CREATE TABLE #TestingIdea (
Id int PRIMARY KEY IDENTITY (1,1),
PostId int NULL,
Tag nvarchar (MAX) NULL
)
GO

SELECT  T1.PostId,
        S.SplitTag
FROM (
    SELECT  T.PostId,
            cast('<X>'+ REPLACE(T.Tag,'>','</X><X>') + '</X>' as XML) AS NewTag
    FROM #TestingIdea AS T
    ) AS T1
CROSS APPLY (
    SELECT tData.value('.','nvarchar(30)') SplitTag
    FROM T1.NewTag.nodes('X') AS T(tData)
    ) AS S
GO

XML parsing: line 1, character 37, illegal qualified name character