CA2118445A1 - Primer composition for metal pipes - Google Patents
Primer composition for metal pipesInfo
- Publication number
- CA2118445A1 CA2118445A1 CA 2118445 CA2118445A CA2118445A1 CA 2118445 A1 CA2118445 A1 CA 2118445A1 CA 2118445 CA2118445 CA 2118445 CA 2118445 A CA2118445 A CA 2118445A CA 2118445 A1 CA2118445 A1 CA 2118445A1
- Authority
- CA
- Canada
- Prior art keywords
- primer composition
- anhydride
- copolymer
- metal
- modified
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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- Adhesives Or Adhesive Processes (AREA)
- Paints Or Removers (AREA)
Abstract
Abstract A primer composition for coating the outside surface of a metal pipeline includes a mixture of solid components and at least one solvent.
The solid components include a tackifying resin and an effective amount of S-EB-S copolymer that has been modified by grafting a functional group onto it. The preferred Functional group is anhydride. The primer composition containing anhydride-modified S-EB-S copolymer has excellent resistance to chemical degradation and has good adhesion to metal surfaces. As well, the primer composition exhibits excellent resistance to cathodic disbondment, and is useful during storage and/or burial of the metal pipe.
The solid components include a tackifying resin and an effective amount of S-EB-S copolymer that has been modified by grafting a functional group onto it. The preferred Functional group is anhydride. The primer composition containing anhydride-modified S-EB-S copolymer has excellent resistance to chemical degradation and has good adhesion to metal surfaces. As well, the primer composition exhibits excellent resistance to cathodic disbondment, and is useful during storage and/or burial of the metal pipe.
Description
~ 2 ~
Ti~le of lovention PRl~aE~ t;:OlVlPOSlTlQN FOR NIET~L PIPES
Field o~ Invention This invention relates to a primer composition, and more particularly to an adhesive primer composition for pro~ecting metal pipes from corrosion during storage and from corrosion and cathodic disbondment while buried under0round.
Background of Invention Metal pipes that are intended to be buried in -the ground as part of a pipeline are subject to corrosion, both during the time o~ storage prior to burial, and while buried underground. It is not uncommon that, metal pipes may be stored for over one year prior to burial. This s~orage is typically outdoors, thus the metal pipes will require protection against corrosion during the storage period. ()ne of the usual methods used to protect metal pipes during storage is to apply a rubber-based primer coating to the pipes. Typically, the storage primer coating is not long lasting in the sense that it need only serve its purpose for the time oF
storage. A different primer composition is used when the metal pipes are buried.
Metal pipelines that are buried in the ground also require protection against chemical and electrolytic corrosion. The usual method ef providing such protection is to wrap the outer surface of the metal pipeline with a protective coating so as to decrease the likelihood of corrosion by reducing exposure of the metal pipeline to moisture and to other sub-surf~ce chemicals. As well, the protective coatings used are designed to insulate the metal pipeline from electrolytic corrosion.
Traditionally, the protective coatings applied to the buried metal pipelines have included a coating of rubber-based primer composition ancl one or more layers of adhesive tape outer-wrap. Notwithstanding these layers of protective coatings, the metal of the pipeline inevitably is 63 ~
exposed to corrosive elements because oF imperfections in the prirner composition and/or the adhesive tape, or, as is more likely, because the protective coatings become perforated for some reason. These perforations, referred to as "holidays", may be th~ result of rocks cutting ~:
5 the coating during back filling when the pipeline is buried in the ground, or other back filling stresses. Holidays may also result from the movement of the soil surrounding the pipeline due to changes in -temperature or moisture content. Alternatively, rnovement of the pipeline itself due to thermal expansion may result in perforation or other damage of the 0 protective coatings.
Primer compositions for use on metal pipes generally include a mixture of a resin and a rubber component. For many years, the resins used in the prim~r compositions were natural resins which had been ~;
reacted with zinc or calcium to form a resinate that was relatively stable ~5 and resistant to chernical degradation. Primer compositions made using such resins provided some improvement in cathodic disbondment resistance over the prior art, but nevertheless did not adequately eliminate the problem.
It is preFerable, and in many cases it is an industry requirement, 20 that all major buried metal pipelines be cathodically protected against corrosion. This is done by connecting the metal of the pipeline to a sacrificial anode and inducing a direct current within the metal and anode so that the rnetal pipeline becomes a cathode and therefore is subjected to less material loss due to corrosion. Cathodic protection has been Found to 25 slow down corrosion caused by sub-surface chemicals and electrolytic action at areas oF the pipelines where the holidays in the protective coatings occur.
Notwithstanding cathodic protection oF buried metal pipelines, corrosion where the holidays occur will nevertheless become significant 30 over time. A further problem caused by cathodic protection at holiday 2 ~ 5 sites is an increased tendency oF the adhesion or bonding of the protective coating, particularly ~he primer composition, to break down on the surface of the pipeline where the holidays occur. This decrease in the adhesion or bonding causes the primer composition and the adhesive tape to separate from the metal pipeline. Accorclingly, the protective coating "disbonds" in the area surrounding the holiday, thereby leading to even more corrosion of the metal pipeline.
This phenomenon of decreased adhesion oF the protective coating system in the area of the holidays is referred to as "cathodic disbondment". It is believed that cathodic disbondment occurs because, initially, there is a negative charge in the vicinity of the holiday. However, with time this negative charge has the effect of creating metal oxides on the metal surface and oF decreasing the adhesion of the primer composition to the metal surface. This results in an increased area where the metal surFace is exposed, and a corresponding increase in corrosion and current flow around a holiday so that the problem of corrosion becomes exaggerated over time.
Cathodic disbondment has, thereFore, become a major concern in the pipeline protection industry. As a result, an important feature of a primer composition for buried metal pipelines is the ability of the primer composition to remain bonded to the metal surFace and resist the tendency of cathodic disbondmenlt despite the presense and formation of holidays therein. The ability oF a primer composition to resist cathodic disbondment is not necessarily directly related to its adhesive strength to the metal surface. That is, a primer composition with strong aclhesion may not have good resistance to cathodic disbondrnent.
United States Patent No. 5,108,809 issued to Patil provides a surnnnary of the art devoted ~o the problem of cathodic disbondment in buried rnetal pipelinas. Interestingly, all oF the prior art discussed in U.S.
Patent No. 5,108,809, including the primer composition disclosed in that ~ 211~ 5 patent, address the problem oF cathodic disbondmen~ by addition of a "cathodic disbondment inhibitor" to the primer composition. None of the prior art discloses the use of a rubber compound that, itself, also acts as a cathodic disbondment inhibitor.
