FPSO Related Piping and Pipe Stress Aspects

FPSO related piping and pipe stress aspects Paul Voorhaar & Hugo Kamphuijs

November 2010

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Rough sea

Who we are

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We are Colleagues at Bluewater Energy Services in Hoofddorp working as stress engineer

What we are not: •Persons that think their approach is simply the best •Stress engineers that have stopped being critical about themselves

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•Technicians that do not listen to other stress engineers

Why are we giving this presentation?

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• Firstly because we were asked by Dynaflow to do so • Secondly because we feel that we can share some of our problems with others and we will all benefit • We appreciate pp Dynaflow y for g giving g these p presentations for all interested relations • We have heard many others, telling about their field of expertise and we were more or less obliged to give our contribution even if we can not reach the high level of the others we have heard • By preparing this presentation we were forced to think about the importance

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and non-importance of several stress items with FPSO’s

FPSO related piping and pipe stress aspects

Difference between: • Land based installations • Coastal installations (Jetties) • Fixed Sea based installations • Floating Sea based installations on a fixed location (FPSO)

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FPSO related piping and pipe stress aspects

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FPSO related piping and pipe stress aspects

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-

Length 248.12 meters Breadth moulded 42 meters Depth moulded 21.2 21 2 meters Draft, design + scantling 14.9 meters Dead weight tonnage 105,000 dwt Deck area 7 7,985 985 m2 Topsides area 6,000 m2 Deck payload 7,000 tonnes Accommodation 84 persons

Ship movements

Space for visuals, tables or info graphics g p

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Determination of loading cases

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RESTRAINT SUMMARY REPORT: Loads On Restraints Various Load Cases LOAD CASE DEFINITION KEY CASE 1 (SUS) W CASE 14 (OPE) W+D4+T2+P2+U1

CASE 15 (SUS) U1 CASE 16 (SUS) U2 CASE 17 (SUS) WIN1 NODE

Load

FX N.

FY N.

FZ N.

MX N.m.

MY N.m.

MZ N.m.

Case 160

Rigid Y 1(SUS)

986

-10794 10794

719

0

0

0

14(OPE)

2729

-9115

167

0

0

0

15(SUS)

186

2796

818

0

0

0

16(SUS)

252

4755

1404

0

0

0

17(SUS) MAX

1 2729/L14

13 -10794/L1

4 1404/L16

0

0

0

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The result of this

Ship movements

Space for visuals, tables or info graphics g p

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Loading Cases

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To avoid numerous combinations of loadings we do calculate the worst combination of acceleration first U1 X Y Z

U2

U3

0.5 0.3 0.2

L1

W+U1+U2+U3

SUS

L2

W+U1+U2-U3

SUS

L3

W+U1-U2-U3

SUS

L4

W+U1-U2+U3

SUS

L5

W-U1-U2-U3

SUS

L6

W-U1-U2+U3

SUS

L7

W-U1+U2-U3

SUS

L8

W-U1+U2+U3

SUS

Loading Cases

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One of these combinations will give the highest stresses. Say it is combination 2 2. In that case only the following accelerations will be used: U1=+0.5X-0.3Y+0.2Z In this way we limit the number of pages of the output.

FPSO related piping and pipe stress aspects

Flexibility analysis Flexibility analysis is performed in order to investigate the effect from alternating bending moments caused by pipe temperature expansion/contraction and other imposed displacements from e.g. thermal expansion of pressurised equipment, FPSO swivel stacks, live load deck deflections, sag and hog effect on an FPSO.

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FPSO related piping and pipe stress aspects

Primary Stresses • Primary stresses are those developed by the imposed loading and are necessaryy to satisfy y the equilibrium q between external and internal forces and moments of the piping system. • Typical loads are dead weight and internal pressure pressure. • Sustained stresses are primary stresses. • Primary stresses are NOT self-limiting.

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FPSO related piping and pipe stress aspects

Secondary Stresses • Secondary stresses are those developed by constraining the free displacement p of p piping p g subjected j to thermal loads or imposed p displacements p from movements of anchor points etc. • Hence, Hence thermal-and displacement stresses are in the secondary stress category. • Secondary S stresses are self-limiting. f

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FPSO related piping and pipe stress aspects

Peak Stresses • Unlike loading conditions of secondary stress which causes distortion, peak stresses cause no significant distortion in piping. • Peak stresses are the highest stresses in the region under consideration and should always be taken into consideration in fatigue f and fracture f mechanic calculations.

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Appendix P of ASME B31.3

This Appendix provides alternative rules for evaluating the stress range in piping systems. It considers stresses at operating conditions, including both displacement and sustained loads loads, rather than displacement stress range only only. The method is more comprehensive than that provided in Chapter II and is more suitable for computer analysis of piping systems, including nonlinear effects such as pipes lifting off of supports.

