Seamless and welded are mainly two types stainless steel tube & stainless steel pipe, there is a debate 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.
Obviously, seamless and welded tubes & pipes difference is 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 method.
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, the edges are welded together as they approach the welding rolls.
Typical welding method for strip welded tubes is traditionally autogenous tungsten inert gas (TIG), TIG welding method have some advantages that can effectively protect weld seam.
TIG Welding Tubing
DONGSHANG STAINLESS produce TIG welding stainless steel tubing for boiler, heat exchanger, condenser, excellent performance in corrosive environment.
After welding outside and inside grinding of the weld seam, solution annealing or stress relieving may be necessary by application requirements.
Today, most of the modern welding lines are equipped with inline induction annealing, then straitening and calibration to control dimension of tube & pipe, cut to standard or special lengths, de-burred, NPD & DT testing and inspection should be carried out as standard or requirement.
When large outside diameter or heavy wall or both welded tubes & pipes 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.
Large Diameter Pipe
Colded 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 same with strip welded tubes.
For testing and inspection, large diameter sizes, radiography test (RT) and hydrostatic test (HT) are often required.
For large diameter welded pipes, double welding method can be accepted.
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.
Solution annealing should be made through offline annealing furnace, then straightening and pickling, these are important steps in manufacturing seamless stainless steel pipe and tubes.
Despite many advantages with 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.
Welded Tube
DONGSHANG has the capability to manufacture the welded stainless steel tube in wide range sizes, 304/304L and 316/316L stainless steel grades.
Seamless Tube
DONGSHANG has the capability to manufacture the seamless stainless steel tube in wide range sizes, 304/304L and 316/316L stainless steel grades.
In reality, seamless & welded manufacturing process both can provide tubes & pipes with quality, reliability and excellent corrosion resistance, generally complement each other.
Depending on specific application and cost aspect, decide which type is better choice to use.
Tubes and pipes can be produced in both seamless and welded types depending on application requirement, with Austenitic stainless steels, duplex and special grades.
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