Many forces acts on the weld puddle with different welding conditions.
Swirling motion of weld puddle can be more often seen precisely with autogenous arc welding process.
This swirling motion ensures proper fusion of edges of the weld joint.
This can be more observed in PAW and GTAW process.
Thickness range qualified for base metal & weld metal is given as per table QW-451.1, ASME Sec. IX
If I have to weld 130 mm thick plate with only SMAW process, then for PQR, you can use the following base metal thickness and weld metal for qualification.
Base metal thickness : above 38 mm thickness, qualifying range of BM is 5-200 mm. So you can take 40 mm thick plate.
Deposited Weld metal thickness : above 19 mm thickness of weld metal deposited, qualifying thickness is upto 200 mm. So you can weld upto 20 mm.
So, you can take base metal 40 mm thick and deposit weld metal upto 20 mm for PQR.
keep reading, happy welding