AN IMPROVED CORROSION RESISTANT BURIED DUCTILE CAST IRON
PIPING MEMBERS, METHOD FOR APPLYING ZINC-ALUMINIUM
PSEUDO ALLOY FOR THE OUTSIDE OF DUCTILE CAST IRON PIPING
MEMBERS AND THE ARRANGEMENT THEREOF
FIELD OF THE INVENTION
[0001] This invention relates to improvement of the outside anticorrosive
treatment of ductile cast iron piping members, through the development of a
Pseudo Alloy metallic film on the external surface. More particularly the
present disclosure relates to the improved corrosion resistant to ductile cast
iron piping members, specially when used in buried condition, the coating
method that can form an anticorrosion pseudo metal alloy layer in the
peripheral surface and also to an arrangement to obtain uniform deposition of
the pseudo alloy over the external surface of the piping member and the
piping member produced by the disclosed method
DESCRIPTION OF THE PRIOR ART
[0002] The corrosivity of iron in soil environment is a special phenomenon,
which differs in nature from the corrosive behavior of iron exposed to open
atmosphere. The corrosivity of soil varies depending upon the state of the
formation of soil. The resistivity, salinity, microbial content in the soil imparts
variable corrosion potential. The soils are categorized as non-corrosive, mildly
corrosive, corrosive, aggressive soil. The iron materials buried in the soil is
continuously under corrosion attack resulting in the formation of pittings on
the pipe metal wall with gradual loss and disintegration of iron materials as
iron oxide, Iron hydroxide, Iron sulphide etc. The corrosion mechanism is
further complicated by the fact that the soils are heterogeneous and very
diverse in nature. Therefore, there is a need for the protection of buried iron

pipes and this need is satisfactorily fulfilled by the Pseudo Alloy metallic film
coating on the exterior of the piping members.
[0003] The development of special sacrificial anodic coating to protect the
substrate from corrosion is possible. A coating with an alloy of metallic Zinc
and Aluminium performs excellently for corrosion resistance. Further, ease in
procurement of materials, and the ease of spraying through proper facility
makes the coating operation furthermore suitable for mass production.
[0004] Individually, both Zinc and Aluminium coatings have its own
advantages and limitations for effective corrosion protection to the iron
substrate. Comparative cost, ease in application coupled with optimum
corrosion protection ability are the factors that restrict the use of Zinc or
Aluminium individually. Although, Zinc is used individually for general
corrosion protection, Aluminium is not used individually. The coating with an
alloy of Zinc and Aluminium overcomes the above limitation and the corrosion
resistance is far more effective.
[0005] Several forms of Zinc-Aluminium thermal spray coatings have been
developed. Controversy exists concerning the merits of the various Zinc
Aluminium coatings combinations. Controversy also exists concerning the
most favourable Zinc-aluminum coatings compositions. Presently most
research in the area of thermally sprayed Zinc-aluminum coatings has been
centered around an optimum wt% of zinc and Aluminum composition catering
to the various types of aggressive soils in contact with iron pipes.
[0006] In a disclosure by Dainippon Toryo & Kurimoto Ltd, in a Japanese
application JP2005342717, there is disclosed a method for preventing
corrosion of a cast iron pipe by using a coating material, which can be coated
on the surface of white rust produced in outdoor temporary placing and on
white rust produced in steam curing. The disclosed method comprise the
steps of thermally spraying Zinc, Zinc-aluminum alloy to form a thermal spray

coating layer onto the outer surface of a cast iron pipe, coating an aqueous
two-component epoxy emulsion coating material having a solid content of not
less than 5% by weight and comprising a first component of an epoxy resin
having an epoxy equivalent of 475 to 1,800 and a second component of an
amine curing agent having an active hydrogen equivalent (on a solid basis) of
160 to 600 onto the outer surface of the cast iron pipe to form an epoxy resin
film, and coating an acrylic emulsion coating material having a solid content of
not less than 15% by weight on the epoxy resin film to form an acrylic resin
film.
[0007] In another disclosure by Pedeutour et al in an US specification
US5706866 discloses a cast iron piping system element has an outer coating
comprising a first, inner porous layer consisting of Zinc/Aluminium alloy
containing from 5 to 60% of Aluminium, and a second outer pore occluding
layer of an organic or mineral binder in an aqueous, solvent or powder phase
with a coating thickness of 100-140 micron . The alloy layer is meant to be of
a quantity of at least 200 gms/m2
[0008] External coating of Dl Piping member, with alloy of Zn and Alluminium
as a first layer followed by a second layer of paint as barrier coating, serves
satisfactorily as cathodic protection to the piping member, even when laid
underground in an aggressive soil. However, the Zn-AI coating quantity (in
gms/m2) and the ratio of Zn/AI may have to be optimized depending on the
soil condition in which the Dl Piping member is laid.
[0009] In practical applications it is mostly felt that the due to the different
conditions / nature of the soil at different places the coating standards/ratios
are to be maintained and changed with great care by producing ductile iron
pipes best suited for the particular soil characteristic of the place and
moreover for an economical cost of the ductile iron pipe. The use of the
pseudo alloys provides a solution best suited for the aforesaid problems.

