Ultrasonic testing (UT) of molybdenum crucibles is an efficient and non-destructive testing method. It is mainly used to find defects such as cracks, inclusions, pores, delamination and loose structure inside the crucible. It is especially suitable for molybdenum, a metal with high density, difficult to process and used in high temperature environments.
- Why do molybdenum crucibles need ultrasonic testing?
Molybdenum crucibles are generally used in high-temperature smelting, single crystal furnaces, rare metal refining and other working conditions. If there are defects inside, it is easy to:
Explosion, leakage, and breakage occur;
Leading to furnace contamination and test failure;
Shorten life or cause safety accidents.
Therefore, ultrasonic flaw detection is an important means to detect its quality stability and safety reliability.
- Applicable ultrasonic flaw detection methods
| method | illustrate | Applicable types |
| Longitudinal wave flaw detection (L wave) | Ultrasonic wave is incident vertically to detect internal defect reflections | Suitable for cylindrical/thick-walled crucibles |
| Shear wave flaw detection (S wave) | Ultrasonic wave is incident obliquely, suitable for surface or near-surface defects | Thinner wall structures and welding parts |
| Immersion testing | Put the crucible into the water tank, the coupling is uniform and the signal is stable | Small size and high precision detection |
| Phased Array Ultrasound ( PAUT ) | Multi-beam scanning can achieve two-dimensional imaging | For advanced products or sophisticated evaluation |
- Testing process steps
Surface preparation:
Remove surface oil, scale and residue;
Polish or sand uneven areas;
Ensure good acoustic wave coupling.
Select couplant:
Generally, a special coupling agent, engine oil or glycerin aqueous solution is used;
Ensure the transmission of acoustic energy between the probe and the workpiece.
Device parameter settings:
Probe frequency: 2.5~10 MHz (commonly used is 5 MHz);
Probe type: straight probe (longitudinal wave) or oblique probe (transverse wave);
Gain, scanning speed, etc. are adjusted according to the crucible thickness and diameter.
Scanning method:
Longitudinal wave: scans vertically across the wall thickness from the bottom or top;
Shear wave: Scan obliquely from the outer side wall or weld;
Move in spiral or linearly point by point;
For larger crucibles, a robotic arm or automated equipment can be used.
Signal analysis and judgment:
Defect reflection signal position, amplitude, phase change, etc.
Combined with **DAC (distance-amplitude compensation curve) or TCG (time-base gain curve) ** for quantitative analysis;
Determine whether the defect level allowed by the customer/standard is exceeded.
- Common defect types and signal manifestations
| Defect Type | Back to the port characteristics | Possible sources |
| crack | Clear peak echo, narrow waveform | Cold working or welding residual stress |
| Pores | Weak and diffuse echo | Gas does not escape during smelting |
| Layering | Double or multi-peak reflection | Insufficient forging or cold welding |
| Inclusions | Irregular strong reflection | Impurity elements are not removed |
| Loose area | Scattered band, chaotic signal | The metallurgical structure is not dense |
- Related Standards Reference
GB/T 12604.1-2020 Nondestructive Testing Terminology Part 1: Ultrasonic Testing
《GB/T 11345-2023 Manual ultrasonic testing of metal welds》
《ASTM E114-20 : Standard Ultrasonic Terminology》
Internal enterprise standards or customer technical agreements
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