Metec12/21/200By Jose HAbraham

A new mepipelines

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agnetic field in

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he residual mamagnetic field.

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agnetic field ar

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elines in souths of 8, 10, and

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ore its insertio

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The simu1104.7 Acoercivity

The simu

• t = WT.

• n = num

• I = solde

• x0 = coi

• D = OD

• Hg = res

Table 2 pcombinat

Results

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ariables:

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tic field intensi

ariables of the3,584 simulatio

ware estimated levels in the g possible stag

n.

pipe sections worm of a ring prial produced

gh the coil and

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ty in the groov

e simulation ruon runs.

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with a groove produced the rthe different v

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ve.

uns and their r

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consistent witresidual magnvalues of the r

e.

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magnetic fieldf 3,584 valuesn process: un

th dimensions etic field in theesidual magne

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ring all possib

o compensate ant magnetic fiation, compens

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le

for the ield, Hr. sation,

Fig. 4 shogroove x0

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Equation procedurmagnetic

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ows examples0 for seven int

ows the applies a function of

sation dependson that the co

m amount of en

eral rule, there, will ultimatelyry to obtain the

sating for the rple step-by-steof the selectedntroducing theatical function

xamination of magnetic field and directly pr

1 reduces to re aims to appc field (Hr) belo

OD are knownance by wrappuation 1 turns 2 is a simple nI) required to

2 yields grapve. Fig. 5, for esation coil poseld a completetions of the fieorward tool for

s of the relatiotensities of the

ed magnetic fif the position os directly on th

oil must be planergy.

efore, operatoy depend on the appropriate

residual magnep procedure. d simulation vae whole datasebest fitting the

Equation 1 exHa (nI) necess

roportional to t

a simple exprly a magnetic

ow 30 G, inclu

n fixed parameing the coil as

s into Equationrelationship bavoid arc blow

hs with sets oexample, showition. Applying

e set of such geld parametersr avoiding arc

nship betweee residual mag

eld Ha requireof the coil x0. The position of ced in the imm

ors should wrahe residual maarc length for

netic field in thEquation 1 is ariables obtainet into the SPSe data with the

xplains the inflsary for compethe position of

ression when rfield (Ha) cou

uding a best ca

eters for each s closely as pon 2, where A (Ebetween the rew.

of curves for thws two sets ofg Equation 1 tographs makings (t, D, I) and vblow.

n Ha (proportiognetic field Hg

ed to compensThe amount othe coil relativ

mediate vicinit

ap the coil as cagnetic field bthe given elec

he groove coula general expned with the rSS multivariate polynomial e

uence of eachensation is invf the coil x0.

real-life conditnteracting thease of Hr = 0 (

particular casossible to the gEquation 3) is

esidual magne

he compensatif curves obtaino all possible g graphs similavariables (n, x

onal to nI) andon two pipelin

sate for the givof energy Ha (pve to the groovty of the groov

closely as posbeing compensctrode.

ld be a complepression of theesults of the 3te statistical soexpression 1, o

h variable in thversely propor

tions are takene residual mag(Fig. 1).

se. Operators groove. Bearin

s a constant deetic field (Hg) in

ion of any valuned for differeranges of the ar to those shox0 ) available to

d the position nes of 0.5-in. W

ven residual mproportional tove, OD, and Wve to achieve c

ssible to the grsated for and t

ex task for opee resultant ma3,584 simulatiooftware alloweobtaining a co

he compensatrtional to WT (

n into accountgnetic field (Hg

generally inteng these paraependent on an the groove a

ue of the residnt pipeline WTvariables conown in Fig. 5 fo operators an

of the coil relaWT and 10 an

magnetic field o nI) to achieveWT. Fig. 4 supcompensation

roove. The cothe optimum c

erators withouagnetic field Hr

on runs perfored proposal oforrelation coef

tion process. T(t) and OD (D)

t. The compeng) to obtain a r

end to optimizeameters and inactual field parand the amoun

dual magnetic T, OD, and sidered in thefor different nd providing a

ative to nd 24 in.

Hg in the e

pports the n with a

il position, current

ut a clear r as a rmed with f a fficient R2

The ) of the

nsation resultant

e system ntents in rameters. nt of

field in

e model

a

Proposed procedure

The first step of the welding process is to adjust the current through the electrode to obtain the optimum arc length. Electrode selection itself depends on many factors, including welder skill and base metal properties. The operator will always know in advance the range of current to be used for a specific welding task according to the electrode selection. Applying Equation 1 can reduce and optimize each case's compensation curves.

A step-by-step compensation procedure follows:

1. Measure the strength (magnitude) and polarity (direction) of the residual magnetic field in the groove with a gaussmeter.

2. With the magnitude of the residual magnetic field (Hg) known, and knowing the characteristics of the pipeline under repair, select the appropriate set of graphs. The position of the compensation coil is important during this selection. It should lay as close as possible to the groove. The value Hg allows the necessary Ampere-turns (nI) to be estimated with the proper compensation curve (Fig. 5).

