Download pdf - Aspects of Piperack Design

Dipesh H Dahanuwala Date : 25-June-2013

Agenda

Aim

Key Objectives

Aspects of Pipe racks

Optimization Idea

Summary

Aim

To present different aspects of pipe rack

Key Objective

Purpose of Pipe rack

Materials of Construction

Execution Stages

Analysis and Design Concepts

Purpose of Pipe rack

To support group of parallel pipes running at different elevations with emerging or merging branches


Concrete

Cast-in-situ

Precast

Application : Concrete Pipe racks are

made in case of corrosive environment


Structural Steel

Structural Steel has been used for pipe rack in all projects executed by NPCC

Reason :

FEED requirements

Other advantages are :

Speed of Construction

Better Quality Control

Execution Stages

Preliminary sizing of Pipe rack based on geometry and loading firmed up by Piping

Raise PR for procurement of items

Detailed Engineering

Construction Engineering

Fabrication / Painting

Erection of Pipe rack at site


Geometrical Planning

Loading

Structural Design

End Connection

Base Plate and Anchor Bolt Design

Foundation Design



Grid Location

Tier Elevation

Planning of Beams

Planning of Elevation Bracings

Planning of Plan Bracings

Expansion Joint


Grid Location : by Piping Discipline

Basis :

Width of pipe rack : No. of pipes to be routed with future allowance.

Grid distance :

Based on Piping Support requirements.

Road crossing horizontal clearance

Geometrical Planning Grid Location


Tier Elevations : by Piping Discipline

Basis :

To maintain the minimum headroom for the pipes crossing the roads

Tie-in elevation

Sloping lines

Geometrical Planning Tier Elevation


Planning of Beams : Location of main beam as per Main Grid distances

provided by Piping

Location of secondary beam between Main Grid beams depends on support for small bore pipes provided by Piping

Longitudinal beams to stabilize the Grid Frames, transfer longitudinal forces to vertical braced bay and support secondary beam.

LARGE BORE PIPES

SMALL BORE PIPES


Planning of Elevation Bracings In the middle of pipe rack to allow thermal expansion of

pipe rack on either side thus minimizing thermal restraint in longitudinal direction

To transfer longitudinal forces to foundation

To provide stability to pipe rack in longitudinal direction

Avoid multiple braced bay on same pipe rack to avoid thermal forces in longitudinal beams and braces


Planning of Plan Bracings

Purpose :

To effectively transfer horizontal forces to column

Make better use of structure by introducing truss action instead of bending.


Expansion Joint

Purpose :

To account for thermal expansion of structure

Basis :

As per Company requirement

Methods :

Provide slotted hole connection in the longitudinal beam at all levels at identified location

Pipe rack with slotted joint as expansion joint

Loading

Loads Generated by Civil Discipline

Dead Load (DL)

Live Load (LL)

Temperature Load on Structure (TL)

Earthquake Load (EQ)

Wind Load (WL)

Contingency Load (CL)

Miscellaneous Load (ML)

Loading

Loads Furnished by Piping Discipline

Pipe Empty Load (PE)

Pipe Operating Load (PO)

Pipe Hydro test Load (PT)

Pipe Anchor / Guide Load (PA)

Pipe Friction Load (PF)

Loading

Dead Load (DL)

Weight of Structure

Weight of Fireproofing

Weight of Grating and Handrail in case of platforms on pipe rack

Loading

Live Load (LL)

Applicable in case platform on pipe rack

Normally LL = 5 kPa, but depends on platform use defined by Piping.

Loading

Temperature (Thermal) Load on structure (TL) Due to difference between highest and lowest mean

temperature and based on Design Basis. Typical value for UAE is taken as 60 deg C.

Thermal loads can be minimized by providing Flexible Structure i.e. reduce structural redundancy.

Note : Length of slotted hole connection is based on deflection due to thermal expansion / contraction of structure.

