Greetings,
As per Sec. IX, you have to qualify the welders in accordance with QW-301 for joining the base material portion of the cladded pipe. And for welders who will apply the cladded portion of a weld between clad materials, shall be qualified in accordance with QW-381.
If the welder is qualified on P1 material, then the welder is qualified to weld only base material portion of the cladded pipe.
The welders can qualify as per QW-301 & QW-381 separately or alternatively the welders may qualify using cladded test coupon of at least 3/8in. (10mm) thick and of dimension such that a groove weld can be made to join the base material and the corrosion resistant weld metal overlay can be applied to the completed groove weld as per QW-383.
Regards,
Sajeev