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VISAKH SPM REFINERY PROJECT
LONG TERM REMEDIAL ACTION PROPOSED FOR
HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA
PREPARED FOR
HINDUSTAN PETROLEUM CORPORATION LIMITED
(HPCL)
INTECSEA PROJECT NO : 21534102
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
TABLE OF CONTENTS
1. INTRODUCTION............................................................................................................... 2
1.1 Objective ........................................................................................................................... 2
2. DISCUSSION, CONCLUSION AND RECOMMENDATION ...................................... 3
2.1 Discussion ......................................................................................................................... 3
2.2 Conclusion & Recommendation ....................................................................................... 3
3. LONG TERM REMEDY ................................................................................................... 5
3.1 General .............................................................................................................................. 5
3.2 Remedial Action – Piled Support for Pipeline .................................................................. 5
ATTACHMENTS
POST DREDGING SURVEY DATA
REMEDIAL DETAILS
SOIL BOREHOLES (BH-12/R13) DATA
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
1. INTRODUCTION
Hindustan Petroleum Corporation Limited – Visakh Refinery (HPCL-VR) is planning
to develop crude unloading facilities to handle a large crude parcel of size about
300,000 MT by VLCC Tankers to meet the crude requirement of their existing as well
as future crude processing requirements. HPCL-VR is presently receiving crude at
Offshore Tanker Terminal (OSTT) of Visakhapatnam Port Trust (VPT). The tanker
size at OSTT is limited by the available water depth of 19m, and can not receive
VLCC. HPCL-VR proposes to install Single Point Mooring (SPM) Terminal and
connected facilities off the coast of Visakhapatnam Port to receive and offload crude by
VLCC tankers.
HPCL-VR as part of this project, will install Single Point Mooring (SPM) terminal and
related facilities at the water depth of about 35m, at a distance of about 4.0 km from the
coast. Crude from SPM will be pumped and transported via 48 inch NB line pipe from
SPM to Crude Oil Storage Facility of Indian Strategic Petroleum Reserves LTD
(ISPRL) and also will be hooked up to the existing 36” crude oil pipeline to refinery.
The offshore section of the pipeline route is about 4.0 km from SPM to LFP (Land Fall
Point) and onshore section from LFP to ISPRL is 1.2 km.
1.1 Objective
This document presents the long term remedial action proposed for the 260m section of
the offshore pipeline route i.e. from Ch150 to Ch410 m wherein the seabed and
pipeline profile was noticed to have been changed from the as-built status due to sand
dredging activity by Visakhapatnam Port Trust (VPT) in the close vicinity of the 48”
HPCL pipeline route.
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
2. DISCUSSION, CONCLUSION AND RECOMMENDATION
2.1 Discussion
The current situation is due to dredging too close to the pipeline by the Dredger hence
removing the soil below the pipeline, allowing pipeline to be vertically displaced and
free spanning at few locations. It is understood that the dredging operation has been
carried out by Dredging Corporation of India on behalf of VPT using one Hopper
Suction Dredger. Some of the soil might have also been removed by the propellers of
the dredger.
Temporary measures were undertaken immediately to reduce the free spans which were
developed due to the removal of sand underneath the pipeline. There were several sand
bag supports placed in order to reduce the length of the free spans which occurred due
to dredging. Survey of the pipeline profile and the seabed profile was performed before
and after placement of the sandbag supports. The survey data had revealed important
changes in subsoil and pipeline levels with free spanning of pipeline at some locations
which are within the allowable limits.
The dredging in the sand trap area is the routine annual activity of VPT. Since 48”
crude pipeline is located in very close proximity of sand trap area, permanent solution
is considered necessity in order to avoid further increase in pipeline spans and stress
levels. A detailed feasibility study was performed to evaluate the possible remedial
action that will aim to permanently protect the pipeline from such dredging mishaps on
account of slippage of sand support from underneath of the pipeline. The following
action was identified as part of the study and the most feasible which is recommended
as the way forward for the long term remedial action to permanently protect the
pipeline. The remedial action is discussed in detail in Section 3.0 of this report:
Remedial Action – Piled Support for Pipeline
2.2 Conclusion & Recommendation
2.2.1 Conclusion
It is concluded that a long term remedial action is required due to the impact of sand
trap dredging works on the 48” subsea pipeline to ensure the pipeline is protected
during the entire operation life and the pipeline stresses & spans are always within the
allowable limits to maintain operability in a safe condition. VPT while discussions on
the subject indicated that movement of sand towards the sand trap shall also not get
unduly obstructed otherwise it may affect the port operation on long term basis.
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
2.2.2 Recommendation
The following action is recommended which needs to be implemented in consultation
with VPT/ CWPRS and IIT Chennai:
Remedial Action – introducing permanent piled supports for the pipeline at a
certain interval in the pipeline section of concern i.e. Ch150 to Ch410 m.
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
3. LONG TERM REMEDIAL ACTION
3.1 General
Following the sand trap dredging activity by DCI in the month of March 2010,
Leighton Contractors (India) Pvt. Ltd. had performed a survey and based on the review
of the survey data it is found that the subsoil and pipeline levels have been affected.
The bathymetric survey data and cross sections after the sand trap dredging are
presented in Appendix A.
