B737-700
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 275
Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Procedure; Human Factors; Aircraft
At push; jetway pulled; Ramp Agents informed us of a scratch on the outside of the #2 engine. First Officer looked out the window; but couldn't see anything. Ramp told us they'll have a Ramp Supervisor check it out. The Ramp Supervisor said we were good to go; and I suppose I fell into the 'We're good to go' trap; as I got the impression that this was a small scratch and that it was not unusual at all for him to do an inspection like this. I was also concerned with arriving at our destination on time to avoid the weather that was moving in. After arriving; both the First Officer and I decided to have a look at the scratch. We realized that the scratch was quite long and stretched about two feet along the outer lip of the engine cowl; so I decided to notify Maintenance Control. The Maintenance Controller was (understandably) rather irate and basically chewed me out (not understandable). The aircraft was taken out of service and another aircraft was found for us rather quickly. I accept full responsibility for this event. I allowed myself to be influenced by various factors; instead of pausing and considering my decisions. I will proceed very differently next time; should I be faced with a situation like this again. Some possible contributing factors [is] somewhat long day the previous day; with weather diversion and delays; resulting in a fairly short overnight (approximately 10 hours) and early wake up. I believe that I was also somewhat distracted by the approaching weather at the destination and thereby allowing myself to be lulled into a false sense of compliance with the Ramp Supervisor's inspection.
After the gate pulled back from our aircraft; ramp notified us that there were a few small scrapes on the engine cowling of the #2 engine. Ramp Supervisor subsequently waved us off that it was fine.  I had performed the walk around in the dark at ZZZ and did not notice anything of significance on the engine.  We assumed that they were the typical small scratches seen over the airplane and continued the flight. I went out and looked at the engine in ZZZ1 and found the large scratch. The Captain called Maintenance and the plane was grounded.
Ramp person advised crew of a scratch on the aircraft; pilot had Maintenance check it out; Maintenance said to go. Scratch was larger then flight crew expected and was grounded at destination.