Technician reported a B737-700 aircraft arriving at the station did not have a clamp installed on the APU bleed air duct in the keel beam area. The aircraft was removed from service to effect repairs. The Technician stated this is a common occurrence.

Narrative

Aircraft X arrived with APU duct pressure seal clamp not installed at aft bulkhead in wheel well keel beam. Aircraft goes out of service for a minimum of 4 hours anytime this clamp comes off. For more detailed info about this duct design see previous Report A and Report B.After further investigation it appears in most cases the clamp is being pushed off because of the bad design of the older style duct. [We] need to change out the older (bad design) duct. As long as the older duct is installed we will continue to have this issue. When the clamp is not installed; or missing or comes off; it can lead to pressurization; air conditioning; cab temp control and overheating issues. Overheat sensing element is located directly beside this pressure seal. How will the overheat sensor ever work if cold air from the cabin is constantly being blown onto the sensor. Just a thought. Fleetwide - inspect pressure seal clamp and verify duct part number installed. The bad duct manufacturing part needs [to be] removed from all aircraft and install good duct manufacturing part. Also making this clamp installation inspection buy back to prevent future occurrences. There have been too many occurrences of this clamp missing or not installed correctly causing aircraft to go out of service; flight delays; operational disruption and passenger inconvenience. What are our priorities?