AUSTRALIAN STANDARD PIPELINES - GAS AND LIQUID PETROLEUM

Transcription

1 AUSTRALIAN STANDARD PIPELINES - GAS AND LIQUID PETROLEUM LAUNCH SEMINAR Pipeline Stress Requirements Version1.1

2 Pipeline Stress Requirements STATEMENT OF THE DESIGN PROBLEM The design task is to carry out sufficient preliminary stress analysis to select a pipe wall thickness for internal pressure design for the transmission pipeline. The pipeline will be buried with a minimum cover to the relevant requirements of the Standard. Most of the buried length will be fully restrained both laterally and longitudinally by the soil. Parts of the buried pipeline will not be fully restrained (i.e. bends) and are treated as being unrestrained. The Study Pipeline internal pressure calculations are for both the buried fully restrained lengths and the buried unrestrained lengths. Slide 2

3 Pipeline Stress Requirements DESIGN TASKS 1. Calculate wall thickness for internal pressure design. 2. Calculate the relevant components of stress. 3. Establish the upper and lower temperature capabilities of the pipeline (RESTRAINED ONLY). 4. Calculate the relevant stress levels in accordance with the Standard. 5. Check that the calculated stress levels are within allowable limits. Slide 3

4 Pipeline Stress Requirements REQUIREMENTS OF AS AS 2885 requirements for wall thickness are contained in Section The requirements for stress and strain are contained in Section The calculation basis for stresses in restrained and unrestrained pipelines is contained in Appendix U. 4. Guidelines for the consideration of combined equivalent stress levels and temperature differentials in RESTRAINED LINES are contained in Appendix W. Slide 4

5 Pipeline Stress Requirements PIPELINE PROPERTIES External diameter mm Design factor 0.8 Design pressure 15.3 MPa Material grade X70 SMYS 483 MPa Young s modulus 207,000 MPa Poisson s ratio 0.3 Upper design temperature 65 o C Lower design temperature 0 o C Closing temperature 15 o C Expansion coefficient 1.17 x 10-5 / o C Slide 5

6 Pipeline Stress Requirements PART (A) RESTRAINED The limits of stress for restrained parts of the pipeline for stress types that include internal pressure are listed in Table These stress types are: Hoop stress. Sustained stress. Total longitudinal stress. Combined equivalent stress. Slide 6

7 Pipeline Stress Requirements - Restrained Wall Thickness for Internal Pressure Containment Reference Clause Equation t P = P 2F D D D Y 15.3 x t P = = mm 2 x 0.8 x 483 Slide 7

8 Pipeline Stress Requirements - Restrained Required Wall Thickness for Pressure Containment Reference Clause The required wall thickness t W shall be greater than: the wall thickness for internal pressure containment t P. Therefore t W mm Round up t W to 8.1 mm Slide 8

9 Pipeline Stress Requirements - Restrained Longitudinal Pressure Stress Reference Appendix U2.2 Equation U2(3) PD D L =ν 2t W 15.3 x L = 0.3 = 115 MPa 2 x8.1 Slide 9

10 Pipeline Stress Requirements - Restrained Longitudinal Thermal Stress Reference Appendix W Internal Pr essure H ν H Thermal Heating comp From W 5(8) putting and T Y = T f = y f L = Y, T = ν comp H = ν H comp T comp comp = = 0.3 x Y Y ( Y ) Slide 10

11 Pipeline Stress Requirements - Restrained Thermal Compressive Stress Limit Reference Appendix W5.1.2 comp = Y comp = x 483 = 200 MPa Slide 11

12 Pipeline Stress Requirements - Restrained comp Δ t = Eα Upper Value of Temperature Reference Appendix U2.3 Equation U2(4) 200 Δ t = = o C o T 1 = = 97 C max. o Design T1 is 65 C, thenδt = 50 C andcomp = o 121MPa Slide 12

13 Pipeline Stress Requirements - Restrained Total Longitudinal Stress Limit Reference Table T = 72 % Y = x 483 = MPa Slide 13

14 Pipeline Stress Requirements - Restrained Derived Thermal Tensile Stress Limit Reference Appendix U2.3 & U2.7 Equations U2(5) & U2(8) ER = T SUS ER = = 232 MPa EB = 0, and ER = EA = 232 MPa Slide 14

