Pig Trap Design and Assessment Considerations - Pipeline & Gas Journal

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A pig trap mut e deigned to match t he pipeline ection deign pecication. The mechanical deign characteritic of the pig trap hould meet or

exceed the deign preure, have the ame deign factor, have compatile material tpe, e deigned uing the ame deign code and e uitale for the

ame temperature range a the pipeline ection that it erve.

Alo, a pig trap mut e dimenionall uited for the tpe of pigging that i expected on the pipeline ection. The critical length of the arrel and lineize pipe ection mut e long enough to accommodate the longet pig t hat will e ued in the pipeline ection.

When deciding where to locate a pig trap, there are variou thing to conider. The pig trap hould not e placed near an open ame or ignition

ource. Man uilding code and pipeline companie have rule and regulation a out what tpe of powered equipment i allowed within certain

ditance of an opening to the pipeline uch a a cloure door. If the pig trap i to e located in an area where horizontal pace i not at a premium (uch

a on an ohore platform or a rener), then care hould e taken to provide ucient work pace adjacent to the cloure door for pigging operation.

Thee operation can take the form of loading and unloading long inpection pig, removal of liquid and deri from the pipeline and into a wate

container, intallation and operation of a temporar eparator, etc.

Another conideration that i important to the afe and ecient operation of a pig trap i how the arrel i oriented at the pigging tation. An valve or

intrumentation aociated with the operation of the pig trap hould e given adequate pace to provide routine maintenance or replacement. The

cloure door hould face awa from other equipment and place where people tpicall congregate (i.e. reak area, parking lot, etc.). There have een

rare occurrence where pig have hot out of pig trap and damaged equipment, a well a, injured people. The overized pipe ection of a pig trap i notnamed arrel coincidence.

In recent ear, the energ indutr ha ecome increaingl focued on what eect it operation are having on the environment. The placement of a

pig trap i alo a concern in thi area. When a pig trap i vented or a cloure door i opened, forethought hould e taken to minimize or eliminate the

occurrence of hazardou contaminant within a pipeline from reaching the outide atmophere or contaminating the near ground or water.

Pipeline companie that operate large-diameter pipeline hould conider the ue of material-handling equipment when it come to conducting pigging

operation. Mandrel or pherical pig ued in a pipeline that i 20 inche in diameter or large can e too heav or awkward for one or two people to

handle afel. In addition, even mall-diameter inpection tool are tpicall too heav and long for one or two people to eail manipulate into or out of

a pig trap. There are variou deign of pig tra availale on the market. ome pig tra have wheel while other are tationar. There are other pig tra

that have automation for puhing a pig into or pulling a pig out of a pig trap. Man pig tra are tted with drip pan for collecting liquid or ne deri

that ma fall o of a pig once it i out of the receiver. In ome cae, lifting equipment ma e necear to move large pig into poition. Ji crane,

gantr crane and fork lift are all example of pig-handling equipment.

Pig trap and pigging tem hould e deigned according to the ame deign code a the pipeline to which the are connected. The predominant

code ued for pipeline deign in man countrie are written AM. The AM code commonl encountered in the pipeline indutr are AM 31.4

which govern the deign of liquid pipeline; AM 31.8 which govern the deign of ga pipeline; AM 31.3 which govern the deign of proce

piping and AM ection VIII, Div. 1 and 2 which govern the deign of preure veel (ometime referred to a the oiler Code). There are other code

in ue that govern the deign of pig trap uch a CA Z-662 in Canada or AM 31.11 for lurr pipeline.

Pig Trap Deign And Aement ConiderationJanuar 2011 Vol. 238 No. 1 (http://pgjonline.com/iue/januar-2011-vol-238-no-1/)
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It i helpful to the purchaer of pipeline equipment to undertand ome of the dierence among the commonl ued AM code. AM 31.4

Pipeline Tranportation tem for Liquid Hdrocaron and Other Liquid (crude oil, liquid petroleum ga, anhdrou ammonia, alcohol and caron

dioxide) allow for deign with certain teel material ATM A694 F42 to F70, A707 L3 CL3, A105, A350 LF2, A182 F316, A182 F51 (Duplex) and other;

the deign maximum allowale tre value are determined deign factor (0.72 or 0.6) multiplied pecied minimum ield trength (MY) of

material; Pipe Wall Thickne Formula: wt = PD/2F (wt=wall thickne; P=deign preure; D=pipe diameter(OD); =allowale tre; F=deign factor);

aed upon the allowale hoop tre of the material in quetion; welding tandard i per API 1004.

AM 31.8 Ga Tranmiion and Ditriution Piping tem. Ga (not gaoline) a ued in thi code commonl refer to natural ga, manufactured

ga and liqueed petroleum ga ditriuted a a vapor. Thi code allow for deign with imilar material a in AM 31.4. Deign maximum allowale

tre value are determined deign factor (0.8, 0.72, 0.6, 0.5 or 0.4) multiplied MY of material. Deign factor are related to population denit in

proximit of the pipeline. Pipe Wall Thickne Formula: wt = PD/2F (wt=wall thickne; P=deign preure; D=pipe diameter(OD); =allowale tre;

F=deign factor); aed upon the allowale hoop tre of the material in quetion. Welding tandard i per API 1004.

