Pipelines transport
many different fluids. These are liquids and gases including, natural gas,
crude oil, refined products like gasoline and jet fuel, natural gas liquids and
derivatives like propane, hydrogen, supercritical CO2, sour gas (natural gas
with H2S), carbon monoxide, amines, hot water, and steam. Each medium being
moved has different issues when it comes to sealing challenges to prevent leaks
and corrosion challenges. In several cases, pipelines of specific design, strength,
and materials are required to move specific fluids. Sour gas (H2S), steam, CO2,
CO, hydrogen, and amines are among the most challenging fluids to transport via
pipeline. Steam and CO2 are both used extensively in enhanced oil recovery
(EOR). Temperature is another challenge for pipelines since they can range from
very low (cryogenic) to very high. Different materials for sealing components
such as gaskets are required for different media and temperatures. The main
issues revolve around how different chemistry, temperatures, and pressures
affect materials.
While hydrogen
and CO2 pipelines have been around for a while, the skilled workforce to install,
inspect, and maintain them is not large. Installing certain types of gaskets
can be difficult and require training. Those pipelines won’t benefit from highly
profitable sales agreements like oil & gas pipelines do. Thus, budgets and
timelines can be tighter.
Gas pipelines
have unique challenges. Sealing and corrosion focused more on oil pipelines in
the past. Both adequate sealing at connections and corrosion prevention and reduction
are the keys to emissions reductions in the midstream sector.
Sealing and Gaskets for Pipelines: Types, Materials,
Applications, and Limitations
Gaskets at
pipeline connections, valves, and flanges are the main mechanisms of sealing. Gaskets
form a mechanical seal that fills the space between two or more mating surfaces.
Gaskets are of three general types: non-metallic (soft), semi-metallic or
composite, and metallic. Effective pipeline sealing ensures equipment
reliability, safety, and environmental compliance by helping to prevent leaks
and contamination, and by minimizing downtime and ensuring operational safety. Early
gaskets were made of phenolic plastic or resin. Phenolic gaskets have been in
use since 1908. They are still in use but are not suitable for many
applications. Compared to modern analogs, they are a poor gasket material
that is subject to cracking. For many applications, including pipelines, they
need to be phased out.
Non-metallic
gaskets are made of CNAF (Compressed non-asbestos fiber), PTFE (Polytetrafluoroethylene),
rubber, Teflon, or graphite. These are generally used for low-temperature and low-pressure
applications with the exception of graphite, which can withstand temperatures up to 460 degrees C. Elastomer gaskets such as rubber are not used for pipelines
that transport hydrocarbons.
Source: Enerpac
Metallic gaskets
are used for ring-type joints (RTJs) in high-pressure applications for oil
& gas pipelines and refineries on valves and pipework. Sealing RTJs is
challenging as they can corrode and degrade under high stress conditions.
Composite gaskets
are made of a combination of metallic and non-metallic components. They ere
used on raised face, male-female, and tongue-and-groove flanges. They are cheaper
than metallic gaskets but require careful handling.
There are also
three gasket types in terms of configuration: 1) full face, 2) inner bolt
circle (IBC), and 3) ring-type joint (RTJ). Full face gaskets cover the entire
flange face and include bolt holes. They can only be used with full face
flanges. Inner bolt circle gaskets are used on raised face (RF) flanges. RF
flanges concentrate more pressure on a smaller gasket area thus raising the
pressure sealing capability of the joint. RTJs are typically metallic.
Another material
used for gaskets is glass-reinforced epoxy (GRE) which was invented in 1942. It
works great for low-pressure applications but is permeable at higher pressures.
They are damaged by steam which ruins the epoxy. They are also damaged by sour
gas/H2S which enters the material as bubbles and softens the gasket through
time.
Metal core
isolation gaskets have been used since 1981 and are now the industry standard. They
are resistant to corrosion, impermeable and work well at high pressure. Fire-safe
isolation gaskets were invented in 2010 and are used in applications where fire
is a concern to prevent explosions and slow fires so they can be more easily
extinguished. Inner diameter (ID) seal gaskets were invented in 2011 and have
the sealing element on the inner diameter of the joint which more directly contacts
the media. They are made of PDFE and are chemically resistant but not fire safe.
Stainless steel metal core gaskets are affected by sour gas so in those
applications more exotic metals are used for metal core gaskets which are more
costly. While GRE and PTFE gaskets are not fire-safe, they can be altered with
other materials to make them fire-safe. This is expensive.
Teflon seal jackets
embedded onto the face of the gasket rely on GRE material being permeable at
higher pressure, so the pressure gets to the seal to make it seal. The inner
diameter is always exposed to corrosive materials.