U.S. Patent No. 5,108,809 to Patil describes the use of a phenolic resin as the cathodic disbondment inhibitor in primer compositions.
Phenolic resin is said to improve the bonding of the adhesive tape to the metal pipe. The examples set out in U.S. Patent No. 5,108,809 demonstrate that the addition of the phenolic resin to a prirner composition increases resistance to cathodic disbondment.
The rubber-based components o~ the primer compositions described in U.S. Patent No. 5,108,809 include butyl rubber, chloro-butyl rubber and therrno-plastic rubber. Although butyl rubber is a substantial improvement over natural rubber compounds, it nevertheless has many double bonds which are available For chemical action and thereFore it is subject to chemical degradation over time. Chloro-butyl rubber does not have as many double bonds. On the other hand, it has other side efFects, including the potential release of chlorine ions which would react with the metal pipeline and significantly increase corrosion.
Stable, synthetic rubber compounds which have superior resistance to chemical degradation are known in the art. For instance, from U.S.
Patent Nos. 4,797,322 and 4,801,346 both issued to Huddleston, it is known that compositions comprising a copolymer having styrene end blocks and a poly~ethylene-butylene) mid-block (hereinafter raFerred to as "S-EB-S") provides good resistance to chernical degradation in the presence oF atmospheric weather and sunlight. However, S-EB-S
copolymer is relatively poor in its adhesion properties to metal. For instance, tests have shown that the adhesive peel strength oF S-EB-S
copolymer on steel is approximately 60 to 80 ounces per inch oF width, ;
2 ~
. ~
whereas for purposes of a primer composition on pipelines, a peel strength of at least 300 ounces per inch of width is required.
United States Patent No. 4,578,429 issued to Gergen discloses block copolymers that have been modified by grafting an acid component to the midblock. Examples of such modified copolymers are S-EB-S
copolymers on which anhydride functionalities have been graFted. One example in Patent No. 4,578,429 indicates that the anhydride-modified S-EB-S copolymer possesses the same resistance to chemical degradation as the unmodified S-EB-S copolymer, but its adhesive strength to metal is significantly enhanced.
United States Patent No. 4,801,346 issued to Huddleston discloses a protective coating containing S-EB-S copolymer for use as a storage protective system for metal pipes. Although the adhesion of S-EB-S
copolymer is insufficient for long-term use on buried pipelines, it was found to provide sufficient protection during typical storage periods of the metal pipes. A drawback with the use of the storage protective coating disclosed in United States Patent No. 4,801,346, and indeed with all the prior art, is that, when the metal pipe is ready to be buried underground, the storage protective coating must be removed Itypically using a wire brush or abrasive blasting) before the long-term primer composition and ~dhesive tape are applied to the metal pipelina. There are, therefore, additional expenses incurred and time required to store metal pipes before they are used in pipelines.
Accordingly, it would be desirable if the storage protective coating did not have to be removecl when the metal pipe is to be buried.
Preferably, significant advantages are achieved if the storage protective coating is the same as the primer composition used on buried pipelines.
Since typical buried metal pipelines are protected with a layer of prinler composition covered by one or more layers of an adhesive tape, one of the functions of the primer composition is to form an adhesive ~ ;
r , bond between the inner adhesive tape and the surface of the metal pipe.
As well, it is preferable if the primer composition is capable of holding that bond despite the formation of holiclays in the protec~ive coating. That is, it is preferable if the primer cornposition has good resistance to ca~hodic 5 disbonding.
Additionally, the primer cornposition should also provide 3 relatively impervious film to create an electrical barrier or insulation between the metal pipeline and its surroundings. It is also desirable that the primer composition be inert to chemical degradation for long periods of time 0 (normally in the order of 30 years), and that it have a degree of elasticity so that it can withstand the stress of pressure due to longitudinal movement of the pipeline relative to the surrounding soil.
Summary of the Invention Accordingly, the present inventiol- provides a primer composition 15 for coating the outside surface of a metal pipe. The primer composition comprises a mixture of solid components that includes a tackifying resin and an effective amount of modifiad S-EB-S copolymer, and ona or more solvents capable of solvation with the modified S-EB-S copolymer. The modiFied S-EB-S copolymer has grafted onto it a functional group, 20 preferably an anhydride.
The present invention also provicles a metal pipeline systern comprising a metal pipe having an outer surface, a layer of a primer composition and at least one layer of adhesive tape over the layer oF
primer composition. The primer composition consists of a mixture of solid 25 components that includes a tackifying resin and an eFFective amount oF
anhydride-modiFied S-EB S copolymer.
~n~l~s:[lptLQn oF the Present InventiQ~
Primer compositions For coating metal pipes have been made by combining a rubber-based cornpound having desired elasticity with a resin 30 designed to impart the necessary bonding and adhesive strength to the ~ 8 ~ ~ ~
primer composition. It has been found that a suitable rubber compound for use in primer compositions is reclaimed natural rubber made from inner tubes and the like. These products are made with rubber that has been ~ulcanized and otherwise treated so that the rubber is relatively stable and 5 inert to chemical degradation for the requisite time period. Reclaimed natural rubber continues to this day to be one of the preFerred rubber compounds for use in primer compositions, however, the addition of cathodic disbondment inhibitors are required.
It has been found, surprisingly, that primer compositions containing 10 anhydride-modified S-EB-S copolymer as their rubber components not only have excellent adhesive properties, but also exhibit good resistance to corrosion and to cathodic disbonding. As discussed above, S-EB-S
copoiymer has excellent resistance to chemical degradation, but its adhesion or bonding to metal is relatively poor so that it is useful as a 15 short-term storage protective coating, but not in a primer composition for buried pipelines. Modification of the S-EB-S copolymer by grafting anhydride functionalities onto it results in a compound having a resistance to chemical degradation comparable to S-EB-S copolymer, thus useful in a storage protective coating. In addition, the anhydride-modified S-EB-S
20 copolymer exhibits increased adhesion and bonding to metal surfaces. It has also been found by the invantor that primer compositions incorporating anhydride-modified S-EB-S copolyrner are surprisingly resistant to cathodic disbondment.
Typically, primer compositions for use on metal pipelines include a 25 resin component, a rubber component, and various additives such as colorants, solvents, anti-03(idants, etc. The prior art has addressed ~he problem of cathodic disbondment by including in the primer compositions an additional component, generally described as a cathodic disbondment inhibitor. The primer composition of the present invention, however, does 30 not include an additional component that acts as a cathodic disbondment ,~ 2 ~
inhibitor. Rather, the primer composition of the present invention has a rubber matrix or backbone that, itself, inhibits cathodic disbondment.