SUMMARY OF INVENTION
[0010] According to a first aspect of the present invention there is provided
ductile iron pipe member for buried piping having an external coating provided
thereon comprising a first layer formed of a pseudo metal alloy and applied
over the said first layer a second layer based on organic or inorganic binder in
aqueous, solvent or powder phase, wherein said first layer is formed of a
pseudo alloy of Zinc and Aluminium. The formation of the metal film is done
by simultaneously applying Zinc, Aluminium from separate sources such as
separate electro-spraying guns having different feed speeds to ensure that
the required proportions are achieved.
[0011] An exemplary object of the present invention is to provide a pseudo
alloy coating with any ratio of the alloying members which, gives amazing
effects to the piping member when coated upon and the test results are
comparable with those of cast iron pipes coated with prealloyed Zn-AI.
[0012] Another exemplary object of the present invention is to provide a
corrosive resistant piping member which has similar corrosion resistant
property as discussed in the prior patents but yet is economical, inexpensive,
convenient, safe, and which is competitive.
[0013] Yet another exemplary object of the present invention is to provide A
method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members comprising the steps of:
providing an uniform coating of a pseudo alloy of Zinc-Aluminium as first
layer; providing an uniform coating of epoxy or polyurethane paint as second
layer; wherein the quantity of the pseudo-alloy deposited over the said pipes
is at least 130 gm/m2 (min) over the full external surface.
[0014] As per another aspect of the present invention there is provided a
method and arrangement for the deposition of the pseudo alloy over the said

piping member in order to have a uniform deposition of the pseudo Zn-AI
alloy.
[0015] As per yet another aspect of the present invention there is provided a
method and arrangement for the smooth deposition of different protective
coatings (second layer) over the piping member.
[0016] As per a preferred embodiment of the present invention the said
method and arrangement provides an uniform coating of Al (6-25%) and Zn
(balance) as first layer.
[0017] As per another exemplary embodiment of the present invention there
is provided a method for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members comprising the steps
of: providing an uniform coating of a pseudo alloy of Zinc-Aluminium as first
layer; providing an uniform coating of epoxy or polyurethane paint as
second layer; wherein the quantity of the pseudo-alloy deposited over
the said pipes is at least 130 gm/m2 (min) over the full external surface.
[0018] As per another embodiment of the present invention the coated ductile
cast iron pipes are subjected to second layer of epoxy or polyurethane paint
as a secondary protection to the piping member for long life.
[0019] As per another aspect of the present invention the said method
provides a cost effective and efficient solution with respect to the known
methods of coating of ductile iron pipes and fittings.
[0020] As per another exemplary embodiment of the present invention there
is provided an arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members comprising of:- a
holder for holding the piping member and rotating it with respect to a central
axis with uniform speed; a Zinc spray gun with Zinc wire of suitable diameter;

an Aluminium spray gun with Aluminium wire of suitable diameter; an
arrangement for carrying the Zinc and Aluminum spray guns configured to
move in a horizontal direction with uniform speed; a processor / controller
configured for automatically controlling the rotation of the piping member and
the movement of the gun carriage and a regulator configured for regulating
the feed speed of the wire to the spray guns with respect to the coating
thickness and pseudo alloy composition .
[0021] As per another exemplary embodiment of the present invention the
method and the arrangement as disclosed provides a versatility among the
pseudo alloying percentage and the coating thickness with a simple change in
various operating parameters in the arrangement.
[0022] These together with other objects of the invention, along with the
various features of novelty, which characterize the invention, are pointed out
with particularity in the claims annexed to and forming a part of this
disclosure. For a better understanding of the invention, its operating
advantages and the specific objects attained by its uses, reference should be
had to the accompanying drawings and descriptive matter in which there are
illustrated preferred embodiments of the invention.
BRIEF SUMMARY OF THE ACCOMPANYING ANNEXURES AND
FIGURES
[0023] To enable the invention to be fully understood, preferred embodiments
will now be described with reference to the accompanying annexure / figures,
in which:
[0024] Fig 1 shows the Corrosion data obtained by salt spray tests according
to the present invention;
[0025] Fig 2 shows the Potential Vs Pol. Plot for Al-coat on Ductile Iron pipes
in NACE environment according to the present invention;

