SQL Server - como pasar numeros hexadecimales a decimales

si alguien tiene idea de como hacerlo en un stored procedure se lo agradecere

Gracias

SELECT @newalarms = sum(charindex(substring(h, i, 1), '123456789ABCDEF') * power(16., len(h) - i))
FROM (SELECT @newalarmshex AS h) AS N, (SELECT 1 AS i UNION all SELECT 2) AS I GROUP BY h