Integrity Operating Windows - IOW

Some thoughts on the subject:

In 1950’s the equipment , piping in a Refinery/Petrochemical complex had 4 major parameters to assure their integrity. These were – pressure , temperature , material of construction and corrosion allowance. The Plants were practically shutdown every year and if the corrosion rates were not matching with design corrosion rates there was possibility of performing corrective actions.

However towards the end of 20 th century operations  were changing  and the shutdowns were spread apart mostly the aim was 4 or 5 years of uninterrupted operating run for the unit. Further  the damage mechanisms became comparatively complex (or identified that these are complex) and if a failure (pressure boundary breech) was to be avoided then damage mechanisms needed a monitoring which could be ONLINE or OFFLINE with the sole intention that enough time is available to tackle possible higher rate of deterioration.

This required a study and documentation of what can happen in various scenarios of process condition – what are those parameters which can give information which would indicate that the process behavior is changing for worse and what needs to be done to arrest such change ??

This is exactly the requirement of Process Safety Management and understanding and establishing the parameters which will not permit /avoid breech of process boundary became the main focus and today we have full guidance by way of API 584 – recommended practice (to establish) Integrity Operating Windows.

We have to check thoroughly the chemicals in the process and see if these are going to change/further help in accelerated damage , may be sometimes some data like iron ppm in fluid can give information if corrosion rates are in control or changing . Sometimes online instrumentation like corrosion probes , FSM (field signature method) etc may be used to monitor damage happening. Sometimes the increased velocities (post choking) may play havoc , sometimes vapour release due to changes of pressure – there can be many such parameters which need monitoring and if leading to accelerated damage – the mitigation mechanism.

There are limits set for normal operation . But then knowing that we want to make profits (use opportunity to make quick money) we may cross such limits with knowledge and with full understanding that most of these parameters are having some margin {eg values similar to High alarm (standard level high) , high high alarm (critical limit high)

The exhaustive study includes all possible scenarios and also possible mitigation strategies – just to make sure that UNINTERRUPTED OPERATION of desired period of “X” years achieved !!