drying of pipelines prior to commissioning — ceps a.s
DESCRIPTION
Drying of pipelines prior to commissioningTRANSCRIPT
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
1/6www.ceps-as.cz/en/products/drying-of-pipelines.html
english / česky
all / products / projects / about the company /
expert articles / contact
product
ON THIS PAGE
Reasons for drying of gas pipelines
after construction
Sources of water inside pipelines
Pipeline drying using deeply pre-
dried air
Vacuum drying
GO TO THE RELATED ITEMS
Products
Information about Company
Contacts
DOWNLOADS
Product catalogue
PDF for screen (464 kB)
Product catalogue
PDF for print (1746 kB)
DRYING OF PIPELINES PRIOR TO
COMMISSIONING
The water inside the operating pipeline is a source of many problems. The
company CEPS can perfectly dry it—drying of pipelines it performs prior to
putting it into operation by the extremely pre-dried air and also vacuum.
Reasons for drying of gas pipelines after construction
Water inside a gas pipeline in operation causes a number of problems.
In medium-pressure gas pipelines, house pressure regulators tend to freeze in
winter, which is very unpleasant both for the customer, who is suddenly deprived of
heating and for the gas company because emergency crews need to go out to the
field to repair this, which influences the economics of gas supplies.
In high-pressure pipelines, complications with natural gas hydrates tend to form in
addition to the problems with pressure regulating stations. The hydrates may clog
even a large diameter pipe. In addition to this operational trouble, water in high-
pressure pipelines primarily poses a direct risk of failure. Internal corrosion caused
by free water has been already detected in many pipelines.
However, it is only recently that a much more dangerous consequence of free water
has been proved in gas pipelines transporting normally treated natural gas—internal
stress corrosion cracking (SCC) which, in a relatively short time of operation (several
Drying of pipelines prior
to commissioning
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
2/6www.ceps-as.cz/en/products/drying-of-pipelines.html
years), may cause a complete failure of extensive stretches of the line. At the same
time there is no reliable method at present to detect the creation and beginnings of
SCC development on the inside of the pipe wall.
Sources of water inside pipelines
Water enters a pipeline before putting into operation usually due to lack of
discipline at work during construction. In some cases, the reason may be the
construction technology itself, for example where underground river crossings are
laid which requires that the pipe is flooded with water.
Hydrotests or stresstests are another stage of construction when water enters a pipe.
This is evident when the tests are carried out using water but we should not ignore
tightness-tests using air when water contained in air condenses in the pipe after the
air is compressed.
Although some of the water is removed from the pipeline when it is cleaned, a
significant proportion of water cannot be removed from the pipeline even when
repeatedly applying mechanical cleaning techniques using water-absorbing cleaning
pigs because the water adheres to the pipe walls due to capillary forces. This water
can only be removed by special drying techniques.
CEPS carries out pipe drying before commissioning, using both methods that are
currently used throughout the world—deeply pre-dried air and vacuum drying.
Both of these technologies can also be deployed for drying other pipelines facilities
(metering stations, interconnecting nodes, etc.) or even pieces of equipment
requiring a high level of dryness (chemical apparatuses, high-performance steam
turbines, etc.).
Generator of very dry air JUV 3600 allows to dry up to 3600 m³ of air per hour—
pipeline DN 1000 with a length of 10 to 15 km can be dried in one to two days
pipeline drying using
deeply pre-dried air
Pipeline drying using deeply pre-dried air
This technique is suitable for pipes made of steel and plastic materials, and also for
process equipment. At first step the air is dried to a temperature of water dew point
below −80 °C in a special unit based on a molecular sieve, and then blown into the
pipeline for being dried. The water, which is present in the line evaporates into the
pre-dried air, and in this air is carried to outside the pipeline.
CEPS has two big units available. Each unit has a drying capacity of one cubic metre
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
3/6www.ceps-as.cz/en/products/drying-of-pipelines.html
of air per second, i.e. 3,600 cu. m/hour. This is sufficient capacity to dry a pipeline
having a nominal diameter DN 1000 (40 in.) and a length of 10 to 15 km in one or two
days. In case of need (particularly to speed up the drying process) both units can be
connected in parallel. Both units are housed in containers and are transported on
off-road vehicles capable to manage the navigation throughout the difficult terrain,
and therefore can be transported over the construction strip (r.o.w).
