Integrity Operating Windows (IOW) typically define the maximum or minimum operating process variables that must be maintained in order to meet the intended design life of a system or facility. Key variables, such as temperature, flow rate, concentration, etc., are defined for each system based on an estimated susceptibility of equipment to known damage mechanisms.
Plant Integrity Operating Windows
If an IOW is exceeded, the Engineering Department should be immediately notified to determine whether a FFS evaluation is necessary based on the incident. The incident should then be logged in the asset’s operation history for future reference for RUL calculations.
Examples of an incident might be as follows:
1. A temperature excursion in a process containing liquid sulphur, which could activate sulphidation.
2. A temperature drop resulting in the formation of corrosive salt in a sour water line.
3. An exchanger tube leak (or even loss of flow in an exchanger) resulting in fouling and component damage.
The definition of IOW parameters is predicated on the assumption that operating parameters that can affect the onset of a damage mechanism or the exacerbation of an existing damage mechanism (i.e., pressure temperature, and flow rate) can be continuously monitored by operations in the control room. However, during the process of the Safaniya Utility Units’ IOW review, it became apparent that the parameters that would affect the onset or exacerbation of an expected damage mechanism were best addressed by measuring process chemistry parameters not through measurement of process operating parameters.
As the starting point for the Safaniya Utility Units’ IOW review, the Intertek team reviewed the Safaniya Plant G26U IOW Parameters with Target – 2012 document. After review of the corrosion problems listed as part of that document the following conclusions were drawn:
• The key determinant of the onset of potential damage mechanisms leading to failure within the Washwater and Formation Water units are primarily a function of process chemistry (e.g., O2 concentration, pH, etc.) rather than process operating conditions (temperature, pressure, etc.).•
The external corrosion problems (under insulation corrosion, field weld joints failure, well casing external corrosion, coating failure, and external corrosion in buried piping and above ground tank bottom) arise from damage mechanisms that do not lend themselves to on-line monitoring.
To address the IOWs, the Intertek team defined damage Loops within the Washwater and Formation Water units. They were then evaluated to determine if IOW operating parameters and/or process chemistry parameters that could be monitored via the DCS in the control room could be identified. This was accomplished using the following process:
• Damage loops for the Washwater and Formation Water Systems were defined.
• Likely damage mechanisms that could occur given the specified vessel or piping metallurgy and operating parameters were identified for each loop.
• An assessment was undertaken to determine if the effect of system operation on equipment or piping at conditions outside of IOW limits could either induce or exacerbate identified damage mechanisms.
During the evaluation, the effects of normal equipment operation, startup, shutdown, and temporary removal from active service conditions on damage mechanism activity were evaluated.
As a result of the evaluation, four potential internal damage mechanisms, Boiler Water Condensate Corrosion†, Microbiologically Induced Corrosion (MIC), Pitting, and General (or Uniform) corrosion were identified. Boiler Water Condensate Corrosion could occur in the MED unit in the boiler feedwater and condensate return systems. MIC could occur as a result improper control of organisms in the raw seawater intake. Pitting and Uniform corrosion would occur primarily from long term changes in process chemistry or in the event of stagnate, low flow conditions over extended periods of time.