AM 31.3 Proce Piping (ha een referred to a rener piping) Allowale material are retricted to 31.3 lited material uuall A105, A350

LF2, A182 F316. ome commonl ued high-ield material (i.e. A694 & A707) are not permitted under thi Code. Deign maximum allowale tre

value are determined the leer of (1/3 x u(tenile trength)) or (2/3 x (ield tre)); the allowale tre value are found in 31.3 a taulated

value. Overall, material thicknee calculated uing 31.3 tend to e more conervative or thicker than thoe calculated uing 31.4 or 31.8. Pipe Wall

Thickne Formula: wt = PD/2(+PY) (wt=wall thickne; P=deign preure; D=pipe diameter(OD); =allowale tre; =qualit factor; Y=coecient) ;

aed upon the tenile trength of the material. Welding tandard i per AM ection IX.

AM ection VIII Diviion 1 AM oiler & Preure Veel Code Rule for Contruction of Preure Veel. Allowale material are retricted to AM

ection II lited material uuall A105, A350 LF2, A182 F316. ome commonl ued high-ield material (i.e. A694 & A707) are not permitted

under thi Code. Deign maximum allowale tre value are found in AM ection II a taulated value. Overall, material thickne calculated uing

AM ection VIII Div. 1 tend to e more conervative or thicker than thoe calculated uing 31.3. Pipe Wall Thickne Formula: wt = PR/2(-0.6P)

(wt=wall thickne; P=deign preure; R=pipe radiu(inide radiu); =allowale tre [leer of (u(tenile trength) divided 3.5) or (2/3 multiplied

(ield tre))]; =qualit factor) ; aed upon the tenile trength of the material. U tamp the ocial Code U mol for tamp (marking) on the

veel or cloure to denote inpection and teting in compliance with Code requirement.

All of the code dicued can e ued to deign pig trap. Inpection criteria var among thee dierent code. Generall, given the ame pipeline

deign parameter, a pig trap deigned from AM 31.3 will tend to e cotlier than for one deigned from AM 31.4 or 31.8 ecaue of the

dierence in material grade and thicknee. In addition, a pig trap deigned from AM ection VIII Div.1 will tend to e more expenive than one

deigned from AM 31.3 for the ame reaon.

Pig Trap/Pigging tem Aement

Like an other piece of equipment connected to the pipeline, pig trap hould e aeed at regular interval for variou reaon. The pipe and tting

that make up a pig t rap will age and deteriorate over time. Pipeline companie ma acquire exiting pipeline with pig trap and i t will e important to

know the condition of thee ued aet. ome exiting pipeline undergo a change in ue whether it ha to do with a reveral of ow direction or achange in product eing tranported. xiting pig trap can change the wa the are ued. A pig trap ized for cleaning pig ma need to e modied o

that it can accommodate inpection pig. A launcher ma need to e changed from a manuall operated pigging tem to an automated pigging

tem.

A receiver ma need to e modied o that it can receive more than one pig at a time. The initial deign of the pig trap ma e inappropriate for the

current pipeline condition. At ome point in the hitor of the trap, modication ma have een made that were inappropriate for the proper

performance of the pigging tem. Thee are all reaon for performing an aement on a pig trap or pigging tem.

The time it take to perform a trap aement depend on the level or level of aement required, the experience of the trap aement team, the

working condition where the trap i located, the remotene of the trap to e a eed (onhore and ohore) and the operational circumtance of the

pipeline ection at the time of aement.

There i a dierence etween trap aement and piggailit aement. A trap aement i an evaluation on the piece of pipeline equipment ued

for introducing or retrieving a pipeline tool from the pipeline without interruption of pipeline ow. Thi aement deal with the evaluation of an

exiting piece of pigging equipment or pigging tem ued for launching and receiving pig or pipeline tool. In contrat, a piggailit aement i an

evaluation of an exiting pipeline for the purpoe of determining the necear modication in order to make a pipeline ection capale of afel

launching, running and receiving pipeline tool.

Level Of Trap Aement

A trap aement can range in complexit and ophitication. There are man level of trap aement that can e conducted. Let u look at a

decription of each level of trap aement. It ma e noted that each level of aement increae in complexit.

The rt level or Level 1 trap aement i called a Reearch Aement. Thi level of aement explore the hitor and deign parameter of the

pig trap. It note an modication that have een made to t he pig trap from the time of intallation to the preent, mechanical deign limitation of the

pig trap, the phical location or deignation of the trap or pipeline ection, trap dimenion, the location and ue of each nozzle on the pig trap.

The Level 2 trap aement i called an Operational Aement. Thi level of aement i concerned with the current-da operational condition of the

pig trap and apect of the overall pigging tem. Thi aement oerve whether the cloure open, cloe or eal properl, whether the preure

warning device on the cloure operate correctl, whether the variou valve on the piggi ng tem eal adequatel, whether the pig ignal and preure

gauge work a the hould and whether the kicker or pa nozzle are ized properl.