15 Pipeline Stress Requirements - Restrained EA Δ t = Eα Lower Value of Temperature Reference Appendix U2.3 Equation U2(4) 232 Δ t = = o C o T 2 = = 80 C min. Design o T2 is 0 C, then EA = ER = 36MPa Slide 15

16 Pipeline Stress Requirements - Restrained Hoop Stress for Pressure Containment Reference Appendix U2.1 Equation U2(1) H = PD D 2t W 15.3 x = = MPa H 2 x Slide 16

17 Pipeline Stress Requirements - Restrained Sustained Stress Reference Appendix U2.6 Equation U2(7) = SUS L W F other SUS = L + 0 = 115 MPa Slide 17

18 Pipeline Stress Requirements - Restrained Total Longitudinal Stress Reference Appendix U2.7 Equation U2(8) Tensile : T = SUS + ER = = 151 MPa Compressive : T = SUS comp = = 6 MPa Slide 18

19 Pipeline Stress Requirements - Restrained Combined Equivalent Stress Reference Appendix U2.9 Equation U2(15) C 2 H = + H T 2 T 2 2 Tensile : C = 384 (384x151) = 335MPa 2 2 Compressive : C = 384 (384 x ( 6)) + ( 6) = 387MPa Slide 19

20 Slide 20 AS Pipeline Stress Requirements Stress Summary for Restrained Lines Stress Type (Limit) Hoop (F D Y ) Sustained (54% Y ) Total Long (72% Y ) Combined (90% Y ) Value MPa Limit MPa % Allowable / /2 335/ /89

21 Pipeline Stress Requirements PART (B) UNRESTRAINED The limits of stress for unrestrained parts of the pipeline for stress types that include internal pressure are also listed in Table These stress types are: Hoop stress. Sustained stress. Slide 21

22 Pipeline Stress Requirements - Unrestrained Wall Thickness for Internal Pressure Containment Reference Clause Equation 5.4(2) The equation covers both restrained and unrestrained lines. Therefore use the previously calculated value of wall thickness of mm. Slide 22

23 Pipeline Stress Requirements - Unrestrained Required Wall Thickness for Pressure Containment Reference Clause The required wall thickness for internal pressure containment t P is the same for both restrained and unrestrained lines. Therefore t W = 8.1 mm as before. Slide 23

24 Pipeline Stress Requirements - Unrestrained Longitudinal Pressure Stress Reference Appendix U3.2 Equation U3(3) L = P D 4t W D 15.3 x L = = 192 MPa 4 x8.1 Slide 24

25 Pipeline Stress Requirements - Unrestrained Hoop Stress for Pressure Containment Reference Appendix U3.1 Equation U3(1) H = PD D 2t W 15.3 x = = MPa H 2 x Slide 25

26 Pipeline Stress Requirements - Unrestrained Bending Stress Reference Appendix U3.4 Equation U3(8) Consider a ninety degree 5D buried bend in 8.1 mm thickness subject only to internal pressure in sandy soil with a 90% Proctor compaction density. Pipe stress analysis software gives the following bending moment at the mid point of the bend: Slide 26 Bending moment 43,770 N.m Stress Intensification Factor From which the bending stress W = 72 MPa.

27 Pipeline Stress Requirements - Unrestrained Direct Axial Stress Reference Appendix U3.5 Equation U3(9) From the same analysis the pipe stress analysis software gave the following axial force at the mid point of the bend: Direct axial force 217,000 N From which the axial stress F =21 MPa. As this is not an externally applied axial pressure force the stress need not be included in the sustained stress calculation. Slide 27

28 Pipeline Stress Requirements - Unrestrained Sustained Stress Reference Appendix U3.6 Equation U3(10) = SUS L W other SUS = = 264MPa F Slide 28

29 Pipeline Stress Requirements Stress Summary for Unrestrained Lines Stress Type (Limit) Value MPa Limit MPa % Allowable Hoop (F D Y ) Sustained (54% Y ) Slide 29

30 Pipeline Stress Requirements That Completes the Presentation. Are there any Questions? Slide 30