FACILITY COOL-DOWN
US firm outlines its LNG terminal
cool-down procedure at start-up
Osifo Akhuemonkhan and Roberto Ruiperez Vara, CH•IV International, Baltimore, Maryland
As companies around the world push
forward with their plans to commission
new LNG import facilities, it is common
to see critical activities associated with
the cool-down of such facilities given a
low priority when compared to other
commissioning activities.
The push to make final preparations
for cool-down often results in a “gap”
between the level of preparation and
detail included in procedures and the
expectations
at
the
engineering,
procurement and construction phase.
All too often the owner-operator does
not recognize the “gap” until it is too late.
The quality of operator training is often
compromised and delays in commissioning
are frequent, as late modifications are
made to process piping and equipment to
properly handle the cool-down.
This article identifies commissioning
strategies owner-operators can adopt to
After the completion of LNG import terminals, such as the one above, modifications are made to process piping and
equipment to handle the cool-down procedure. This is before the first LNG cargoes are delivered to the facility
before start-up is defining what is “clean”
should be cut diagonally at their ends so
install heat tracing on the valve trunnions.
when determining pipe cleanliness.
as to prevent entry of water on rainy days.
Valve seat durability is generally
Valves:
proportional to the price you pay for the
bridge the potential “cool-down gap” and
Depending on the party and the level
ensure a smooth, safe and effective
of
usually
Install a locking mechanism in each
valve. But take into account that even
terminal start-up and transition to
somewhere between no hard hats or
valve to avoid accidental opening or closing
the highest quality valve seat may get
operations.
pieces of 2x4s in the lines to no
of the valves during pipeline cleaning or
damaged by foreign materials.
microscopic dust.
other construction activities. In most cases
For the most part, companies that
responsibility,
clean
is
design and construct LNG storage tanks
Clean may best be defined as having
valves are delivered by vendors in an open
Cryogenic dry-out
have well-developed and well-established
removed any foreign matter that could
position, it is best that valves be installed
To allow proper operation of the facility,
procedures for clean-up, dry-out and cool-
harm
and locked in this position.
all cryogenic piping must be thoroughly
down of their tanks.
commissioning and start-up activities.
In particular, during the cleaning
dried out. Small quantities of water, or
equipment
during
ensuing
It is not suggested that there are
Although high flow pipe blows are
process avoid blowing through butterfly
even water vapor, can freeze in valve
typically large gaps in expectation for the
often the approach used to clean lengths
valves, control valves or other valves with
bodies, valve trunnions, pump parts and
commissioning and cool-down of the
of pipe, one must consider the effect of
exposed seats.
passages,
tanks, but the facility owner-operator
welding slag or foam glass dust on soft
debris through butterfly valves can easily
strainer media or any low point in the
should still closely monitor all LNG tank-
valve seals during these blows.
damage the disc. In such situations a spool
piping system.
related commissioning activities.
For example, blowing
instrument
connections,
For example, most LNG pumps use the
piece should be installed in place of these
LNG itself to cool and lubricate the pump
valves and, subsequent to cleaning, the
operation of equipment and/or lead to
Procedure
bearings. Once in operation, if foreign
butterfly valves should be “golden welded”
failure of the bearing materials, such as
Preparations for an LNG facility start-up
materials plug the cooling paths or
into the pipelines to prevent the need for
the galling of trunnion bearings.
require that detailed procedures be
damage the bearings, the pump could
pressure testing.
Some vendors offer
In addition particles of ice that
developed and implemented for the
suffer a total failure.
additional protection for the moving parts
breakaway and are carried through the
In addition to vendor-specific pre-
This
could
prevent
or
restrict
of the valve to prevent damage from
cryogenic system may clog strainers,
Piping and equipment clean-up
installation storage requirements, the
impacts caused by high speed particles.
block the cooling paths in the LNG
Dry-out
following are some other precautionary
Unnecessary opening and closing of
pumps or damage valve seats.
