Investigation of Surface Defects in the Through-process manufacture related to Galvanized Products

Posted on 04 April 2012

The presentation cover the topic of pipe manufacturing process :

  • Pipe forming :    From coil : Cage forming, CBR forming and Spiral forming

From Plate : UO forming, 3Roll Bending, Press Bending (JCO)

2. Seam welding:   Electric Resistance Welding (ERW) and Submerged Arc Welding (SAW)

3.Girth welding:    Onshore and Offshore welding

Explanation of some metallurgy aspect in pipe production :

  • Change in steel properties i.e, the steel material  will experience a change in its strength, toughness (DWTT) property and its resistance to Hydrogen Induced Cracking After forming process in pipe production
  • In ERW process, copper contamination cracking occur along and near the weld bond line and the source of the copper is from contact tip.
  • In SAW process, the joint properties is very influenced by the groove shape, spring back phenomenon, scattering of properties in base metal and T-joint in pipe.
  • Key factors of corrosion resistance (HIC/SSCC) in welded joint are ratio of thickness to diameter, microstructural effect, hardness distribution in welded joint, effect of residual stress during forming and inclusions in steel.

Introducing some product improvement in POSCO including production of  X80 pipe steel & X120 pipe steel for arctic application ,X52/X65 sour service and K55 OCTG

Source: Cheng Ming Chih , China Steel Corporation, Taiwan

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