3. Divide nI by the selected value of current I flowing through the electrode. This provides the number of coil turns.

4. Wrap the welding ground lead around the pipe, according to the selected parameters, in such a way as to produce a magnetic field opposing the residual magnetic field in the groove.

5. Put the gaussmeter probe inside the groove to verify compensation. The welder should use an extra work piece for welding and at the same time perform the magnetic measurement in the groove. This guarantees the electrical circuit is closed, maintaining operator safety.

6. If the residual magnetic field is compensated for (<30 G), remove the gaussmeter probe and start the welding process.

DC arc welding can use two different electric circuits according to electrode type: Direct Current Electrode Positive (DCEP) or Direct Current Electrode Negative (DCEN). Step 4 should be performed carefully to avoid delays and consequent reduction in productivity.

Fig. 6 canthe DC pfield, eithhas the pthis casearrow) co

With a DCthe samecompens

Referenc

1. ProctoInternatio

2. KildishFerromag

3. Meeke

n help operatoower supply her sign or pole

polarity shown, the coil shou

ounteracting th

CEP electrodee polarity as shsation.

ces

or, N.B., "The Ronal, Catalog N

hev, A.N., Nyegnetic Magnet

er, D., Finite E

ors set a circuhas a positive e-type, based by the red ar

uld be wrappedhe residual ma

e the DC powehown in Fig. 6

Removal of DeNo. L51389e,

nhuis, J.A., Dtic Pipes," IEE

lement Metho

it for compensground terminon the orienta

row line, the gd as shown inagnetic field.

er supply has the coil shou

etrimental MaHouston: Tec

obrodeyev, P.EE Internationa

od Magnetics,

sation. It assunal. All gaussmation of the megaussmeter ren Fig. 6 to prod

a negative grld be wrapped

gnetic Fields achnical Toolbo

.N., and Volokal Magnetics C

Version 4.0, U

mes a workingmeters give theasurement p

eading will be pduce a magne

ound terminald in the oppos

at Pipeline Tieoxes Inc., 1980

khov, S.A., "DeConference, K

User Manual,

g electrode of e polarity of throbe. If residupositive, or wil

etic field Ha (m

. If the residuaite direction to

e-Ins," Pipeline0.

eperming TecKyongju, Korea

http://femm.fo

f DCEN type, mhe measured mual magnetic fill mark a north

marked with the

al magnetic fieo achieve

e Research C

chnology in Laa, May 18-21,

oster-miller.net

meaning magnetic ield Hg h pole. In e blue

eld has

ouncil

arge 1999.

t/.

4. Bakunov, A.S., and Muzhitskii, V.F., "Testing Residual Magnetization of Parts before Welding," Russian Journal of Nondestructive Testing, Vol. 40, No. 3, pp. 209-210, March 2004.

5. Galvery, W.L., and Marlow, F.M., Welding Essentials: Questions & Answers, pp. 117, New York: Industrial Press Inc., 2000.

6. Operation instructions FH-51 Gauss-Teslameter, Magnet-Physik Dr. Steingroover GMBH, www.magnet-physik.com.

7. API Standard 1104, "Welding of pipelines and related facilities," 20th Ed., American Petroleum Institute, 2005.

The authors

Jose Hiram Espina Hernandez (jhespina@gmail.com) is a professor at the Instituto Politecnico Nacional (IPN). He is a researcher at the Convenio de Investigacion y Desarrollo de Integridad Mecanica (CIDIM) of the IPN. He holds a BS in electrical engineering, an MS in automation, and a PhD in technical sciences from the Instituto Superior Politecnico Jose Antonio Echeverria of Havana.

Francisco Caleyo (fcaleyo@gmail.com) is a professor at the IPN. He is a senior researcher at the CIDIM of the IPN. He holds a BS in physics and an MS in materials science from Universidad de La Habana and a PhD in materials science from Universidad Autonoma del Estado de Mexico.

Gabriela Lourdes Rueda Morales (gruedamorales@yahoo.com.mx) is a professor at the IPN. She is researcher at the CIDIM of the IPN. She holds a BS, an MS, and a PhD in physics from IPN.

Jose Manuel Hallen (j_hallen@yahoo.com) is a professor at the IPN and heads the CIDIM, which has service contracts with Pemex to conduct mechanical integrity and risk analyses of onshore and offshore pipelines. He holds a BS and MS in physical metallurgy from IPN and a PhD in physical metallurgy from the University of Montreal.

Abraham Lopez Montenegro (alopezmon@pemex.pep.com) is a superintendent of pipeline reliability at the Gerencia de Transporte y Distribucion de Hidrocarburos, Pemex Exploracion y Produccion. He holds a BS in industrial chemistry engineering from IPN and an MS in project management engineering from the Universidad de las Americas, Mexico.

Eloy Perez Baruch (eperezb@pemex.pep.com) is maintenance vice-manager at the Gerencia de la Coordinacion Tecnica Operativa Region Sur, Pemex Exploracion y Produccion. He holds a BS in industrial chemistry engineering from IPN and an MS in pipeline management engineering from the Universidad de las Americas, Mexico.