There are several different compositions called String Quartet in B-flat Major. Below is a listing (which may not be exclusive):

Ludwig van Beethoven - String Quartet No. 13 Bâ™­ major, Op. 130

Antonín Dvořák - String Quartet No. 13 in G major, Op. 106, (B. 192)

Wolfgang Amadeus Mozart - String Quartet No. 13 in D minor, K.173

Franz Schubert - String Quartet No. 13, n A minor (the Rosamunde Quartet), D. 804, Op. 29

Dmitri Shostakovich - String Quartet No. 13 in B flat minor, Op. 138

Louis Spohr - String Quartet No. 13 E minor, Op. 45, No. 2