Loading Thermal Load

Good Design

Release of thermal stresses (free to move in both directions)

Loading Thermal Load

Bad Design

Thermal stresses are arrested (restrained by bracings at ends)

Loading

Pipe Empty & Cable Tray Load (PE)

< 12 Pipes : ~ 1.2 kPa

>=12 Pipes : concentrated load (as per Pipe Stress Analysis)

Empty Equipment Load, if any

Cable Tray Load : 1 kPa for each level of cable tray

Critical for checking uplift on foundation

Loading

Pipe Operating Load (PO)

< 12 Pipes : ~ 2 kPa

>=12 Pipes : concentrated load (as per Pipe Stress Analysis)

Operating Equipment Load, if any

Loading

Pipe Hydro Test Load (PT)

To account for pressure testing of pipes

As per Pipe Stress Analysis

Hydro-test weight of equipment

For larger dia pipes (>12) only one pipe hydro tested and other pipes empty (To be confirmed by Piping Discipline and reflected in piping isometric and hydro-test specification)

Loading

Pipe Anchor / Guide Load (PA)

Load to be defined by Piping Discipline

Anchoring lug configuration to be confirmed by Civil in case of high anchor loads

Only Top flange effective Both Flanges effective

Anchor Lug

Loading

Pipe Friction Load (PF)

Cause : Hot lines sliding across beam

Loading Pipe Friction (PF)

For Global Check Longitudinal direction = 5% of Pipe operating Load

Transverse direction = 5% of Pipe operating Load

0.05 P

0.05 P

P = Piping Operating Load

Loading Pipe Friction Load

For Local beam check

1

2

3

4

5

6

8

7

0.3 P

0.1 P

0.2 P 0.1 P

P = Piping Operating Load

Loading Pipe Friction Load

For Local beam check

In Longitudinal direction :

10% of the operating weight (no of pipes >= 7)

20% of the operating weight (no of pipes = 4 to 6)

30% of the operating weight (no of pipes

Loading

Earthquake Load (EQ)

As per project geotechnical investigation and design basis

Earthquake load to be generated for following conditions

a) Erection : DL + PE

b) Operating Case : DL + PO + LL

Loading Earthquake Load (EQ)

As per IBC 2009 & ASCE-7-10, typical parameters for ZADCO site is as follows : Site Class = D

Ss (Short period Spectral Acceleration) = 0.32

S1 (1 sec Spectral Acceleration) = 1.32

I (Importance Factor) = 1 (depends on occupancy category)

R (Response Reduction Factor)

= 3.5 (for ordinary moment resisting frames)

= 7.0 (for special truss frames)

Earthquake Load is generated in STAAD-Pro as per parameters defined in Design Basis.

Loading

Wind Load (WL) As per project design basis

As per ASCE-7-10, typical parameters for ADCO site is as follows :

Basic wind speed (V) = 44.7 m/sec

Importance factor (I) = 1.15

Exposure Category = C

Wind Directionality Factor (Kd) = 0.85

Topographic factor (Kzt) = 1.0

Velocity Pressure Coefficient (Kz) = depends on height of structure

Velocity Pressure (qz) = 0.613 x Kz x Kzt xKd x V2 x I

Loading Wind Load

Gust effect factor (G) = 0.85

Force coefficient Cf = 2 for flat surface members

Cf = 0.8 for tubular members

Wind Force on members = qz x G x Cf x size of member

Wind Load on Pipes = qz x G x Cf x (Pipe Dia)

Pipe Dia = D1+D2+D3 for pipe rack width 4m

D1, D2, D3 and D4 are largest pipe dia in descending order.

Loading

Contingency Load (CL) To account for accidental load on members (e.g.

maintenance load)

Shall be considered for the design of local member

For Beam Design = 10 kN at midspan

Loading

Miscellaneous Load, if applicable (ML) Crane Load

Dynamic Load (considered as equivalent static load)

Blast Load

Structural Design

Member end releases

Support Condition at base plate level

Load Combinations

Design Parameters

Support reactions

Structural Design

Member end releases Main Grid members transverse direction : fixed

Main Grid members longitudinal direction : pinned

Vertical bracings : pinned (to account for local bending due to fireproofing load)