Purge
steps that will minimize issues arising
valves may encourage build up of debris
Once a system is inventoried with
Pre-cool-down
from poor cleaning and/ dry-out.
and other particles present in piping. If
LNG, these issues become extremely
Cool-down
Piping:
valves need to be operated prior to or
difficult
Confirm that the design of the piping
during pipe cleaning, these operations
lines/components may have to be de-
Piping clean-up
includes low point drains throughout the
should be properly supervised and proper
inventoried,
After construction, piping, valves and
cryogenic system.
procedures should be utilized for cleaning
repaired, purged again, re-dried, re-
vessels often contain certain amounts of
Store piping components with end
soft seats.
cooled and re-inventoried.
construction debris and possibly free
caps in place until they are installed.
A method to confirm that valve
Such actions could also cause a delay
water that has accumulated over the long
Seal opens ends of piping during
trunnions are absolutely dry (no free water)
in the start-up schedule and become very
months of construction. One of the first
construction when access is not required.
prior to initiation of piping dry-out should
costly for the owner-operator or EPC
gaps encountered in the closing months
Large diameter vents to atmosphere
be developed. One example would be to
contractor.
following activities:
Reprinted with permission from LNG Journal.
LNG journal
to
resolve
purged,
•
February 2009
as
these
warmed-up,
•
23
FACILITY COOL-DOWN
Less obvious are the potential issues
most effective method of assuring that the
gas in petrochemical industries can
systems that involve multiple elevations, a
on how to re-cool the repaired section of
cryogenic systems are properly dried out.
freeze under cryogenic temperatures.
significant number of elbows and/or a
the plant with LNG present in other
With the “Sweep and Soak” technique
sections. Hence, it is very important that
the
tight envelope is less predictable. Final
the drying medium (dry air or nitrogen
commissioning team should have a well
cool-down is not the time to find out that
all piping systems expected to experience
with a dew point of -60°C/-80°F) is
prepared procedure detailing the method to
the piping did not move as expected.
cryogenic temperatures are dried out
introduced at one or more points in the
be used to purge the system and in
Unexpected pipe movement can result in
before placed in operation.
cryogenic piping system and allowed to
particular, the sequence and timing of steps,
insulation
It is also important that consideration
flow through a large portion of the
including rate of introduction of the purge
misalignment and/or mechanical damage
be given to drying out the facility long
system and is then vented to atmosphere.
medium and verification of end points.
to the pipe and/or pipe support systems. A
before mechanical completion of the
As the name implies, the goal is to
Once the amount of nitrogen needed
test can confirm that piping will move as
cryogenic piping as many problems in
sweep the entire piping section or system
has been accurately calculated a supply
expected. Critical pipe supports should be
dry-out can occur as a result of poor (or
until the TDP is reached.
of the whole amount has to be arranged.
pre-marked with initial and expected
hurried) planning and preparation.
Starting process
Perform
visual
inspection
(may
require specialized equipment) of large-
Much
as
with
dry-out,
damage,
pipe
guide
This by no means indicates that that
The commissioning team will need to
piping section is dry, it only indicates that
decide whether a displacement or dilution/
3. Confirmation
dry media is available throughout the
mixing method will be used for the purge.
procedure: Often, cool-down of the LNG
section or system to complete the dry-out
procedure.
movement before the start of the test. .
of
final
cool-down
In the former, the purging gas is
transfer system is performed with an
introduced to remove the existing gas
LNG carrier connected to the unloading
bore piping to verify that no stagnant
Once the TDP is reached, the main
without mixing both gases. Although
system.
water is found. It is important to start the
vent point(s) is closed and a drying flow is
some mixing cannot be avoided, with the
difficult to test the cool-down procedure
dry-out with as little water as possible in
established to piping laterals, equipment,
use of lower pressures and proper exit
before the carrier arrives. On the other
the system as this may greatly extend the
instrument taps, etc. through various
points it can be minimized.
hand, if vaporized liquid nitrogen is to be
time required to achieve dry-out. Pay
ambient vent locations.
