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Collapse resistance of a tubular, release 10a, issued 11 May 2008. 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 JIT version displays all intermediate calculations, plus adds tutorial text to explain the methodology.

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 inputs of tubular OD, wall thickness, grade, axial force, internal pressure and temperature. It uses the formulae defined in the referenced documents to calculate the collapse resistance and will account for the effects of temperature, internal pressure and tension.

Tension or compression at the depth of interest can be entered to allow the biaxial effect to be calculated. It is normal to account for the reduction in collapse resistance due to axial tension but not usual to take advantage of the increase in burst due to tension. This may be defined by your own company’s policy.

You can also enter a Design Factor to include in the calculation, or set the DF to 1 if this is not required.

User input

Select a casing

100000

kgflbfNkN

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

80

FCK

Enter the temperature at the depth of interest. Temp =

3000

psiPakPaMPa

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

80

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

1

Enter design factor for collapse or use 1 if design factor is not to be considered. DFc =

Enter the temperature at the depth of interest. Temp =

0

psiPakPaMPa

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

125

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.

Results

Pipe cross sectional area

Ratio of OD to wall thickness, D/t ratio

Temperature Correction Factor

Pipe body axial stress at depth of interest

(Axial stress as a % of Minimum Yield Stress)

API collapse resistance, ambient, no axial force or DF

API collapse resistance with TCF, DF and Biaxial

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

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 1 January 2008.

Version 10 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