The pilot reported that a 6-inch drainage pipe was lying across his private airstrip at the 1,600-foot mark of his 3,800-foot grass airstrip. He did two practice landings and takeoffs to make certain that he could land and takeoff without hitting the drainage pipe. After the second landing, he took three passengers for a flight. He reported that the takeoff was fine and he lifted off the runway 200 - 300 feet from the pipe. He reported that during the landing he did not get the airplane stopped in time and the airplane struck the drainage pipe and the airplane sustained substantial damage. The pilot and the passengers were not injured.