Problem:

How to model the load on a piping system installed on a ship, Rig, or FPSO (Floating Production Storage and Offloading) when using AutoPIPE?

Solution:

Q1. How to define acceleration loads?

Answer:

Enter as seismic g acceleration load cases, E1, E2, E3

Q2. How to define structural deflection loads?

Answer:

Enter as displacements in User defined cases e.g. U1, U2 etc

Q3. The load combinations (see 1.5) are adequately for each stress analysis problem.

Answer:

Stress evaluation to B31.3 sustained, expansion, and occasional stresses except fatigue

Q4. How to calculate fatigue?

Answer:

Suggest that the method of fatigue assessment would be considered from DNV classification note 30.2 “Fatigue Strength Analysis for Mobile Offshore units” and allowable stresses from British Pressure vessel code PD5500 -2000. 

Suggest two fatigue cases:

Fatigue Case-1: (Loading/Unloading and Thermal effects)

Fatigue Case-2: (Wave motion and 100 year storm)

Suggested combinations:

Recommend that the piping system be analyzed for the effects of static, dynamic and occasional loading as required for each stress analysis problem. This can result in many code and non-code load combinations so one of the best approaches is to envelope the worst case sustained, expansion and occasional load cases.

Operating Case: GR + P + T + E + U

Sustained Case: GR + P + U

Expansion Case: T + U

Occasional Cases: Wind, transport, blast, slug, or surge

Where,

GR = Weight of pipe including fluid, insulation and components

P = Design pressure

T = Temperature range (includes maximum and minimum)

U = Equipment nozzle movement and Structural deflection due to ship motion, hogging/sagging

E = Acceleration in X, Y and Z directions due to ship motions (roll, pitch, heave)

In order to reduce the no. of cases to a minimum; discuss with team members and take collective decision. Eliminate the least severe cases. Make combination of worst cases.

Consider the following for your discussion: 

A) Operating: With operating temp., Design (hot) temp, and design (cold) temp. and Upset temp. with combination of i) wind ii) without wind iii) acceleration  iv) without acceleration

B) Hydro testing

C) Dynamic analysis

See Also

Bentley AutoPIPE