API Casing Strengths – Work

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API Casing strengths Worksheet, release 10, issued 30 August 2019. WORK version.

This worksheet exists in two versions. They are identical apart from the way they are formatted. The Work version hides intermediate calculations and allows the user to see the results just below the inputs. This is useful for quick “what-if” games, changing various inputs to see what works best. The audit version displays all intermediate calculations.

ALL the figures published in API 5C2 for burst, tension, collapse and biaxial have been checked against this worksheet. Only three are different by more than rounding errors. These are noted at the bottom of the worksheet.

Description

This worksheet takes a set of inputs typical for tubular design. It uses the formulae defined in the referenced documents to calculate the tubing design parameters and will account for the effects of temperature, internal pressure and tension. All tension and burst results have been verified OK against API 5C2 Table 1. All biaxial collapse resistances were verified against API 5C2 Table 4.

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.

There is no tutorial version of this worksheet but all of the individual elements have tutorials with other worksheets, such as Collapse. There is an Audit version however which allows the user to verify all of the procedures used.

User input

Select a casing

Select a connection type.

For the OD and connection selected, additional weight per

If no connection data exists in the worksheet, you can enter a figure here for the additional weight per connection. If no value is entered in this field, then the worksheet will instead use the API nominal weight per foot to calculate downhole stresses.

Manually enter the additional weight per connection. Wt_conn =

Enter average joint length. L =

Enter axial force at the depth of interest (tensile is +ve). F_a =

Enter the temperature at the depth of interest. Temp =

Enter the internal pressure at the depth of interest. p_i =

Enter the number part of the steel grade eg for L80, enter 80 (units are kpsi). Gr =

Enter design factor for collapse. DF_c =

Enter design factor for burst. DF_b =

See the recommended DF in the results below.

Enter design factor for tension. DF_t =

Click here when any values are modified to update the result.

Results

Maximum possible pipe OD within API tolerances

Minimum possible pipe OD within API tolerances

API nominal wall thickness

Ratio of OD to nominal wall thickness, D/t ratio

Minimum possible wall thickness within API tolerances

API nominal ID

API Drift Dia

ID for minimum amount of steel used within tolerances

Nominal cross sectional area

Minimum possible cross sectional area

Recommended Design Factor for tension

Temperature Correction Factor

API Minimum Yield Strength, nominal, ambient

API Minimum Yield Strength, with TCF and DF

Pipe body API Minimum Burst Strength, ambient

Pipe body API Minimum Burst Strength, with TCF and DF

Pipe body axial stress at nominal CSA

API collapse resistance, ambient, no axial force

API collapse resistance with TCF, DF, Biaxial & internal pressure

Plain end pipe weight, nominal dimensions

Pipe weight average with connections, nominal dimensions

CHECK CONNECTION STRENGTHS vs PIPE STRENGTHS AND USE THE LEAST!!

Worksheet references

API Specification 5CT, 5th Edition, April 1 1995 “Specification for Casing and Tubing (U.S. Customary Units)”.

API Bulletin 5C3, 6th Edition, October 1 1994 “Bulletin on Formulas and Calculations for Casing, Tubing, Drill Pipe, and Line Pipe Properties”, also ISO/TR10400:2007 which is expected to replace API 5C3 during 2008.

API Bulletin 5C2, 21st Edition, October 1999 “Bulletin on Performance Properties of Casing, Tubing and Drill Pipe”.

Formulae for Temperature Correction Factor taken from the Exxon Casing Design Manual.

SG of steel from http://www.simetric.co.uk/si_metals.htm taken as 7.85.

Version 1 of this worksheet released on 8 January 2008.

Release 8 released after testing against API 5C2 21st Edition for burst, tension, collapse and biaxial. The only significant differences were found in Table 4 (biaxial) as follows, with all other results the same within normal rounding;

9.625″ 40ppf Grade 80 at -10,000 psi axial load, this worksheet showed 3167 psi vs API 3107

7.625″ 45.3ppf Grade 95 at -10,000 psi axial load, this worksheet showed 14,241 psi vs API 14,330

9.625″ 43.5ppf Grade 110 at 25000 psi axial load, this worksheet showed 4205 psi vs API 4130

Release 8a fixed a small problem in the casing list, where the 8.625″ 44ppf casing appeared at the end of the list rather than in the correct order.

Release 9 of this worksheet added a recommended Design Factor in tension for the selected pipe. This accounts for dimensional tolerances to compare nominal cross sectional area with the minimum possible cross sectional area and limits the uniaxial tensile stress to 90% of API Minimum Yield Stress.

Release 10 made a correction to the factor to calculate the minimum wall thickness, -12.5% of nominal. The factor 0.85 had been used rather than 0.875.

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