FORM 2
THE PATENTS ACT, 1970
AND
THE PATENT RULES,2003
COMPLETE SPECIFICATION [SEE SECTION 10]
“GALVANIZED IRON POLYETHYLENE COATED PIPE AND PROCESS
THEREOF”
Maharashtra Seamless Ltd, a company organized and existing under the laws of India, of Pipe Nagar, Village: Sukeli, N.H. 17, Taluka: Roha, Dist: Raigad,
Maharashtra - 402126, INDIA
The following specification particularly describes the invention and the manner in which it is
to be performed:

The present invention relates generally to the field of pipes, and more specifically, to galvanized iron pipes and their coating with polyethylene thereon.
BACKGROUND OF THE INVENTION
Pipelines in the oil, gas and water transportation industries worldwide are usually protected by external coatings.
Galvanized Iron Pipes (GI) are those pipes that have been covered with a layer of zinc metal. During the galvanizing process, pipe is immersed in a molten zinc bath, ensuring a tough, uniform barrier coating. However, galvanizing process, though providing a barrier against corrosion, has limited utility since zinc is also prone to corrosion due to air, water and corrosive elements in soil and cement/ mortar.
Galvanised Iron Pipes are manufactured using mild steel strips of low carbon hot rolled steel Coils. The strips are passed through a series of fin rolls to give them a circular shape. The slit ends of the strips are then welded together by continuously passing high frequency electric current across the edges. The welded steel pipes are then passed through sizing sections where any dimensional deviations are corrected. The pipes are then cut into desired lengths by automatic cutting machines. The tubes are then pressure tested for any leaks randomly. The galvanization and varnishing of pipes are done as per specific requirements.
The GI Pipes are generally used for distribution of treated or raw water in rural or urban areas. These pipes are cheaper, light weight and easy to handle. GI pipes are used as water and sewage pipes, electric poles, structural purposes, engineering purposes, automotive purposes, oil and gas transmissions.
Pipe Coatings are used to increase the life of pipelines. The solution providers are offering various types of products tailored to the needs of their clients. Some of these common pipeline coating products include two-layer and three-layer coating systems that provide excellent anti-corrosion protection to pipes.
Two-layer systems refer to coatings that contain one layer of adhesive and another of polyethylene.
Three-layer system generally consists of an epoxy layer, a copolymer adhesive layer and a layer of polyethylene. This system can be operated at higher temperatures, however, due to the fact that an epoxy layer is required, it is more expensive with a more complex and critical application process. There is therefore a need to have improvements over the existing coated pipes.
Accordingly, it is the objective of the present invention to provide a Galvanised Iron Polyethylene coated (hereinafter also referred to as GIP) pipe which can: Withstand Elevated operating temperatures. The GIP pipe can withstand -40 and + 85 degree Celsius; has better resistance to compression. GIP pipe has a better impact resistant, is safe to transport and store; GIP is pinhole resistant; Possesses Increased life span - Expected life of 50-60 years; and has good aesthetic looks as GIP pipes provides excellent surface finish.

