Next Inspection Date (NID) – Horserace

In IMS, the different approaches for the Schedule’s Next Inspection Date (NID) compete against each other in a Horserace. This way the most conservative NID is selected. This is illustrated for a PEI Inspection Schedule in the figure below.

The NID of the Schedule is really a horserace between the different approaches.IMS considers things like:

• (Default) Intervals
• Legal requirements
• Shutdown / Event intervals
• RBI Assessments
• Wall Thickness (WT) readings

The Inspection Schedule NID that won the horserace is only one of the dates to be considered for when you will need to inspect your Equipment. It is important to adhere to all Schedules and to ensure the Equipment is in good working order and safe to use. The image below displays the different NIDs on which a piece of Equipment can be inspected. The soonest NID should always be adhered to.

This horserace will determine the NID that you will see on the Equipment Main Screen. 

Below we show the horserace for the PEI Schedules.

The Equipment NID of the Equipment is the horserace between all Schedules on the Equipment.

(Default) Intervals

Default Schedules act as “safety nets” for which the NID is set (by default) to 12 months from Equipment creation date. See Default Schedules. 

Also, a User Interval can be set.

Legal requirements

Legal requirements can drive the User Interval Date of a Schedule. The legal requirements can also be set through RBI, via the Legal Inspection Interval (LII), and will then be considered as part of the horserace for the RBI interval.

Shutdown / Event interval

Schedules can be tied to an upcoming event (see Tying Schedules to Upcoming Events). However the Event date does not take part in the NID horserace.

RBI Assessment

When Components are in Scope of a Schedule, the RBI Maximum Inspection Interval (MII) and NID can be included in the horserace. The figure below illustrates an RBI Analysis for a Component with an Age-Related (AR) Degradation Mechanism (DM). The Criticality and Confidence is used to determine an Interval Factor (IF). The IF and Remnant Life (RL) is then used to determine a MII and from this, and the Last Inspection Date (LID), an Ultimate NID can be determined. Notice that the Next Legal Inspection Date (NLID) is also included in the calculation.

RBI analysis for a Component with an Age-Related DM.

The next illustrates a Non-Age-Related (NAR) DM. In this case the RL is not applicable. The MII and Inspection Strategy (IS) are determined from lookup tables.

RBI analysis for a Component with a Non-Age-Related DM. 

Wall Thickness readings (PEI Corrosion Schedules)

Wall Thickness (WT) measurements are inputted on a Circuit. This is where the Corrosion Rate (CR) calculations take place. The CR and Remaining Corrosion Allowance (RCA) are then used to determine the RL. Then from the RL and an IF a NID can be determined for the Corrosion Schedule. See the figure below.

WT readings (inputted on a Circuit) is used to calculate CR and then the Corrosion Schedule NID.

When a Circuit and Component are linked (inherit) then the Component can inherit the CR and RCA from the Circuit. This way the WT measurements are used in the RBI Analysis to determine the RL and then the RBI MII and NID. The RBI IF can, in turn, be linked back to the Circuit. This way the RBI influences the Corrosion Schedule’s NID calculation. This inheritance is further explained in Relationship between CLs, Components and Circuits. See the figure below.

When Circuits and Components are linked, the Circuit’s CR and RCA are used in the Component RL calculation and the Component’s RBI IF is used on the Circuit’s NID calculation.

Horserace examples in IMS

Lastly, the next two figures illustrate a horserace for the NID of an Inspection Schedule and Calc Summary of a Circuit.

The NID horserace on an Inspection Schedule.  

The NID horserace in the Calc Summary of a Circuit.

For more information on the NID calculations see - Schedule NID Calculation.