1. www.worldpipelines.com Reprinted from World Pipelines April2008
( development in coatings )
Ian Robinson, 3M E Wood, UK, analyses
the performance of high solids internal
flow efficiency coatings for pipelines. First,
Craig Thomas, 3M E Wood, provides an
introduction to internal flow coatings.
he application of a two component epoxy coating to the internal surface of
gas pipelines was first carried out in the 1950s. Gas transmission pipelines
are a key element in the transportation of fuel, supplying energy and power
to many countries and providing sustained growth and development all over the
world. The operation and pumping costs of a gas pipeline are substantial and the
capacity of gas delivered by the pipeline depends to a large degree on key design
parameters; those being diameter and length. In recognising these factors, the
concept of internally lining gas pipelines was developed, providing enhanced flow
and thereby engendering a reduction in operational costs.
International oil and gas companies such as Shell, BP, Exxon, Total, Transco,
Statoil, Reliance and CNPC, to name but a few, have now recognised the many
benefits of internally coating gas pipelines, which has become industry practice. For
this application, 3M E Wood, Corrosion Protection Products, 3M United Kingdom
2. Reprinted from World Pipelines April2008 www.worldpipelines.com
( development in coatings )
Plc (formerly E Wood Ltd) pioneered a range of internal flow
coatings under the COPON Pipelinings brand.
In addition to enhanced flow, there are many other
economical and technical benefits available to pipeline
operators in both an onshore and offshore environment, as
well as to pipeline contractors and pipe coaters:
Ë Corrosion protection in storage.
Ë Reduced energy costs in pumping and compressor
Ë Reduced energy requirements - reduced emissions of
Ë Low capital costs.
Ë Reduced commissioning costs.
Ë Faster commissioning (inspection).
Ë More effective pigging/scraping.
Ë Sealed surface - product purity.
Ë Diverse pipeline use - easier product switch.
Ë Rapid payback.
Ë Reduced valve maintenance.
Ë Improved application.
No review of the advances made in high solids internal
flow coatings would be complete without using the
experience of a coatings manufacturer that has supplied
product for over 140 000 km of lined pipe worldwide
during a period spanning more than 45 years and that has
developed a range of flow efficiency coatings (48% solids,
75% solids and 100% solids - solvent-free) fully approved
to API RP 5L2 and ISO 15741.
High solids internal flow efficiency
Thin film epoxy coatings have long been known to reduce
the internal roughness, and hence the friction factor, of
natural gas flowlines. A new generation of high solids
materials provide the pipe coater with a choice of
environmentally sustainable solutions without
increased coating thickness or loss of
This article will illustrate the
environmental benefits of high
solids internal coatings, and
present a study of the surface
roughness parameters of
internally coated pipe as a
function of flow coating volume
Internal coating of natural
gas pipelines is employed to reduce
friction and improve flow efficiency
when conveying non-corrosive natural
gas, and to offer adequate corrosion
resistance during subsequent storage and
transportation of coated pipe. The coating
functions by reducing surface roughness and hence
reducing the friction factor of the pipe wall.
The use of thin film (<100 microns) epoxy resin based
coatings for this purpose is well known and has an
extensive track record with many pipeline operators. By
convention, such coatings have typically been formulated
around solid ‘1-type’ epoxy resins (molecular weight
approximately 1000) in conjunction with either polyamine
adduct or polyamide curing agents. The solid/semi-solid
nature of the epoxy resin and curing agent necessitates
the use of substantial levels of organic solvents in order
to provide a suitable liquid coating composition. A typical
commercial coating product would therefore contain
40 - 45% by weight of solvent, equating to a volatile
organic compound (V.O.C) content of 400 - 450 g/litre.
The performance attributes required for an internal flow
efficiency coating are detailed in a number of internationally
recognised performance specifications and standards - API
RP 5L2 (‘API’), TRANSCO CM2 (‘British Gas’) and more
recently ISO 15741.
Whilst there are differing requirements within each,
many common requirements exist, such as:
Ë Corrosion resistance.
Ë Water resistance.
Ë Chemical resistance.
Ë Resistance to gas pressure variations.
The overall package of properties required from the cured
flow coating presents a number of challenges
to the formulator seeking to reduce V.O.C
The use of liquid epoxy resin, rather
than solid ‘1-type’ resins, enables
solvent contents to be reduced.