That is, the anhydride-modified S-EB-S copolymer is, in effect, the rubber component and the cathodic disbondment inhibitor of the primer 5 composition. This is a significant advantage over the primer compositions of the prior art. Since the rubber component is itself a cathodic disbondment inhibitor, there is no need to acld a separate cathodic disbondment inhibitor to the primer composition, thereby eliminating any disadvantages encountered when compounds are added to a mixture.
In order to obtain the required adhesive qualities for primer compositions used in pipeline coating, it is necessary-to create a strengthened bonding between the primer composition and the metal pipeline. The adhesive and bonding characteristics of S-EB-S copolymer are increased by the addition or graFting of an anhydride functionality to the S-EB-S copolyrner. The anhydride functionality can be graFted onto the S-EB-S copolymer by reaction with maleic anhydride. This process and the resulting modified S-EB-S copolymer has been described in U.S.
Patent No. 4,578,429 issued to Gergen, and the anhydride-modified S-EB-S copolymer is commercially available from Shell Chemical Company under the trade-marks l<RATC)N 1901X and KRATON 1924. The anhydride modified S-EB-S copolymer is said to exhibit increased adhesive `
strength to metal surFaces as compared to the unmodiFied S-EB-S
copolymer.
Patent No. 4,578,4~9 does not disclose, or even contemplate, the use of anhydride-modiFied S-EB-S copolymer in primer compositions for use on metal pipes. In particular, the surprising improvement in cathodic disbondment oF primer compositions incorporating modified S-EB-S
copolymer is not contemplated.
U.S. Patent No. 4,578,429 discloses that the Functional group grafted onto S-EB-S copolymer need not be limited to an anhydride `" 2~8~
functional group. F;a~her, the class of preferred functional groups that can be grafted onto S-EB-S copolymer include carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups, acid chlorides and the like. The preferred modifying functional groups include anhydrides 5 such as acrylic anhydride, maleic anhydride, itaconic anhydride and citraconic anhydride.
The addition of the anhydride functionality to the S-EB-S copolymer is believed to provide sites for creating an effective bond between the copolymer and the iron in the metal pipe. That is, the anhydride 10 functionality on the S-EB-S copolymer provides chemically active sites which promote the formation of bonds with the iron on the surface of the rnetal pipe. As a result of the use of the anhydride-modified S-EB-S
copolymer, the primer composition of the present invention has been found to have excellent adhesion strength iover 350 ounces per inch oF
15 width).
The primer composition of the present invention comprises a mixture of solid components and at least one solvent. The solid components include a tackifying resin component and the anhydride-modified S-EB-S copolymer component. The solvents useful in the 20 present invention are those capable of solvation with the mixture of solid components and the anhydride-modilFied S-EB-S copolymer.
Other components commonly used in primer compositions may also be used in the primer composition of the present invention. For example, various colorants may be used, the main function bein0 to provide colour 2s to the primer composition so as to enable the user to ensure that the surface oF the metal pipe is completely covered with primer composition.
For this purpose, carbon black is the best known and least expensive coloran t .
Typically, the adhesive tape used For protectin~ metal pipes has a 30 backing material made olF a blend of polyolefins. The adhesive layer ~ 2 1 ~ 8 ~ ~
:LO
usually is composed oF butyl and butyl-reclaimed rubber that is tackified with petroleum resin and polybutene, and filled with clay. Examples of formulations for the adhesive layer are found in United States Patent Nos.
4,687,794 and 4,692,352, both issued to Huddleston. For example, a 5 suitable adhesive layer comprises the following:
_ _ butyl rubber 76 Ibs.
_ _ _ reclaimecl butyl rubber 145 Ibs.
polybutene tackifier 63.5 Ibs.
clay 220 Ibs.
I . . _ ¦ anti-oxidan-t 2 . 5 Ibs .
TOTAL: 507 Ibs.
Various-tackifying agents, anti-oxidants and solvents which are already known in the art may be used in the primer composition of the 0 present invention, so long as they are compatible with the anhydride-modified S EB-S copolymer rubber base and the other ingredients.
Examples of various tackifying resins that are known and marketecl to the adhesive industry include -the following: resins such as gum, wood or-tall oil resins; rnodified resins, for example polymerized resin or hydrogenated 15 resin; resin esters such as pentaerythri-tol-wood resin; glycerin-hydrogenated resin, glycerin-highly stabilized resin, and a pentaery-thritol-highly stabilized resin; polymerized petroleum hydrocarbons, for example cycloaliphatic hydrogenated olefins, olefins, aliphatic petroleum hydrocarbons, modified aromatic hydrocarbons, dicyclopentadiene, mb(ed ~0 olefins, alkyl-aroma~ic petroleum hydrocarbons, modified aromatic hydrocarbons; polymerized terpenes such as alpha-pinene, d-limonene, beta-pinene, terpene, etc.; miscellaneous resins such as alpha-~ 8 ~ ~ ~
methylstyrene, vinyi-toluene, alpha-me~hylstyrene, styrene, terp~ne phenolic, etc.; and metallic resinates such as mixed calcium/zinc and zinc resinates.
As discussed in U.S. Patent No. 4,578,429, the modified S-EB-S
copolymer will usually contain from 0.02% wt. to 20% wt., preferably 0.1% wt. to 10% wt., and most preferably 0.2% wt. to 5% wt. of the functional group. It has been found that the preferred range for the primer composition of the present invention is from about 0.07% wt. to 3.3%
wt. maleic anhydride based on the total weight of the mixture of solid components. In other words, the anhydride component of the anhydride-modified S-EB-S copolymer makes up about 0.07% wt. to 3.3% wt. of the total mixture of solid components. Preferably, the mixture of solid components will have about 2% wt. of maleic anhydride.
In the primer composition of the present invention, the rnixture of solid components will be from about 6% wt. to about 30% wt. of the total primer composition. In the preferred primer compositions, the mixture of solid components will comprise about 12% wt., about 19%
wt., or about 27% wt. of the total primer composition.
The relative amounts of tackifying resin and anhydride-modified S-EB-S copolymer in the primer composition oF the present invention is also important. Too much tackifying resin results in a procluct that is brittle when dried, whereas too much anhydride-modified S-EB-S copolymer results in a product that has lower adhesion to metal. It has been found that the ratio of tackifying resin to anhydride-modified S-EB-S copolymer should be in the rangs of about 20 to about 175 parts resin to 100 parts of anhydride-rnodified S-EB-S copolymer, by weight. Preferablv, the ratio is in the range oF about 75 to about 1~5 parts resin to 100 parts anhydride-modified S-EB-S copolymer, by weight.
