The pipes come in various keys. The most popular being the key of D (The D above middle C on the piano i.e. Concert pitch) These were developed in the 1920`s by the Taylor Brothers in Chicago who needed pipes which were louder and could play in ensembles. The previous pipes made were for solo playing and were in the keys of C
Composers need to be aware of the properties of the pipes. I have gone to recording sessions in well-known London studios where famous and expensive film composers have written music incorporating the pipes only to find that what was written, was virtually impossible to play!