Pipe Welding Build up using SMAW

In welding, Build Up is kind of repair weld which is used to minimize the weld imperfections. The technique involves the excavation of previous (defected) weld by grinding or gouging, followed by depositing a new weld. Here we will discuss on How to reduce the lack of penetration in Pipe weldment using a Buid Up process. Lack of Penetration (LOP) is one of the common weld imperfections (seen in industries) and its major causes are;

  • Smaller Root opening
  • Lower Heat Input
  • Larger Root face
  • Irrelevant Electrode Size

In order to reduce the level of lack of penetration, a welder must use suitable welding supplies according to concerning joint configuration. One bigger reason for weld lack of penetration is lower heat applied. The welding associates must use pre-heated welding rods and ensure the good heat settings by giving adequate current and voltage. Also see How to minimize lack of fusion in weldment?
Below video is about pipe welding build up, to repair lack of penetration. The welder made a repair weld using Shield Metal Arc process.  

Some Basics of Stick Welding Process
As we know Shield Metal Arc (SMAW) process is type of arc welding which melts and joins the work piece by the creation of high temperature arc. The groove between the work pieces is filled by addition of flux coated welding electrodes. Flux helps to maintain arc and provides a protective covering of shield gases on weld. The core of a flux coated electrode, is the metal of similar type and composition of work piece to be joined. The core metal is melted in the heat of arc and is transferred to molten weld pool, passing through an ionized arc pathway. During solidification of molten weld metal, a protective coating of fused slag (from flux), is produced that assists the solidification mode and also prevents any contamination that may lead to catastrophic porosity and cavities.

Heat Settings in Stick Welding
The provision of constant current by electric power supply, assists to build an arc between filler electrode and work piece. Both direct and alternating current modes can be executed according to electrode and procedure type, but normally quality welding results are achieved by DC current modes. Welding current is a primary concern in arc process and normally refer to as amperages. Amperages required in stick welding, is a function of electrode size, material thickness and even the position of welding. So the upper and lower ends of current are selected, primarily according to the above mentioned parameters.

Also in groove welding, distortion is one major problem, to make your weld defective. It results from the expansion and shrinkage of weld plus base metal during heating and cooling cycles of welding. Actually this process of distortion is associated with the change of mechanical and physical properties of metal, primarily on applying heat. The change of these properties has bad influence on circulation of heat throughout the metal resulting in distortion. There are many ways to minimize weld distortion by;

  • Selection of suitable heat parameters
  • Use of clamps to the joint
  • Tack welds before welding
  • Some post welding techniques 
  • Distortion minimization techniques using pressure jacks etc. 

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