BRIEF DESCRIPTION OF DRAWINGS
These and other features and advantages of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings:
Figure 1- Construction of coating on the GIP pipe
Figure 2 - Chromate application by flooding method
Figure 3 - Flow Diagram of coating on Galvanized Iron pipes
DESCRIPTION OF THE INVENTION
The present invention envisages a unique coating process on galvanized iron pipes in the following layers (see Figure 1):
1. Chromate Coating on the galvanized (zinc coated) surface.
2. Adhesive Layer
3. Polyethylene Layer
Chromate Coating is a type of conversion coating used to passivate zinc on outside surface of the pipe. The process is named after the chromate found in chromic acid. Chromating is used to reduce the reactivity and to improve durability and surface finish of metals.
The Chromating is important because:
. The layer acts as a cost-effective corrosion inhibitor, protecting vital components
from material degradation. . It acts as a primer. . It improves electrical conductivity.
Chromating usually works like a coat of paint on zinc, protecting the zinc surface from white corrosion, and improving durability of zinc components several times over, depending on thickness of the coat. Darker coatings of chromate provide higher corrosion resistance, thus enhancing the lifespan. Curing is required, which can be accelerated by providing heat less than 70°C, as higher temperatures can slowly damage the coating.
Adhesive Layer is either mastic-based or copolymers of polyethylene. Mastic-based adhesives, although being relatively inexpensive and providing good cathodic disbondment (CD.) resistance, have low shear and peel strength values and are restricted to low temperature applications. Copolymers have very good adhesion and shear resistance but generally poor cathodic disbondment resistance.
Black Polyethylene Layer has excellent resistance against sunlight which is evident in many applications like overhead water tank, overhead cable sheathing etc. polyethylene can withstand continuous outdoor exposure at least for 60 years. Polythene coating on GI pipes

will also provide excellent protection from corrosion due to air water and corrosive elements in cement/ mortar. Hence polyethylene coating will increase service life for GI pipes.
Advantages of GIP Pipe: It is an object of the present invention to provide a GIP pipe which can:
• Withstand Elevated operating temperatures - Galvanized Iron Polyethylene (GIP) pipe can withstand -40 and + 85 degree Celsius;
• Better resistance to compression - GIP is a better impact resistant. The primary function of polyethylene (Top Coat) is mechanical protection.
• Gouge resistance is also another useful parameter. Also it provides better indentation, this property is important during handling and construction.
• Safe to transport and store.
• GIP is pinhole resistant;
• Also it provides UV protection as the polyethylene layer is UV stabilized by using 2-2.5 % carbon black content.
• Aesthetic Looks - GIP Pipe provides excellent surface finish.
• High Density Polyethylene can be used up to 85°C service temperature of the pipeline when combined with the grafted adhesives.
• After the successfully coating on GI pipes life will be radically increased to 50 - 70 years.
• Shipping and Storage: Pipe coated with Multilayer (Chromate + Adhesive + High
Density Polyethylene) Coatings can be stored for one year or more under most
climatic Conditions without deterioration of the coating. The coating does not soften
or flow even at high storage or operating temperatures. Coated pipe can be shipped
throughout the world with minimal coating damage using all common modes of
Transportation. Thus, quality plant-applied coating is available even at remote,
inhospitable construction sites.
• These pipes are natural corrosion resistant and hold functional durability, even in outdoor environments. Apart from preventing water corrosion, it is equally effective in dry, indoor environments.
• It can also be used for all piping inside a building; for handrails or for replacement of existing pipe.
Applications: GIP pipes of the invention has manifold applications, including, but not limited to:
* Raw water supply
* Fire fighting purpose
* GAS steam and air lines
* General engineering purpose
* Irrigation purpose *Boilers and Heat Exchangers *Conduits

The present invention is directed to coated GIP pipe wherein the coating consists of Chromating, an Adhesive layer (or the tie layer) and Polyethylene which is the top Coat (Figure 1). The invention is for a new process which applies three successive coating layers over the GI Pipes and further utilizes grafted adhesive. The layers are of chromate, adhesive and Polyethylene (LDPE, MDPE and HDPE). Application of Chromate interfacing with properly prepared GI pipe surface, an adhesive tie layer and a polyethylene top coat offers top-notch protection against pinholes, has excellent impact resistance especially at elevated temperatures, aesthetic looks etc.
Construction of coating is illustrated in Figure 1. This system consists of Chromate interfacing with properly prepared GI pipe surface, an adhesive tie layer and a polyethylene top coat.
The Chromating gives the pipe an attractive, corrosion resistant finish. The adhesive layer acts as a bridge between polyethylene and chromate. The adhesive is compatible and fuses with both layers. Finally Polyethylene (Top Coat) provides a high degree of impact resistance, low moisture permeability.
Key application steps to consider when applying Polyethylene & Adhesive are preferred as follows:-Polyethylene and adhesive can be applied either by using flat die or crosshead technique and provides good surface finish over a broad range of conditions.
EXAMPLE 1
The following conditions are one of the preferred embodiments when starting up the extruder.
For Chromate Application
GI Pipe Temperature before Application: ambient to 50 deg C
For Adhesive: -
Melt temperature 210 – 230°C
Max recommended melt temperature <260°C
For Polyethylene:-Melt temperature 220 – 240°C Max recommended melt temperature <260°C
Coating thickness details of individual layer applied on GI pipes:-Chromate applied in the range of 3 - 5 microns.

