CA1194449A

CA1194449A - Method and apparatus for cathodic protection of metal piping

Info

Publication number: CA1194449A
Application number: CA000458680A
Authority: CA
Inventors: Henri S. St. Onge
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-11
Filing date: 1984-07-11
Publication date: 1985-10-01

Abstract

ABSTRACT OF THE DISCLOSURE
According to the present invention a cathodic protection system for metal piping systems and fittings therefor is possible which is easy to install and manufacture. The system for fitting uses a unique sacrificial washer installed on the bolts used to fasten the fitting and includes a nonsacrificing portion to maintain the mechanical connection during and after depletion of the sacrificing metal. A unique ring anode is also taught which is secured to the bellmouth of a section of pipe and to provide an extension thereof and can be factory or field installed. Preferrably each anode is designed to protect two connected pipe sections or a pipe section and fitting.

Description

1 TITLE: MET~OD AND APPAR~TUS FOR CAT~IODIC PROTECTI~N OF
METAL PIPING

BACKGROUND OF T~IE INVENTION
The present invention rela-tes to cathodic protecti.on of iron piping systems and -the fit-tings therefor for use in aggressive soil environments. In particular, the invention relates to a simple sys-tem for adding sacrificial metal annodes to such systems and fittings.
Corrosion protection of iron piping systems and metal tanks by means of sacrificial annodes is well known. The most common practice places sacrifical annodes along side the tank or pipe line and electrically connects the annodes there-toO Because of the different metal of the pipe line and -the sacrificial annodes, the annodes are sacrificed and will protect the pipe line or tank against corrosion until the annodes have been depleted. These systems work satisfactorily1 however they do require care and skill in installation. Therefore there still remains a need for a cathodic protection system for ductile ircn piping and the like which is simple and can be installed with relatively unskilled labour.
Other examples of known catnodic protection for various applications are exemplified in United Sta-tes Patent 2~974,389 Tatum which discloses a metal casket having sacrificial annodes attached thereto, United States 1 Patent 3,574,080 Jones et al which discloses a unique screw fas-tener having a portion thereof of sacri-ficial metal and United States Patent 1,646,7~6 Mills which discloses a combination pipe connector and sacrificial metal annode.
The above listed patents are examples of more complicated s-tructures which although lnstallation of the cathodic protection is simplified, the manufacturing cost of the various structures disclosed is greatly increased.
Therefore, the ease of installation must be accomplished while siill providing a structure -for a sacrificial anode which is easily manufac-tured. Furthermore, sacrificial annodes if used in a fitting must be such -that the seal of -the fitting to the pipe lines remains intact even a-Fter the sacrificial anode has been depleted.
The present invention provides a corrosion protection system for ductile iron sectional buried piping systems which is easily installed while providing a structure which can be manu-factured a-t low cost. The sacrificial anode may be secured to individual lengths o-f piping prior to installation in -the system, or -the anno~es can be secured during the installation thereof. There is no requirement -for skilled expertise during the installation and -the anode can be connected in a manner to protect a number of sections of pipe simultaneously.

