DECLARE @position INT;
DECLARE @string VARCHAR(max);

SET @string = '9FX8173';

WHILE 1 = 1
BEGIN
  SET @position = (SELECT Min(position)
                   FROM   (VALUES (Patindex('%[^''0-9][0-9]%', @string)),
                                  (Patindex('%[0-9][^''0-9]%', @string))) AS T(position)
                   WHERE  T.position > 0);

  IF @position IS NULL
    BREAK;

  SET @string = Stuff(@string, @position + 1, 0, '''');
END

PRINT @string;

SET @string = 'PAYGA0102'

WHILE 1 = 1
BEGIN
  SET @position = (SELECT Min(position)
                   FROM   (VALUES (Patindex('%[^''0-9][0-9]%', @string)),
                                  (Patindex('%[0-9][^''0-9]%', @string))) AS T(position)
                   WHERE  T.position > 0);

  IF @position IS NULL
    BREAK;

  SET @string = Stuff(@string, @position + 1, 0, '''');
  END

  PRINT @string;

  SET @string = '00086K'

  WHILE 1 = 1
  BEGIN
  SET @position = (SELECT Min(position)
                   FROM   (VALUES (Patindex('%[^''0-9][0-9]%', @string)),
                                  (Patindex('%[0-9][^''0-9]%', @string))) AS T(position)
                   WHERE  T.position > 0);

  IF @position IS NULL
    BREAK;

  SET @string = Stuff(@string, @position + 1, 0, '''');
  END

  PRINT @string;

  SET @string = 'ADEP'

  WHILE 1 = 1
  BEGIN
  SET @position = (SELECT Min(position)
                   FROM   (VALUES (Patindex('%[^''0-9][0-9]%', @string)),
                                  (Patindex('%[0-9][^''0-9]%', @string))) AS T(position)
                   WHERE  T.position > 0);

  IF @position IS NULL
    BREAK;

  SET @string = Stuff(@string, @position + 1, 0, '''');
  END

  PRINT @string;