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 Revision Revision Level Date

0

14/02/2012

Revision Description

Prepared By

For Internal Review

PRP

Department Head (Approver)

SS

This document and all contained herein are proprietary of PUNJ LLOYD LIMITED OFFSHORE DIVISION and is subjected to confidentiality restrictions between PUNJ LLOYD LIMITED OFFSHORE DIVISION and the Recipient. Copyright Reserved.

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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

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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 Edition 4.1.2 COADE pipe stress analysis seminar notes 4.1.3 Designing of piping systems by M.W.Kellogg Company, A Wiley –Interscience Publication Revised Second edition

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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 circumstances will lead to the generation of slug flow. For instance, if an oil-gas mixture flows along a pipe on the seabed and then rises to a platform level up a vertical pipe, the liquid may collect upstream of the bend until it reaches a given level, at which point it is swept up the vertical leg, giving rise to mechanical problems 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.

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Then use following formula for velocity calculation.

Q = ρ × A ×v

Eqn 6.1.1

Now calculate slug mass,

M =ρ×v

Eqn 6.1.2

Where,

v =volume Π 2 v = ×Di ×L 4

Eqn 6.1.3

Where, L= Slug length, Note: Thumb rule for calculation of slug length.

L = 5 × D0 [ m]

Now slug force can be estimated using following formula :

F =

DLF

×m ×v 2 2g

Eqn 6.1.4

Where, F A

v ρ

DLF M g

= = = = = = =

Slug force at elbow [N] Area of the pipe through which the fluid is moving [m2] Estimated velocity of fluid [m/sec] Density of fluid [kg/m3] Dynamic load factor Slug mass [kg] Gravitational constant [9.81m/sec2]

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

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