Secondary beams : pinned

Plan Bracings : Truss

Structural Design Member end release

Fixed

Pinned

Truss

Structural Design Member end release

Pinned Connection Fixed Connection Truss Connection

Structural Design

Support Condition at base plate level

Fixed Base Pinned Base

Structural Design Support Condition at base plate level

Fixed in transverse and pinned in longitudinal

Reduce main frame column and beam size

Reduce lateral deflection

Increase base plate size, anchor bolt, pedestal and footing size

Reduction in structural steel Increase in foundation concrete

Structural Design Support Condition at base plate level

Pinned in both direction

Increase main frame column and beam size

Increase lateral deflection

Decrease base plate size, anchor bolt, pedestal and footing size

Reduction in foundation concrete Increase in structural steel

Choose support condition to maintain balance between structural and foundation system

Structural Design

Load Combinations

Erection Case :

0.6 (DL+PE) + WL (or 0.7EQ)

Operating Case :

DL+TL+LL+PO+PA+PF+CL

DL+TL+PO+PA+PF+0.75(LL+WL)

DL+TL+PO+PA+PF+0.75(LL+0.7EQ)

DL+TL+PO+PA+PF+WL

DL+TL+PO+PA+PF+0.7EQ

Structural Design Load Combinations

Test Case :

DL+TL+PT+LL

DL+TL+PT+0.75(LL+0.5WL)

DL+TL+PT+0.5WL

Maintenance Case :

DL+TL+PO+PA+PF+ML

DL+TL+PO+PA+PF+0.75(LL+ML)

Local member Case :

DL+TL+PO+PA+PF (Full)+CL

Structural Design

Design Parameters Design code and method of analysis

Yield strength of steel

Slenderness ratio limit

Unsupported length of member in major and minor axis (Ly & Lz)

Unsupported length of compression flange (UNB, UNT)

Deflection limit (DFF)

Deflection parameters (DJ1, DJ2)

Structural Design

Support Reaction Obtained from STAAD-Pro

For base plate and anchor bolt sizing

For pedestal and foundation design

End Connection

Welded Type

For onshore projects, complete welded pipe rack modules is not feasible due to :

Size restrictions imposed by Local Transport Authority

Hindrances at site due to existing facilities

End Connection

Shop Weld :

Used for gusset plate, base plate welding

Field Weld :

Limited to few location

FEED requirement

Expensive and poor quality control

End Connection

Bolted Type FEED requirement

Easy to install and remove

Easy to transport at site in small assembly


Base Plate Design based on support reaction from STAAD-Pro

Size depends on

Allowable bearing stress on grout due to Compression + Bending from superstructure

Anchor bolt spacing on base plate

Thickness depends on bending stress caused due to

Bearing stress in grout

Tensile force in anchor bolt

Thickness can be reduced by providing stiffeners


Anchor Bolt Design is based on support reactions from STAAD-Pro

Size and arrangement depends on Tension + Bending from superstructure

Designed to carry on tension force

Shear from superstructure to be carried by shear key

Minimum spacing >= 7 x dia of bolt

Minimum edge distance from concrete >= 4 x dia of bolt

Foundation Design

Type of foundation Depends on bearing capacity and settlement criteria

Generally shallow isolated foundation

Deep foundations (pile) in case of unusual foundation loads

For isolated footing, foundation depth preferred 1.5 m below grade to allow space for utilities (e.g. cable trenches, UG pipes etc)

Foundation Design

Stability Checks Bearing capacity for individual footing design

Overturning and Sliding for overall pipe rack structure with foundation.

Optimization Idea

Reduce the piping load on pipe rack by using loads from Stress analysis output

Place heavy Loads on lower tier and near support

Reduce thermal load on pipe rack (long stretches) by introduction of loops

Use of high yield strength steel to reduce usage of structural steel --> reduction in foundation --> Ultimately reduction in overall cost.

Summary

Planning of beams & bracings : It plays a key role in the overall economy of pipe rack structure and foundation

Understanding of loading application

Various design aspects such as member releases, support at base plate level, load combinations, design parameters, end connection type, base plate and foundation design

Optimization Idea

Acknowledgement Mr. Rachid Younis (EM-Civil)

Thank You