Tube is mainly divided into seamless tube and welded tube in manufacturing technology, the main difference is whether the tube wall has a welded seam.
Seamless tube is made using a round billet as raw material for piercing, the manufacturing process of seamless pipes includes hot rolling, cold rolling, cold drawing, extrusion and many other methods. There are no welded seams on the surface, resulting in high strength and pressure resistance, and excellent performance in high-pressure and high-temperature environments.
Welded tube is made of a plate or strip after being rolled and shaped by a series of rollers and molds, two edges are welded to connect longitudinally, and there is a welded seam on the inner wall of the tube.
Seamless VS welded tube in the manufacturing process.
Welded Tube Manufacturing Process
Welded tube is made from strip and coil that is passed through grooved rollers till the shape is formed and the free edges are properly shaped for welding, cold forming is performed step by step from flat strip into a round profile, and the edges are welded together as they approach the welding rolls.
The typical welding method for strip welded tubes is traditionally autogenous tungsten inert gas (TIG), TIG welding method has some advantages that can effectively protect weld seam.
DONGSHANG STAINLESS produces TIG welding stainless steel tubing for boiler, heat exchanger, condenser, with excellent performance in corrosive environments.
Depending on the outer dimension, wall thickness and final application, there are different ways of manufacturing welded tubes and pipes and different manufacturing methods, like laser welding, plasma welding, ERW, EFW, etc.
When large outside diameter or heavy wall or both welded tubes & pipes are produced, pipe is made from plate or sheet, the forming is done in a roller bending machine or a hydraulic press, then some steps are the same with strip welded tubes.
There are different welding methods and processes, for large diameter and heavy wall pipes, EFW, ERW and other welding methods can be adopted, for large-diameter pipes, double and spiral seams may needed.
- Coil
- Inspection and analysis
- Slitting
- Auto-welding
- Seam-grinding
- Solution treatment
- Cut to length
- Straightening
- Picking
- End-facing
- Eddy current test
- Hydrostatic test
- Final inspection
- Marking
- packing
Advantages of Welded Tube
- Lower cost compared to the equivalent seamless alternative.
- Short lead time.
- Better surface finishing of outside and inside, the internal material surface for welded tubes can be checked before manufacture.
- Thinner wall thickness, and more uniform.
- Tighter tolerance.
Seamless Tube Manufacturing Process
Seamless tubes are generally made in complex steps starting with the drilled hollows from billets, then rolling and drawing the material to the desired sizes, cold pilgering is the preferred production process since this technique provides a high forming rate, narrow tolerances and good productivity yields, but cold drawing gives narrower tolerance ranges and better surface quality. Seamless tube dimension is difficult to control compared to the welded tube in outside diameter and wall thickness.
- Round bar
- Inspection and analysis
- Cut to length
- Centering
- Peel
- Heating
- Perforation
- Inspection of size
- Pickspanng
- Inspection of surface
- Lubricating
- Cold drawing / cold rolspanng
- Degreasing
- Anneaspanng
- Straightening
- Cut
- Picking
- Final inspection
- Marking
Advantages of Seamless Tube
- Heavy and thick wall thickness.
- No weld seam. generally be considered as having better properties and corrosion resistance
- Better ovality or roundness
Seamless VS Welded Tube, What is the Difference?
| The Difference | Seamless Tube | Welded Tube |
|---|---|---|
| Manufacturing Process | Drawn from a solid billet | Welding from strip, plate or sheet |
| Surface | No seam | Better surface, a welding seam on the surface |
| Cost | High cost and more expensive | Low cost and cheaper |
| Size | Can be a heavy wall | More shapes, uniform thickness |
| Lead times | More time due to complex processes, especially for small tubes | Fast relatively |
| Strength | Stronger and more durable | Weeker |
| Corrosion resistance | Better | Not good as seamless tube |
| Applications | High-pressure and high-temperature | Structural and mechanical purpose |
Choosing Welded or Seamless Tube?
Despite many advantages of welded tubes, seamless tube is still treated better than welded type, especially used in rough environments, considered as higher strength, higher pressure, and better corrosion resistance.
Seamless and welded are mainly two tube types in the production process, there is a debate about whether seamless is better than welded for a long time.
Although with improved metallurgy and welding processes in welded tubes, the arguments typically focus on structural integrity and corrosion resistance in weld areas.
In reality, seamless & welded manufacturing processes both can provide tubes & pipes with quality, reliability and excellent corrosion resistance, which generally complement each other.
Depending on the specific application and cost aspect, decide which type is a better choice to use. Tubes and pipes can be produced in both seamless and welded types depending on application requirements, with Austenitic stainless steels, duplex and special grades.