Dec > Hex

function dec2hex(value: dword): string[8];
const
  hexdigit = '0123456789ABCDEF';
begin
  while value <> 0 do
  begin
    dec2hex := hexdigit[succ(value and $F)];
    value := value shr 4;
  end;
  if dec2hex = '' then dec2hex := '0';
end;

Взято с https://delphiworld.narod.ru