There are mainly two reasons to add filler metal at pipe manufacturing,

• To fill up the gap at welding of thick wall pipe from sheet
• To improve the corrosion resistance of the weld by adding overalloyed filler metal

European tube and pipe standards leave the decision to use filler metal to the manufacturer, while it is specified in the ASTM standards.

ASTM A312 and ASTM A790 do not allow filler metal, while it is a must when ASTM A358 and A928 is specified.