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1 SUMMARY OF THE INVENT:[ON
__ According to the present invention, a uni~ue ring anode is disclosed for use in a corrosion protection system for ductile iron secti.onal buriecl piping systems.
The anode comprises a sacrificial rnetal 9 a nonsacrificial metal embedded in the sacrificial metal which has a bore For the passage oF a s-tructural meMber therethrough For mechanically securing oF the anode to a section oF the piping system means for making electrical contact with the adjacent section of the piping system is provided whereby each sec-tion is at least partially protected by one annodeO Such an anode is particularly sui-table For use in piping systems having a bellmouth and spigot type connection between adjacent pipe sections and -the ring anode is directly secured to -the bellmouth o-f a pipe section to provide an extension thereof extending generally in the length of the pipe section. ~he mechanical securement of the anode is provided through the nonsacrificial metal which directly contacts the bellmou-th connection and as such is not effected when -the sacrificial metal has been depleted. In an associated form oF the invention, the anode is made in the -Form oF a washer having an interior steel collar which passes therethrough wi-th sacrificial high grade ~inc exterior -to -the steel collar and of a thickness approximately the same as the steel collar. Such a sacrificial washer can easily 1 be secured on the bolt type connections used to secure fittings on pipe lines with -the bolt providing the electrical contact between -the two sections of pipe. In this way the sacrificial washer protects bo-th sections of pipe. Such an arrangement is suitable For fire hydran-t and mechanical joints -For connection to water piping systems where a plurality of bolts are spaced about the fire hydrant joint and sacriFicial washers can be placed on each of the bolts as a simple method for providing lû cathodic protection for the hydrant and the associated length oF piping. In another forrn of the invention, a ring type anode is provided with a plurality oF steel type sleeves inset in the ring anode spaced about the circumference of the anode for securing of the ring anode to the bellmouth of a pipe section. The sleeve provides the bore for allowing passage of a securing member to attach the ring anode to the bellmouth.
BRIEF DESCRIPTION ûF THE DRAWINGS
Preferred embodiments of the invention are shown 2û in the drawings wherein:
Figure 1 is a par-tial exploded view of a bellrnouth spigot connection between two sections of pipe with a ring anode about to be secured -to the bellmouth of one of the sections;
Figure 2 is a partial sectional view through a ring anode secured to the bellmouth of a pipe section;

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1 Figure 3 is a partial sectional view through a mechanically secured pipe section having a bolt and wedge type connection wi-th a washer to one side of -the bolt connection to provide cathodic protection;
Figure ~l is a perspective view of a washer annode;
Figure 5 is a sectional view through the washer anode of Figure 4;
Figure 6 is a top view of a split ring anode;
Figure 7 is a section through line 7-7 of Figure 6; and Figure 8 is a section through line 8-8 o-f Figure 6.
DETAILED DESCRIPTION OF THE PREFF.RRED EMBODIMENTS
As shown in Figure 1, two sections of pipe 1 and