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Loading Cases

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W

SUS

L2

WW+HYD

SUS

L3

W+P1

SUS

L4

W+T1+P1

OPE

L5

W+T2+P1

OPE

L6

W+T1+P1+WIN1

OPE

L7

W+T2+P1+WIN1

OPE

L8

W+T1+P1+U1+WIN1+D1

OPE

L9

W+T1+P1+U1+WIN1+D1+F1

OPE

L10

W+T1+P1+U1+WIN1+D2 W T1 P1 U1 WIN1 D2

OPE

L11

W+T1+P1+U1+WIN1+D2+F1

OPE

L12

W+T2+P1+U1+WIN1+D1

OPE

L13

W+T2+P1+U1+WIN1+D1+F1

OPE

L14

W+T2+P1+U1+WIN1+D2

OPE

L15

W+T2+P1+U1+WIN1+D2+F1

OPE

L16

W+T2+P1+U2+WIN1+D3

OPE

Supress

Supress

Supress

Supress

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L1

Loading Cases

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L17

L8-L6

EXP

U1+D1

Supress

L18

L10-L6

EXP

U1+D2

Supress

L19

L16-L7

EXP

U2+D3

Supress

L20

L4-L3+L5-L3

EXP

T1+T2

Abs

L21

L17+L18+L19

EXP

2U1+D1+D2+T1+T2

Abs

L22

L6-L5

OCC

WIN1

L23

L9-L8

OCC

F1

L24

L11-L10

OCC

F1

L25

L13-L12

OCC

F1

L26

L15-L14

OCC

F1

L27

L2

FAT

1

L28

L3-L1+L20

FAT

3650

L29

2L19

FAT

50000000

WW+HYD P1+(T1+T2)

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2(U2+D3)

FPSO related piping and pipe stress aspects

Flexibility analysis • So S we have h seen th thatt we h have tto perform f an analysis l i th thatt ffulfils lfil our requirements i t since i the notified bodies involved not always support us in the required solutions. • If we look at the codes there are some requirements to get approval of the notified body. • We do make a difference between the requirements of the notified body in order to get an approval and the requirements of the company we work for. • Although we have to comply with the applicable codes we also have to get a safe “feeling” about our design.

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FPSO related piping and pipe stress aspects

Flexibility • Deck Displacements • Forces on restraints (supporting, nozzles) • Friction

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Hogging and sagging

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Space for visuals, tables or info graphics

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FPSO related piping and pipe stress aspects

FPSO related piping and pipe stress aspects

Ship displacements

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FPSO related piping and pipe stress aspects

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Ship displacements

FPSO related piping and pipe stress aspects

Flexibility • Deck Displacements • Forces on restraints (supporting, nozzles) • Friction

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Supporting

Supporting

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The bending moment decreases as the distance of the load from the support increases. Bending force f1 is slightly less than force f2 and this difference (f1-f2) is transferred inward toward the web by the longitudinal force (fs)

Supporting

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This force also has an equal component in the transverse direction. A transverse force applied to a beam sets up transverse (and horizontal) shear forces within the section.

Supporting

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In the case of a symmetrical y section (A) ( ) a force (P) ( ) applied pp in line with the principle axis (y-y) does not result in any twisting action on the member. This is because the torsional moment of the internal transverse shear forces (Æ) is equal to zero.

Supporting

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On the other hand,, in the case of an unsymmetrical y section (B) ( ) the internal transverse shear forces (Æ) form a twisting moment. Due to the above there will be a twisting action applied to the member which will twist under load, in addition to bending.

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Supporting

Supporting

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Supporting that is very flexible is not advisable on an FPSO In this system this type of supporting is used frequently Probably because the pipe itself was thought to be light

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Here it caused problems once it was filled with water as was to be expected

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Supporting

FPSO related piping and pipe stress aspects

Flexibility • Deck Displacements • Forces on restraints (supporting, nozzles) • Friction

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FPSO related piping and pipe stress aspects

Friction • Approximate and simplified methods of analysis may be applied only within the range for which it has been demonstrated to the satisfaction of the competent b d th body thatt th they are sufficiently ffi i tl accurate. t • It is important that we assess the highest load case. Friction is included in most analyses. • The most severe load case of the two (with or without friction) should be send to the notified body and report that the other one leads to lower stresses (with the exceptions, if any).

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FPSO related piping and pipe stress aspects

Wishful thinking • Since a ship is moving all the time no build-up of friction forces will occur • Since a ship is moving all the time the direction of the friction forces changes with time

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FPSO related piping and pipe stress aspects

Increase Flexibility by means of: • Sliding Couplings (Victaulic, Dresser or alike) • Expansion pa s o Bellows e o s • Expansion Loops

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FPSO related piping and pipe stress aspects

Loadings • G-forces due to waves • Blastload • Slugflow • Waterhammer • Hydraulic Shock (Water Piston)

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Modifications

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Modifications

FPSO related piping and pipe stress aspects

Any questions?

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