However, the lower molecular
weight of liquid resin results in the
formation of polymer networks
with an increased crosslink density,
yielding coatings of limited flexibility.
The use of flexibilising agents generally
leads to reductions in corrosion, water
and/or chemical resistance and the use
of non-reactive diluents or plasticisers
must be avoided to prevent out-gassing
from the coating as a result of in-service
Figure 1. Steel pipe coated with
Copon EP2306 HF, creating a
smooth, low friction internal
†Article adapted from 'Advances in high solids efficiency coatings', a paper given at BHR's 17th
Conference on Pipeline Protection, Edinburgh, 17 - 19th
3. www.worldpipelines.com Reprinted from World Pipelines April2008
( development in coatings )
Despite these constraints, appropriately formulated
flow efficiency coatings can now be produced with V.O.C
contents ranging from 225 g/litre down to zero.
Comparison of V.O.C emissions for
different flow coating technologies
Solvent emissions, and associated carbon emissions,
for a range of coating technologies are illustrated below,
calculated on the basis of a nominal 200 km/36 in. I/D
internal coating project. The reduced environmental
impact of high solids/solvent free formulations is clearly
Conventional solvent based flow
Ë V.O.C content = 440 g/litre.
Ë For 200km, 36 in. I/D pipe.
Ë Practical applied coating film thickness (wet)
= 200 microns.
Ë Coating consumption = 120 000 litres.
Ë V.O.C emissions = 120 000 x 0.44kg = 52.8 t.
Ë Assuming typical aromatic hydrocarbon/alcohol solvent
blend, carbon emissions = 45.0 t.
High solids solvented flow coating
Ë V.O.C content = 225 g/litre.
Ë For 200 km, 36 in. I/D pipe.
Ë Practical applied coating film thickness (wet) = 125
Ë Coating consumption = 75 000 litres.
Ë V.O.C emissions = 75 000 x 0.225 kg = 16.9 t.
Ë Assuming typical aromatic hydrocarbon/alcohol
Ë solvent blend carbon emissions = 15.0 t.
100% solids, solvent free flow coating
Ë V.O.C content = 0 g/litre.
Ë For 200 km, 36 in. I/D pipe.
Ë Practical applied coating film thickness = 75 - 100
Ë Coating consumption = 45 - 60 000 litres.
Ë V.O.C emissions = nil.
Ë Carbon emissions = nil.
Effect of internal flow coating on
A number of roughness/profile parameters can be utilised
to characterise pipeline surfaces,1 including:
Ë Average roughness (Ra).
Ë Root mean square roughness (Rq).
Ë Maximum height of profile (Rt).
Ë Average maximum height of profile (Rz).
Impact of flow coating volume solids
It might be assumed that dry film thickness is the principal
driver in reducing the surface roughness of a blast cleaned
surface. However, study of the roughness parameters
obtained from a range of flow coating compositions, at
equivalent dry film thickness, reveals the volume solids
of the liquid coating to be highly significant in reducing
Roughness parameter plots for three flow coating
variants applied to blast cleaned steel linepipe (Rz = 40
microns) at a dry film thickness of 75 microns are shown
in Figure 1, with a summary of the data detailed in Table 1.
Solvented, thin film epoxy flow efficiency coatings have
served pipeline operators well for many years. However,
their high solvent (V.O.C) content may be considered
environmentally undesirable and ultimately unsustainable.
The advent of a new generation of reduced solvent
content (‘high solids’) and solvent free (‘100% solids’) flow
coatings enables the environmental impact
of internal coating processes to be minimise
without compromising coating performance.
Furthermore, hitherto unexpected benefits in
reducing the surface roughness of internally
coated pipe are realised by the adoption of
these new coating technologies, without any
increase in applied coating thickness.
1. KOEBSH et al, Measuring roughness of blasted steel
pipe surfaces: a case study, (16th
on Pipeline Protection, 2005).
Table 1. Roughness parameters for a range of flow coatings @ 75 microns dft
Roughness parameters (microns)
Ra Rq Rz
45 440 1.38 1.64 5.90
75 225 0.65 0.81 3.88
Solvent free 100 0 0.16 0.20 0.83
Figure 2. Roughness plots for a range of flow coatings @ 75
microns dft. (Left to right - blast cleaned steel, conventional
solvented coating, high solids coating, solvent free coating).