Função - Converter BLOB para CLOB

SQL: 

create or replace function blob_to_clob (b in blob) return clob is
  pos       pls_integer  := 1;
  buffer    varchar2( 32767 );
  res       clob;
  lob_len   pls_integer  := dbms_lob.getlength( b );
begin
  dbms_lob.createtemporary( res, true );
  dbms_lob.open( res, dbms_lob.lob_readwrite );
     
  loop
    buffer := utl_raw.cast_to_varchar2( dbms_lob.substr( b, 16000, pos ) );
     
    if length( buffer ) > 0 then
      dbms_lob.writeappend( res, length( buffer ), buffer );
    end if;
     
    pos := pos + 16000;
    
    exit when pos > lob_len;
  end loop;
     
  return res;
end blob_to_clob;

Chamada da função:

select blob_to_clob(utl_raw.cast_to_raw('Valor Blob')) from dual

Retorno:

Valor Blob