Design Guide for Slug Force Calculation Procedure

PIPING DISCIPLINE DESIGN PROCEDURE

DTP-P-GEN-10001-00 (Document Numbering)

Design Guide for Slug Force Calculation Procedure

Revision History

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Revision Date

Revision Description Prepared By Department Head (Approver)

0 14/02/2012 For Internal Review PRP SS

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TABLE OF CONTENTS

Contents

1 Purpose

The purpose of this document is to provide the calculation method for evaluating the slug force due to travelling of slug through elbow .Also the procedure gives the guide lines for using these loads in piping and pipeline stress analysis & development of relevant load cases for analysis.

2 Scope




The scope of this design guide covers calculation method for slug force in piping systems containing two phase fluid.

3 Responsibilities

3.1 Stress Lead

Identify preliminary Critical list of lines to be analyzed based on a general defined criteria and Specific

project requirement.

Review & provide Piping & Instrumentation Diagram & Process Flow Diagram to piping stress Engineer.

Check for Adequacy of Support & Type of Support used.

Provide final verification of piping stress isometrics. For compliance with piping code and any computer

calculations.

Check all the calculations performed by stress engineer for purpose of stress analysis.

3.2 Stress Engineer

Calculate necessary parameters required for estimating slug force.

Calculate slug forces for computerized analysis. (For modelling in CAESAR II or AutoPipe Ref.)

All Piping Stress Engineers working in the Piping and Plant Design group are responsible for

Reading, understanding, and implementing all of the instructions found in this and other associated

Procedure.

4 References

4.1.1 Piping handbook by Nayyer & Mohinder, Mac graw hill publications Seventh Edition4.1.2 COADE pipe stress analysis seminar notes4.1.3 Designing of piping systems by M.W.Kellogg Company, A Wiley –Interscience Publication

Revised Second edition




5 Definitions

5.1 Slug

Slug flow is phenomenon where short cylinder of fluid, moves independently thru otherwise gaseous

piping system, as shown roughly in the figure 5.1.1.

Very often, severe problems can occur if slug flow is present in the pipeline. A number of circumstanceswill lead to the generation of slug flow. For instance, if an oil-gas mixture flows along a pipe on theseabed and then rises to a platform level up a vertical pipe, the liquid may collect upstream of the benduntil it reaches a given level, at which point it is swept up the vertical leg, giving rise to mechanicalproblems in the platform equipment. In power plants, a similar phenomenon may occur in a pocketed line. Also, slug flow causes pressure fluctuations in piping, which can upset process conditions and cause inconsistent instrument sensing.

Existence of two-phase flow in a pipeline may also cause more severe fluid transient problems than occur in a single-phase condition. Should a two-phase flow condition be unavoidable in the system operation, the impact of two-phase flow transient condition should be taken into consideration in system design and piping support evaluation.

6 Procedure

6.1 Procedure for calculating slug force at 900 elbow

Slug force at 90º elbow can be estimated by the following procedure.




Then use following formula for velocity calculation.

vAQ ××=ρ Eqn 6.1.1

Now calculate slug mass,

vM ×=ρ Eqn 6.1.2

Where,

volumev=

LDv i ××Π= 2

4Eqn 6.1.3

Where,L= Slug length,

Note: Thumb rule for calculation of slug length. [ ]mDL 05×=Now slug force can be estimated using following formula :

g

vmDLFF

2

2××= Eqn 6.1.4

Where,F = Slug force at elbow [N]A = Area of the pipe through which the fluid is moving [m2]v = Estimated velocity of fluid [m/sec]ρ = Density of fluid [kg/m3]DLF = Dynamic load factorM = Slug mass [kg]g = Gravitational constant [9.81m/sec2]




This slug force should be applied on elbows depending on flow direction.




Design Guide for Slug Force Calculation Procedure

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