Instrumentation and Pigging

8/10/2019 Instrumentation and Pigging

http://slidepdf.com/reader/full/instrumentation-and-pigging 1/60

1PE 607: Oil & Gas Pipeline Design, Maintenance & Repair

Dr. Abdel-Alim Hashem

Professor of Petroleum EngineeringMining, Petroleum & Metallurgical Eng. Dept.

Faculty of Engineering – Cairo University

[email protected]@yahoo.com

Part 7: Instrumentation and Pigging

Oil and Gas Pipeline Design,

Maintenance and Repair




PIGGING OPERATIONS




REASONS FOR PIGGING

• Batch or separate dissimilar products

• Displacement purposes

• Internal inspection.




SELECTION CRITERIA

The purpose:

• Type, location, and volume of the

substance to be removed or displaced in

conventional pigging applications,• Type of information to be gathered from an

intelligent pig run,

• Objectives and goals for the pig run




SELECTION CRITERIA

Characteristics of the pipeline

• The minimum and maximum internal line

sizes,

• Maximum distance pig must travel,• Minimum bend radius, and bend angles,

• Additional features such as valve types,

branch connections, and the elevation

profile.




UTILITY PIGS

Foam pigsMandrel pigs




IN LINE INSPECTION TOOLS

• In Line Inspection provides information on

the condition of the pipe and/or itscontents.

• With few exceptions, the In Line InspectionTool itself is simply the tool which gathers

the data, which is then analyzed by the

engineers and technicians to determineand report on the condition of the line.




GEL PIGS• Gel pigs are a series of gelled

liquid systems which have been

developed for use in pipelineoperations, either during initialcommissioning, or as a part of acontinuing maintenance program.

• Most pipeline gels are water-based, but a range of chemicals,solvents, and even acids can begelled.

• Some chemicals can be gelled as

the bulk liquid and others onlydiluted in a carrier.

• Gelled diesel used as a carrier ofcorrosion inhibitor in gas lines.




TYPES OF GEL

• Batching, or separator gel

• Debris pickup gel

• Hydrocarbon gel

• Dehydrating gel




PRINCIPLE APPLICATION OF GEL PIGS

• Product separation

• Debris removal• Line filling/hydro testing

• Dewatering and drying• Condensate removal from gas lines

• Inhibitor and biocide lay down

• Special chemical treatment• Removal of stuck pigs




DUAL DIAMETER PIGS




MULTI DIAMETERS PIGS




WHY DO PIG STUCK?

• Pigs plug a pipe and cause a blockage

• Build up of wax in front of a pig causing a wax plug• Unidirectional bypass leading to a stuck pig with

product flowing past to it

• Jack knifing of a dual module pig

• Excessive wear leading to failure of seals and drive

• Mechanical damage

• Failure due to environment material selection

• Others that do not fail in the categories above




SPHERE JAMMED IN OFF TAKE

Cause

• Due to flow diversion, Flowfrom branch line

Solution

• Require to provide a bararrangement in receivers orspecial flow/sphere tees inthe pipeline

• The bearing arrangementshould be checked

• In dual diameter line, specialbearing arrangement maybe necessary




INCORRECT SIZED PIG COMPONENTS




INCORRECT VALVE/VALVE NOT OPENCause

• Use of incorrect valve in line, valves are not fully open

• Happens in smaller diameter line 12 in and smaller Solution

• Checks in the operating procedures should be in place tocheck opening the valve

• Pig design should consider this eventually




INSUFFICIENT INFORMATION

(wrong bend radius)

Cause

• Insufficient informationregarding pipeline design,

especially older one

Solution

• Pigs must be designed for

the line

• Some conservative

assumptions must be madeand agreed




PIG PUSHING ON PIG IN FRONTCause

• when one pig pushes into the rear of another pig. It actson the seals, forcing them harder against the pipe wall

