In order to replace an inoperable, damaged DN1200 valve at No1 ammonia washer, JES group were awarded the project to design, manufacture and install a new DN1200/DN900 coke oven gas line to allow the existing DN1200 valve to be bypassed. The pipework was designed and installed on a permanent basis with necessary connections for a future plant modifications. The work was carried out while the plant remained live and only 2 plant shutdown days were taken to undertake all tie-ins. Whilst all enabling works had been carried out the final piece was to remove and replace a DN1200 Donkin valve which was done by following very strict isolations including water seals, the valve was then replaced through a seqence of complex lifting operations which were all planned and executed by JES personnel.