[0026] Fig 3 shows the Potential Vs Pol, Plot for Zn-coat on Ductile Iron pipes
in NACE environment according to the present invention;
[0027] Fig 4 shows the Potential Vs Pol. Plot for Zn-AI (pseudo) on Ductile
Iron pipes in Nace environment according to the present invention;
[0028] Fig 5 shows the Potential Vs Pol. Plot for 2!n-AI (pre alloy) on Ductile
Iron pipes in Nace environment according to the present invention;
[0029] Fig 6 shows the Linear Pol Map for Zn-AI (Pseudo) on Ductile Iron
pipes in NACE environment according to the present invention;
[0030] Fig 7 shows the OCP-Exposure time graph for Zn-130, Zn-AI (Pseudo)
and Zn-AI
(Alloy) Coatings on Ductile iron pipes in NACE Environment according to the
present invention;
[0031] Fig 8 shows the EDAX:Spectrum analysis "Al" (85%) rich spot
according to the present invention;
[0032] Fig 9 shows the EDAX:Spectrum analysis "Zn(85%)-AI" (15%) rich
spot according to the present invention;
[0033] Fig 10 shows the SEM: The substrate revealed ferrite matrix with
nodules of graphites according to the present invention;
[0034] Fig 11 shows the SEM: General view of the Continuous interfaces:
coating and the substrate according to the present invention;
[0035] Fig 12 shows the Scanning Electron micrograph General view: Coating
-according to the present invention;
[0036] Fig 13 shows the SEM: Typical Coating Zone on Ductile iron pipes
(spots analysed indicated spots of Zn & Al rich areas and Zn-AI (85-15)
pseudo alloy rich areas in a Continuum way according to the present
invention;
DETAILED DESCRIPTION
[0037] The coatings of Zinc and Aluminium are used for corrosion protection
in a big way. Thermally sprayed Zinc and Aluminium coating have been used
in the past to offer corrosion protection to steel structures and more preferably

to the Ductile iron pipes for many years now. There are instances for use of
Zn-AI coating with prealloyed wire.
[0038] The present invention discloses a process and arrangement for
coating of ductile iron pipes with Zn-AI (Pseudo Alloy), wherein the disclosure
demonstrates very tough corrosion resistance in Nace environment and Salt
Spray environment containing chlorine, such as salt water.
Zinc
[0039] The use of Zinc for cathodic protection of steel has become
increasingly popular, because of its galvanic power. It can protect steel from
corrosion even in unprotected adjacent areas. Zinc allows for easier spraying
and has better adherence to the steel substrate.
[0040] The disadvantages of Zinc include its heavy weight and the mild
toxicity of its fumes, which produce what is commonly known as Zinc fever or
Zinc chills. As a general rule, Zinc performs better in alkaline environments.
But in certain environments, like salt water or chemical atmospheres, it is
consumed rapidly as it cathodically protects metal on which it is applied,
thereby reducing the life expectancy of Zinc. Also, Zinc cannot be applied to
surfaces that exceed a working temperature of 140 ° F.
Aluminium
[0041] Aluminium has an advantage of being a lightweight metal, though it
costs more than Zinc. Aluminium coatings function best where Zinc may
rapidly fail, such as in salt water and chemical atmospheres. It also protects
steel in temperatures exceeding 1000 ° F. The coating of Aluminium has good
mechanical properties and good abrasion resistance under corrosive
conditions. It can usually provide longer protection with its thickness equal to
that of Zinc. Moreover, the material consumption of Aluminium is twice less
than that of Zinc to obtain the coating in the same thickness.

