Pipeline Submerged Arc Welding Closeup
Submerged Arc Welding is a type of an arc welding process in which arc gets submerged by thick granular flux in order to facilitate and protect the welding process. Like MIG welding a continuous metal wire is fed and arc is generated between the wire and work piece. The only difference is that the arc and weld zone are protected under the consistent supply of flux without using additional gas shielding. It is widely used in large diameter pipe welding where the work piece is rotated under the fixed gun and welding is carried out in flat position. SAW is commonly used to weld stainless steels, duplex stainless steels, carbon steels, carbon-manganese steels in pressure vessel and structural fabrication.
How SAW works?
Submerged Arc welding is an automatic process usually carried out under the supervision of operator. The filler metal is fed consistently in the form of wire which creates an arc with the work metal, under the blanket of flux. Both filler wire and flux are fed at constant supply rate to avoid any defect to happen in the weld metal. After weld metal deposition, a removable fused slag is produced over the beads that during solidification controls the cooling rate along with providing the sound protection. Also the unconsumed flux is recycled which can be reused for another weld run.
Usefulness of SAW
High Production rate.
Comparatively fast process.
Fine welds are produced with good mechanical and corrosion properties.
Good welding properties, deep penetration and complete fusion of weld.
Less loss of energy.
Since the arc is covered, the expected weld is spatter free.
Production of thick welds in a single run.
Equipment
It consists of a welding head through which filler wire is allowed to move into the weld pool with the help of driving rollers. A hopper is attached with the head that assists in supplying and recycling of flux throughout the operation. Power supply (both AC and DC) are connected with the process control and work piece.
Functions of Flux in SAW
The primary reasons for using flux in submerged arc welding process are;
To produce gases for shielding.
Slag formation in order to protect weld and facilitate solidification.
Alloy addition to the weld metal.
Stabilization of while using high amperages.
De-oxidation to avoid porosity and cavities.
Composition of Flux
The flux consists of minerals like calcium fluoride, lime and oxides of silicon, magnesium, aluminum, manganese etc. and is prepared to perform desirable functions during welding. The composition of flux along with filler wire plays a vital role, to give required chemical composition and mechanical properties in the weld metal.
Preparation of Flux
Normally there are two types of flux which are being utilized in SAW process.
Fused – prepared by melting the constituents in furnace, followed by cooling.
Bonded – prepared by bonding the dry constituents with low melting binding materials.
Last Comments
Besides many useful features, there are some limitations that restrict submerged arc welding in different applications. Due to its way of working, it is limited to only few welding positions. It cannot be used to weld a wide variety of materials. SAW is only limited to long run welding and requires high level of operational skills and management. Use of flux can be a serious concern of occupational health and safety.