The primer composition of the present invention is, therefore, useful to protect metal pipes from corrosion during storage. It is also useful on ---` 2~8~
buried pipelines because of its increased adhesion and its superior resistance to chemical disbondrnent. One advantage of the primer composition of the present invention is that it does not have to be removed from stored metal pipes prior to burial underground. Rather, 5 when the metal pipes are removed from storage, and prepared for burial, all that needs to be done is the addition of a fresh layer of primer composition over the existing layer, and then wrapping the adhesive tape around the pipe. The need to remove the storage protective coating is eliminated, thus saving substantial time and expense.
The rnetal pipeline system oF the present invention includes a metal pipe whose outer surface is coated with the primer composition of the present invention. One or more layers of adhesive tape is then applied over the primer composition.
In practice, metal pipes are prepared as follows before storage and 15 before burial in the ground. The outer surface o~ the metal pipe is treated by a cleaning process such as sand blasting or wire brushing. The primer composition of the present invention is then applied onto the outer surface of the pipe, typically by spraying or brushing. The metal pipe can then be stored until needed. When the metal pipe is to be used in a metal pipeline 20 system, a fresh layer of primer composition is applied by spraying or brushing over the existing layer of primer composition. Once the solvents in the primer composition have evaporated, typically about 30 seconds, one or more layers of adhesive tape are helically wound onto the metal pipe. The adhesive tape wrapping used typically consists of a spiral 25 overlapped wrapping. The tape is made oF a baclcing of polyethylene and an internal layer oF butyl rubber, tackifiers, fillers and anti-oxidants.
E2~1~
A primer composition for coating the outsida surFace of a metal 30 pipe was prepared having the Following composition:
-~ 2 ~ 5 _ . _ Component Parts by Weight _ _ . .
Toluene 200 Heptane 520 Isopropyl Alcohol 80 _ TOTAL~ oo , ,, . .~_ _ . . . ~ .
In the above example, KRATON 1901 X is the commercial trade-mark for the S-EB-S block copolymer as rnodiFied with maleic anhydride.
5 KRATON 1901X is available from Shell Chemical Company and includes 2% wt. maleic anhydride.
ESCOREZ 2101 ~a trade-rnark) is a petroleum-based tacki~ying resin available ~rom Exxon Corporation. Toluene, heptane and isopropyl alcohol are solvents capable of dissolving the styrene end-blocks, the ethylene-0 butylene mid-blocks and the anhydride functionality of the anhydride-modified S-EB-S copolymer.
The standard cathodic disbondment test was carried out on a metal pipe having a protective coating that included tha primer composition described above. In this test, an 18 inch metal pipe oF 3 1/2 inches 15 outside diameter was coated with the primer composition and overlaid with a layer oF adhesive tape. The pipe section had been preparsd by abrasive blas~ing to near-white cleanliness rating with a 2 mil profile. The primer composition was applied by brushing and allowed to dry about 15 minutes before applying a 4 inch wide black innerwrap with a 50%
20 overwrap. A 1/4 inch diameter holiday was drilled through the protective '2. ~ 5 coating. The specimen was immersed to a level of 12 inches in a 3%
sodium chloride solution, and the solution was heated to 1 50F. A
potential of 1.5 volts was applied to a platinum wire anode. These test conditions were maintained for 28 days.
Upon termination of the test, the specimen was allowed to cool to room temperature, and the adhesion near the holiday was evaluated.
Resistance to cathodic disbondment was determined by rneASuring the radius from the edge of the intentionally created holiday to the point where the coating exhibitecl good adhesion. It was found that the cathodic disbondment radius averaged approximately 5 millimetres.
Typically, disbondment radii with other primer compositions of the prior art are in the order of 17 to 20 millimetres.
The cathodic disbondment radius obtained using the primer composition of the present invention was approximately the same as ~he cathodic disbondment radius reported in U.S. Patent No. 5,108,809, where phenolic resins were added as cathodic disbondrnent inhibitors.
Accordingly, the use of anhydride-modified S-EB-S copolymer as the rubber component of the primer composition of the present invention provides sirhilar results in terms of cathodic disbondment to the addition of a phenolic resin to the primer composition.
Isopropyl alcohol was included in the primer composition of the above Example as it aids in dissolving the anhydride functionality of the modified S-EB-S copolymer. Isopropyl alcohol also serves to combine with moisture on the surface structure of the metal pipe, thereby promoting the wettability of the steel by the solvent which carries the mixture of solid components of the primer composition of the present invention.
Tha use of anhyclride-modified S-EB-S copolymer as the rubber component of a primer composition has, therefore, been found to provide a primer composition with chemical stability, superior adhesion qualities to metal, and superior resistance to cathodic disbondment. It is useful as a component of a protective system during both storage and burial of the metal pipe.
Modifications and variations of the present inven~ion are possible 5 within the sphere and scope of the claims appended hereto.
Ti~le of lovention PRl~aE~ t;:OlVlPOSlTlQN FOR NIET~L PIPES
Field o~ Invention This invention relates to a primer composition, and more particularly to an adhesive primer composition for pro~ecting metal pipes from corrosion during storage and from corrosion and cathodic disbondment while buried under0round.
Background of Invention Metal pipes that are intended to be buried in -the ground as part of a pipeline are subject to corrosion, both during the time o~ storage prior to burial, and while buried underground. It is not uncommon that, metal pipes may be stored for over one year prior to burial. This s~orage is typically outdoors, thus the metal pipes will require protection against corrosion during the storage period. ()ne of the usual methods used to protect metal pipes during storage is to apply a rubber-based primer coating to the pipes. Typically, the storage primer coating is not long lasting in the sense that it need only serve its purpose for the time oF
storage. A different primer composition is used when the metal pipes are buried.
Metal pipelines that are buried in the ground also require protection against chemical and electrolytic corrosion. The usual method ef providing such protection is to wrap the outer surface of the metal pipeline with a protective coating so as to decrease the likelihood of corrosion by reducing exposure of the metal pipeline to moisture and to other sub-surf~ce chemicals. As well, the protective coatings used are designed to insulate the metal pipeline from electrolytic corrosion.
