Solids injection lances (27a, 27b) for injecting solids into a metallurgical vessel are normally supplied with cooling water from a cooling water circuit through water supply lines (71) and return lines (72). Supply lines (71) are provided with spaced pairs of connectors (80) and bypass valves (73), and return lines (72) are provided with similar pairs of spaced connectors (81) and bypass valves (74). Flexible hoses (75, 76) can be connected between the pairs of connectors (80, 81) to establish supply and return flows of cooling water which bypass segments of the main supply and return lines (71, 72) which can be isolated and removed to allow withdrawal and subsequent replacement of the lances.