Sealing Flange Joints
According to
Wikipedia: “A flange is a protruded ridge, lip or rim, either external or
internal, that serves to increase strength.” Flanges are often attached by
a circle of bolts as shown in the image of a gas pipeline flange joint below. In
the U.S. ASME standards specify flanges by pipe size and pressure ratings. Gasket
type and bolt type are often generally specified by the standards. There are choices
regarding materials used for gaskets. Materials suited to the application and
environment should be chosen. Flange type/size, pressure, operating temperature,
and media inside the pipe are the factors that are used to determine gasket materials.
Two ASME type
flanges, bolted together on a gas pipeline. Source: Wikipedia.
Bolt tension and tightening
sequences are important for optimizing sealing. Bolt tension specs are ensured
by using bolts with the right amount of elasticity at the right amount of
tightening for the application. This is because the forces acting on the bolts
make them act like springs. Another factor is the flange face finish, which
must be free of scratches, pits, or dents which invite leaks. Flange facing
machines are used to smooth flange faces to spec.
Importance of Training to Install Gaskets in Pipelines
One very
important issue is training workers to install gaskets correctly. These sealing
implements have very little room or tolerance and need to be installed
precisely and correctly. Mis-installation is a problem due to the lack of
skilled labor. Companies such as industry leader Garlock Pipeline Technologies
(GPT) provide training and certification for gasket installation. Metal core
isolation gaskets are thicker than other gaskets and can be more challenging to
install. At RTJs it is important to avoid increased stresses on the inner
diameter of the gasket. Gaskets must be aligned perfectly. Misaligning them
even by small amounts can result in higher potential for leakage. Different
bolt-tightening patterns are used for different gaskets. Some can be intricate.
GPT notes that the majority of sealing/gasket failures are due to mis-installation.
Challenges for Pipeline Gaskets
GPT’s webinar
on sealing and corrosion mentioned the following challenges for gasket sealing:
1)
Make fire-safe gaskets more economical.
2)
Improve chemical and thermal properties of
materials and composites.
3)
There is a need for thinner (metal core) gaskets
for easier installation.
4)
There is a need for gaskets to seal at higher
pressures.
5)
Prevent leaks at flanges.
Pipeline Corrosion Issues, Prevention, and
Mitigation
More than 40%
of the world’s natural gas and oil resources are sour. Sour crude is sour due
to the sour gas, or hydrogen sulfide (H2S), dissolved within it. H2S makes iron
sulfide which creates a conductive electrical bridge. It is a black powder that
builds up on the inside of a pipeline and up against flange isolation gaskets
where electrical current is trying to be isolated. An electrical bridge ruins
that function so that the gasket is no longer able to isolate it.
Corrosion on Steel Pipeline Flange Connection. Source: GPT
GPT estimates
that the annual cost of corrosion in the oil & gas industry is very high at
$60 billion. In the U.S. alone the annual cost is thought to be $27 billion including
upstream, midstream, and downstream. Offshore wells in deeper waters are producing
more hydrocarbons that are sour crudes with higher levels of H2S. These are
often marine carbonate reservoirs. These higher levels of sour gas present
challenges to those tasked with pipeline sealing and corrosion prevention. GPT
has developed flat gaskets that can prevent corrosion by better sealing against
incompatible materials and media coming into contact with one another. As
corrosion issues can develop through time there is also a need to assess
changes through time. As more sour hydrocarbons are produced the importance of
sealing and corrosion grows as well. This is a major safety issue and costs vs.
safety must be weighed well. With aging infrastructure, there is always a need
to know as much as possible about sealing integrity and corrosion progress.
Corrosion Under Insulation in the LNG Industry
The paint manufacturer Sherwin Williams put out an interesting white paper about the problem of corrosion under insulation (CUI) and how to mitigate it. They define the issue as follows: “CUI is a severe form of localized corrosion. It takes hold when water, inorganic salts and other contaminants become trapped beneath the insulation commonly used to cover process pipes, industrial valves, storage tanks, and other assets. Those elements work together to form corrosion cells on the steel substrates found under insulation. Hidden from view, the corrosion can proliferate and spread unnoticed, leading to pitting and metal loss that may cause leaks and potentially catastrophic failures.” The presence of the combination of moisture, oxygen, and chlorides, makes CUI a potential problem for both cryogenic and hot applications where pipes are insulated for temperature control as they stay in contact with steel pipes. LNG temperatures can accelerate corrosion. The moisture from condensation is the biggest factor. The LNG industry pipes are made of stainless steel rather than carbon steel as used in the refinery industry. This is because stainless steel is stronger and better able to prevent corrosion in general. However, it is more susceptible to chloride stress corrosion cracking (CSCC). CSCC often occurs at a microscopic scale and can be difficult to detect.
