Seamless and welded are mainly two types stainless steel tube & stainless steel pipe, 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 area.
Seamless and welded tubes & pipes difference in the manufacturing process.
Welded Tube Manufacturing Process
Depending on the outer dimension, wall thickness and final application, there are different ways of manufacturing welded tubes and pipes and different manufacturing methods.
Strip welded tubes & pipes
Welded tube start from stainless steel 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.
After welding outside and inside grinding of the weld seam, solution annealing or stress relieving may be necessary by application requirements.
- 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
- Shipping
Today, most of the modern welding lines are equipped with inline induction annealing, then straitening and calibration to control dimensions of tube & pipe, cut to standard or special lengths, de-burred, NPD & DT testing and inspection should be carried out as standard or requirement.
Heavy wall tubes & pipes
When large outside diameter or heavy wall or both welded tubes & pipes are required, there is a different welding method and process, for large diameter and heavy wall pipes, EFW, ERW and other welding methods can be used.
Cold-finished welded & seamless large diameter heavy wall stainless steel pipe manufacturer in China, 304/304l, 316, 321, 347H stainless steel grades.
Starting from stainless steel plate or sheet, the forming is done in a roller bending machine or in a hydraulic press, then some steps are the same with strip welded tubes.
- Plate
- Inspection
- Plasma-cutting
- Edging
- Bending
- Seam cleaning
- Forming
- Auto- welding
- Degreasing
- Anneaspanng
- Roundness caspanbrating
- End-facing
- Eddy current test
- Hydrostatic test
- Final inspection
- Marking
- Packing
- Shipping
For testing and inspection, large diameter sizes, radiography test (RT) and hydrostatic test (HT) are often required.
For large-diameter welded pipes, the double welding method can be accepted.
Seamless Tube Manufacturing Process
Seamless tubes are generally made in complex steps starting with the drilled hollows from billets, by cold drawing and cold rolling manufacturing process with cold drawing & cold rolling machines.
To control outside diameter and wall thickness, seamless type dimension is difficult to control compared to welded tube, cold work improves the mechanical properties and tolerances.
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.
- 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/passivating
- Final inspection
- Marking
- Packing
- Shipping
Solution annealing should be made through an offline annealing furnace, then straightening and pickling, these are important steps in manufacturing seamless stainless steel pipe and tubes.
Advantages of welded tubes & pipes
- 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.
Advantages of seamless tubes & pipes
- Heavy and thick wall thickness.
- No weld seam. generally be considered as having better properties and corrosion resistance
- Seamless pipes have better ovality or roundness
How to choose tubes & pipes, welded or seamless?
Despite many advantages of welded tubes, seamless tube is still treated better than welded type, especially used in rough environment, considered as higher strength, higher pressure, and better corrosion resistance.
DONGSHANG can manufacture welded stainless steel tubes in a wide range of sizes, 304/304L and 316/316L stainless steel grades.
DONGSHANG can manufacture the seamless stainless steel tube in a wide range of sizes, 304/304L and 316/316L stainless steel grades.
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.