[0042] However, there are certain disadvantages associated with Aluminium,
There is more porosity and oxide in the coating. If it is not thick enough and a
suitable sealing step is not included, rust spots appear on the coating which
gives the coating surface an unattractive red spotty appearance.
Combination of Zinc and Aluminium
[0043] In view of above as described in texts with captions Zinc and
Aluminium, coating with a combination of Zinc and Aluminium performs better
in corrosion protection rather than that with Zinc or Aluminium individually.
[0044] An experimental study of electric arc spraying of Zinc/Aluminum alloy
coatings demonstrates the suitability of the systems for anticorrosion
applications. Experiments were conducted using Boxtype, fractional-factorial
designs. The process parameters that were varied include nozzle diameter,
current, spray distance, and system pressure. The experiments were
designed to display the range of processing conditions and their effect on the
coating. The coatings were characterized with bond strength and deposition
efficiency tests and optical metallography. Coating characteristics were
quantified with respect to roughness, porosity, thickness, bond strength, and
microstructure. Performance evaluation of the coatings was quantified with
accelerated corrosion testing. A parameter-property-performance relationship
has been developed for each material system.
[0045] Thermally sprayed Zinc and Aluminium coatings have been used as
sacrificial anodic coatings since many years to provide protection to steel
structures. Coatings of Zinc and Aluminium are used extensively through two
methods, namely, the twin wire arc spray system and the wire flame spray
system. When two dissimilar wires are sprayed simultaneously in a twin wire
arc spray system, a pseudo alloy structure is formed in the coating. Similarly,
Aluminium and Zinc wires can be flame sprayed to form Zinc-Aluminium
pseudo alloy coatings. There are also instances where wires, prealloyed with
Zinc and Aluminium, are arc sprayed to get alloy coating.

[0046] In the presently disclosed arrangement with two different arc spray
guns, one for spraying metallic Zinc and the other for spraying metallic
Aluminium by feeding respective wires through the guns with different speed
to the respective spray guns such that the Aluminium and the Zinc
depositions are controlled over a point and an uniform desirous thickness of
the deposition is maintained over the whole piping member. The same results
can be achieved by the use of the metal wires with different gauge fed with
same speed simultaneously.
[0047] The Zinc-AI coatings formed as a pseudo alloy of Zinc and Aluminium
coating by the arc spray process provide enhanced corrosion protection of
Ductile Iron piping member. Moreover, Zinc-AI coatings offer a clean and
economical way of protecting Ductile Iron piping member from corrosion. Arc
spraying used, as part of the process does not cause any distortion of the
substrate. Moreover, the Pseudo Zinc-AI process does not use the costly
alloy wire of Zinc Aluminium. Instead pure Zinc and Aluminium wires can be
utilized separately which costs less and provide versatility of the alloy
composition. This is quite advantageous as the earlier mentioned Zinc-
Aluminium alloy wire coating has certain limitations in comparison to Pseudo
Zinc-AI coatings. For instance, the alloy wire has to be manufactured with a
fixed ratio and separate premanufactured wires are to be made available for
separate ratios, as and when required. Moreover , when Aluminium content in
the prealloyed wire is more than 15 % , there is a tendency of developing
brittleness in the alloyed wire making it all the more difficult in wire drawing
during arc spraying . In contrast, the disclosed coatings can be prepared with
much desirous and regulated content of Aluminium depending upon the
nature of the end use. As a result desired and effective corrosion resistance
can be achieved with preset Zn/AI ratio in the disclosed coating process,
using only a single type of Zinc and Aluminium wire.