Adhesive applied in the range of 100 - 200 microns.
Top coat (Polyethylene) applied in the range of 800-1000 microns.
EXAMPLE 2
The process for making the GIP pipe of the invention has been outlines in the flowchart as presented in Figure 2 and the steps as illustrated herein below:
1. Pre-Inspection of GI pipe
Prior to pipe cleaning operations all pipes are inspected, preferably visually, for surface defects. Any oil, grease and other organic contaminants detrimental to the formation of a good coating bond or coating quality can be removed using non-oil solvent cleaning. Gasoline or kerosene is recommended not to be used for this purpose.
2. Pipe Conveyor
After inspection the GI pipes are sent through conveyors towards Chromating and to final station by same method. The preferred embodiment is to have a linear motion in the movement of the pipes.
3. Chromating and Induction heating
The steel pipe is zinc plated (GI) and then chromate coated. This gives the pipe an attractive, corrosion resistant finish. The zinc plating offers sacrificial protection to the steel, but the zinc itself would quickly corrode and become an unsightly mess of white rust, discoloration, and pitting unless it is itself protected. The preferred embodiment for the Chromating working solution concentration is 1 to 2 %, more preferably 2%. For consistency of operation, the surface temperature of the pipe should be kept as constant as possible, in the range ambient to 45°C, to aid even drying of the wet film. It is more preferable that the surface temperature is in the range 35 to 45°C.
After the film has been applied and dried, the surface temperature of the work is raised to above 130°C. An induction heater is used for heating the pipe. The heating system is capable of continuous & uniform and not causing contamination or oxidation (in the form of bluing or other apparent oxide formation) of the cleaned surface. Temperature of the pipe surface is continuously monitored and recorded by using suitable instruments such as infrared sensors, contact thermometers, etc. This assists in correct formation of the Chromating coating.
The process for chromate application by flooding method has been illustrated in Figure 2 and is described herein: The GI pipe as shown in Figure 2 move in axial motion and pass through a ring filled with chromate, through the said ring the chromate is sprayed by pressure on pipe, after that is passed through a wiper which makes a uniform film over GI pipe

4. Application of Adhesive and Polyethylene by Cross Head Extrusion Technique
Extruded adhesive layer is applied before Extruded polyethylene layer within the time limit the extrusion temperatures of the adhesive and polyethylene, preferably the maleic grafted polyethylene adhesive and high density polyethylene are continuously monitored and recorded with calibrated instruments.
In the cross head extrusion process the preheated pipe is axially conveyed through the annulus of a ring die. In general, thicker coatings are applied in fewer steps using cross head processing due to the ability to apply more material per pass through the plant.
Resultant coating has a uniform gloss and appearance and is free from air bubbles, wrinkles, irregularities, discontinuities, separation between layers of polyethylene & adhesive, etc.
5. Quenching by water
Tap water with below 32°C temperature is used for quenching of coated pipes. The coated pipe is subsequently quenched and cooled in water for a period that sufficiently lowers the temperature of pipe coating to allow handling and inspection.
6. Coating thickness and Visual Inspection
The coating thickness is determined by taking at least 10 measurements at locations uniformly distributed over the length and periphery of each pipe.
Each coated pipe is visually checked for imperfections and irregularities of the coating. The resultant coating shall have a uniform appearance with natural colour & gloss and shall be free from air bubbles, blisters, wrinkles, scratches. Coating surface is preferably not physically damaged or contaminated with any foreign material such as dirt, metal particles, coating debris during application, curing and handling process.
7. Holiday / Pin Hole Test (If required)
Randomly (10%) coated pipe length may be checked over 100% of coated surface by means of a “holiday detector” for detecting holidays in the finished coating. The holiday detector is preferably a low pulse D.C. full circle electronic detector with audible alarm and precise voltage control. The coated pipe is inspected with the holiday detector set at minimum 10 kV. Coated pipes with 2 holiday of an area equal or less than 100cm2 may be accepted after repair.