The Level 3 trap aement i called the Functionalit Aement. Thi level of trap aement determine if the pigging tem i performing to it

eak eectivene. If it i deirale to launch or receive in ection tool, i the tra or the urroundin area dimenionall ca ale of handlin thi


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operation? Are there phical otruction (handrail, tair, piping, etc.) that make it dicult to afel load or unload pig? Are piping modication

needed to allow for inpection pigging? hould a n equalization line e added acro the trap reducer for afet or to improve pigging operation?

hould additional vent and preure gauge nozzle e added to the line ize pipe for afet? hould additional drain nozzle e added to the pig trap?

Thee are all quetion that thi level of trap aement eek to a nwer.

The Level 4 trap aement i called the Corroion Aement. Thi level of aement i the mot complex and tpicall will require an ND technician

or engineer to e on the trap aement team. Thi evaluation eek to determine the exitence of corroion agent acting on the component of the

pig trap and whether or not thee corroion agent have aected the tructural integrit of the caron teel enough to caue the trap to e unafe to

operate. Are liquid or deri ample eing taken? If o, are the ample analzed for corroion agent? Are there ampling port for otaining liquid or

deri ample on the pigging tem? Have an inhiitor or iocide een applied to thi pipeline ection? If o, what wa the name of the inhiitor or

iocide ued and what wa the interval of application? Did the inhiitor or iocide have a poitive eect or not? Have in-line inpection een conducted

on thi pipeline ection? Ha an form of ND een conducted on the trap ince it wa intalled? If o, ha the data een analzed to ae minimum

pipe wall thicknee? I ND performed regularl on the trap to monitor corroion growth rate? If previou ND data i provided, corroion growth

rate can e ued to etimate the time when repair or replacement of the trap would e necear.

Trap Aement Team

A Trap Aement Team hould e compoed of the following memer at a minimum:

(1) Team Leader/Project Manager thi memer i reponile for the aement team in the eld and enure that the necear data i collected for

the technical writer to create the aement report.

(2) Project ngineer thi memer i the te chnical expert on the deign and operation of pig trap and pigging tem. Thi memer can aume the

role of Team Leader/Project Manager for econom of workforce.

(3) Technical Writer thi memer a emle the data collected into a technical report which explain to the client the nding of the aement.

(4) ND Technician (optional memer, for Level 4 Aement onl) t hi memer perform the non-detructive examination on the trap and provide

the data to the Project ngineer for mechanical integrit evaluation.

Aement Procedure

1. Aemle a much information aout the trap and pipeline ection a poile efore conducting the on-ite aement. Note the hitor of the trap,

pipeline/trap deign parameter, location, etc.

2. Onite Aement. a) Compare the exiting trap with the a-uilt drawing. If there are an dierence, note and ketch them. ) If an a-uilt drawing

i not availale, make a ketch of the trap with dimenion. Note nozzle ize and ue. Alo note valve tpe, make and condition in the pigging tem.

c) Quetion the operator and pigging crew aout the pigging tpe, frequenc and the operational condition of the dierent part of the pigging

tem. d) Take picture of the t rap. Care hould e taken to capture an area of concern on the trap or pigging tem. It ha een aid that a picture i

worth a thouand word. Thee picture will e ueful a illutration within the Aement Report. e) If poile, look inide the trap and note the

condition of the inide pipe wall and cloure door. f) If a Level 4 Aement i conducted, the ND technician hould take ultraonic tet reading and

record them for further evaluation. g) Aemle the data in an organized fahion and tranmit the data to the technical writer.

3. Write the Aement Report and umit it to the client.

Concluion

Pig trap development ha occurred over man ear and will continue a long a there remain the need to pig a pipeline. An undertanding of the

component, the function of each component and certain performance enhancing and afet feature for a launcher and receiver help one to grap the

function of the overall pigging tem and procedure for launching and receiving a pig.

Deign conideration hould extend eond the limit of the pig t rap to the oundarie of the pigging tation. Trap aement are extremel valuale

to the reponile pipeline operator that i concerned with the condition of the pipeline equipment and the afet of the pigging crew in the eld.

Acknowledgment

Thi article i aed on a preentation at t he 22nd Pipeline Pigging and Integrit Management (PPIM) Conference held Fe. 17-18, 2010 in Houton.

Author

Chritian J. Clode, P.., i operation manager of the Pigging Product Diviion of T.D. Williamon, Inc. He graduated from The C itadel in 1993 with a

.. degree in civil engineering and i a licened profeional engineer in Oklahoma. He ha experience with g eotechnical and material teting;

geotechnical invetigation; hot-dip galvanizing proce; municipal deign review; pipeline deign of water, torm water and watewater tem;

pipeline equipment aement; and automated pigging tem. He i a founding memer of the Profeional Intitute of Pipeline ngineer (PIP). He

can e reached at: [email protected].

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Pig Trap Design and Assessment Considerations - Pipeline & Gas Journal