Overhaul & Upgrade

During the operational life of a large plant, it may be necessary to carry out overhauls and/or upgrades to ensure the products produced at the plant remain competitive in the market place. The role of Overhauls differs from that of Upgrades as their justifications and intended outcomes are different.

Overhauls

Overhauls are carried out to restore existing assets and functions to an acceptable condition (not necessarily as-good-as-new) following deterioration and wear that has accumulated over time and use. Some failure modes occur over a long time period, are relatively slow to develop and are cumulative in nature. There may not be an effective or convenient maintenance restoration task available to prevent or reduce the impact of these failure modes. Overhauls are often required to correct these long term deterioration mechanisms such as deterioration of linings and refractory, corrosion of vessels etc. In many cases these deteriorating mechanisms do not have routine maintenance tasks assigned (except in some cases where inspections may be carried out) but which have to be restored when they have reached some unacceptable level of deterioration.

The overhaul or ‘turnaround’ is usually complex and expensive and involves significant planning and resourcing to minimise the cost and disruption of the overhaul. Typically, overhauls are carried out on large combinations of equipment such as power station boilers, paper machine chests, ships, locomotives, refinery vessels etc. and are often typified by limited access during normal operation and high setup and repair costs when carried out. Large overhauls attract significant planning and scheduling to ensure the work packages are delivered on time, resources are available when needed and access to parts of the plant are coordinated to prevent delays and minimise the total event duration.

Upgrades

Unlike overhauls, which are designed to restore existing functions, upgrades are carried out to add new features or capacity to an existing plant over and above that originally designed into the plant. Upgrades are required when the need for additional functionality or increased capacity, cannot be met by limited changes to existing plant, cannot be postponed any longer and where the cost of completely replacing the asset is not justified on economic grounds.

An upgrade may be more attractive than a complete replacement when:

• The cost/benefit relationship of the upgrade is more favourable than for a complete replacement plant.

• The upgrade involves a relatively small percentage of the equipment and the rest of the plant has valuable remaining life.

• If the upgrade is relatively simple.

• The plant downtime for the upgrade is significantly shorter than for a complete replacement.

• No new technical enhancements are available or attractive.

• The projected remaining life of the overall plant is too short to support the larger investment of a new plant.

The need for additional features or capacity can arise for similar reasons as those at the ‘identify need’ phase. Typical reasons for upgrades include the following.

• Existing assets are at the end of their ‘technological life’ and need to be upgraded for the organisation to remain competitive.

• Existing assets do not have sufficient capacity to meet current needs and need to be upgraded to increase capacity.

• Existing assets cannot continue to be operated due to unacceptable safety or environmental problems associated with the asset.