The calculated distance (air line) between Sint-Pieters-Leeuw and Seraing is approximately 57 miles respectively 91 kilometers.
By car or train, the actual journey to Seraing is certainly longer, as only the direct route (as the crow flies) between Sint-Pieters-Leeuw and Seraing has been calculated here.
Air line (approximately)
91 kilometers
49 nautical miles