WELDING SYMBOLS

TYPES OF WELDING SYMBOLS    

TYPES OF JOINTS

By mean so welding, it is possible to make continuous, load bearing joints between the members of a structure. A variety of joints is used in structural steel work and they can be classified into four basic configurations namely , Lap joint,Tee joint, Butt joint and Corner joint.

      For lap joints, the ends of two members are overlapped and for butt joints, the two members are placed end to end, The T joints form a Tee and in Corner joints, the ends ae joined like the letter L.
Most common joints are made up of fillet weld or the butt also called groove weld. Plug and slot welds are not generally used in structural steel work. Fillet welds are suitable for lab joints and Tee joints and groove welds for butt and corner joints.

Butt welds can be of complete penetration or incomplete penetration depending upon whether the penetration is complete through the thickness or partial. Generally a description of welded joints requires an indication of the type of both the joint and the weld.

   Though fillet welds are weaker than butt welds,about 80% of the connections are made with fillet welds. The reason for the wider use of  fillet welds in that in the case of fillet welds, when members are lapped over each other, large tolerances are allowed in erection. For butt welds, the members to be connected have to fit perfectly when they are lined up for welding. Further butt welding requires the shaping of the surfaces to be joined.
     To ensure full penetration and a sound weld , a backup plate is temporrily provided.

BUTT WELDS

     Full penetration butt welds are formed when the parts are connected together within the thickness of the parent metal. For thin parts , it is possible to achieve full penetration of the weld. For thicker parts, edge preparation may have to be done to achieve the welding.

• SQUARE
• SINGLE V
• DOUBLE V
• SINGLE U
• DOUBLE U 
• SINGLE J 
• DOUBLE J
• SINGLE BEVEL 
• DOUBLE BEVEL

     In order to qualify for a full penetration weld there are certain conditions to be satisfied while making the welds.
   
     Welds are also classified according to their position into flat, horizontal, vertical and overhead. Flat welds are the most economical to make while overhead welds are the most difficult and expensive.

  Butt welds have high strength , high resistance to impact and cyclic stress. They are most direct joints and introduce least eccentricity in the joint. But their major disadvantages are , high residual stresses , necessity of edge preparation and proper aligning of the members in the field.

WELDING SYMBOLS
     The information concerning type, size , position , welding process etc, of the welds in welded joins is conveyed by standard symbols in drawings. The symbols representation includes elementary symbols,along with.

• Supplementary symbol,
• A means of showing dimensions, 
• Some complementary indication 

Welding symbols,Elementary symbols represent the various categories of the weld and look similar to the shape of the weld to be made.Combination of elementary symbols may also be used, when required .