Hydrocarbon Processing - July 2022 - 31

Valves, Pumps and Turbomachinery
As rust accumulates around the valve,
the opening and closing limits of the
valves reduce. The check valves cannot
provide a full path for fluids to pass. At
the same time, the process operating conditions
are kept constant, with the pumps
supplying fluids at optimum capacity.
The partially open check valve disc obstructs
the flow of corrosive fluids, resulting
in a rapid buildup of pressure in the
upstream piping equipment. With time,
the excess fluid pressure weakens the
pipes, causing rupture and explosion.
Prevention and maintenance. Selecting
the appropriate valve for corrosive
fluid service eliminates safety risks arising
from the gradual degradation of valve
components. One way to protect valves
used for corrosive fluid service is by performing
metal surface treatment. A protective,
non-reactive coating is applied
between a metal surface and its surroundings
to create a physical barrier. This prevents
chemical reactions at the surface of
the metallic component. Other treatment
methods include surface coating, passivation
or oxidation. The protective coatings
use corrosion-resistant materials and alloys
like chromium, zinc, metal oxides and
phosphates.4,5
To protect valves against
electrochemical corrosion, manufacturers
use anodic or cathodic protection, which
converts galvanic pairs into passive components
to prevent electron flow. Other
valves use non-metallic corrosion inhibitors
like ceramics, metal oxide ceramic
coatings and non-metal substrates. To
combat and inhibit corrosion, operators
should remain vigilant in their inspection
and maintenance procedures (FIG. 3).
Heavy-duty, severe service valves
contain ports for the lubrication of internal
valve surfaces to enable the smooth
movement of dynamic parts. This reduces
the impact of frictional corrosion.
Corrosion predominantly attacks a
check valve's disc, as it is the most dynamic
component. To minimize the impacts
of corrosive chemical attacks on the
check valve discs, they are often coated
with 0.3 mm-0.6 mm of ethylene chlorotrifluoroethylene
(Halar) material.
Another way to protect the discs is by
coating metallic valve components with
polyethylene or perfluoroalkoxy (PFA)
materials. These thermoplastic materials
possess better mechanical and chemical
resistance than Halar.
FIG. 3. To combat and inhibit corrosion, operators should remain vigilant in their inspection and
maintenance procedures.
The choice of valve material varies
depending on the concentration of the
dominant corrosive compounds. Piping
systems with high concentrations of sulfur,
with suitable conditions for the formation
of sulfuric acid (H2
SO4
), should
use valves made from alloy stainless steel,
such as Alloy-20. Fluoroplastic valves can
be used for low-pressure, low-temperature
H2
SO4
service.
Pipelines conveying fluids with less
than 30% hydrochloric acid concentrations
at temperatures below 120°F
(50°C) can use valves made from steel alloys
containing suitable quantities of molybdenum.
Non-metallic valve materials
are appropriate for hydrochloric acid service
as long as the process temperatures
do not exceed 300°F (150°C). Hightemperature
nitric acid service pipelines
use titanium alloy valves. Nitric acid corrodes
most metals at room temperature
and pressure. Where there is a high concentration
of H2
S gas in the service media,
the valve stem is electroplated using
phosphorous and nickel coatings.
Non-metallic materials such as PTFE,
synthetic rubbers, nylon and strong thermoplastics
are used to create seals in
valves. Although they provide sufficient
sealing, their use is limited to low-temperature
applications.
When installing non-metallic valves
for corrosive fluid service, avoid distorting
the flanges. The machining of nonmetallic
flanges is not as smooth as that of
most metallic valves and can be a source
of external leakages.
Always use the correct valve and piping
materials that are resistant to the service
media. Installing the valves in the appropriate
locations and orientations prevents
instances of choked flows, stagnation or
contamination that can exacerbate the
corrosive action of the working fluid.
LITERATURE CITED
1
Driscoll, R., " What is the cracking pressure of a
check valve? " Valveman, online: https://valveman.
com/blog/what-is-the-cracking-pressure-of-acheck-valve/
2
Wood,
R., " Erosion-corrosion interactions and their
effect on marine and offshore components, " U.S.
Department of Energy, Office of Scientific and
Technical Information, 2004, online: https://www.
osti.gov/etdeweb/biblio/20671857
3
Zulkarnaini, M. A., et al., " Analysing petroleum
leakage from ground penetrating radar signal, "
ResearchGate, January 2019, online: https://
www.researchgate.net/publication/325115239_
Analysing_Petroleum_Leakage_from_Ground_
Penetrating_Radar_Signal
4
5
Waters, R., " Selection of severe service valves, "
Chemical Engineering, June 2017.
SpecialChem, " Corrosion resistance and anti-corrosion
coatings-All you need to know, " SpecialChem:
The material selection platform, online: https://
coatings.specialchem.com/coatings-properties/
corrosion-resistance
GILBERT WELSFORD JR. is the
Founder of Valveman.com and a
3rd-generation valve entrepreneur.
He has learned valves since a
young age and brought his
entrepreneurial ingenuity to the
family business in 2011 by creating
the online valve store Valveman.com. Mr. Welsford's
focus is building on the legacy his grandfather
started, his father grew, and he has amplified.
Hydrocarbon Processing | JULY 2022 31

https://valveman.com/blog/what-is-the-cracking-pressure-of-a-check-valve/ https://valveman.com/blog/what-is-the-cracking-pressure-of-a-check-valve/ https://valveman.com/blog/what-is-the-cracking-pressure-of-a-check-valve/ https://www.osti.gov/etdeweb/biblio/20671857 https://www.osti.gov/etdeweb/biblio/20671857 https://www.researchgate.net/publication/325115239_Analysing_Petroleum_Leakage_from_Ground_Penetrating_Radar_Signal https://www.researchgate.net/publication/325115239_Analysing_Petroleum_Leakage_from_Ground_Penetrating_Radar_Signal https://www.researchgate.net/publication/325115239_Analysing_Petroleum_Leakage_from_Ground_Penetrating_Radar_Signal https://www.researchgate.net/publication/325115239_Analysing_Petroleum_Leakage_from_Ground_Penetrating_Radar_Signal https://coatings.specialchem.com/coatings-properties/corrosion-resistance https://coatings.specialchem.com/coatings-properties/corrosion-resistance https://coatings.specialchem.com/coatings-properties/corrosion-resistance http://www.Valveman.com http://www.Valveman.com

Hydrocarbon Processing - July 2022

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