Traditionally, the protective coatings applied to the buried metal pipelines have included a coating of rubber-based primer composition ancl one or more layers of adhesive tape outer-wrap. Notwithstanding these layers of protective coatings, the metal of the pipeline inevitably is 63 ~
exposed to corrosive elements because oF imperfections in the prirner composition and/or the adhesive tape, or, as is more likely, because the protective coatings become perforated for some reason. These perforations, referred to as "holidays", may be th~ result of rocks cutting ~:
5 the coating during back filling when the pipeline is buried in the ground, or other back filling stresses. Holidays may also result from the movement of the soil surrounding the pipeline due to changes in -temperature or moisture content. Alternatively, rnovement of the pipeline itself due to thermal expansion may result in perforation or other damage of the 0 protective coatings.
Primer compositions for use on metal pipes generally include a mixture of a resin and a rubber component. For many years, the resins used in the prim~r compositions were natural resins which had been ~;
reacted with zinc or calcium to form a resinate that was relatively stable ~5 and resistant to chernical degradation. Primer compositions made using such resins provided some improvement in cathodic disbondment resistance over the prior art, but nevertheless did not adequately eliminate the problem.
It is preFerable, and in many cases it is an industry requirement, 20 that all major buried metal pipelines be cathodically protected against corrosion. This is done by connecting the metal of the pipeline to a sacrificial anode and inducing a direct current within the metal and anode so that the rnetal pipeline becomes a cathode and therefore is subjected to less material loss due to corrosion. Cathodic protection has been Found to 25 slow down corrosion caused by sub-surface chemicals and electrolytic action at areas oF the pipelines where the holidays in the protective coatings occur.
Notwithstanding cathodic protection oF buried metal pipelines, corrosion where the holidays occur will nevertheless become significant 30 over time. A further problem caused by cathodic protection at holiday 2 ~ 5 sites is an increased tendency oF the adhesion or bonding of the protective coating, particularly ~he primer composition, to break down on the surface of the pipeline where the holidays occur. This decrease in the adhesion or bonding causes the primer composition and the adhesive tape to separate from the metal pipeline. Accorclingly, the protective coating "disbonds" in the area surrounding the holiday, thereby leading to even more corrosion of the metal pipeline.
This phenomenon of decreased adhesion oF the protective coating system in the area of the holidays is referred to as "cathodic disbondment". It is believed that cathodic disbondment occurs because, initially, there is a negative charge in the vicinity of the holiday. However, with time this negative charge has the effect of creating metal oxides on the metal surface and oF decreasing the adhesion of the primer composition to the metal surface. This results in an increased area where the metal surFace is exposed, and a corresponding increase in corrosion and current flow around a holiday so that the problem of corrosion becomes exaggerated over time.
Cathodic disbondment has, thereFore, become a major concern in the pipeline protection industry. As a result, an important feature of a primer composition for buried metal pipelines is the ability of the primer composition to remain bonded to the metal surFace and resist the tendency of cathodic disbondmenlt despite the presense and formation of holidays therein. The ability oF a primer composition to resist cathodic disbondment is not necessarily directly related to its adhesive strength to the metal surface. That is, a primer composition with strong aclhesion may not have good resistance to cathodic disbondrnent.
United States Patent No. 5,108,809 issued to Patil provides a surnnnary of the art devoted ~o the problem of cathodic disbondment in buried rnetal pipelinas. Interestingly, all oF the prior art discussed in U.S.
Patent No. 5,108,809, including the primer composition disclosed in that ~ 211~ 5 patent, address the problem oF cathodic disbondmen~ by addition of a "cathodic disbondment inhibitor" to the primer composition. None of the prior art discloses the use of a rubber compound that, itself, also acts as a cathodic disbondment inhibitor.
U.S. Patent No. 5,108,809 to Patil describes the use of a phenolic resin as the cathodic disbondment inhibitor in primer compositions.
Phenolic resin is said to improve the bonding of the adhesive tape to the metal pipe. The examples set out in U.S. Patent No. 5,108,809 demonstrate that the addition of the phenolic resin to a prirner composition increases resistance to cathodic disbondment.
The rubber-based components o~ the primer compositions described in U.S. Patent No. 5,108,809 include butyl rubber, chloro-butyl rubber and therrno-plastic rubber. Although butyl rubber is a substantial improvement over natural rubber compounds, it nevertheless has many double bonds which are available For chemical action and thereFore it is subject to chemical degradation over time. Chloro-butyl rubber does not have as many double bonds. On the other hand, it has other side efFects, including the potential release of chlorine ions which would react with the metal pipeline and significantly increase corrosion.
Stable, synthetic rubber compounds which have superior resistance to chemical degradation are known in the art. For instance, from U.S.
Patent Nos. 4,797,322 and 4,801,346 both issued to Huddleston, it is known that compositions comprising a copolymer having styrene end blocks and a poly~ethylene-butylene) mid-block (hereinafter raFerred to as "S-EB-S") provides good resistance to chernical degradation in the presence oF atmospheric weather and sunlight. However, S-EB-S
copolymer is relatively poor in its adhesion properties to metal. For instance, tests have shown that the adhesive peel strength oF S-EB-S
copolymer on steel is approximately 60 to 80 ounces per inch oF width, ;
2 ~
. ~
whereas for purposes of a primer composition on pipelines, a peel strength of at least 300 ounces per inch of width is required.
United States Patent No. 4,578,429 issued to Gergen discloses block copolymers that have been modified by grafting an acid component to the midblock. Examples of such modified copolymers are S-EB-S
copolymers on which anhydride functionalities have been graFted. One example in Patent No. 4,578,429 indicates that the anhydride-modified S-EB-S copolymer possesses the same resistance to chemical degradation as the unmodified S-EB-S copolymer, but its adhesive strength to metal is significantly enhanced.
United States Patent No. 4,801,346 issued to Huddleston discloses a protective coating containing S-EB-S copolymer for use as a storage protective system for metal pipes. Although the adhesion of S-EB-S
copolymer is insufficient for long-term use on buried pipelines, it was found to provide sufficient protection during typical storage periods of the metal pipes. A drawback with the use of the storage protective coating disclosed in United States Patent No. 4,801,346, and indeed with all the prior art, is that, when the metal pipe is ready to be buried underground, the storage protective coating must be removed Itypically using a wire brush or abrasive blasting) before the long-term primer composition and ~dhesive tape are applied to the metal pipelina. There are, therefore, additional expenses incurred and time required to store metal pipes before they are used in pipelines.
Accordingly, it would be desirable if the storage protective coating did not have to be removecl when the metal pipe is to be buried.
Preferably, significant advantages are achieved if the storage protective coating is the same as the primer composition used on buried pipelines.
Since typical buried metal pipelines are protected with a layer of prinler composition covered by one or more layers of an adhesive tape, one of the functions of the primer composition is to form an adhesive ~ ;
r , bond between the inner adhesive tape and the surface of the metal pipe.