Source: Sherwin Williams
CUI is
mitigated by applying protective coatings over the stainless steel to prevent
contact between the chlorides and the steel. Currently, the lifespan of
insulated LNG pipes is just 5-13 years. However, that lifespan is expected to
grow as more advanced materials come on the market. The new materials can
better withstand chloride corrosion, extreme temperatures, rough handling, UV
exposure during outdoor storage, and moisture from condensation and humidity
(many U.S. LNG facilities are along the Gulf Coast where humidity is naturally high).
One type of coating that can be effective is thermal sprayed aluminum (TSA)
which can provide up to 25-30 years of maintenance-free prevention of CUI. This
solution is expensive, cumbersome to apply, and energy-intensive. Other options
include “spray-applied organic liquid coatings, such as high-temperature
epoxy phenolics; high-temperature, high-solids alkylated amide epoxies; and
ultra-high-solids novolac amine epoxies.” They are also meticulous to apply
but offer cost and time advantages over TSA.
Newer
formulations feature “minimum concentrations of 25 percent micaceous iron
oxide (MIO) pigment by weight in the dried coating film. This heavy load of MIO
reinforcements imparts enhanced properties into the coatings to deliver greater
durability against impacts, chemicals and corrosion compared to other
formulations.” Mica is a mineral that forms oriented plates. That crystal
structure property gives it the ability to deflect UV rays and slow penetration
of oxygen, moisture, and chlorides into the coating. One of this type of
coatings recommended by Sherwin Williams is a two-component, high-solids
alkylated amide epoxy (AAE) coating for excellent CUI protection. It offers
better protection in multiple environments than traditional epoxy phenolics and
other AAE epoxies. They also tout a newer coating in development: “A newer
ultra-high-solids advanced CUI epoxy novolac coating offers even better
performance than the MIO-enhanced formulations. It features a functional
chemical enhancement to mitigate CUI and represents a new class of
CUI-mitigation coatings because it is free from flake-filled pigmentation. The
ultra-high volume solids coating is also solvent-free, making it more
sustainable than alternative CUI-mitigation epoxies, which are typically 60-80%
volume solids formulations. With minimal to no volatile organic compounds
(VOCs) released from the ultra-high volume solids coating, applications offer
better environmental stewardship by reducing their overall carbon footprint.
Applicators can also realize lower permitting costs for their shops.”
“The advanced ultra-high-solids CUI epoxy coating far surpassed
the capabilities of solvent-based epoxy phenolic and novolac coatings designed
for CUI mitigation in various tests.”
Thus, mitigating CUI and CSCC with new coatings formulas
can significantly extend the maintenance-free lifespans of insulated pipe,
particularly in LNG applications, resulting in cost-savings, better safety
ratings, and with the newer coatings, provide lower environmental impact.
Corrosion in CO2 Pipelines
Corrosion is
an issue for CO2 pipelines utilized in enhanced oil recovery and in CCS
projects. CO2 can be transported in a gaseous, dense liquid, or a supercritical
state, according to temperature and pressure applied to it within the pipe. CO2
in CCS projects is typically transported in a supercritical state which gives
the gas some liquid properties. The key to minimizing corrosion in CO2 pipelines
is keeping moisture levels low as water content enhances corrosion.
Contaminants in captured CO2 can also be an issue. A 2011 paper in the International
Journal of Greenhouse Gas Control describes corrosion reactions in CO2 pipelines
as follows:
In a water-mediated system, three types of reactions
can occur:
(a)
The absorption of gaseous CO2 and the
acidification of the moisture layer (Carter, 2010, Connell, 2005, Gale and
Davison, 2004).
(b)
Cathodic (Spycher et al., 2003, Ayello et
al., 2010) and anodic (Zhang and Cheng, 2009) reactions.
(c)
Reactions leading to the formation of an
oxide layer (Glezakou et al., 2009, Nešić, 2007, Granite and O’Brien, 2005).
As the successfully
maintained extensive network of CO2 pipelines for EOR shows, corrosion in CO2 pipelines
can be effectively minimized. Strict limitations on contaminants like free
water, H2S, sulfur compounds, and oxygen have successfully led to minimized
corrosion effects. The paper concludes:
“If conditions in a pipeline are maintained so that the
water content and other contaminant levels are kept extremely low (i.e. from
drying), as is currently the case for EOR pipelines, then corrosion rates are
also likely to be sufficiently low, as suggested by empirical evidence.”
