Pipe Welding and Filler Metal Considerations

The pipeline industry and pipe metallurgy has evolved over time, giving rise to a great demand for welding processes and products. For this purpose, many multipurpose welding machines with multi process capabilities have been developed with inverter based engine drives. One of the key factors that welders need to determine in welding process pipe is which wires provide the best results for every weld pass. They also need to select the highest quality filler metal. Process piping has its unique requirements and challenges where welders need to comply with strict codes and take precautions to eliminate the risk of defects that could compromise weld integrity. Some welders have moved from gas tungsten arc welding to wire processes. Technologies such as pulsed gas metal arc welding (GMAW-P) have the capacity to increase production and produce the highest quality welds in process pipe applications. One of the major tasks of the welder is to choose the right filler metal.

Types of filler metals

Carbon steel in diameters from 4 to 36 inches is widely used in process piping applications. For the semiautomatic process, the most common diameter is 18 inches or smaller. The filler metal wire options in such applications are solid wire; metal cored wire; and gas shielded flux cored wire. Each type of wire has its unique features and benefits, which must be considered prior to selecting a filler metal for the job. Solid wire is one of the most popular choices since a greater amount of filler metals goes into the weld joint when compared with SMAW electrodes. On the other hand, to speed productivity on process pipe welding applications that use SMAW or GTAW, tubular gas shielded flux cored wire is an ideal alternative. They meet industry mechanical properties such as high strength and side-wall fusion to help reduce weld defects. Metal cored wires, like solid wires can be used with a modified short circuit GMAW process, and allows welders to standardize one wire and gas for the entire application. 

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The Basics of MIG and TIG Welding

MIG is one of the easiest welding processes to learn. However, there is more to MIG welding than running beads. MIG or metal inert gas welding is one of the oldest techniques where a spool of steel wire is fed through a liner and then out of a contact tip on the MIG gun which is either heated or electrically charged when the trigger is pulled and melts the wire for the weld puddle. This is accomplished through short circuit welding. In this technique, droplets of molten wire which heats when short circuited, flows to make a puddle as it touches the base metal.

Benefits of MIG welding

An inert gas like argon or helium that flows from the gun keeps the weld puddle protected from the atmosphere. Later on it was discovered that carbon dioxide also works well although it is not an inert gas, which is why it is also known as GMAW or gas metal arc welding. For the most part, MIG welding is an indoor process and is used in shops and factories. One of the major benefits of MIG is the potential for high productivity since there is no need to change rods or chip and brush welds frequently. It is also easy to learn and can weld stainless steel, mild steel and aluminum.

TIG welding

TIG or tungsten inert gas welding is a process that uses a non-consumable tungsten electrode to deliver current to the welding arc. The tungsten acts as a torch, generating heat, which melts the metal. A filler metal is usually used. A shielding gas such as argon protects the weld area from contamination. TIG welding is used to weld thin section of stainless steel and non-ferrous metals like magnesium and aluminum. TIG welding requires more skill and takes longer to master when compared with MIG welding.

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