FPSO related piping and pipe stress aspects

FPSO related piping and pipe stress aspectsPaul Voorhaar & Hugo Kamphuijs

November 2010

p. 2Rough sea

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p. 3Who we are

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

What we are not:

•Persons that think their approach is simply the best•Persons that think their approach is simply the best

•Stress engineers that have stopped being critical about themselves

•Technicians that do not listen to other stress engineers

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p. 4Why are we giving this presentation?

• Firstly because we were asked by Dynaflow to do so

• Secondly because we feel that we can share some of our problems withSecondly because we feel that we can share some of our problems with

others and we will all benefit

• We appreciate Dynaflow for giving these presentations for all interested pp y g g p

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

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

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p. 5FPSO related piping and pipe stress aspects

Difference between:

• Land based installations

• Coastal installations (Jetties)

• Fixed Sea based installationsFixed Sea based installations

• Floating Sea based installations on a fixed location (FPSO)



- Length 248.12 meters- Breadth moulded 42 meters- Depth moulded 21 2 meters- Depth moulded 21.2 meters- Draft, design + scantling 14.9

meters- Dead weight tonnage 105,000 dwt

Deck area 7 985 m2- Deck area 7,985 m2- Topsides area 6,000 m2- Deck payload 7,000 tonnes- Accommodation 84 persons

p. 8Ship movements

Space for visuals, tables or info graphicsg p

p. 9Determination of loading cases

RESTRAINT SUMMARY REPORT: Loads On RestraintsVarious Load CasesLOAD CASE DEFINITION KEY

CASE 1 (SUS) WCASE 1 (SUS) WCASE 14 (OPE) W+D4+T2+P2+U1

CASE 15 (SUS) U1CASE 16 (SUS) U2CASE 17 (SUS) WIN1

NODE Load FX N. FY N. FZ N. MX N.m. MY N.m. MZ N.m. Case

160 Rigid Y1(SUS) 986 10794 719 0 0 01(SUS) 986 -10794 719 0 0 0

14(OPE) 2729 -9115 167 0 0 0

15(SUS) 186 2796 818 0 0 016(SUS) 252 4755 1404 0 0 017(SUS) 1 13 4 0 0 017(SUS) 1 13 4 0 0 0

MAX 2729/L14 -10794/L1 1404/L16

p. 10The result of this

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p. 11Ship movements

Space for visuals, tables or info graphicsg p

p. 12Loading Cases

To avoid numerous combinations of loadings we do calculate the worst combination of acceleration first

L1 W+U1+U2+U3 SUSU1 U2 U3

L1 W+U1+U2+U3 SUSL2 W+U1+U2-U3 SUSL3 W+U1-U2-U3 SUS

X 0.5Y 0.3Z 0.2

L4 W+U1-U2+U3 SUSL5 W-U1-U2-U3 SUSL6 W-U1-U2+U3 SUSL7 W-U1+U2-U3 SUSL8 W-U1+U2+U3 SUS

p. 13Loading Cases

One of these combinations will give the highest stresses.

Say it is combination 2 In that case only the following accelerations will be used:Say it is combination 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.


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.


Primary Stresses

• Primary stresses are those developed by the imposed loading and are

necessary to satisfy the equilibrium between external and internal forces and y y q

moments of the piping system.

• Typical loads are dead weight and internal pressure• Typical loads are dead weight and internal pressure.

• Sustained stresses are primary stresses.

• Primary stresses are NOT self-limiting.


Secondary Stresses

• Secondary stresses are those developed by constraining the free

displacement of piping subjected to thermal loads or imposed displacements p p p g j p p

from movements of anchor points etc.

• Hence thermal-and displacement stresses are in the secondary stress• Hence, thermal-and displacement stresses are in the secondary stress

category.

S f• Secondary stresses are self-limiting.


Peak Stresses

• Unlike loading conditions of secondary stress which causes distortion, peak

stresses cause no significant distortion in piping.stresses cause no significant distortion in piping.

• Peak stresses are the highest stresses in the region under consideration and

f fshould always be taken into consideration in fatigue and fracture mechanic

calculations.

p. 18Appendix 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 rather than displacement stress range onlysustained loads, rather than displacement stress range 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.

p. 19Loading Cases

L1 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 Supress

L9 W+T1+P1+U1+WIN1+D1+F1 OPE

L10 W+T1+P1+U1+WIN1+D2 OPE SupressL10 W T1 P1 U1 WIN1 D2 OPE Supress






L16 W+T2+P1+U2+WIN1+D3 OPE

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p. 20Loading Cases

L17 L8-L6 EXP U1+D1 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 WW+HYDL27 L2 FAT 1 WW+HYD

L28 L3-L1+L20 FAT 3650 P1+(T1+T2)

L29 2L19 FAT 50000000 2(U2+D3)

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Flexibility analysis

S h th t h t f l i th t f lfil i t i• So we have seen that we have to perform an analysis that fulfils our requirements since

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.


Flexibility

• Deck Displacements

• Forces on restraints (supporting, nozzles)

• FrictionFriction

p. 23Hogging and sagging

Space for visuals, tables or info graphics

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Ship displacements


Ship displacements

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Flexibility




p. 28Supporting

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p. 29Supporting

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)

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p. 30Supporting

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.

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p. 31Supporting

In the case of a symmetrical section (A) a force (P) applied in line with the y ( ) ( ) ppprinciple 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 ( ) is equal to zero.

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p. 32Supporting

On the other hand, in the case of an unsymmetrical section (B) the , y ( )internal transverse shear forces ( ) 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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p. 33Supporting

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p. 34Supporting

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

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

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p. 35Supporting

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Flexibility





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 t th ffi i tl tbody that they are sufficiently accurate.

• It is important that we assess the highest load case. Friction is included in most analyses.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).


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 timewith time


Increase Flexibility by means of:

• Sliding Couplings (Victaulic, Dresser or alike)

• Expansion Bellowspa s o e o s

• Expansion Loops


Loadings

• G-forces due to waves

• Blastload

• SlugflowSlugflow

• Waterhammer

• Hydraulic Shock (Water Piston)

p. 41Modifications

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p. 42Modifications

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Any questions?

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FPSO related piping and pipe stress aspects

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