As part of the short term remedial action, Leighton Contractors have undertaken the
following actions for quick support of the pipeline free span sections.
a) Conduct full video survey of 48” pipeline and surrounding sea bed, KP 200
through KP 320 (visibility permitting). Pipeline condition to be confirmed as
acceptable.
b) Provide four nos. of sand bag supports in the region where free spans were
found to be more than 20m.
c) Conduct full video survey of pipeline confirming (or not) adequate support
afforded pipeline at KP’s 210, 260 and 320.
INTECSEA have also performed the bottom roughness analysis of the section of the
pipeline in the sand trap area and the findings concluded that all existing spans along
the pipeline route from KP0.0 to KP0.51 are within the allowable span limits.
Equivalent stresses also do not exceed the pipeline allowable stresses limits.
It is noted that natural backfilling occurs from time to time that fills up the pipeline
free spans space and further covers the pipeline in relatively short terms. However,
considering the frequency of the dredging works (yearly basis) a long term remedy is
required and following is the selected remedial measure to be implemented as the
permanent solution.
3.2 Selected Remedial Action – Piled Support for Pipeline
The selected remedial action is a proposal to provide permanent steel supports for the
pipeline at regular intervals along the pipeline section in the proximity of sand trap
area. These steel pipeline supports are bolted to the two piles driven adjacent to the
pipeline. Please refer to the attachments for details of piles and support. The 48”
pipeline shall be supported by a plate connected to a beam which is further held by 2
piles driven into the seabed on either side of the HPCL pipeline. This arrangement will
always hold the pipeline in its vertical as well as horizontal alignment even if the
dredger removes sand below the pipeline. This also will have minimum restrictions to
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
sand movement towards the sand trap. In view of all above this action is considered
most appropriate.
Thus, the piled support for the 48” pipeline is recommended as this action provides an
effective solution to protection for the entire pipeline design life. This action also
ensures continuous movement of sand towards the sand trap area.
The piled support consists of a 12.7mm thick × 300mm wide plate supporting the 48”
pipeline. This plate shall be connected to a horizontal beam with stiffener plates which
will be on top of the pipeline with an acceptable clearance. The beam will be held by
means of bolted connections to 2 piles driven into the seabed adjacent to the pipeline
on both the sides of pipeline i.e. sand trap side and Dolphin Hill side. The piles to be
driven shall be 24” × 19.1mm thick structural steel.
Diagrammatic detail of the remedial action is presented in the attachment of this report.
The additional scope of this remedial work (Engineering, Procurement, Construction
and Installation – EPCI) shall be undertaken under a separate tender package which is
planned to be executed before the next dredging season of Feb 2011.
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL ACTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedy Action.doc
POST DREDGING SURVEY DATA
CHAINAGE EASTING NORTHING SEABED TOP OF PIPE
160 743543.73 1956377.33 6.20 4.69165 743546.52 1956373.18 6.34 4.83170 743549.30 1956369.03 6.47 4.97175 743552.08 1956364.87 6.65 5.13180 743554.85 1956360.70 6.81 5.30185 743557.62 1956356.54 6.92 5.42190 743560.29 1956352.52 7.04 5.54195 743563.16 1956348.22 7.13 5.62200 743565.93 1956344.05 7.21 5.71205 743568.70 1956339.89 7.30 5.79210 743571.32 1956335.96 7.38 5.88215 743574.24 1956331.57 7.55 6.03220 743577.01 1956327.41 7.72 6.19225 743579.78 1956323.24 7.93 6.39230 743582.55 1956319.08 8.14 6.61235 743585.32 1956314.92 8.36 6.82240 743588.09 1956310.76 8.59 7.05245 743590.87 1956306.59 8.80 7.26250 743593.64 1956802.44 8.96 7.46255 743596.43 1956298.29 9.18 7.66260 743599.22 1956294.14 9.35 7.83265 743602.01 1956289.99 10.27 7.99270 743604.80 1956285.84 11.18 8.18275 743607.59 1956281.69 10.48 8.23280 743610.38 1956277.54 9.78 8.28285 743613.17 1956273.39 11.01 8.25290 743615.96 1956269.24 12.24 8.24295 743618.74 1956265.11 11.27 8.11300 743621.53 1956260.96 10.29 7.98305 743624.32 1956256.81 10.07 7.85310 743627.11 1956252.66 9.84 7.73315 743629.90 1956248.51 9.68 7.64320 743632.69 1956244.37 9.52 7.56325 743635.48 1956240.22 9.21 7.47330 743638.27 1956236.07 8.90 7.40335 743641.06 1956231.92 8.95 7.29340 743643.85 1956227.77 9.01 7.18345 743646.64 1956223.62 8.84 7.07350 743649.43 1956219.47 8.67 6.96355 743652.23 1956215.31 8.46 6.85360 743655.02 1956211.16 8.23 6.78
XYZ DATA EVERY 5m INTERVAL
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL WORK OPTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedial Option - ITB.doc
REMEDIAL OPTION DETAILS
HPCL - VISAKH REFINERY SPM PROJECT
LONG TERM REMEDIAL WORK OPTION
PROPOSED FOR HPCL SUBSEA PIPELINE
AT THE SAND TRAP AREA
Pipeline Remedial Option - ITB.doc
SOIL BOREHOLES (BH-12/R13) DATA