The third one, smaller unit has a capacity of drying 650 cubic metre of air per hour
and is used for drying of low profile pipelines.
Very dry air generator JUV 650
The units’ operating pressure of 4 to 8 bar is strong enough to push porous cleaning
pigs through the pipe during the drying process, which helps to achieve the high rate
of drying. At forked/branched pipelines or those whose dimension changes
significantly, or in process equipment, i.e. wherever the porous elements cannot be
pushed through the equipment, the drying takes a proportionately longer time. The
drying of a complex pipeline node, after the hydrotest or stresstest water has been
simply released, would take several days.
Pipes are dried to the standard level of the temperature of water dew point in
the pipe of minus 20 °C. However, in case of need, particularly for process
equipment, up to minus 70 °C can be achieved.
vacuum drying Vacuum drying
Vacuum drying is based on a generally known physical phenomenon—as the
pressure drops, also the boiling point of liquids drops. At an absolute pressure of
about 2 kPa, water boils at the temperature of the soil that surrounds the pipe.
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
4/6www.ceps-as.cz/en/products/drying-of-pipelines.html
The drying process by this method should be very carefully followed because at too
high pumping speed of the out coming air, pipeline is not sufficient to complement
the evaporative heat of water supply through the wall of pipe, but instead the
evaporative heat is taken from the water inside the pipe, which causes its cooling.
This phenomenon consequently does not lead to the evaporation of water but water
inside pipe freezes. The pipeline then apparently acts as dry, but after putting into
operation ice gradually melts and the problems with water appears again. Therefore
it is necessary follow carefully process of drying, including control dead time. This
dwell time when pumping is stopped, which is repeated according to pipeline
diameter prevents water freezing. These dwell times the other hand significantly
prolong the drying time.
Vacuum drying is also suitable for a complicated internal piping
The vacuum drying is suitable particularly for branched steel pipes and pipeline
facilities. For pipes having a nominal diameter of more than DN 500 (20 in.), the
geometric stability of the pipes under deep vacuum always needs to be assessed.
This technique now cannot be employed with plastic pipes—application of method
for this purpose requires to perform the certification tests that are currently carried
out.
In comparison with drying based on deeply predried air supported by porous pigs
pushed through the pipe, vacuum drying is slower. However, where the porous
elements cannot be used, vacuum drying may even be faster for more complex
pipeline nodes.
CEPS operates several vacuum units, each one with the capacity of up to
200 cu. m/hour. In case of need, the units can work in parallel.
Vacuum drying is very appropriate for drying complexly shaped distribution network
pipes, because in addition to the drying itself, it also makes the first gas admittance
into the pipes much easier. The gas is flowing into vacuum and therefore there is no
risk of forming an explosive mixture in the pipe, and the pipe does not need to be
deaerated.
Both technologies of pipeline drying used by CEPS, meet the requirements of
TPG 702 13.
related products
Together with this product are usually
Cleaning and gauging
of pipelines
Stresstests and hydrotests
of high-pressure pipelines
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
5/6www.ceps-as.cz/en/products/drying-of-pipelines.html
provided the following products and
services
all products
High-pressure steel pipelines
rehabilitation after long-time
of operation
Decontamination of pipelines
transporting petroleum liquids
before repairs or shutdowns
Products and services
show all products and
services
related documents
More documents and other
information, see the section about
the company CEPS
all about company
ISO 9001:2008
ISO 14001:2004
OHSAS 18001:2007
ISO 3834-2:2005
About CEPS company
show everything about the
company CEPS
contact
If you have any questions, do not
hesitate to contact technical experts
and business persons of CEPS
Contact us
Ing. Aleš Brynych
executive director
phone +420 241 021 547
Ing. Bc. Aleš Crha
commercial director
and welding engineer
phone +420 241 021 549
Head office of CEPS a.s.
phone +420 241 021 511
fax +420 241 021 512
3/25/13 Drying of pipelines prior to commissioning — CEPS a.s.
6/6www.ceps-as.cz/en/products/drying-of-pipelines.html
e-mail [email protected]
all contacts and maps
© 2013 CEPS a.s. / RSS / Genera l terms and conditions CZ / Technica l speci fications CZ /
Contacts
back to top