I have passed the 9-rank exam about the piano这句话对不对

不对，应是I have passed the exam about the 9-rank piano.

建议:

I have passed the exam for the 9th rank/grade of piano.

I have got the level 9 certificate of the piano.

1.I've passed the exam of grade 9 piano.

2.I was examined in grade 9 Piano and passed in 2009.

3.同上楼：I have passed the exam for the 9th grade of piano.（不建议采用）

4.I have got the certificate of Grade 9 Piano.

关于3：既然都知道是九级钢琴又何必罗罗嗦嗦的说exam for the 9th grade of piano/exam for grade 9 Piano呢，直接了当grade 9 piano exam/grade 9 piano就好了。
其实那个exam挂上去也是多余的，grade 9 piano最好。