2 are shown with pipe section 1 having a spigot type connection 3 for insertion within the bellmouth connector 4 of pipe section 2. The bellmouth ~I has been provided with a flat surface annulus 6 to which the ring anode 20 is to be secured and in abutment therewith. The ring anode 20 has a generally flat surface for contact with the flat surface of annulus 6 of the bellmouth 4 and posi-tive contact between the ring anode 20 and annulus 6 is provided by mechanical securement of the anode to the annulus through screw pins 22 which pass through bores 24 in the ring anode 20 and engage within the recesses 26 pxovided in annulus 6. In addition, and in order to 1 provide elec-trical continuity between pipe section 1 and section 2, electrically conduct.ing bracket members 28 are provided through which the connectors 22 pass and these brackets 28 provide electrical communication between the bellmouth connector of pipe section 2 and the spigot connection 3 of pipe section 1. Oe-tails of this electrical connection can be apprecia-ted from Figure 20 Turning to Figure 2, it can be seen that the ring anode 20 has a sacrificial me-tal portion 30 preferrably of a high grade zinc conforming -to ASTM B418-73. Embedded in the sacrificial metal and within each of the bores 24 is a sleeve 32 which is of a nonsacrificing metal relative to the ductile iron pipe sections 1 anci 2. The screw type mechanical fastener 22 includes a head 23 which is in contact with one surface of the metal sleeve 32 which is in direct contact wi-th the bracket 28. Bracket 28 7 on the opposite side of sleeve 32 is in direct contact with annulus 6 of the bellmouth 4. Therefore, the bracket 28 which is electrically conductive is in direct contact with annulus 6 and is in contact with the sleeve 320 Furthermore, the screw fastener 22 is in contact wlth the sleeve and the bellmouth of pipe sec-tion 2 thereby providing a further electrical conducting pa-th as the screw fastener 22 is made of a electrically conductive material. The bracket 28 includes a bent end portion 29 for engaging the exterior surface of the spigot 3 oi~ pipe l section l. Therefore the ring anode 20 is now in electrical con-tact wi-th bellmou-th ~ and spigot 3, thereby providing cathodic protection to both sections of pipe l and 2. The seal between spigot 3 and bellmouth 4 is partially provided by the compressible seal member 5 shown trapped between the exterior surface oF the spigot 3 and the interior surface of the bellmouth 4. An example of this type of connection is sold in the -trade as a ~*Ty-ton Joint".
A slightly different cathodic protection arrangement is shown in Figure ~ and is suitable for use in protecting fittings which are secured to pipe sections. In this case, a fitting having a stem 40 is secured to the pipe section 38 by means of a plurality oF
bolts one of which is shown as 42. 1his bolt 42 in combination with nut 44 and wedge memher 46 and seal 48 provides a simple means for sealing the stem 40 and pipe section 38. By tightening the nut 44, wedge member 46 is driven between the pipe sections and compresses seal 28 to positively maintain the connection between the s-tem 40 and section 38. In order to provide cathodic protection for at least the fitting of stem 40, an anode washer 50 is secured to each of the bolts 42 intermediate the bol-t head 41 and nut 44. As the washer is part of the mechanical *Trade Mark connection maintaining the stem 40 connected to section 38, an interior steel nonsacrificing ring collar 51 is provided which will remain intact even when the sacrifical metal portion 53 has been depleted. The bolt 42 provides electrical contact the anode washer 50 and stem 40 and if desired, wedge member 46 can be such that it establishes electrical contact with pipe section 38 whereby the washer will also serve to protect this pipe section.
As shown in Figures 4 and 5, steel collar 51 of the washer anode 50 is centrally located and provides a bore through which bolt member 42 can pass. Collar 51 is the same thickness as ring anode 50 and as such is in contact with the nut 44 and wedge member 46. Collar 51 of the washer anode provides part of the mechanical connection and will remain uneffected after the depletion of the sacrificial metal 53 preferrably of high grade zinc.
The ring anode 20 and the sacrificial anode washer 50 can be manufactured independently of the parts to which they are to be applied and are easily installed during installation of the piping system. The ring anode 20 could be secured to sections of pipe prior to shipping the pipe sections to site or may be installed as the sections are laid. Both annodes are of a structure easily manufactured and conveniently installed as required.
Furthermore, there is no need to change any of the remaining components of the piping system in the event 1 that corroslon protection is not required~ The ring anode 20 merely provides an extension oF -the bellmouth and does not form part of the securement of plpe sections. In the case of the washer anode of Figures 3 -through 5, -the nut would merely be threaded on the bolt a Further distance or probably a normal washer would be substi.tuted in i-ts place.
The electron output of the anode can be increased i~ it is coated with a low resistant depolarizing activator material and this will resul-t in improved operation o~ the system. This coating, preferrably a gypsum base coating containing sodium sulphate and bentonites, allows the zinc to remain active in all kinds o~ soil environment subject to low to high current requirement. In this case, electrical contact is maintained due to the nonsacrificial portions 51 and 32 of the washer and ring anode respectively, remaining in electrical contact via the mechanlcal securement of the components. Preferrably, -the pipe secti.ons are coated with a protecti.ve dielectric coating to provide a barrier to electron flow to the soil thereby further increasing the liFe of the annode and its protective capabilities.
Suitable pipe coa-tings include polyethylene, epoxy, urethane or polymeric type coatings. Such coa-tings act as a barrier against an aggressive environment, however during installation scratches in the coating inevitably 1 occur and the ring anode or washer will serve to protect the exposed sections which are subject to the corro~ive environmen-t. The ring anode effectively protects the pipe sections by a) providing an electron flow to the iron pipe to cause the iron pipe to become nega-tively charyed and preferrably negatively charged such tha-t i-t has a negative voltage of at least about 700 and preFerrably about 850 millivolts with reference to a copper/copper sulpha-te electrode or -300 millivolts more negative then the initial iron potential; b) -the negative charging of the pipe sec-tions at-tracts positive soil ions and zinc ions to form a protective ionic barrier to the exterior o-F`
the piping (this effect is termed ionic shield), and c) the dielectric coating restricts electrons and hydrogen ions from mating to form hydrogen gas. However, at coating flaws this mating does occur to plate out the would be corrosion of the iron pipe.
A split ring anode 20a having two halves 21a and 21b, is illustrated in Figures 6 through 8 and can be used as an alternative to the ring anode of Figure 1~ The split anode is sui-table for securement to a bellmouth and spigot connection of pipe sections with nonsacrificing electrically conducting wedges 46a and 46b embedded i.n the sacrificial zinc 30a of the annode. The wedges 46a and ?5 46b have a hardened tapered conductivity section 45 For contacting the bellmouth of one pipe section and -the 6~16 - 10 - 018~G

