Sentence:  A standard Flight Refuelling Ltd Mk 8 probe nozzle was attached to the probe structural tube and fuel <WSD>pipe</WSD>. The <WSD>pipe</WSD> was double-walled, and passed through into the fuselage aft of the flight deck; ... A non-return valve was fitted within the fuel <WSD>pipe</WSD> aft of the probe nozzle, thus preventing any leakage of fuel if the aircraft lost the probe nozzle inadvertently. 
Meaning of the word marked with <WSD> tags:  A rigid tube that transports water, steam(,) or other fluid, as used in plumbing and numerous other applications. (from 10th c.)