As well, it is preferable if the primer composition is capable of holding that bond despite the formation of holiclays in the protec~ive coating. That is, it is preferable if the primer cornposition has good resistance to ca~hodic 5 disbonding.
Additionally, the primer cornposition should also provide 3 relatively impervious film to create an electrical barrier or insulation between the metal pipeline and its surroundings. It is also desirable that the primer composition be inert to chemical degradation for long periods of time 0 (normally in the order of 30 years), and that it have a degree of elasticity so that it can withstand the stress of pressure due to longitudinal movement of the pipeline relative to the surrounding soil.
Summary of the Invention Accordingly, the present inventiol- provides a primer composition 15 for coating the outside surface of a metal pipe. The primer composition comprises a mixture of solid components that includes a tackifying resin and an effective amount of modifiad S-EB-S copolymer, and ona or more solvents capable of solvation with the modified S-EB-S copolymer. The modiFied S-EB-S copolymer has grafted onto it a functional group, 20 preferably an anhydride.
The present invention also provicles a metal pipeline systern comprising a metal pipe having an outer surface, a layer of a primer composition and at least one layer of adhesive tape over the layer oF
primer composition. The primer composition consists of a mixture of solid 25 components that includes a tackifying resin and an eFFective amount oF
anhydride-modiFied S-EB S copolymer.
~n~l~s:[lptLQn oF the Present InventiQ~
Primer compositions For coating metal pipes have been made by combining a rubber-based cornpound having desired elasticity with a resin 30 designed to impart the necessary bonding and adhesive strength to the ~ 8 ~ ~ ~
primer composition. It has been found that a suitable rubber compound for use in primer compositions is reclaimed natural rubber made from inner tubes and the like. These products are made with rubber that has been ~ulcanized and otherwise treated so that the rubber is relatively stable and 5 inert to chemical degradation for the requisite time period. Reclaimed natural rubber continues to this day to be one of the preFerred rubber compounds for use in primer compositions, however, the addition of cathodic disbondment inhibitors are required.
It has been found, surprisingly, that primer compositions containing 10 anhydride-modified S-EB-S copolymer as their rubber components not only have excellent adhesive properties, but also exhibit good resistance to corrosion and to cathodic disbonding. As discussed above, S-EB-S
copoiymer has excellent resistance to chemical degradation, but its adhesion or bonding to metal is relatively poor so that it is useful as a 15 short-term storage protective coating, but not in a primer composition for buried pipelines. Modification of the S-EB-S copolymer by grafting anhydride functionalities onto it results in a compound having a resistance to chemical degradation comparable to S-EB-S copolymer, thus useful in a storage protective coating. In addition, the anhydride-modified S-EB-S
20 copolymer exhibits increased adhesion and bonding to metal surfaces. It has also been found by the invantor that primer compositions incorporating anhydride-modified S-EB-S copolyrner are surprisingly resistant to cathodic disbondment.
Typically, primer compositions for use on metal pipelines include a 25 resin component, a rubber component, and various additives such as colorants, solvents, anti-03(idants, etc. The prior art has addressed ~he problem of cathodic disbondment by including in the primer compositions an additional component, generally described as a cathodic disbondment inhibitor. The primer composition of the present invention, however, does 30 not include an additional component that acts as a cathodic disbondment ,~ 2 ~
inhibitor. Rather, the primer composition of the present invention has a rubber matrix or backbone that, itself, inhibits cathodic disbondment.
That is, the anhydride-modified S-EB-S copolymer is, in effect, the rubber component and the cathodic disbondment inhibitor of the primer 5 composition. This is a significant advantage over the primer compositions of the prior art. Since the rubber component is itself a cathodic disbondment inhibitor, there is no need to acld a separate cathodic disbondment inhibitor to the primer composition, thereby eliminating any disadvantages encountered when compounds are added to a mixture.
In order to obtain the required adhesive qualities for primer compositions used in pipeline coating, it is necessary-to create a strengthened bonding between the primer composition and the metal pipeline. The adhesive and bonding characteristics of S-EB-S copolymer are increased by the addition or graFting of an anhydride functionality to the S-EB-S copolyrner. The anhydride functionality can be graFted onto the S-EB-S copolymer by reaction with maleic anhydride. This process and the resulting modified S-EB-S copolymer has been described in U.S.
Patent No. 4,578,429 issued to Gergen, and the anhydride-modified S-EB-S copolymer is commercially available from Shell Chemical Company under the trade-marks l<RATC)N 1901X and KRATON 1924. The anhydride modified S-EB-S copolymer is said to exhibit increased adhesive `
strength to metal surFaces as compared to the unmodiFied S-EB-S
copolymer.
Patent No. 4,578,4~9 does not disclose, or even contemplate, the use of anhydride-modiFied S-EB-S copolymer in primer compositions for use on metal pipes. In particular, the surprising improvement in cathodic disbondment oF primer compositions incorporating modified S-EB-S
copolymer is not contemplated.
U.S. Patent No. 4,578,429 discloses that the Functional group grafted onto S-EB-S copolymer need not be limited to an anhydride `" 2~8~
functional group. F;a~her, the class of preferred functional groups that can be grafted onto S-EB-S copolymer include carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups, acid chlorides and the like. The preferred modifying functional groups include anhydrides 5 such as acrylic anhydride, maleic anhydride, itaconic anhydride and citraconic anhydride.
The addition of the anhydride functionality to the S-EB-S copolymer is believed to provide sites for creating an effective bond between the copolymer and the iron in the metal pipe. That is, the anhydride 10 functionality on the S-EB-S copolymer provides chemically active sites which promote the formation of bonds with the iron on the surface of the rnetal pipe. As a result of the use of the anhydride-modified S-EB-S
copolymer, the primer composition of the present invention has been found to have excellent adhesion strength iover 350 ounces per inch oF
15 width).
The primer composition of the present invention comprises a mixture of solid components and at least one solvent. The solid components include a tackifying resin component and the anhydride-modified S-EB-S copolymer component. The solvents useful in the 20 present invention are those capable of solvation with the mixture of solid components and the anhydride-modilFied S-EB-S copolymer.
Other components commonly used in primer compositions may also be used in the primer composition of the present invention. For example, various colorants may be used, the main function bein0 to provide colour 2s to the primer composition so as to enable the user to ensure that the surface oF the metal pipe is completely covered with primer composition.
For this purpose, carbon black is the best known and least expensive coloran t .