8. Final Marking (Optional)
Marking / Stencilling of all external surfaces of the coated pipes is at a minimum distance of 1000 mm one end with the following information:- Manufacturer Name And Monogram; Pipe Size & Grade; Mm Od X Mm Wt.
The preferred embodiment of the invention to carry out the process as described in Figure 3 utilizes the following plant equipped machinery

SR. NO. NAME OF MACHINE CAPACITY
01. Chromating & Induction Oven 200 litres per hours with 2.5 Kw capacity motor and SS tank.
Induction coil of 400 kw
02. Adhesive Extruder Extruder is provided with 90 mm diameter, and feeding neck & extrusion capacity 150 Kg/Hr. with temperature controller system.
03. PE Extruder Extruder is provided with 130 mm diameter, and feeding neck & extrusion capacity 420 Kg/Hr. with temperature controller system.
04. Quenching Zone 20 Meters Long, Provided with water distribution system, hydraulic power units, & motors Cooling water circulation rate 200m3/hr.
05. Air Compressor 1 Nos. - 472cfm
The product as disclosed in the invention has several advantages over the existing coated GI pipes as illustrated below:
• Higher durability and longevity
• Weld consistency and integrity
• Amenable to rigorous fabrication
• Superior finish and anti - rust coating
• Greater resistance to corrosion
• Strict adherence to quality standards

The higher durability of the GIP pipe of the inventions leads to high product life to the pipes as the inner diameter of the pipe as well as the outer diameter are protected from corrosion.
COMPARISON BETWEEN VARIOUS PROTECTIVE COATINGS ON MILD STEEL PIPES

COMPARISO N GALVANISED 2
LAYER
POLYETHYLEN
E PIPES (GIP
PIPE) GALVANISE
D IRON
PIPES (GI
PIPE) 3 LAYER
POLYETHYLEN
E COATED
PIPES (3LPE) 3 LAYER
POLY
PROPYLEN
E COATED
PIPES
(3LPP) FUSION BONDE
D
EPOXY
PIPES
(FBE)
Surface treatment before
application of coating Not Required Required Required Required Required
Chromate Application Yes No No No No
Approximate Product Life High; since both ID (zinc) and OD are protected from corrosion. Low; since both OD and ID are protected by Zinc which is prone to oxidation and reaction with chemicals in water, soil, cement/ mortar and atmosphere. Medium, since ID is not protected and is prone to oxidation and reaction with chemicals in water. Medium, since ID is not protected and is prone to oxidation and reaction with chemicals in water. Medium, since ID is not protected and is prone to oxidation and
reaction with
chemicals in water.
Moisture barrier on OD Excellent Medium Excellent Excellent Poor
Moisture barrier on ID Medium Medium Poor Poor Poor
Outdoor Weathering Excellent Limited Excellent Moderate Limited
Resistance to Chlorides Excellent Limited Excellent Excellent Poor
Damage in
handling/
transportation Nil Nil Virtually Nil Virtually Nil Moderate
Repair ability Yes No Yes Yes Yes
Protective Coating Cost Very Low Lowest Moderate High Low
The coated GIP pipes of the invention as disclosed clearly has advantages over the existing GI pipes without coating as well as over three layer polyethylene coated pipes (3LPE), three layer poly propylene coated pipes (3LPP), and fusion bonded epoxy pipes (FBE) as seen in the above table.
Several tests were conducted to check the GIP pipes of the invention and some of them are present herewith. For example, tests were conducted on GIP pipes of 60.30 mm OD@