Corrosion and Sealing Issues in Hydrogen Pipelines
Hydrogen pipelines
have been used extensively in refinery processes and when properly designed to
carry hydrogen, will operate effectively. Polymer pipelines can work better
than steel for hydrogen. The U.S. has over 1600 miles of H2 pipelines, 90% of
which are along the Gulf Coast among refineries and petrochemical plants.
Hydrogen is a
smaller molecule than natural gas and carries less energy in a similar volume.
This makes it more challenging to control leakage in hydrogen pipelines. It
also means natural gas compressors won’t work for pure hydrogen. Most experts
think that hydrogen can be blended with natural gas up to 20% in existing
natural gas pipelines without too much concern about leakage and corrosion. At
higher hydrogen blending levels the pipelines would have to be coated to
prevent corrosion, the sealing gaskets would have to be upgraded, the compressors
would have to be reconfigured, and valves and seals would have to be upgraded. Welds
and leak detection systems would also need to be upgraded.
Corrosion of
steel via hydrogen occurs as hydrogen embrittlement. This occurs when
the steel’s ductility is reduced by absorbed hydrogen. Hydrogen atoms, being
small, can permeate solid metals and lower the stress required for cracks in
the metal to initiate and propagate, resulting in embrittlement.
As a smaller
molecule, hydrogen is more prone to leakage than methane. It also more readily
disperses into the atmosphere. It is not a greenhouse gas like methane. Its
flammability range is broader than methane, but it does not burn as hot. Thus,
it is a significant safety concern for explosions, more than natural gas in
many cases, but the explosions are often less damaging and easier to extinguish
than natural gas explosions. Hydrogen fires can be difficult to see so that
creates an added safety concern.
As mentioned,
tighter gasket seals are required to prevent hydrogen leakage. GPT touts their
Evolution isolation gaskets for both sour gas and hydrogen applications. Evolution
gaskets are thin but fully encapsulated to ensure better sealing. These are
already being used in hydrogen pipeline applications. The video below gives
details about these gaskets:
References:
Navigating
the obstacles encountered by pipeline professionals: an emphasis on sealing and
corrosion prevention. Webinar. Pipeline & Gas Journal. October 12, 2023
How
Liquid Coatings Curb Corrosion Under Insulation (CUI) in LNG Service. Mark
Rubio. Sherwin Williams. White Paper. 2023. How
Liquid Coatings Curb Corrosion Under Insulation in LNG Service
(gpc-whitepapers.com)
Gasket
Types in Oil and Gas, Explained. Scott Hamilton. Hex Technology January 27, 2021.
Gasket Types in
Oil and Gas, Explained – Hex Technology
Gasket
Handbook. 1st Edition. European Sealing Association. June 2017. FSA-Gasket-Handbook-June-2017.pdf
(fluidsealing.com)
Flange.
Wikipedia. Flange - Wikipedia
The
Cost of Corrosion in Oil & Gas. GPT Industries. July 2022. Cost-of-corrosion-in-oil-gas-GPT-Industries.pdf
(gptindustries.com)
Safe,
Reliable, and Compliant: The Three Pillars of Sealing Solutions. Sepco.
November 16, 2023. Safe,
Reliable, and Compliant: The Three Pillars of Sealing Solutions – SEPCO, Inc.
Types
Of Gasket For Oil, Gas, Petrochemicals and Power Generation. Enerpac. October
10, 2018. Types
Of Gasket For Oil, Gas, Petrochemicals and Power Generation - Enerpac Blog
Corrosion
of pipelines used for CO2 transport in CCS: Is it a real problem? Ivan S. Cole,
Penny Corrigan, Samson Sim, Nick Birbilis. International Journal of Greenhouse
Gas Control. Volume 5, Issue 4, July 2011, Pages 749-756. Corrosion
of pipelines used for CO2 transport in CCS: Is it a real problem? -
ScienceDirect
Addressing
Carbon Dioxide and Hydrogen Pipeline Transport Challenges. Jim Cahill, Paul
Dickerson. Emerson Automation Experts. March 20, 2023. Addressing
Carbon Dioxide and Hydrogen Pipeline Transport Challenges
(emersonautomationexperts.com)
Pipeline
Transportation of Hydrogen: Regulation, Research, and Policy. March 2, 2021.
Congressional Research Service. Pipeline
Transportation of Hydrogen: Regulation, Research, and Policy (congress.gov)
Could
Hydrogen Transport Mean Sustainability for the Pipeline Industry. Della
Anggabrata. GPT Industries. CorrosionPedia. September 17, 2021. Could
Hydrogen Transport Mean Sustainability for the Pipelin (corrosionpedia.com)
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