Typically, the adhesive tape used For protectin~ metal pipes has a 30 backing material made olF a blend of polyolefins. The adhesive layer ~ 2 1 ~ 8 ~ ~
:LO
usually is composed oF butyl and butyl-reclaimed rubber that is tackified with petroleum resin and polybutene, and filled with clay. Examples of formulations for the adhesive layer are found in United States Patent Nos.
4,687,794 and 4,692,352, both issued to Huddleston. For example, a 5 suitable adhesive layer comprises the following:
_ _ butyl rubber 76 Ibs.
_ _ _ reclaimecl butyl rubber 145 Ibs.
polybutene tackifier 63.5 Ibs.
clay 220 Ibs.
I . . _ ¦ anti-oxidan-t 2 . 5 Ibs .
TOTAL: 507 Ibs.
Various-tackifying agents, anti-oxidants and solvents which are already known in the art may be used in the primer composition of the 0 present invention, so long as they are compatible with the anhydride-modified S EB-S copolymer rubber base and the other ingredients.
Examples of various tackifying resins that are known and marketecl to the adhesive industry include -the following: resins such as gum, wood or-tall oil resins; rnodified resins, for example polymerized resin or hydrogenated 15 resin; resin esters such as pentaerythri-tol-wood resin; glycerin-hydrogenated resin, glycerin-highly stabilized resin, and a pentaery-thritol-highly stabilized resin; polymerized petroleum hydrocarbons, for example cycloaliphatic hydrogenated olefins, olefins, aliphatic petroleum hydrocarbons, modified aromatic hydrocarbons, dicyclopentadiene, mb(ed ~0 olefins, alkyl-aroma~ic petroleum hydrocarbons, modified aromatic hydrocarbons; polymerized terpenes such as alpha-pinene, d-limonene, beta-pinene, terpene, etc.; miscellaneous resins such as alpha-~ 8 ~ ~ ~
methylstyrene, vinyi-toluene, alpha-me~hylstyrene, styrene, terp~ne phenolic, etc.; and metallic resinates such as mixed calcium/zinc and zinc resinates.
As discussed in U.S. Patent No. 4,578,429, the modified S-EB-S
copolymer will usually contain from 0.02% wt. to 20% wt., preferably 0.1% wt. to 10% wt., and most preferably 0.2% wt. to 5% wt. of the functional group. It has been found that the preferred range for the primer composition of the present invention is from about 0.07% wt. to 3.3%
wt. maleic anhydride based on the total weight of the mixture of solid components. In other words, the anhydride component of the anhydride-modified S-EB-S copolymer makes up about 0.07% wt. to 3.3% wt. of the total mixture of solid components. Preferably, the mixture of solid components will have about 2% wt. of maleic anhydride.
In the primer composition of the present invention, the rnixture of solid components will be from about 6% wt. to about 30% wt. of the total primer composition. In the preferred primer compositions, the mixture of solid components will comprise about 12% wt., about 19%
wt., or about 27% wt. of the total primer composition.
The relative amounts of tackifying resin and anhydride-modified S-EB-S copolymer in the primer composition oF the present invention is also important. Too much tackifying resin results in a procluct that is brittle when dried, whereas too much anhydride-modified S-EB-S copolymer results in a product that has lower adhesion to metal. It has been found that the ratio of tackifying resin to anhydride-modified S-EB-S copolymer should be in the rangs of about 20 to about 175 parts resin to 100 parts of anhydride-rnodified S-EB-S copolymer, by weight. Preferablv, the ratio is in the range oF about 75 to about 1~5 parts resin to 100 parts anhydride-modified S-EB-S copolymer, by weight.
The primer composition of the present invention is, therefore, useful to protect metal pipes from corrosion during storage. It is also useful on ---` 2~8~
buried pipelines because of its increased adhesion and its superior resistance to chemical disbondrnent. One advantage of the primer composition of the present invention is that it does not have to be removed from stored metal pipes prior to burial underground. Rather, 5 when the metal pipes are removed from storage, and prepared for burial, all that needs to be done is the addition of a fresh layer of primer composition over the existing layer, and then wrapping the adhesive tape around the pipe. The need to remove the storage protective coating is eliminated, thus saving substantial time and expense.
The rnetal pipeline system oF the present invention includes a metal pipe whose outer surface is coated with the primer composition of the present invention. One or more layers of adhesive tape is then applied over the primer composition.
In practice, metal pipes are prepared as follows before storage and 15 before burial in the ground. The outer surface o~ the metal pipe is treated by a cleaning process such as sand blasting or wire brushing. The primer composition of the present invention is then applied onto the outer surface of the pipe, typically by spraying or brushing. The metal pipe can then be stored until needed. When the metal pipe is to be used in a metal pipeline 20 system, a fresh layer of primer composition is applied by spraying or brushing over the existing layer of primer composition. Once the solvents in the primer composition have evaporated, typically about 30 seconds, one or more layers of adhesive tape are helically wound onto the metal pipe. The adhesive tape wrapping used typically consists of a spiral 25 overlapped wrapping. The tape is made oF a baclcing of polyethylene and an internal layer oF butyl rubber, tackifiers, fillers and anti-oxidants.
E2~1~
A primer composition for coating the outsida surFace of a metal 30 pipe was prepared having the Following composition:
-~ 2 ~ 5 _ . _ Component Parts by Weight _ _ . .
Toluene 200 Heptane 520 Isopropyl Alcohol 80 _ TOTAL~ oo , ,, . .~_ _ . . . ~ .
In the above example, KRATON 1901 X is the commercial trade-mark for the S-EB-S block copolymer as rnodiFied with maleic anhydride.
5 KRATON 1901X is available from Shell Chemical Company and includes 2% wt. maleic anhydride.
ESCOREZ 2101 ~a trade-rnark) is a petroleum-based tacki~ying resin available ~rom Exxon Corporation. Toluene, heptane and isopropyl alcohol are solvents capable of dissolving the styrene end-blocks, the ethylene-0 butylene mid-blocks and the anhydride functionality of the anhydride-modified S-EB-S copolymer.
The standard cathodic disbondment test was carried out on a metal pipe having a protective coating that included tha primer composition described above. In this test, an 18 inch metal pipe oF 3 1/2 inches 15 outside diameter was coated with the primer composition and overlaid with a layer oF adhesive tape. The pipe section had been preparsd by abrasive blas~ing to near-white cleanliness rating with a 2 mil profile. The primer composition was applied by brushing and allowed to dry about 15 minutes before applying a 4 inch wide black innerwrap with a 50%
20 overwrap. A 1/4 inch diameter holiday was drilled through the protective '2. ~ 5 coating. The specimen was immersed to a level of 12 inches in a 3%
sodium chloride solution, and the solution was heated to 1 50F. A
potential of 1.5 volts was applied to a platinum wire anode. These test conditions were maintained for 28 days.