In this scenario it is very
The quantity of purge gas needed is
used to cool down the LNG transfer
special attention to dead legs and low
As TDP is reached at each of these
therefore about equal to the quantity of
system prior to introducing LNG then
points in the system as water is likely to
locations the vent is closed such that the dry
gas to be displaced. The latter method is
pre-cool-down testing can take place.
accumulate at these points.
media is allowed to sit for a while i.e., “soak.”
used when the piping limitations force
This will be particularly useful if there
Field confirm that the identified dew
After a pre-determined period of time,
you to pressurize and depressurize the
are unique aspects to the cool-down path
point sample points are readily accessible
the dew point is checked again at these
system to remove the gas to be purged.
chosen or peculiarities with the location
and, if not, viable alternatives are identified.
various test points to confirm that the TDP
Ensure an adequate number of
has been maintained in the piping.
of the cool-down equipment with respect
Pre-cool-down test
to the LNG transfer system. Does one
quality dew point meters are available
If the testing shows dew point has not
For example, when purging LNG tanks,
wait until a ship loaded with high-value
during dry-out. They should be portable
remained at the TDP or below, then water
an effective way to proceed would be to
cargo is sitting at the berth before
with back-lit readouts and rated for
vapor has been absorbed into the drying
introduce the purge gas via the bottom
confirming that the piping can be
temperatures and pressures of the gas
media.
fill line at low pressures. This would
properly cooled to commence unloading?
slowly displace the total volume of air in
Testing of the balance of plant may also
the tank with little mixing.
be beneficial if vaporized liquid nitrogen
samples expected. Ease of use and rapid
The effected sub-system should be
response time are critical for large
swept again and re-tested after soaking.
system dry-outs with multiple dew point
Once the dew point testing indicates the
If there is to be a pre-cool-down test of
sample points. If dry natural gas is to be
pipe subsection has remained dry, the
any portion of the facility, the purge can
used for dry-out, the instruments must
sub-system can be isolated until purge or
be deferred until then as the test will also
Why cool-down?
also have proper electrical classification.
cool-down commences.
purge the system piping.
Unless specifically designed for such a
is used in the final cool-down.
Dry media delivery equipment should
If after multiple soaks, the piping
A pre-cool-down test can help provide
condition, when a small flow of LNG at -
be thoroughly tested to confirm that it is
section fails to maintain the TDP, it can be
assurance that ensuing cool-down and
260°F [-160°C] flows into a large
capable of guaranteeing the desired flow
assumed that there is standing water in
start-up
diameter pipe that is at ambient
at the required maximum dew point for
the system and further action should be
smoothly.
extended periods of time. If the facility’s
taken to resolve this.
procedures
will
advance
temperature, such as a 36" LNG transfer
It requires additional costs and adds to
line, the bottom of the line rapidly cools
during
the schedule during the commissioning/
due to the heat transfer from the LNG,
used, it is important that the system is
commissioning require detailed procedures
start-up phases, however its benefits
while the top of the pipe stays relatively
fully commissioned and designed to
and accurate record keeping to confirm the
typically far outweigh any negatives.
warm for some time.
operate at continuous, high capacity for
entire cryogenic piping system is properly
The test involves cooling some or all of
Stainless steel contracts at a rate of
the duration of the entire facility dry-out.
dried and that “wet” media has not been
the cryogenic piping to near operating
about 3" per 100 feet [125 mm per 50m].
pushed into previously dried sections.
temperatures
instrument air compressors are to be
Many of these steps should be taken
Dry-out
activities
the
Such contraction results in the pipe
objectives. The objectives typically are
bowing upwards (the bottom of the pipe
significantly affect the remainder of the
categorized in three areas:
shorter than the top of the pipe).
schedule delays during initial and
commissioning activities and subsequent
1. Confirmation of dry-out effectiveness:
Depending on the pipe support/restraint
subsequent commissioning activities.
operations.
