloration.

2. Lighting and Hammering Assistance: Illuminate the vessel with a strong light when lighting is insufficient to enhance the contrast of crack shadows; gently tap the vessel surface. A dull or abnormal sound may indicate internal delamination or cracks.

✅ Applicable Scenarios: Routine inspections, shutdown inspections, or as a preliminary assessment before non-destructive testing.

II. Non-Destructive Testing – Precise Confirmation of Crack Presence and Characteristics
When suspicious areas are found during visual inspection, or when periodic testing is required according to regulations, non-destructive testing techniques must be used for precise determination.

1. Magnetic Particle Inspection (MT) – Suitable for surface/near-surface cracks in ferromagnetic materials.

Principle: Local magnetization of the container generates a leakage magnetic field at the crack, attracting magnetic powder and forming a visible accumulation.

Advantages: High sensitivity, can detect micron-sized cracks, relatively simple operation.

Limitations: Only applicable to ferromagnetic materials (such as carbon steel and low-alloy steel), cannot detect deep internal defects.

2. Penetrant Testing (PT) – Suitable for surface-open cracks in non-porous materials.

Principle: Utilizes capillary action to allow penetrant to enter the crack; after cleaning, a developer is applied to reveal the defect.

Advantages: Applicable to various metallic and non-metallic materials, highly adaptable to complex-shaped workpieces.

Limitations: Cannot detect closed cracks or internal defects; penetrant may be toxic, requiring precautions.

3. Ultrasonic Testing (UT) – Suitable for internally buried cracks and depth measurement.

Principle: High-frequency sound waves propagate through the material and are reflected when encountering interfaces such as cracks; the location and size of the defect are determined by the echo signal.

Advantages: Strong penetration ability, can measure crack depth, suitable for thick-walled containers.

Limitations: Requires high surface coupling, needs to be ground smooth, and results are greatly affected by operator experience.

4. Radiographic Testing (RT) – Suitable for intuitive imaging of internal weld cracks

Principle: X-rays or gamma rays penetrate the container; the absorption rate varies in the crack area, forming an image on film.

Advantages: Intuitive results, can be permanently stored, suitable for weld quality assessment.

Limitations: Expensive equipment, high radiation safety requirements, lower detection rate for fine cracks than UT.

5. Other Auxiliary Methods

Eddy Current Testing (ET): Suitable for surface cracks in conductive materials, often used for rapid in-service screening.

Acoustic Emission Testing (AT): Monitors elastic waves generated by crack propagation during pressure testing of containers, suitable for dynamic monitoring.

Circumferential Guide Wave Testing: Used for far-field localization of cracks in long-distance pipelines, improving detection efficiency.

III. Key Inspection Areas – Enhancing Targeted Inspection The following areas are high-risk for cracking and should be the focus of inspection:

Welds and heat-affected zones (especially areas requiring multiple repairs)

Around nozzles and openings

Transition zone between end caps and shell

Stress concentration areas such as supports and flanges

Areas subject to long-term contact with corrosive media or thermal cycling IV. Assessing Potential Risks Based on Operating Status
Even if cracks are not directly detected, the following operational anomalies may indicate the presence of latent cracks:

Frequent safety valve tripping or abnormal pressure fluctuations

Periodic leakage at flanges or welds

Abnormal localized temperature rise in the container (can be detected using an infrared thermal imager)

Increased vibration or unusual noises