H2Tech - Q4 2021 - 35

INFRASTRUCTURE AND DISTRIBUTION
H2 COMPATABILITY
OF PIPING AND PIPELINES
Material selection. Most pipeline materials
for transmission distribution and
service for gas networks are carbon steel
and polyethylene plastic pipes, depending
on the operating pressure of the system.
Research is being conducted regarding
the compatibility of the materials-
H2
, when contained under high partial
pressure in combination with high temperatures,
can induce cracking to the
metal surface, also known as H2
embrittlement
(FIG. 2).
The higher stresses induced by higher
operating pressures inside pipes of low or
moderate yield strength (API 5L, A, B,
X42, X46, etc.) can raise concerns for the
durability of the material.
Generally, carbon steel is acceptable
service and operating temperafor
H2
tures below 250°C and moderate partial
pressures, as shown in the modified Nelson
diagram from API 941 (FIG. 3).2
It is known that the degradation of
polymer materials in normal environmental
conditions is caused by UV radiation,
chemical attack and thermal breakdown.
With an H2
tion between H2
attack, little or no interacgas
and polyethylene is
expected. Considering that H2
does not
does
provide radicals that can cause polymer
breakdown, it is expected that H2
not promote polymer degradation.
H2
ecule, H2
permeability. As the smallest molis
very permeable and has a great
tendency to leak through pipes, valves,
seals and gaskets. The permeation rates
for H2
CH4, and the volume leakage rate of H2
three times the volume leakage rate of natural
gas; therefore, the accumulation of H2
in confined space can raise safety issues.
Adding H2
levels.
are four to five times faster than
is
into natural gas modifies
the properties of the gas mixture. Subsequently,
it is necessary to calibrate the gas
meter when measuring blending mixtures
at various H2
The threaded and flanged connections
are considered potential leakage sources
and should be minimized, and the threaded
connections should be avoided, leaving
no exposed points of possible leakage.
With flanges, gasket reliability is a critical
factor. Spiral-wound gaskets-a serrated
solid metal ring sandwiched between
a soft/deformable sealing material-
FIG. 3. Material suitability for H2
application.
should be used for lower pressure classes,
whereas " RTJ " (confined metal) gaskets
are more suitable for the higher pressures.
The valves included in H2
tion times for carbon steel piping in different
operating conditions are stipulated
in FIG. 4.
blending
systems should be high quality (body
seals and stem packing) and with a tight
shutoff; check valves should be avoided.
Fatigue cycle analysis. The occurrence
and the severity of H2
defects on
metallic materials depend on the type of
the materials, H2
concentration and operating
parameters.
H2
cracking begins once the service
diffused into the
conditions (high pressure and high temperature)
allow the H2
steel to react with the carbon and carbides
in the steel. Under fatigue loading,
the period of time until mechanical
damage can be detected is commonly
referred to as " incubation time, " which
defines the lifetime of the steel pipeline.
According to API 941,2
the incubaSafety.
H2
can ignite in a broader range
of conditions related to natural gas, so the
probability of ignition and subsequent
risk (risk = probability × severity) for the
blended pipelines is higher.
Risk factors depend on the H2
FIG. 2. H2-induced cracks.
concentration
(i.e., 20%, 50%), the type of gas
pipeline system (transmission, distribution),
the pipeline material and the operating
conditions.
Nevertheless, gas network systems
pose a lower risk of severe accidents compared
to similar scale's energy systems,
such as petroleum, nuclear and hydropower.
The major failure factor in natural
gas pipeline networks is leakage. Failure
causes for leak incidents include corrosion;
material and construction defects related
to defective welds, stripped threads,
H2Tech | Q4 2021 35
H2Tech - Q4 2021

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