By cooling the cryogenic piping system to
system, substantial stresses can be
temperatures well below freezing, such as -
placed on the system or, if not restrained
vertically, substantial upward movement.
into consideration during the design of
An inadequately dried system can
the facility as this may reduce costs and
depending
on
Preferred cryogenic
dry-out procedure
Purge
40°C/F,
Assuming that LNG or LNG vapor is to be
particularly those with valve trunnions,
Although some large bore piping
Dry-out of cryogenic piping is typically
used for piping system cool-down, the piping
can be stroked once cold to confirm that the
systems, such as the deck piping on many
considered complete when the Target Dew
systems need to be purged of air to avoid
valve is free to move, i.e., no ice formation.
LNG carriers are designed for the “trickle
Point (TDP) of -40°C/°F is reached.
developing flammable concentrations.
2. Confirmation of pipe movement: In
cool-down” approach, the piping systems
the
valves
in
the
system,
Although there exists a variety of dry-out
Nitrogen gas is the preferred medium
some cases pipe movement is predictable
installed at LNG facilities typically are
approaches, experience suggests that the
for LNG terminal purging as carbon
and not subject to concern. However, in
not.
“Sweep and Soak” approach provides the
dioxide gas, the other predominant purge
other cases the movement of piping
24
•
LNG journal
• The World’s Leading LNG journal
Unless specifically designed for trickle
Reprinted with permission from LNG Journal.
FACILITY COOL-DOWN
cooling with LNG, large-bore LNG piping
There is no “one-size-fits-all” technique
berthed at the facility for an extended
installed with spring straps, it is very
needs to be cooled with a cryogenic vapor
for cooling down LNG piping. There are
period of time the cool-down process is
unlikely that all the detectors installed
flow prior to the introduction of LNG to
three main sources for cool-down vapor and
susceptible to interruptions in the case of
will provide accurate readings and once
minimize pipe stresses.
the suitability of each source is dependent
bad sea conditions.
insulation has been installed it becomes
Additionally, LNG is “sneaky fast,” i.e.,
on the facility and the circumstances
3. Vaporized Liquid Nitrogen (LIN): The
costly to replace the detectors.
once introduced into “warm” piping,
surrounding cool-down and commissioning.
most likely method of getting LIN into
Therefore, although installing a large
because of its low viscosity and high
The three main sources are:
the cryogenic piping would be via trucks.
number of temperature detectors on the
differential temperature with the base
1. Vapor
tank(s):
Since the trucks are generally mobile
piping marginally increases construction
metal, LNG can move very quickly
Depending on the piping design features,
there is an advantage in terms of
costs, the improved indication of cool-down
throughout the piping system riding on a
cold vapor can be sourced from LNG tanks
accessibility to favorable injection points.
status can actually result in savings.
vapor blanket as it vaporizes.
during the tank cool-down or from tanks
Of the three sources discussed, the
from
the
LNG
method
provides
the
coldest
It
is
important
to
note
that
This means that LNG can reach areas of
with existing liquid levels in the case of an
LIN
the piping system long before volumetric
expansion facility cool-down. In either
injection temperature i.e., -275°F. This
using
calculations or even elevation would suggest.
case, a large volume of gas will be available
temperature can also be controlled to be
installation methods may accumulate
temperature detectors installed on piping
spring
straps
or
similar
differential
for piping cool-down. A significant fraction
cooler or warmer using the vaporizer
some ice between the device and the
temperature the lower the likelihood that
of these volumes can also be recovered if
installed on the truck.
piping during contraction and expansion.
a cold vapor front will flow in advance of
pipeline compressors are installed and
Using LIN also provides an advantage
The method of installation should ensure
the LNG helping pre-cool the piping.
have already been commissioned in the
from the standpoint of venting during
that there is always a dry, continuous
The
larger
the
collapses
facility. One of the drawbacks of this source
cool-down. With this advantage, cool-
contact between the pipeline and metal
underneath the LNG there can be rapid
of vapor is the relatively low pressure (if
down of deadlegs in the system becomes
skin temperature detectors to minimize
bowing of the piping due to the large
boil-off gas compressors are not used) and
less of a problem.
inaccurate temperature readings.
temperature differential between the
the instability of the temperature of the
However, there are some drawbacks to
bottom and top of the pipe.