Upon termination of the test, the specimen was allowed to cool to room temperature, and the adhesion near the holiday was evaluated.
Resistance to cathodic disbondment was determined by rneASuring the radius from the edge of the intentionally created holiday to the point where the coating exhibitecl good adhesion. It was found that the cathodic disbondment radius averaged approximately 5 millimetres.
Typically, disbondment radii with other primer compositions of the prior art are in the order of 17 to 20 millimetres.
The cathodic disbondment radius obtained using the primer composition of the present invention was approximately the same as ~he cathodic disbondment radius reported in U.S. Patent No. 5,108,809, where phenolic resins were added as cathodic disbondrnent inhibitors.
Accordingly, the use of anhydride-modified S-EB-S copolymer as the rubber component of the primer composition of the present invention provides sirhilar results in terms of cathodic disbondment to the addition of a phenolic resin to the primer composition.
Isopropyl alcohol was included in the primer composition of the above Example as it aids in dissolving the anhydride functionality of the modified S-EB-S copolymer. Isopropyl alcohol also serves to combine with moisture on the surface structure of the metal pipe, thereby promoting the wettability of the steel by the solvent which carries the mixture of solid components of the primer composition of the present invention.
Tha use of anhyclride-modified S-EB-S copolymer as the rubber component of a primer composition has, therefore, been found to provide a primer composition with chemical stability, superior adhesion qualities to metal, and superior resistance to cathodic disbondment. It is useful as a component of a protective system during both storage and burial of the metal pipe.
Modifications and variations of the present inven~ion are possible 5 within the sphere and scope of the claims appended hereto.
Claims (21)
1. A primer composition for coating an outside surface of a metal pipe, comprising:
a) a mixture of solid components comprising a tackifying resin and an effective amount of a modified S-EB-S copolymer, and b) at least one solvent for the mixture and capable of solvation with the modified S-EB-S copolymer, whereby the modified S-EB-S copolymer has grafted thereon a functional group selected from carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups and acid chloride.
a) a mixture of solid components comprising a tackifying resin and an effective amount of a modified S-EB-S copolymer, and b) at least one solvent for the mixture and capable of solvation with the modified S-EB-S copolymer, whereby the modified S-EB-S copolymer has grafted thereon a functional group selected from carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups and acid chloride.
2. The primer composition claimed in claim 1, wherein the functional group is an anhydride group derived from an anhydride selected from acrylic anhydride, maleic anhydride, itaconic anhydride and citraconic anhydride.
3. The primer composition claimed in claim 2, wherein the functional group is derived from maleic anhydride.
4. The primer composition claimed in claim 3, wherein the mixture of solid components comprises from about 0.07% wt. to about 3.3% wt. of maleic anhydride.
5. The primer composition claimed in claim 4, wherein the mixture of solid components comprises about 2% wt. of maleic anhydride.
6. The primer composition claimed in claim 3, comprising from about 6% wt. to about 30% wt. of the mixture of solid components.
7. The primer composition claimed in claim 6, comprising about 12%
wt. of the mixture of solid components.
wt. of the mixture of solid components.
8. The primer composition claimed in claim 6, comprising about 19%
wt. of the mixture of solid components.
wt. of the mixture of solid components.
9. The primer composition claimed in claim 6, comprising about 27%
wt. of the mixture of solid components.
wt. of the mixture of solid components.
10. The primer composition claimed in claim 3, comprising from about 20 to about 175 parts by weight of the tackifying resin to 100 parts of the anhydride-modified S-EB-S copolymer.
11. The primer composition claimed in claim 10, comprising from about 75 to about 125 parts by weight of the tackifying resin to 100 parts of the anhydride-modified S-EB-S copolymer.
12. The primer composition claimed in any one of claims 1, 2, 3, 4, 5, 6 or 10, wherein the at least one solvent is selected from the group consisting of heptane, toluene and isopropyl alcohol.
13. A metal pipeline system, comprising:
a) a metal pipe having an outer surface;
b) a layer of a primer composition on the outer surface, comprising:
i) a mixture of solid components comprising a tackifying resin and an effective amount of anhydride-modified S-EB-S copolymer; and c) at least one layer of adhesive tape over the layer of primer composition.
a) a metal pipe having an outer surface;
b) a layer of a primer composition on the outer surface, comprising:
i) a mixture of solid components comprising a tackifying resin and an effective amount of anhydride-modified S-EB-S copolymer; and c) at least one layer of adhesive tape over the layer of primer composition.
14. The metal pipeline system claimed in claim 13, wherein the mixture of solid components comprises from about 0.07% wt. to about 3.3% wt.
of maleic anhydride in the primer composition.
of maleic anhydride in the primer composition.
15. The metal pipeline system claimed in claim 13, wherein the mixture of solid components comprises about 2% wt. of maleic anhydride in the primer composition.
16. The metal pipeline system claimed in claim 13, comprising from about 20 to about 175 parts by weight of the tackifying resin to 100 parts of the anhydride-modified S-EB-S copolymer in the primer composition.
17. The metal pipeline system claimed in claim 13, comprising From about 75 to about 125 parts by weight of the tackifying resin to 100 parts of the anhydride-modified S-EB-S copolymer in the primer composition.
18. The metal pipeline system claimed in claim 13, further comprising an initial layer of the primer composition applied on the outer surface of the metal pipe prior to storage of the metal pipe, and a subsequent layer of the primer composition applied over the initial layer after storage of the metal pipe.
19. A method of protecting a metal pipe from corrosion, comprising coating an outside surface of the metal pipe with the primer composition claimed in claim 1.
20. A method of protecting a metal pipe from corrosion, comprising coating an outside surface of the metal pipe with the primer composition claimed in claim 3.
21. A method of protecting a metal pipe from corrosion, comprising coating an outside surface of the metal pipe with the primer composition claimed in claim 5, or claim 6 or claim 10.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US14325893A | 1993-10-29 | 1993-10-29 | |
| US08/143,258 | 1993-10-29 | ||
| US22571194A | 1994-04-11 | 1994-04-11 | |
| US08/225,711 | 1994-04-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2118445A1 true CA2118445A1 (en) | 1995-04-30 |
Family
ID=26840847
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2118445 Abandoned CA2118445A1 (en) | 1993-10-29 | 1994-10-19 | Primer composition for metal pipes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2118445A1 (en) |
-
1994
- 1994-10-19 CA CA 2118445 patent/CA2118445A1/en not_active Abandoned
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