1 spigot of an associated section and include an anchoring portion 43 embedded centrally in -the cast zinc. A
depolarizing coating layer 47 is also provided about -the zinc annode. In addition to the wedge connec-tion, the split annodes are pinned -to the bellmouth of a pipe section by drive screws 60 received in countersink cavlties 62 within the sacrificial cast zinc split annodes 21a or 21b. A steel nonsacrificing steel insert 64 is provided within cavity 62 and a flat anode face 65 is provided for abut-ting contact with surface 6 of a bellmouth of a section of pipe. This split ring arrangement may be more convenient when installation is to be completed during pipe installation, whereas -the full ring anode of Figure 1 is more convenient for factory installed cathodic protection.
The washer anode is suitable for all mechanical fittings as the bolt sizes are normally standardized for a given system. For example in water piping sys-tems, 3/4 inch bolts are mos-t common. Similarly, slip-on elbows, tees, valves etc. for a given piping sys-tem, have a standardized bellmou-th and as such can easily receive a ring anode. Such an arrangement simplifies installation and eliminates the need for specialized corrosion pro-tection anodes. In slip on connections -the ring anode is ~sed, whereas the washer anode is used on mechanical connections secured with bol-ts.

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1 Although various preferred embodiments o-f the present invention have been described herein in detail, it will be appreciated by those skilled in the art 9 that variations may be made thereto withou-t departing ~rom -the spirit of the invention or the scope of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a corrosion protection system for a ductile iron sectional buried piping system, a ring anode comprising a sacrificial metal, a non-sacrificial metal embedded in said sacrificial metal, said non-sacrificial metal including a bore for receiving a structural member which extends therebeyond to mechanically secure said anode at one end of a section of such piping system, said sacrificial metal being in electrical communication with such piping system at least partially by means of said non-sacrificial metal, and said sacrificial metal is associated with said non-sacrificial metal such that said non-sacrificial metal remains mechanically secured to such piping system with the depletion of said sacrificial metal.

2. In a system as claimed in claim 1 wherein said anode is of a diameter generally corresponding to the diameter of such piping system and is secured to the bellmouth end of a section of such piping system, said anode including at least two non-sacrificial metal elements each having a bore for receiving a structural member, said non sacrificial elements being spaced in said anode to maintain contact of said anode with said bellmouth when said structural members secure said anode to said bellmouth.

3. In a system as claimed in claim 2 wherein said ring anode is at least partially coated with a depolarizing activator material on the surface of said anode.

4. In a system as claimed in claim 3 wherein said coating is gypsum base and contains sodium sulphate and bentonite.

5. In a system as claimed in claim 2 including at least three nonsacrificial members equally spaced about the circumference of said anode.

6. In a system as claimed in claim 5 including means for making electrical contact with an adjacent section comprising at least one electrically conducting wedge means between the interior of said bellmouth and the exterior of an adjacent pipe, said wedge means including a portion being secured between said anode of the opposing face of said bellmouth and in a manner to have said structural member extend through said portion and maintain said wedge portion intermediate said anode and said bellmouth.

7. In a system as claimed in claim 5 wherein said nonsacrificial metal is a steel sleeve in direct contact with said structural member and said sacrificial metal is a high grade zinc.

8. In a system as claimed in claim 1, wherein said anode is a ring shaped washer having a interior steel collar passing therethrough with sacrificial high grade zinc exterior to said steel collar and of a thickness approximately the same as said steel collar.

9. In a system as claimed in claim 8, said washer being at least partially coated with a gypsum base coating which contains sodium supphate and bentonite.

10. In a system as claimed in claim 8, said washer when connected to said system capable of providing polarization of a portion of said iron piping system in excess of about -850 millivolts with reference to a copper/copper sulphate electrode.