minimum 1.0 mm total coating thickness. The different tests conducted included the Impact Strength Test, the Bond Strength Test (Peel test), the Elongation test, the Indentation test, the Shore D-harness test, the Holiday test, the electrical insulation test and the Chemical resistance test. Results of such tests are tabulated below:
1. The Impact strength test on the GIP pipes provided satisfactory results.
Impact Strength Test on GIP Coated pipes

No of
Sample
pipe
for
Testing No. of Impacts
1 10 Impacts on GIP
Coated pipe along the
length
2 10 Impacts on GIP
Coated pipe along the
length
3 10 Impacts on GIP
Coated pipe along the
length

Referance
Standard /
Specification
DIN 30670 / MSL SPEC.

Acceptance criteria Result Remarks
Total impact energy 5
Joules No break down
over impact area.
Impact Height – 7.0” No holiday found over
impact area when tested at
10 kV. Satisfactory
Total impact energy 5
Joules. No break down
over impact area.
Impact Height – 7.0” No holiday found over
impact area when tested at
10 kV. Satisfactory
Total impact energy 7
Joules. No break down
over impact area.
Impact Height – 10.0” No holiday found over
impact area when tested at
10 kV Satisfactory

Bond Strength Test (Peel Test) on GIP Coated pipes

No of
Samples
for
Testing Test Temperature Referance
Standard /
Specification
1 20 ± 5° C DIN 30670

50 ± 5° C

2 20 ± 5° C

50 ± 5° C

3 20 ± 5° C

50 ± 5° C

Acceptance criteria
Minimum 3.5 N/mm @
20 ± 5° C &
Minimum 2.5 N/mm @
50 ± 5° C

Result Remarks
With chromate treatment Without chromate treatment

8 7 Satisfactory
6 5 Satisfactory
7 5 Satisfactory
5 4 Satisfactory
8 6 Satisfactory
5 4 Satisfactory

4 20 ± 5° C 7 5 Satisfactory

50 ± 5° C

4 3 Satisfactory
3. Elongation Test

Elongation Test at Break on GIP Coated pipes
No of Sample pipe for Testing Acceptance Criteria (%) Referance
Standard /
Specification Average Value of 3
samples achieved
(%) R e m a rk s
1 Minimum 200% DIN 30670 632 Satisfactory
2

620 Satisfactory
3

667 Satisfactory

4. Indentation Test

Indentation Test on GIP Coated pipes
No of
Sample
pipe
for
Testing Test Temperature Referance
Standard /
Specification Acceptance Criteria (mm) Value
achieved
(mm) Remarks
1 23 ± 2°C DIN 30670 Maximum. 0.2 0.08 Satisfactory

70 ± 2°C

Maximum. 0.3 0.19 Satisfactory
2 23 ± 2°C

Maximum. 0.2 0.11 Satisfactory

70 ± 2°C

Maximum. 0.3 0.17 Satisfactory
3 23 ± 2°C

Maximum. 0.2 0.14 Satisfactory

80 ± 2°C

Maximum. 0.3 0.25 Satisfactory

5. Shore D Hardness

Shore D Hardness on GIP Coated pipes
No of
Sample
pipe
for
Testing Location Referance
Standard /
Specification Acceptance Criteria (Shore D) (Shore D) Remarks
1 Head ASTM D2240 50 Shore D 55 Satisfactory