[0048] After the application of the pseudo alloy layer the piping members
are coated with epoxy resin or polyurethane paint with a state-of- art
technology. The paint coating not only seals the pores [leak] of the first layer
of the metallic pseudo alloy coating but also creates a barrier coating over
the first layer- The application process of the second layer of paint coating
ensures formation of limited pores on the coating to restrict its disbonding
from the substrate. Paint coatings are characterized by their durability,
strength, adhesion and chemical resistance, making them an ideal product
for their application as a barrier coating and leak sealant.
[0049] Therefore the present disclosure also provide a method for applying
Zinc-Aluminium pseudo alloy for the outside of underground ductile cast iron
piping members comprising the steps of: providing an uniform coating of a
pseudo alloy of Zinc-Aluminium as first layer; and thereafter providing an
uniform coating of epoxy or polyurethane paint as second layer; wherein the
quantity of the pseudo-alloy deposited over the said pipes is at least 130
gm/m2 (min) over the full external surface.
[0050] The steps of operations, in a sequence, that are performed for
applying Zinc-Aluminium pseudo alloy for the outside of underground ductile
cast iron piping members in the workstation is herein described. It generally
comprise the steps like placing of ductile iron pipes at coating station; setting
of individual guns (Zn and Al); activation of guns through individual power
packs; checking of Zn-AI deposit band on pipes through setting of Zn gun & Al
gun; setting of parameters on pipe rotation, speed of gun carriage, movement
w.r.t. individual ratio of Zn & Al and total deposit of Zn-AI (pseudo alloy)
coating; checking of sample deposit w.r.t. visual, individual ratio and total
deposit. Further adjustment, if needed, is done before the mass production.
[0051] After providing an uniform coating of a pseudo alloy of Zinc-Aluminium
as first layer, another set of operations are conducted at paint coating station

for providing an uniform coating of epoxy or polyurethane paint as second
layer using compressed air or air free sprayers.
[0052] Since the process of coating is not isolated to a single piping member
in an industry and a mass production is needed, therefore the steps of
checking of pseudo Zn-AI deposit band on pipe members through settings of
Zn gun & Al gun for Al (6-25%) and Zn (balance) and thereafter setting of
parameters on Pipe rotation, speed of gun carriage movement with respect to
individual ratio of Zn & Al and total deposit of Zn-AI (pseudo alloy) is required.
[0053] Furthermore, the arrangement for the coating of ductile iron pipes with
Zn-AI (Pseudo Alloy) and subsequently in paint coating station the
arrangement for epoxy/polyurethane coating as second layer is disclosed.
The arrangement comprises essentially of a Dl Piping member, Zn Spray Gun
, Al Spray Gun, Gun Carriage, Zn Wire, Al Wire. The arrangement also
comprises of a holder for holding the piping member and rotating it with
respect to a central axis with uniform speed. The Zinc spray gun is connected
with Zinc wire of suitable diameter and similarly the Aluminium spray gun with
Aluminium wire of suitable diameter which is selected as per the required
pseudo alloy composition. The gun carriage is a twin gun carriage for carrying
the Zinc and Aluminum spray guns configured to move in a horizontal
direction with uniform speed. The arrangement further comprises of a
processor / controller configured for automatically controlling the rotation of
the piping member and the movement of the gun carriage and a regulator
configured for regulating the feed speed of the wire to the spray guns with
respect to the coating thickness and pseudo alloy composition.
[0054] The arrangement is configured for uniform coating of a pseudo alloy of
Zinc-Aluminium as first layer, thereafter an uniform coating of epoxy or
polyurethane paint is applied as second layer for the said piping member
wherein the density of the pseudo-alloy deposited over the said pipes is at
least 130 gm/m2 (min) and upto 400 gm/m2 over the full external surface.

Further the settings for the parameters on Pipe rotation speed of gun carriage
movement with respect to individual ratio of Zn & Al and total deposit of Zn-AI
(pseudo alloy) is carried out automatically using a software.
[0055] These coatings are capable of providing effective long-term corrosion
protection to the ductile cast iron structures of any size in a wide range of land
and marine environments. Such coatings, when properly sealed or painted,
have the potential to significantly reduce the maintenance requirements for a
wide range of applications. Further, all arrangements are installed on line
such that quality and productivity is ensured during production.
[0056] Fig 1 shows data on Corrosion Rate on coating with Zinc, Zn-AI
(Pseudo) and Zn-AI (Alloy), this data is derived from salt spray analysis. In the
test piece all sides of the specimens (25mm x 25mm x 1mm thick), were
coated with non-conducting lacquer. These specimens were weighed and
subjected to salt spray mist formation inside a designed spray cabinet.
Volume of liquid of 5% NaCI inside the cabinet was maintained at 50 litres.
The liquid flow rate to mist formation and temperature (23°C) close to rest
specimens were maintained. The specimens were withdrawn every 100 hrs,
washed clean, dried and weighed (mgs). The lacquered surfaces are re-
lacquered, then weighed and salt spray test continued. Typical potentio
dynamic polarization mappings generated are shown in figures 2, 3, 4, 5, & 6
respectively.
[0057] In the assessment of the corrosion characteristics, using potentio
dynamic polarization technique, corrosion potentials are denoted by Open
Circuit Potential (OCP), corrosion potential (Ecorr), Corrosion current (Icorr),
Corrosion Rate (CR), active passive enclaves, weight loss in general, Visual
observations of corrosion reaction at different potentials, a qualitative
assessment technique. Higher the OCP lower is the corrosion rate for the
metal / alloy underscoring its position in the galvanic series. Therefore as per
the data generated and as shown in Fig 7, for Zn-AI pseudo alloy ( Series 1 )

