Why Ultrasonic Testing is Mandatory for Repairing Turbine Thrust Bearings

【Core Problem】Why Can't Dye Penetrant Testing Be Used?

Many experienced technicians prefer the dye penetrant method (PT) for checking cracks due to its simplicity and visual clarity. However, for repaired bearing pads, penetrant testing has three major "fatal flaws":

1. Only Detects Surface Issues, Misses Deep-Seated Debonding

• The principle of dye penetrant testing is to allow a liquid penetrant to seep into surface-breaking discontinuities.
• It can only find cracks open to the surface, but is completely ineffective against internal defects like separation, debonding, or weak bonds between the babbitt metal and the steel backing.
• These internal defects are precisely the "number one killers" of bearing pad failure.

2. Penetrant Residue Can Destroy the Oil Film

• Bearing pads rely on a lubricating oil film for load support during operation.
• If penetrants are used, even if thoroughly cleaned, trace residues may mix with the lubricating oil, disrupting the oil film continuity, causing localized dry friction, and ironically leading to new wear.

3. Repaired Surface Does Not Allow Secondary Contamination

• The repaired bearing surface has high precision and no allowance for further machining. Any chemical attack or wiping from chemical reagents could compromise the surface quality.
• Penetrant testing requires cleaning and developing, an uncontrollable process that carries risk.

✅ Why is Ultrasonic Testing the Only Choice?

Ultrasonic Testing (UT) has become the "gold standard" for inspecting repaired bearing pads because it perfectly matches the unique requirements of these components:

Detects Internal Defects

• Ultrasonic waves can penetrate the babbitt layer and reach the steel-babbitt interface.
• Through the echo signals, internal defects such as debonding, porosity, and inclusions can be clearly identified, with an accuracy up to 0.1mm.

Non-Destructive and Non-Contaminating

• The testing process only uses a couplant (such as glycerin or a specialized couplant), which will not corrode or contaminate the bearing surface.
• It is easy to clean after testing and does not affect subsequent lubrication performance.

Suitable for "Zero-Allowance" Repairs

• Since no further machining occurs after the repair, the inspection must be accurate the first time.
• Ultrasonic testing provides quantifiable data on depth, position, and area, offering a reliable basis for determining fitness for service.

【Recommended Product】—Full-Process Control from Repair to Inspection

The steam turbine thrust bearing pads manufactured by our company not only utilize high-purity tin-based babbitt metal and optimized casting processes to ensure original bond strength, but, more importantly:

• Designed for Inspectability: The pad structure facilitates ultrasonic probe scanning; the interface between the steel backing and babbitt is flat, providing clear echo signals.
• Provides Integrated Repair and Inspection Solution: For old pads requiring on-site repair, we provide dedicated ultrasonic testing procedures and probe selection recommendations to ensure accurate and reliable inspection results.

Multiple power plants collaborating with us have reported: high pass rates after ultrasonic inspection of repaired pads, stable bearing temperatures during operation, and no debonding incidents.