Temperature Correction Factor – Tutorial
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Temperature Correction Factor, release 1, issued 24 January 2008. JIT version.
Description
This worksheet takes temperature and steel grade as input. It uses the formulae defined in the referenced documents to calculate the Temperature Correction Factor for Steel, which accounts for the fact that yield strength of steel decreases with increased temperature. The revised Minimum Yield Stress is also given.
NOTE – this calculation is only valid for steel alloys and for temperatures not exceeding 5000 F or 2600 Celsius.
Mathcad uses metric units internally so if imperial units are entered, they are converted to metric. Intermediate results are metric. Both units will be given as outputs.
This “Just In Time Learning” tutorial version of the worksheet explains the theories behind the calculations, it shows the formulae and intermediate results. It is assumed that you are familiar with the concept of Stress and understand what is meant by API Minimum Yield Stress. Use the Work version of the worksheet if you just want to run the numbers.
Tutorial text is shown in blue. It should take 10 minutes to work through this tutorial.
At the end of this tutorial, YOU will be able to;
1. Describe the theoretical basis for calculating the Temperature Correction Factor for Steel.
2. Correctly apply the Temperature Correction Factor when designing steel components for elevated service temperatures.
User input
100 |
FCK |
Enter the temperature at the depth of interest. Temp =
80 |
Enter the number part of the steel grade eg for L80, enter 80 (units are kpsi). Gr =
Click here when any values are modified to update the result.
Calculations
Check that the temperature entered does not exceed 500F.
Calculate the TCF from the temperature.
Two specific temperature ranges are calculated for. Between 75F or 24C ambient temperature and 300F or 149C, there is a straight-line decrease in yield strength. Between the top of this temperature range and 500F or 260C, the yield strength decreases at a greater rate per degree increase in temperature.
The formula above has three parts. If the temperature is below 75F then a TCF of 1 is returned, otherwise zero. If the temperature is between 75 and 300F, the TCF is calculated and returned, otherwise zero. If the temperature is between 300 and 500F, the TCF is calculated and returned, otherwise zero. Only one of these three parts should return a non-zero result if the temperature entered does not exceed 500F, then the three results are added together to give the TCF.
When a temperature exceeding 500F is entered, all three formulae are out of range and return a zero, therefore the TCF is given as zero. This shows that the TCF cannot be calculated for this temperature.
Convert steel grade entered to API Minimum Yield Stress in psi.
The number part of a steel grade gives the API minimum yield stress in thousands of psi. Multiplying the steel grade number by 1000 gives the API MY stress in psi.
Calculate the revised API Minimum Yield Stress at the entered temperature.
Multiply the MY stress by the TCF to give the revised MY stress.
Results
Entered
Temperature Correction Factor
API Minimum Yield Stress, ambient
API Minimum Yield Stress, with TCF
Worksheet references
Formulae for Temperature Correction Factor taken from the Exxon Casing Design Manual.
Version 1 of this worksheet released on 24 January 2008.