and the pre alloy ( Series 2 ) coating rates for changes in OCP were slower
than for Zn-130 ( Series 3 ) coating and indicate greater corrosion resistance.
After 1200 hrs of exposure graphically convergent characteristics of three
curves also highlights relative life expectancies of the three different coating
materials. For the pseudo and the pre alloy coatings, it appears that these two
coatings would be corroded out highlighting similar life performance. Average
CR's for Zn-AI pseudo alloy, in the two SR's and test environment used, are
comparable to the CR's of the Zn-AI pre alloy coating, in the ratio 9:8 (in
NACE environments).
[0058] Fig.8 and Fig. 9 shows the EDAX Spectrum analysis, of "AC (85%) in
Fig.8 and Zn (85%) - Al (15%) in Fig.9. EDAX analysis data indicates spatial
distribution of (i) Al rich phase (ref Fig 8) (ii) Zn-AI pseudo alloy phase in the
coated zone (ref Fig 9).
[0059] A conclusive study was made wherein the specimens are prepared for
optical microscopic examination in the SEM with EDAX attachment. The
examinations were carried out on the cross-section of the specimen, across
the coated surface into the substrates. Electron micrograph shown in Fig
10depicts general Dl structure consisting of graphite in ferrite matrix.
[0060] Consistent with Zn-AI pseudo alloy composition, the constituents in the
phases are identified by X-ray spectral analysis and quantified by total area
integration technique (software). Electron micrograph revealed continuous
nature of deposition (Fig 11, 12 & 13). The spectral analysis highlights a
favourable Zn-AI pseudo alloy coating process on Dl piping members.
RESULTS
[0061] Potentiodynamic polarization technique quantified the corrosion rates
(CRs) of Zn-AI pseudo and the conventional alloy coatings on Dl in that,
calculated corrosion rates appeared similar for both the coatings in the test
environment (Nace) used.

[0062] OCP and salt spray testing techniques are important long term testing
methods. Analytical work using three tests, particularly OCP Vs exposure
time test, provided meaningful data on life performance in specific corrosive
environments. The test also concludes that the corrosion rates are almost
similar. The rate of loss of Zn coating was nearly complete in 400hrs of
exposure while the Zn-AI pseudo alloy and the conventional Zn-AI alloy
coating continued to corrode beyond 800 hrs.
[0063] SEM-EDAX analysis of the pseudo alloy coating on Dl substrate
provided meaningful data on chemical composition and micro structural
details (SEM) of the alloy concerned as are reported elsewhere. The Electron
micrographs reveal continuous rate of deposition at the desired ratio of Zn-AI.
[0064] Although the foregoing description of the present invention has been
shown and described with reference to particular embodiments and
applications thereof, it has been presented for purposes of illustration and
description and is not intended to be exhaustive or to limit the invention to
the particular embodiments and applications disclosed. It will be apparent to
those having ordinary skill in the art that a number of changes,
modifications, variations, or alterations to the invention as described herein
may be made, none of which depart from the spirit or scope of the present
invention. The particular embodiments and applications were chosen and
described to provide the best illustration of the principles of the invention
and its practical application to thereby enable one of ordinary skill in the art
to utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All such
changes, modifications, variations, and alterations should therefore be seen
as being within the scope of the present invention as determined by the
appended claims when interpreted in accordance with the breadth to which
they are fairly, legally, and equitably entitled.