As
the
vapor
blanket
vapor. Lower pressures in the piping
the use of LIN for cool-down. The major
Procedures
to
reduce residence time of the gas and
drawback is the logistics of utilizing LIN
LNG facility commissioning activities
temperatures that are close to operating
consequently larger volumes are required
trucks.
should not be attempted without properly
temperatures
the
to cool down the piping. In the case where
For example, for a world-scale LNG
potential of pipe bowing by reducing the
the cold vapor is sourced from an LNG
import terminal scores of trucks may be
Cool-down and purging procedures are
top-to-bottom differential temperature,
tank that is itself being cooled down, the
required. The facility would also need to
explicitly mandated by section 14 of
while collapsing the vapor blanket more
initial erratic behavior of the vapor space
have sufficient real estate around the
NFPA 59A (2006 ed.) and to a lesser
quickly thereby promoting a cold vapor
in the tank will greatly affect the
injection point(s) for the pumper/vaporizer
extent by section 17 of EN-1473.
front moving down the piping as the
effectiveness of the vapor as a cool-down
truck to set up.
piping is inventoried with LNG.
medium. In the other case where the cold
Cooling
the
LNG
helps
piping
minimize
Procedures should be finalized early
If nitrogen cooling is contemplated,
and/or
i.e., several weeks before cool-down is
vapor is sourced from an idle tank with an
motor
operating
scheduled to begin. The procedures
Cool-down criteria
established liquid level, the vapor may not
conditions must be considered due to the
should be written in a format that can be
As stated before, the general rule is that
be cold enough to get all the facility piping
higher molecular weight of nitrogen.
easily modified during the process. The
cryogenic liquid piping of a certain size
to the target temperature.
and larger be cooled down using cold
2. Vapor from an LNG carrier:
LNG
chosen, the cool-down flow may be “once-
information should include:
vapor prior to the introduction of LNG.
carriers can supply cold vapor via boil-off
through” or “recirculated”. LNG vapors,
A pre-start valve checklist which indicates
Another general rule is that cool-down
gas or vaporized LNG. A full carrier will
by themselves, rarely provide adequate
valve positions just before cool-down begins
is considered complete when all piping is
have or be able to generate a large enough
cooling to achieve total cool-down.
cooled to or below a pre-determined
volume of vapor to cool a facility. The
Consideration needs to be given to
Other pre-start activities. For example,
temperature. Therefore, two questions
carrier will be directly connected to the
methods to further desuperheat these
confirm inventories of cool-down media,
need to be answered as preparations are
LNG transfer system hence the longest and
flows such that there is ample cooling
confirm blinds have been removed, etc.
made for cool-down:
largest piping system would be cooled first
driving force.
An instrument operability checklist
1) What pipe size should cool-down in
and thoroughly. One strategy that can be
Often, if so designed, vapor return
used by operators to determine the
adopted would be to cool the transfer
blowers or BOG compressors can be used
accuracy or functionality ofinstruments
2) What is the target temperature?
system and the LNG storage tanks then
to provide a re-circulating capability of
especially control valve and temperature
The answer to these questions lies in the
use the vapor from the tanks to cool-down
the cool-down vapors, taking into account
detectors/monitors,
design of the terminal. What did the
over the remaining piping systems as
the heat of compression.
A PSV checklist to confirm that PSVs
engineer set as the basis for various
previously described. A significant fraction
This may also make the use of LIN
stress calculations?
of the vapors used in this method can be
more attractive as the full cooling energy
Details of the facility’s car seal
program by clearly identifying steps
this manner be limited to? and,
capacities
written and reviewed procedures.
Additionally, regardless of the medium
cool-down procedure and the appended
and a valve isolation philosophy,
have been set up for service,
Unfortunately, far too often it is found
recovered if pipeline compressors are
from the LIN can be used if the LIN is
that the engineer(s) did not specifically
available. An issue that should be
injected for desuperheating.
address these cool-down criteria in their
considered for this method is the pressure of
analysis. Combine this with the fact that
the vapor flow through the piping system.
