A systematic approach is presented to retrofit design of a hydrogen distribution network. A methodology is based on the steady-state flexibility index (FIs) for optimizing network and enhancing the efficiency of purifiers. The main object of this technique is to investigate hydrogen network flexibility under severe operation uncertainty and to reduce streams to purifiers by consideration inlet feed purity of purifiers. The presented approach is applied to the hydrogen network of, a real installation. (C) 2016 The Author(s). Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).