We Claim:-
1. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating, said coating comprising of :-
an uniform coating of a pseudo alloy of Zinc-Aluminium as first layer;
an uniform coating of epoxy or polyurethane paint as second layer;
wherein the quantity of the pseudo-alloy deposited over the said pipes
is at least 130 gm/m2 (min) over the full external surface.
2. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating as claimed in claim 1, wherein the
said pseudo alloy comprises of Al (6-25 %) and Zn (balance).
3. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating as claimed in claim 1, wherein the
said pseudo alloy coating is carried out by electric arc spraying.
4. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating as claimed in claim 1, wherein the
second layer coating is carried out by spraying.
5. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating as claimed in claim 1, wherein the
quantity of the pseudo-alloy deposited over the said pipes is upto 400 gm/m2
and above over the full external surface
6. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members comprising the steps of:
providing an uniform coating of a pseudo alloy of Zinc-Aluminium as
first layer;
providing an uniform coating of epoxy or polyurethane paint as second
layer;

wherein the quantity of the pseudo-alloy deposited over the said pipes
is at least 130 gm/m2 (min) over the full external surface.
7. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6, wherein
the said pseudo alloy comprises of Al (6-25 %) and Zn(balance).
8 A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6, wherein
the step of providing an uniform coating of pseudo alloy over the piping
member further comprises the substeps of:
placing of ductile iron pipes at coating station ;
setting of individual zinc and aluminium spray guns;
activation of guns through individual power packs ;
9. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6 further
comprising the steps of:-
checking of pseudo Zn-AI deposit band on pipe members through
settings of Zn gun & Al gun,
setting of parameters on Pipe rotation, speed of gun movement with
respect to individual ratio of Zn & Al and total deposit of Zn-AI (pseudo alloy).
10. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6, wherein
the said pseudo alloy coating is carried out by electric arc spraying.
11. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6, wherein
the second layer coating is carried out by spraying.

12. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 10, wherein
the spraying is done using compressed air or air free.
13. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members as claimed in claim 6, wherein
the quantity of the pseudo-alloy deposited over the said pipes is as high as
400 gm/m2 and above over the full external surface.
14. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members comprising of-
a holder for holding the piping member and rotating it with respect to a
central axis with uniform speed;
a Zinc spray gun with Zinc wire of suitable diameter;
an Aluminium spray gun with Aluminium wire of suitable diameter;
an arrangement for carrying the Zinc and Aluminum spray guns
configured to move in a horizontal direction with uniform speed;
a processor / controller configured for automatically controlling the
rotation of the piping member and the movement of the gun carriage;
a regulator configured for regulating the feed speed of the wire to the
spray guns with respect to the coating thickness and pseudo alloy
composition.
15. An arrangement for applying Zinc-Aluminium pseudo alloy for the outside
of underground ductile cast iron piping members as claimed in claim 14,
further comprising of a sprayer for spraying epoxy or polyurethane paint over
the metallic film of Zn-AI pseudo alloy coating
16. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members as claimed in claim
14, wherein the piping member is subjected to uniform coating of a pseudo

alloy of Zinc-Aluminium as first layer, thereafter an uniform coating of epoxy
or polyurethane paint is applied as second layer;
wherein the quantity of the pseudo-alloy deposited over the said pipes
is at least 130 gm/m2 (min) over the full external surface.
17. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members as claimed in claim
14, wherein the setting of parameters on Pipe rotation, speed of gun carriage
movement with respect to individual ratio of Zn & Al and total deposit of Zn-AI
(pseudo alloy) is carried out automatically.
18. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members as claimed in claim
14, wherein the said pseudo alloy coating is carried out by electric arc
spraying .
19. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members as claimed in claim
14, wherein the second layer coating is carried out by spraying.
20. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members as claimed in claim
14, wherein the density of the pseudo-alloy deposited over the said pipes is
upto 400 gm/m2 and above over the full external surface
21. An improved corrosion resistant buried underground ductile cast iron
piping members with an external coating, substantially as herein described
with particular reference to accompanying drawings.

22. A method for applying Zinc-Aluminium pseudo alloy for the outside of
underground ductile cast iron piping members, substantially as herein
described with particular reference to accompanying drawings.
23. An arrangement for applying Zinc-Aluminium pseudo alloy for the
outside of underground ductile cast iron piping members, substantially as
herein described with particular reference to accompanying drawings.

The present invention relates to improvement of the outside anticorrosive
treatment of ductile cast iron piping members, through the development of a
Pseudo Alloy metallic film on the external surface, more particularly the
present disclosure relates to the improved corrosion resistant to ductile cast
iron piping members, specially when used in buried condition, the coating
method that can form an anticorrosion pseudo metal alloy layer in the
peripheral surface and also to an arrangement to obtain uniform deposition of
the pseudo alloy over the external surface of the piping member and the
piping member produced by the disclosed method.