What is weld types in construction?

A complete joint penetration (CJP) weld fuses the full thickness of the joined material and develops the full strength of the connected part, which is why moment connection flange welds are usually CJP. A partial joint penetration (PJP) weld only fuses to a specified depth, takes less weld metal and labor, and is used where full strength is not required. The cost difference is bigger than the weld metal alone: CJP welds typically require ultrasonic (UT) inspection, which adds a testing line to the estimate that PJP and fillet welds usually avoid.

Fillet weld cross section, and therefore weld metal volume and arc time, grows roughly with the square of the leg size, so a 3/8 in fillet carries about 2.25 times the metal of a 1/4 in fillet, not 1.5 times. There is also a pass break: many shops run 5/16 in as the largest single-pass fillet, so stepping up to 3/8 in often means multiple passes with cleaning between them, which moves labor more than the volume ratio suggests.

Usually not. Most fabricators carry routine shop welding inside their per-ton fabrication labor rate, built from historical job costs, and only break welds out when a job is connection-heavy or unusual. Field welds are the exception: they are almost always taken off explicitly by size and length from the erection drawings and connection details, because field welding labor, access, and inspection are what blow up a steel erection budget.