Monitoring
all too often the “How large?” and “How
Usually, vapor from a carrier is available at
Accurate temperature monitoring is
moving data (direction as well as length),
cold?” questions are asked very late in the
low pressures hence the cooling process
important in conducting a smooth cool-
Sketches
planning process confusion is created.
would be inefficient as a greater volume
down. It is prudent to be liberal with the
installed as well as marked up P&IDs for
where car seals are to be broken ,
A list of cryogenic piping supports (“cold
shoes”) with the corresponding expected
of
temporary
piping
Unless other design specifications
would be needed to cool segments of piping.
amount of surface mounted (bottom and
different stages in the procedure,
exist, practical experience suggests all
Heat leakage into the vapor via the un-
top) temperature detectors installed on
Narratives
LNG piping 8 inches [200 mm] and above
insulated LNG unloading arms would also
large diameter piping.
(operators, cool-down team) understand
should be cooled down to -200°F [-130°C]
have to be accounted for. Additionally, since
Regardless of the installation method
the ultimate goal each section of the
with cold vapor before introducing LNG.
this method will require that the carrier be
i.e., whether welded to the pipe or
procedure is meant to accomplish, and
Reprinted with permission from LNG Journal.
LNG journal
•
that
help
February 2009
the
•
user
25
FACILITY COOL-DOWN
instructions
Finally it is imperative that all plant
Conclusion
up is based on well planned and executed
The procedures
operations personnel involved in the
There are a number of ways to commission
programs. In the case of commissioning
commissioning
the
and cool down LNG facilities. This paper
and final cool-down, adequate preparation
statements about potential hazards/
procedures created. This will reduce the
has identified some key considerations that
and planning should begin as early as the
mistakes applicable to each section of the
chances
are prudent to take into account during
design phase of the project.
procedure.
commissioning.
this process. Successful LNG facility start-
Osifo Akhuemonkhan and Roberto
Ruiperez Vara work for CH•IV
International, a major player
in LNG terminal projects.
CH•IV is a joint venture
between MPR Associates, Inc.
of Alexandria, Virginia, USA,
and CH•IV Corp. of Hanover,
Maryland.
MPR, founded in 1964,
specializes in technical
services for the development,
design, construction and
operation of power facilities
and equipment for energy,
industrial, and government
clients. CH•IV Corp., founded
in 1991 had been providing
LNG engineering and
consulting services to a wide
base of clients ranging from
international LNG trading to
LNG vehicle fleets until the
formation of CH•IV
International. CH•IV
International builds on the
“Owner’s Engineer” model
applied by MPR in the power
industry and transfers it to
the LNG industry. The firm’s
current LNG activities include
providing the front-end
engineering and design for
six North American projects
and one Central America LNG
import venture. CH•IV is also
currently acting as the
Regulatory Engineer for the
State of Connecticut and LNG
Technical Advisor for the
Government of Jamaica. The
firm also successfully
supported the permitting
process of three new import
terminals, including
Cameron LNG in Louisiana.
Among other projects, CH•IV
was very actively involved in
supporting the reactivation
of the US LNG import terminal
at Cove Point, Maryland.
CH•IV has also provided
FEEDs for the US import
projects at Downeast,
Sparrows Point and Oregon
LNG; all three are well into the
FERC permitting process.
In Asia, CH•IV worked for
India’s Petronet on the Dahej
LNG terminal expansion and
for World Energy Corp on a
planned LNG liquefaction
plant in Sulawesi, Indonesia.
Detailed
step-by-step
(with contingencies).
should
also
include
cautionary
of
be
trained
human
error
on
during
References
American
Gas
Association
(AGA),
Purging Principles and
Practices (3rd edition,
2001)
26
•
LNG journal
• The World’s Leading LNG journal
Reprinted with permission from LNG Journal.