SCAN INDIA
“Smoothflow ” Pipes
“Smoothflow” is a registered trademark of Scan India.
Why Powder Coating? :
In conventional 3-layer polyethylene coatings, the outer polyolefin covering is usually
applied by extrusion. The outer polyethylene coating is normally applied by a side-wrap
extrusion process wherein a continuous sheet of molten polyethylene is wrapped
helically around the exterior circumference of the pipe immediately after the FBE and
adhesive have been applied.
Most steel pipes used in pipelines are welded pipes. The manufacturing processes
used to produce large diameter pipes produce welds that protrude both above and into
the pipe diameter. In the conventional 3-layer side-wrap extrusion process, soft silicone
rubber rollers are used to apply pressure to the extruded sheet to improve contact
between the layers, promote adhesion and smoothing of the polyethylene layer and
push the molten polymer into to surface irregularities, including the raised weld. The
effectiveness of the silicone roller depends largely on the weld geometry.
With high raised welds or square welds molten polymer can be pushed into the weld
on the incoming side of the weld as the pipe rotates towards the roller. However, it may
not be able to improve the contact on the exit side, resulting in voids at the weld neck.
With the traditional side-wrap extrusion application, protruding (raised) weld seams lead
to a variety of coating problems. The most common problems are:
Tenting, in which voids develop at the base of the weld neck.
Thinning across the top of the weld, resulting in the thickness of the coating
being well below specification at the top of the weld.
The voids at the weld neck area produce pinholes and entrap water during the
cooling stage.
Powder coating avoids these problems. Scan India uses a specially developed
process for applying all of the components in powder form using powder coating
techniques. The process provides a graded structure coating where there is no definite
boundary between the three layers. Thus this coating behaves like a single layer
monolithic coating thereby eliminating interlayer adhesion failures.
“Smoothflow” Pipe Coating Procedure:
The production procedure of “Smoothflow” pipe is as shown in the diagram
below:
Coating Properties:
Fusion Bonded Epoxy (First Layer): This is the corrosion protective layer. This layer is
of fusion bonded epoxy which offers very good corrosion protection. The fusion bonded
epoxy being polar material, bonds firmly to the blasted steel surface.
Grafted Polymer Adhesive (Second Layer): This layer is of grafted polymer adhesive.
This is a grafted polyethylene compound. This layer blend with the first layer to produces
a physical interlocking of the components with no defined interface and single layer
coating behavior.
Polyethylene (Third Layer): This layer is for physical protection and consists of
polyethylene. Since the grafted polymer adhesive and polyethylene are similar, they
bond well with each other.
Coating Standards:
The coating will be as per German standard DIN 30670 which is a universally accepted
standard for 3LPE coatings. As an alternative Canadian standard CSA Z245.21-02
System B2 or Australian standard AS 4321 can also be adopted. These standards have
some minor differences from DIN 30670.
Quality Testing Plan:
“Smoothflow” pipes are tested in accordance to the testing frequency plan as
described in the following table:
Properties Test Method Frequency
Surface condition after blasting. Visual Every pipe
Surface roughness Comparator Every pipe
Temperature before and during coating - Continuously
Coating thickness testing DIN 30670 One pipe every 25 pipes
Cut back Visual Every pipe
Holiday inspection DIN 30670 100% of all pipes
Impact resistance DIN 30670 Once per order
Indentation test DIN 30670 Once per order
Adhesion test DIN 30670 One pipe every 50 pipes
Electric resistance DIN 30670 Once per order
Elongation test ISO 527 Once per order
Stability against U.V. DIN 30670 Once per order
Thermal stability DIN 30670 Once per order
Resistance to cathodic disbondment ASTM G 8-90 As per agreement
Coating Comparison:
Below is shown the comparison of properties of some coatings and linings used
on steel pipes.
Test 100% Solids 100% Solids Cement Mortar “Smoothflow”
Epoxy Polyurethane Coating & Lining Coating & Lining
Adhesion 925 psi 1000 psi 0 psi 1750 psi
Test
Cathodic 5 in-lbs 75 in-lbs 2 In-lbs 100 in-lbs
Disbondment Radius
Water 2% 6% 7% <1%
Absorption
Abrasion 183 mg 45 mg 1500 mg 40 mg
Resistance weight loss weight loss weight loss weight loss
Impact 15 mm 30 mm N/A 6 mm
Resistance Average Average Average
