What was found
ODOR OF WELDING RESIDUE RIGHT AFTER TAKEOFF. QUICKLY DISAPATED, BUT CAME BACK JUST BEFORE TOP OF DESCENT. CONTINUED THROUGHOUT DESENT, APPROACH, AND LANDING. COCKPIT ONLY, NO ODOR IN CABIN. OPENED THE NR 1 ENGINE FOR BOROSCOPE INSPECTION, NO RESTICTIVE DAMAGE FOUND IAW AMM 72-00-00/601. RESIDUE NOTED DURING BOROSCOPE. INSTALLED ALL REMOVED PARTS IAW AMM 72-00. REPLACED THE LT RECIRCULATION FAN FILTER IAW AMM 21-25. PERFORMED HIGH POWER ENGINE RUNS WITH PACKS ON FULL COLD, FULL HOT, ANTI-ICE ON & OFF. NO ODORS DETECTED.