T-Min Calculations

Minimum Thickness (T-Min) is a value that represents the minimum allowable thickness for a TML. The T-Min value is stored in the Minimum Thickness field of TMLs. The value is used for performing various calculations in Thickness Monitoring (TM), such as corrosion rate, next inspection date, and projected T-Min date calculations. T-Min values are an important component of corrosion analyses because they help determine when assets and components should be inspected and replaced.

T-Min values can be defined for TMLs via the T-Min Calculator workspace.

From the T-Min Calculator workspace, you can:

• Calculate the T-Min value using a formula that has been defined for the Asset type. This may be the baseline formula provided by TM or a custom formula.
• Look up the T-Min value defined by industry standards.
• Look up the default T-Min value that is specified in the TML Analysis Settings record that is linked to each TML.

• Specify a custom T-Min value based upon design specifications or your knowledge of the codes and system.

The Calculated T-Min value is determined by performing calculations using T-Min formulas and values from the Thickness Measurement Location (TML). This calculation may be performed using a default formula that is provided in the baseline Thickness Monitoring (TM), or a custom formula that has been defined for your implementation. A comprehensive document of the formulas used for T-Min calculation is available here.

Details

Calculated T-Min values are determined using the following components:

• Formulas that are stored in the Rules Library.

• Values that are stored in TMLs that serve as inputs to the formulas.

  Note: For Calculated T-Min values to be retrieved, TMLs must contain values in certain fields. Calculations will not be successful for TMLs that do not contain these values.

• Mappings that determine which formula should be used based on the inputs that are supplied. These mappings are stored in records belonging to the Thickness Monitoring Rules Lookup family.

Nominal T-Min is a T-Min value that represents the minimum thickness of a pipe based on accepted industry standards. The Nominal T-Min value takes into account various design specifications to determine the minimum thickness associated with that criteria.

Details

The Nominal T-Min value is located using values from TMLs and records in the Piping Nominal T-Min reference table. For the Nominal T-Min value to be retrieved for a given TML, the TML must contain values in the fields that are required for the lookup to occur, as determined by the Nominal T-Min Lookup preferences in the Application Settings.

The Nominal T-Min value applies only to TMLs on piping equipment. When you calculate the T-Min values via the T-Min Calculator workspace, a Nominal T-Min value will be retrieved only for TMLs with a Design Code that corresponds to the piping equipment type, based upon the references that exist in the MI_ASSET_TYPE System Code Table.

The Default T-Min is the minimum thickness value that appears in the Default field for each TML on the T-Min Calculator workspace. When a T-Min calculation is performed, Thickness Monitoring retrieves the value that is stored in the Default T-Min field in the linked Corrosion Analysis Settings.

User Defined T-Min is a minimum thickness value that is entered manually in the Minimum Thickness field in a Thickness Measurement Location (TML) datasheet. When you enter a minimum thickness, the value in the Minimum Thickness Type field will change to User Defined.

Details

For any TML with a User Defined T-Min, in the corresponding row in the T-Min Calculator workspace, the User Defined box will be populated with the value in the Minimum Thickness field of that TML. If the Minimum Thickness Type is anything other than User Defined, the User Defined box will be empty when you access the T-Min Calculator. Regardless of whether the User Defined box contains a value when you access the T-Min Calculator, you can specify a User Defined T-Min value by entering it in that box.

In the T-Min Calculator workspace, when you select the Calculate T-Min button, the Thickness Monitoring (TM) performs the following operations for each TML for which the check box is selected:

1. Determines the following values:
   • Calculated T-Min, which will be displayed in the Calculated box in the T-Min Calculator workspace.
   • Nominal T-Min, which will be displayed in the Nominal box in the T-Min Calculator workspace.
   • Default T-Min, which will be displayed in the Default box in the T-Min Calculator workspace.
2. Compares the Calculated T-Min, Nominal T-Min, Default T-Min, and User T-Min (if one exists), and determines the most conservative (i.e., largest) of the four values.

3. Populates the T-Min Selected box in the T-Min Calculator workspace with the most conservative value determined in Step 2.

   Note: If you enter a value in the User Defined box after performing a calculation, the value in the T-Min Selected box will be updated with the value you entered in the User Defined box, regardless of whether it is the most conservative value.
4. The default value in the Selected Source list is set to correspond to the value referenced in step 3. You can select a different value.

The Current and Current Source boxes display the value and source of the current minimum thickness defined for the corresponding TML. These boxes are updated after a new T-Min is saved.

When you perform a T-Min calculation, the T-Min Calculation Output dialog box appears, displaying a spinner to indicate the calculations are being performed.

Details

After the calculations are complete, you can interpret the calculations in the T-Min Calculation Output dialog box. If desired, you can copy and paste the results from this dialog box into another document.

You can also view the details of a full calculation history for a specific TML.

Calculation details are logged for Thickness Measurement Locations (TMLs) each time you perform a T-Min calculation.

Details

You can view the Calculation Details on the:

• T-Min Calculation Output dialog box, which displays the details of the calculation that was most recently performed for either a set of TMLs, or a single TML.

• T-Min Calculation Results History dialog box, which displays the details of all the calculations that were attempted for a given TML. The details included in this dialog box are the same as the details displayed in the T-Min Calculation Output dialog box, but in the T-Min Calculation Results History dialog box, the details are repeated once for each time a calculation was performed.