1.
GENERAL
This specification defines the minimum technical and
operational requirements governing pipeline dewatering, drying and nitrogen
packing of the Export Pipeline System. This
specification is to be used in conjunction with the following documents:
•
Basis of Design 84506-60-00-2L-060
•
General Specification 84506-60-00-2L-000 - Definitions
and Specification Directory
•
General Specification 84506-60-00-2L-010 - Quality
Assurance / Quality Control
•
General Specification 84506-60-00-2L-020 – General
Offshore Specification
•
Cleaning Gauging and Hydrotesting Specification
(845-60-30-2L-390)
2. PROCEDURES – EXPORT PIPELINE SYSTEM
2.1 CONTRACTOR
shall supply all equipment, materials and manpower to successfully complete all
de-watering and drying operations and nitrogen packing of the pipeline to the
satisfaction of COMPANY.
2.2 CONTRACTOR
shall develop detailed pipeline pre-commissioning procedures for the pipeline
and submit for COMPANY approval 30 days prior to the commencement of
pre-commissioning activities. These procedures shall include as a minimum the
proposed equipment and operations for the following:
•
Dewatering pig train designed
arrangement
•
Disposal plan for fill water and
chemical additive certificates
•
Vacuum Drying
•
Introduction of inert gas
2.3
Instrument stand(s) shall be manned at
all times during pre-commissioning operations.
CONTRACTOR shall furnish communication equipment for use by CONTRACTOR
and COMPANY during pipeline pre-commissioning, where CONTRACTOR employs
personnel at different locations.
2.4 CONTRACTOR
shall meet the following pre-commissioning requirements for a dew point –10 OC
& nitrogen pack at +5 psi, although detailed acceptance criteria for each
pipeline, or pipeline section shall be agreed between COMPANY and CONTRACTOR
prior to start of pre-commissioning operations.
3. PIG DESIGN
3.1 The design of pipeline pigs for bulk
dewatering and drying the pipelines shall be the responsibility of the
CONTRACTOR. CONTRACTOR shall demonstrate
to the satisfaction of COMPANY the suitability of any pig design.
3.3 Pigs
used during pre-commissioning may be launched from and received in temporary
traps furnished and installed by CONTRACTOR for pipeline cleaning, gauging and
hydrotesting.
3.4 COMPANY
acceptance of any design or procedure will not absolve CONTRACTOR of his
responsibility to complete the work in as diligent and as timely a manner as is
practically possible.
3.5 Every
pig shall be permanently marked with a unique number that shall be clearly
visible in a photograph. The condition
of all pigs shall be recorded photographically prior to and following the
pigging operation.
3.6
If in COMPANY opinion de-watering pigs
have not adequately de-watered the pipeline, the dewatering operation shall be
repeated until results obtained are satisfactory to COMPANY.
3.7
Refer Cleaning Gauging and Hydrotesting
Specification (845-60-30-2L-390) page 8 paragraphs 4.7 & 4.8.
4. DEWATERING REQUIREMENTS
4.1 A flow meter of sufficient size and
accuracy shall be used to measure the quantity of drying
gel, water absorbent liquid, air or inert gas required to bulk dewater and dry
each pipeline, or pipeline section. CONTRACTOR detailed pre-commissioning
procedures shall include methods and equipment used to measure and monitor
pumping rates.
4.2 During
bulk de-watering of the pipeline, samples of water shall be taken from between
each pig batch for salt testing.
Acceptance of the first bulk de-watering operation shall be based on the
test results of the last fresh water batch.
The salt content in the last batch shall be less than 200 ppm. Should the salt content exceed 200 ppm,
CONTRACTOR shall re-swab the pipeline with additional fresh water batches.
4.3 CONTRACTOR
shall be responsible for proper dilution and remediation or disposal of any chemical
additives used during the pipeline hydrotest, subject to prior approval by both
COMPANY and AUTHORITIES.
5. DEWATERING PIG VELOCITY AND DRIVING PRESSURE
5.1 Dewatering
pigs shall be driven at a speed of between 0.3 meters/second and 0.7 m/sec for the
initial bulk de-watering run, and a speed of between 0.5 meters/second and 0.7 m/sec
for additional runs if required.
5.2 Driving
pressure shall be recorded on a COMPANY-approved recording pressure chart. Chart time shall correspond to actual time. Charts and other data relating to dewatering
operations shall be submitted to COMPANY at the completion of each run.
5.3 Pumps
shall be capable of driving pigs at the required speed and pressure range. Pressure, volume and temperature shall be
monitored and recorded at all times during the pigging operations.
5.4
Should any pig become stuck, operations
shall be shut down, the pig located and cut out of the pipeline and the
pipeline shall be repaired. Repaired
pipeline sections shall then be cleaned, regauged, re-hydrotested and
dewatered.
5.5
Refer Cleaning Gauging and Hydrotesting
Specification (845-60-30-2L-390) page 5 section 3 Pig Design.
6. VACUUM DRYING EQUIPMENT AND INSTRUMENTS
6.1 Dew
point, vacuum and temperature recorders, equipped with 24 hour recording
charts, shall be used to record time, dew point, vacuum and ambient temperature
during vacuum drying operations. Vacuum
recorders shall have an accuracy and repeatability of zero point one percent
(+/- 0.1%). Dew point and temperature
recorders shall be accurate to 0.1oC. Temperature effects on the dew point shall be
evaluated by a qualified person, and shall be taken into account in determining
the correct dew point.
6.2 Vacuum
drying shall be performed in accordance with COMPANY approved procedures and
schedules that shall reflect the required completion of individual pipeline
sections.
