Supplementary symbols - Welding Symbols on Drawings - page 21

Melt through
The melt through symbol is used when complete penetration
is required in welds made from one side, the symbol being placed
on the side of the reference line opposite to the main welding
symbol. Figure 8.10 shows a single-V groove weld made from one
side with complete joint penetration.
8.10 Melt through (ISO).
The ISO standard requires that all butt welds shall have complete
penetration unless there are any contrary indications.
In the AWS standard the melt through symbol is used when com-
plete joint penetration is required plus so-called visible root rein-
forcement. The height of the root reinforcement may be specified by
placing the required dimension to the left of the melt through
symbol. Therefore, it is possible to specify the size of the penetra-
tion bead, for example 1/16 in or 1/8 in.
The reason for this is difficult to fathom because complete pene-
tration is always visible and cannot be improved on by specifying
its size. It would be unfortunate if a product was rejected because,
on inspection, penetration was found to be 1/16 in when 1/8 in was
specified. Remedial action would be expensive and unnecessary.
If the size of a penetration bead were to be restricted to a certain
dimension for clearance purposes this would be an important
requirement for which instructions should be given in notes on the
drawing.
Consumable insert
Consumable inserts are specified in the AWS system by placing the
symbol on the side of the reference line opposite the groove
weld symbol, as illustrated in Fig. 8.11 . The type of insert is written
in the tail of the reference symbol or on a note on the drawing.
CLASS 1 INSERT
8.11 Consumable insert (AWS).