Solution

• Have a bumper noses, both front and rear

• This be provided even if it is not only planned to haveone pig in the line




COLLIDING PIGS

Causes

• Possibility of pigs to meet atwyes or tees in complex lines

Solution

• Good communication andpigging operation procedures

• One pig may be made

sacrificial




HIGH FRICTION PIGSCause

• Change from thin wall to

thick wall pipe, lead toserious damage of theseals

Solution• All pigs should be

designed to deal with allinternal diameters of the

line and if in doubt, a testperformed




DEPRIS IN THE LINECause

• Depris such as sand lift the pig up andcause rapid wear

Solution

• Provide strong and sufficient bypass to the

pig




FLOW AROUND THE PIGCause

• Pipeline features suchas branches andofftakes, wyes etc.which can lead to a

stalled pig if thebypass system isincorrect

Solution• Consider the position

of the offtakes




INSUFFICIENT SEALING LENGTHCause

• Components such as wyes and teesSolution

• A dual pig should be used to span the

component




PROXIMITY OF COMPONENTS

Cause

• Too close line components which makes a risk of bypass

as the sealing is incorrectSolution

• The configuration of the pig must be considered andsufficient length between line components should be

allowed




REDUCER LENGTHCause

• When the diameter of the pipe is reduced from a large

diameter to a smaller diameter Solution

• The reducer length should be as long as possible withinspection pigging compared with utility pigging where it

should be as short as possible




DRIVING DUAL MODULE PIG ON REARCause

• Bends makes the pigstend to move laterally,results in seal flapping

Solution

• Pressure should betransferred to the frontmodule via bypassports on the rear

• This allows the rearmodule to be towed




DUAL MODULE PIG WITH LEAKAGECause

• Low density gas leaksthrough a dual modulepig, differentialpressure is set up

across the pig andlateral movement canresult

Solution

• Use better support forthe pig and correctsizing of the seals




WEAR

Cause

• Abrasion cause wear due to large distanceSolution

• Determine the maximum piggable distancedepending on: pig velocity, fluid type, pig

differential pressure, pipeline nominal

diameter, pipe surface type




VELOCITY EXCURSIONSCause

• Large accelerationand velocities dueto thecompressibility of

the systemSolution

• Take into

considerationduring pigselection




COUPLING DAMAGECause

• In dual module pig,

compression and tensionon coupling betweenmodule

Solution

• Strong coupling selection

• Joint must be capable ofopening to the correct

angle to allow the pig tonegotiate the linefeatures




TEARING SEALS OUT OF BOLTHOLES

Cause

• Highly oversizedsealing discs

Solution

• Oversize needs to becarefully selected andthe boltingarrangement such that

the discs is properlyclamped to the pig




PIGS IN FREE FALL

Cause

• Steep sections such asrisers, lead to high

velocity

Solution

• Slow the pig down




ENVIRONMENTAL ISSUESCause

• Line temperature (degradation of the sealmaterials, expansion of metallic parts

• Line pressure (Cavities, explosion, decompression)

• Line contents (incompatibility with the sealmaterials)

• Immersion time

Solution• Check such aspects with pig suppliers

UNUSUAL DAMAGE TO 10” X 16” PIG




UNUSUAL DAMAGE TO 10 X 16 PIG

DURING TESTING

• As an example of the need to “Expect the

Unexpected”, the following photographshows a 10” x 16” pig stuck in the straight

10” line at a flange and offtake



UNUSUAL DAMAGE TO 10” X 16” PIG




DURING TESTING




Ff

Vp

P1 P2

Pipe Wall Pig

PIG MOTION ANALYSIS




PIG MOTION ANALYSIS (Cont.)• The drag force is equal in magnitude but

opposite direction of the contact friction force

• The equation shows that the pig velocity is

smaller than fluid velocity by Vd

N F F f D η ==

AC

N V WhereV V V

D

d d p ρ

η 2=−=




• The leakage ratio is given by:

• Leakage = 1-Vp/V

• Where• CD = Drag coefficient

• A = Area

• Ρ = Fluid density

• η = Contact friction coefficient

• N = Angular speed, rpm

• kd = Diameter ratio of the disk

( )

4

22

4

1

d d D d

d

k DC k

Dk

= =

−

PIG MOTION ANALYSIS (Cont.)




Example• A pig with two end disks having an

effective disk diameter of Dd=0.98 D isused in a 10 in steel pipe for cleaning thepipe interior. The fluid is water flowing at 6

fps. The pig being squeezed into the pipeexerted a total normal force of 400 lb onthe pipe wall and the contact friction

coefficient between the pig and the pipe iso.6. Find the velocity of the pig and thepercentage of the leakage flow

Instrumentation and Pigging

Documents

Transcript of Instrumentation and Pigging