Differences between welded molybdenum tubes and seamless pipes
Not every situation requires seamless pipes, which is also why both types of pipes coexist:
1. For large-diameter or large-size molybdenum pipes, seamless processing is extremely difficult and costly, making welded pipes more cost-effective;
2. If used only for insulation covers, support sleeves, or low-temperature normal-pressure structural parts, with no airtight, high-pressure, or strong thermal cycling requirements, welded pipes are perfectly sufficient;
3. Seamless pipes have complex processing and low material yield, so their price is much higher than welded pipes.
4.welded pipes are formed by welding sheets together, with straight weld seams, have lower costs, and are suitable for medium and low pressure / non-critical high-temperature scenarios.
The main differences between molybdenum seamless pipes and welded pipes lie in the presence or absence of welds, forming processes, mechanical uniformity and applicable working conditions . seamless pipes are formed as a single piece without welds, resistant to high temperatures and pressures / vacuum / alternating loads, and are expensive;
Comparison of Molybdenum Seamless Pipes and Welded Pipes
| / | Molybdenum seamless pipe | Molybdenum Welded pipe |
| Weld seam | No welds,The structure is continuous throughout | There are straight weld seams,and the weld area is a weak zone |
| Density | ≥ 10.1 g/cm³ (close to the theoretical value) | Slightly low |
| Pressure-bearing capacity | High (suitable for high pressure / high vacuum) | Medium-low, weld seams are prone to stress concentration |
| Temperature resistance | Excellent resistance to high temperatures / thermal cycling (stable at 1200–1800℃) | Generally, welds are prone to deterioration at high temperatures. |
| Mechanical uniformity | isotropic, without weak points | The strength/hardness of the weld zone is slightly lower. |
| Size range | Mainly small and medium-sized diameters (Φ6 – 50 mm) | capable of large diameters / ultra-thin walls (Φ20 – 200 mm) |
| Purchase Cost | high (due to complex process and low yield rate) | Low (with high efficiency and low cost, approximately 30–50%) |
1
Quality Control Key Points
Seamless Pipe: No cracks / sand holes / voids; Microstructure uniform with fine grains; No leakage in water pressure / air tightness tests; Strict dimensional tolerance.
• Welded Pipe: 100% ultrasonic/ radiographic testing of welds; No pores / incomplete welding; Weld seam flush with base material; Anti-oxidation treatment.
In these scenarios, weld seams are unacceptable
1
High vacuum conditions (the most common)
Vacuum equipment requires zero leakage. The micro gaps and weld micro-pores of welded tubes will continuously leak gas, damaging the vacuum level and preventing the equipment from operating normally; seamless tubes are integrated as a whole and have excellent air tightness, which is the standard for vacuum systems.
2
High temperature + thermal cycling conditions
Furnace tubes, temperature measurement tubes, and protective tubes are repeatedly heated and cooled in the range of 1000-2000℃, generating cyclic stress.
3
High pressure / gas flow erosion conditions
For molybdenum tubes used for transporting process gases and protective gases, there is internal pressure and gas flow erosion. Weld seams have poor pressure resistance and erosion resistance, and are prone to damage and gas leakage; seamless tubes have strong overall pressure-bearing capacity.
4
High purity environment requirements
In the semiconductor and precision sintering industries, it is not allowed for tube materials to release impurities. Welding residues and loose weld structures will release trace substances, contaminating the workpiece; seamless tubes have uniform material and dense structure, meeting the requirements of high-purity production.
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