11. In a system as claimed in claim 10 including a plurality of washers each secured on a bolt used to secure a hydrant valve or fitting to such piping.

12. In a corrosion protection system for use with coated iron piping systems having lengths of iron pipe each with a bellmouth end and an opposite end for insertion within the bellmouth of another pipe, a ring anode of a diameter for securement to the end of a bellmouth to provide an extension thereof while maintaining the same interior clearance, said ring anode including at least three non-sacrificing metal washers generally equally spaced about the bellmouth, each with a central bore for receiving a pin, at least 3 pin members one for each metal washer passing through the central bore of said washer and in contact with said non-sacrificing metal to maintain contact therewith and said bellmouth irrespective of the state of said sacrificial metal, electrical contact means held between one of said washers and said bellmouth in an electrical contact with said bellmouth and in electrical contact with a pipe inserted in said bellmouth whereby said ring anode provides a negative polarization to two lengths of pipe.

13. In a corrosion protection system as claimed in claim 12, wherein said lengths of iron pipe have a dielectric coating and said sacrificial metal is a high grade zinc, said anode being coated with a depolarizing and activating material thereby increasing the effectiveness of said anode in various soil environments.

14. In a corrosion protection system for an iron pipe system a generally flat ring washer type anode having a high grade zinc portion and associated therewith a steel collar type insert, said collar type insert being exposed either side of said anode and including a generally central bore to allow the shank of a connector to pass therethrough, said collar to one side of said anode presenting a surface for contact with a head of said connector with the opposite side of said collar presenting a surface for contact with said iron pipe system, said connector shaft passing through said bore to permit positive mechanical securement of said collar to said pipe system.

15. In a ductile iron piping system having a plurality of sections interconnected by bellmouth and spigot connections a corrosion protection system comprising ring anodes of a sacrificial metal each directly secured to the bellmouth of each section of pipe, each ring anode including non sacrificial metal securing sleeves embedded in said sacrificial metal each providing an open bore through which securing means partially extends and secures said anode to said bellmouth to provide an extension thereof in the length of said pipe section, said securing means in combination with said sleeves providing electrical communication between said bellmouth and said anode which is of a size to negatively charge the associated section of pipe.

16. In a ductile iron pipe system as claimed in claim 15, said iron pipe sections being coated with a dielectric coating to provide a barrier to restrict electron flow to the soil environment.

17. In a ductile iron piping system as claimed in claim 16, wherein said coating is both interior and exterior of said pipe and is of a polyethylene, epoxy, urethane, or polymeric type coating.

18. In a ductile iron piping system as claimed in claim 15, wherein each anode is exteriorly coated with a low resistant depolarizing activator material.

19. A length of iron pipe for use in a piping system subject to corrosion t said iron pipe having a bellmouth type connection at one end thereof and a spigot type connection at the opposite end for insertion in the bellmouth type connection of a similar length of pipe, said bellmouth having a flat annular surface about the end thereof to which a sacrificial ring anode of similar size is mechanically secured in a manner to be in electrical conduction with said iron pipe, said sacrificial ring anode being made of a high grade zinc and having a substantial area of contact with said flat annular surface, said anode including a non-sacrificial metal means for maintaining mechanical and electrical contact of said high grade zinc and said iron pipe as said system is subject to corrosion.

20. A length of iron pipe as claimed in claim 19, wherein said sacrificial ring anode is coated with a low resistant depolarizing activator material.

21. In a ductile iron piping system as claimed in claim 15, wherein said ring anode is split and each split anode includes non-sacrificing conducting wedges partially embedded therein for insertion between a bellmouth and spigot connection of pipe sections.

22. In a system as claimed in claim 21, wherein each conducting wedge includes an anchor portion generally centrally extending in said spilt anode.

23. In a corrosion protection system as claimed in claim 1, wherein said non-sacrificial metal is a steel nut and said bore is threaded to engage a bolt.

24. In a corrosion protection system as claimed in claim 23, wherein said nut is fusion bonded to said sacrificial metal which is high grade zinc.