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EXECUTIVE SUMMARY AND INTRODUCTION FOR NLNG CP TRAINS 1 2 AND 3.doc

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EXECUTIVE SUMMARY This document is the report for the Cathodic Protection troubleshootin for ! !# trains $% &% and ' plant section( This document comprises the data collected for the Cathodic Protection Potential Sur)e*% transformer recti+er inspection% round bed anodes inspection% and the SI, inspection( These surveys were carried out in the month of September/October and completed in October 2011. This document basicall* i)es a direct and simple reportin of the outcome of the tro
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   EXECUTIVE SUMMARY This document is the report for the Cathodic Protection troubleshootin for ! !# trains $% &% and ' plant section( This document comprises the data collected for the Cathodic Protection Potential Sur)e*%  transformer recti+erinspection% round bed anodes inspection% and the SI, inspection(  These surveys were carried out in the month of September/October and completed in October 2011. This document basicall* i)es a direct and simple reportin of the outcome of the troubleshootin e-ercise( Cathodic Protection circuits are s*stems desined to pro)ide protecti)e current in the .C rane to protect underround buried structures aainst corrosion currents( These circuits are of t/o t*pes% the sacri+cial anode s*stems and the impressed current s*stems(  The type of system installed at the NLN trains is the impressed current system.  The ob!ective of optimi in# a $% desi#n is to select the type and location of the anodes to deliver the optimum level of protection that covers the lar#est area of the structure to be protected.&n con#ested areas li'e the NLN plant( the cathodic protection current is a)ected by shieldin# and this becomes a problem( therefore( it becomes unpractical to rely on the remote type of $% system( where we use a sin#le #round bed of anodes. Therefore( to avoid the problem of shieldin#( the impressed current $% system at the NLN plant area has been desi#ned and installed usin# the distributed anodesystem at close intervals. These anodes are distributed in such a way that the area of in*uence surroundin# the anodes overlap su+ciently to permit development of protective potentials on the entire interconnected structures.,ut in this system( the distributive anode system will re-uire increased power consumption from the transformer rectier. P0 MA1 IMITE.  &n this system( it should be noted that the distributed #round bed anodes are not depended upon as the source of the drivin# electrical ener#y. &nstead( the eternal source of direct current power( that is( the transformer rectier is relied upon to deliver the drivin# power needed and it is connected or impressed between the structure to be protected and the anodes. nd also( current re-uirements from the transformer rectier needed to maintaina polari ed potential of an O33 value of 40.56volts 7$( will increase with time from the date of installation as lon# as the circuit remains in service. &n line with this( the needed current output bein# #iven out by the anodesfor the protected structure to attain full $athodic protection polari ationlm must not fall below a #iven value based on desi#n parameters. Therefore( the transformer rectier and the anodes form the heart andblood of this system. &t therefore means that that the e+ciency of the transformer rectier and the current output of the anodes must meet the desi#n considerations at all times for the cathodic protection system to be fully e)ective. So( all other circuit components( ne#ative distribution cables( positive distribution cables( structure insulation !oints S&8s( N7,,s( %7,,s( earthin#( connection points( etc( becomes secondary points of concern.&t should also be noted that( when ta'in# ON and O33 potential measurement on structures that have been in service for a period of yearsand the transformer rectier is no more operatin# at desi#n e+ciency( it will be found that the O33 potential between the structure and the earth with a #iven value of current will decrease with time or ta'e more time to reach full structure polari ation at protective potential criteria of 40.56volts 7$. This is caused by the delay of the development of completepolari ation lm. 9nder certain conditions full protective polari ation mi#ht be delayed for lon#er periods. Therefore( eperience and #ood en#ineerin# !ud#ement comes to play indeterminin# the inte#rity of a $% system under varyin# conditions. P0 MA1 IMITE.  CAT20.IC PR0TECTI0! 3I!.I!#S 30R TRAI!S $% & A!. ' TRAI! $  The transformer rectier is operatin# at only :1; of its ori#inal desi#n function. &t should have a minimum of <6; rated e+ciency. lthou#h it is still supplyin# enou#h protective power to enable the anodes deliver protective current to the protected structure( it will not last up to the desi#n life. Therefore( the T== should be placed for replacement within the net : months.ll the anodes are in #ood wor'in# condition and supplyin# the re-uired protective current needed to protect the structures bein# protected( but as earlier discussed( the T== is the heart of the system and when the T== #oes down nally the anodes will cease to dischar#e the needed protective current forthe structure to attain full protective polari ation potential. TRAI! &  The transformer rectier for train 2 is down and needs immediate replacement. ll the anodes are still in #ood wor'in# order. ,ut as it stands ri#ht now( as far asthe T== is not wor'in#( there is no supply of cathodic protective current by the anodes to the pipin# circuits and as such the pipes are not protected. TRAI! '  The ne#ative distribution cable from the transformer rectier meant to supply the N>T&?> 7&ST=&,9T&ON ,ON7 ,O@ was not connected to the board. This ne#ative supply cable is meant to form the return complete connection for the protective circuitA the non connection of this cable ma'es the structures to be protected not protected. 3rom our investi#ations and the condition of this cable and the N7,,( that cable has bein# in such state for -uite a lon# time.On connection of the cable to the supply board within the N7,, and allow for a 2B hour full polari ation period( we found all the structures protected and all the anodes in perfect wor'in# condition.   P0 MA1 IMITE.  The e-act number of SI,s that are bad and their speci+c desinations are as follo/s4TRAI! &4 SI,56% 57% 58% 59% A!. 6: ARE ;A.TRAI! '4 SI,'7% '8% '9% <:% <$% <&% <'% <<% <5% <6% <7% <8% <9% 5:% 5$% 5'% 5<% 55% and 56 ARE ;A. (Also% the sacri+cial anode installed at train & has dried out% /hich means it is no loner able to suppl* the needed protecti)e current to protect the line( These anodes should be replaced immediatel* for continuous protection of the buried line(=e also did a chec> on unit &5:: and disco)ered that the transformer recti+er /as not i)in out an* .C output po/er to the CP circuit in order to protect the buried structures( There is need for further In)estiation to determine /h* the TRR is not performin( ;ut all the anodes are still intact and still possess the abilit* to dischare the re?uired cathodic protecti)e current needed to protect the buried structures(Arimoro C*ril 0buse#roup 2ead Enineerin Polma@ limited(  P0 MA1 IMITE.

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