6.3 Vacuum-recording
instruments shall be tested and calibrated before pre-commissioning
begins. Vacuum recorders shall be
capable of measuring in increments of 10.0 kPa.
6.4 Dew
point and vacuum recorders and gauges shall be installed in parallel on a
manifold, with individual instrument valves and vents. CONTRACTOR shall provide to COMPANY
calibration certificates from an independent laboratory for the chart recorders
and gauges, showing they have been calibrated within sixty (60) days prior to
use.
6.5 Vacuum
pumps shall be connected to the system through a check valve and leakproof
block valve. Vacuum pumps shall be
easily separable from the system to be evacuated.
7. VACUUM DRYING
Vacuum pumps shall be equipped with a digital counter, that
shall be zeroed before starting. During
evacuation operations the counter reading and vacuum gauge reading shall be
recorded, with time of day, at 15 minute intervals. Mean pipeline temperature shall be recorded
at the beginning and end of commissioning and at least two (2) hour
intervals. Completed vacuum drying
charts shall be submitted to COMPANY on completion of pipeline commissioning.
7.1 Vacuum Drying
Vacuum drying of the pipelines shall require the effective
removal of the residual water to achieve an absolute level of moisture as
detailed in Section 2.4. Vacuum drying operations shall commence upon
completion of dewatering and vacuum shall be pulled from at least two points in
the pipeline system.
CONTRACTOR shall monitor the pipeline temperature during
drying adjacent to the vacuum plant to ensure that freezing does not occur due
to excessive vacuum drawdown. In the
event of freezing, the vacuum units shall be taken off-line until the freezing
has stopped. Hand held radiation
thermometers should be used to determine pipeline temperature.
The vacuum drying operation shall comprise the following
steps:
CONTRACTOR shall run the vacuum plant on the temporary
pipework down to a pressure of 1 mbara to ensure it is leak tight. When the temporary pipework is leak tight the
Gas Export Line shall be depressurized to 200 mbara, recorded at the pipeline
ends, and held until all major leaks have been repaired and the CONTRACTOR is
satisfied that any remaining leakage shall not affect the achievement of the
acceptance criteria.
The leakage rate shall be quantified for a specific
pressure. The leakage rate shall not
exceed 10% of the vacuum spread capacity at 1 mbara.
The pressure in the pipeline shall be gradually reduced.
During this phase the pressure shall be gradually reduced to
a pressure lower than the saturated vapor pressure. The vacuum shall be maintained until the Contractor and Operator are satisfied
that this phase is complete and that a pressure reading of 1 mbara or less
is consistently recorded.
The low-pressure air purge shall be carried out by allowing
dry airflow into the pipeline whilst simultaneously pulling vacuum at the
opposite end. The pressure shall be
allowed to rise above the saturation vapor pressure to a more efficient pumping
pressure (approximately 20 mbara). The
purge air at the purging pressure shall have an absolute level of moisture
which is lower than a vapor content of 0.8835 gm/m3. The purging shall continue until at least two
pipeline volumes at the purging pressure, have been passed through.
This phase shall be considered complete when consistent
internal dewpoint readings of ‑10oC or lower are achieved over a
period of time.
The pressure shall be drawn down to 1 mbara or less. The Contractor
shall then isolate the pipeline system and perform a soak test, holding the
pressure for 24 hours.
This phase shall be considered complete when either the
pressure remains at 1 mbara or the increase in pressure is demonstrated to be
caused by temperature variation or leakage quantified but not rectified during
the leak test. Evidence that the pressure
time plot, for reducing pressure from the air purge pressure of 15 mbara down
to 1 mbara, is significantly different from the original pressure time plot may
also be used to gain acceptance of the soak test.
The air in the pipelines shall be replaced with nitrogen
(purity greater than 99% nitrogen) to the positive pressure given in Section
2.4.
Nitrogen shall be introduced at one end of the pipeline,
with a dew point lower than ‑50oC, at a controlled rate to prevent
over compression and subsequent re-condensation of water. The rate and controlling pressure shall be
determined and approved by COMPANY prior to introduction of nitrogen. As the pressure increases in the pipelines
the nitrogen pack rate may increase.
The nitrogen dew point at the outlet end of the pipeline
shall be monitored. This phase shall be
considered complete when the nitrogen dew point is lower than -10oC at atmospheric pressure
and pipeline packed to final pressure.
7.3 Demobilization
Once the dewatering operation has been accepted, Contractor shall remove temporary pig
launchers and receivers as appropriate.
The Contractor
shall ensure that all consumables, temporary equipment and personnel are
removed from site in a timely manner.
The Contractor shall leave
the site in a condition as good or better than it was before mobilization
8. ACCEPTANCE CRITERIA
The dewatering phase shall be accepted on the following
basis:
•
All the dewatering pigs have traversed
the pipeline and that the last three pig’s sealing disc diameters remain
greater than the nominal pipe bore.
•
Relatively small volumes of water
precede the last two pigs.
•
Water preceding the final pig has a
salt content less than 200 ppm.
The vacuum drying shall be accepted on the following basis:
•
Pressure of 1 mbara is achieved
•
Air purge achieves a dewpoint of less
than -10oC
•
Drawdown following air purging
indicates the line is dry
•
Soak test indicates minimal pressure
rise
•
Nitrogen pack dewpoint indicates the
line has achieved specification
9. SUBMISSIONS BY THE CONTRACTOR
In addition to the requirements stated herein, CONTRACTOR
shall combine and submit to COMPANY all documents, records, charts and test
certificates in a detailed final report at the end of the job.
All
data to be submitted to COMPANY in both hard copy and electronic format.