Middle

54 Satisfactory
2 Head

53 Satisfactory

Middle

55 Satisfactory
3 Head

52 Satisfactory

Middle

54 Satisfactory
6. Holiday Test

Holiday Test at 10 kV on GIP Coated pipes
No of
Sample
pipe
for
Testing Test Voltage Referance
Standard /
Specification Acceptance criteria Observations Remarks
1 10 kV/mm DIN 30670 Maximum 2 no's of holiday allowed of area
less than 100 cm2
allowed when tested at
10 kV/mm No Holiday found Satisfactory
2


No Holiday found Satisfactory
3


No Holiday found Satisfactory

7. Electrical insulation test

Electrical Insulation test (Shock Proof coating) on GIP Coated pipes
No of Sample pipe for Testing Test Voltage Referance
Standard /
Specification Acceptance criteria Observations Remarks
1 AC current 230 -240 Volts MSL SPEC. No current passes
through the coating
found when give supply
of AC current 230 -240
Volts No current passes
through the coating
found Satisfactory
2


No current passes
through the coating
found Satisfactory
3


No current passes
through the coating
found Satisfactory

8. Chemical resistance test

Chemical Resistence test on GIP Coated pipes
No of
Sample
pipe
for
Testing Test Temperature Referance
Standard /
Specification Acceptance criteria Value achieved (mm) Remarks
1 +50 °C MSL SPEC. POLYETHYELENE
COATING WILL HELP
TO PROTECT GI
FROM CORROSION 1) WITHOUT
POLYETHYLENE
COATING GOT
HIGHLY
CORRODED.
2) GIP PIPE GOT
ONLY CORRODED
WHERE IT WAS
ARTIFICIALLY
DAMAGED. For reference pics taken
All the above tests indicate that the GIP pipe of the present invention is performing better than the prior inventions and can be used for additional advantages.
Although the preferred embodiments of the present invention have been described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects.

We Claim:
1. A galvanized iron polyethylene coated pipe (GIP pipe) comprising a zinc coated iron pipe further coated with three layers, wherein said first inner layer is Chromate Layer, the said second coating is of an Adhesive Layer and said third outer layer is Polyethylene Layer.
2. The galvanized iron polyethylene coated pipe as claimed in claim 1, wherein the thickness of the said three layers is:
a. Chromate: 3 - 5 microns.
b. Adhesive: 100 - 200 microns.
c. Polyethylene: 800-1000 microns.
3. The galvanized iron polyethylene coated pipe as claimed in claim 1, wherein the said galvanized iron polyethylene coated pipe withstand -40 and + 85 degree Celsius temperature and possesses increased product life.
4. The galvanized iron polyethylene coated pipe as claimed in claim 1, wherein the said Polyethylene layer comprises of LDPE, MDPE and HDPE.
5. A process for preparing galvanized iron polyethylene coated pipe or GIP pipe comprising
a. Coating steel pipe with zinc to obtain Galvanized pipe
b. Chromate coating the Galvanized pipe
c. Applying Adhesive to the Chromate coated pipe
d. Applying Polyethylene coating to the adhesive coated pipe to obtain the GIP
pipe.
6. The process for preparing galvanized iron polyethylene coated pipe or GIP pipe as
claimed in claim 5, wherein the said chromate coating is by using working solution in
the concentration of 1 to 2 % at a surface temperature of the pipe in the range 35 to
45°C, and after the solution applied is dried, the surface temperature is raised above
130°C.
7. The process for preparing galvanized iron polyethylene coated pipe or GIP pipe as
claimed in claim 5, wherein the said chromate coating is by flooding method
8. The process for preparing galvanized iron polyethylene coated pipe or GIP pipe as
claimed in claim 5, wherein the said application of the said Adhesive and Polyethylene
is by Cross Head Extrusion Technique

9. The process for preparing galvanized iron polyethylene coated pipe or GIP pipe as claimed in claim 5, wherein the said step (d) is is followed by quenching by water so as to cool the GIP pipe.
10. The galvanized iron polyethylene coated pipe and process for preparing the same substantially as herein described along with the accompanying examples and drawings.