Document Number and Title - HPCLtenders.hpcl.co.in/tenders/tender_prog/TenderFiles/3710/Tender/SPM... · Point) and onshore section from LFP to ISPRL is 1.2 km. 1.1 Objective This

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






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.






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.






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.






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






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.






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


LONG TERM REMEDIAL WORK OPTION



Pipeline Remedial Option - ITB.doc

REMEDIAL OPTION DETAILS


LONG TERM REMEDIAL WORK OPTION



Pipeline Remedial Option - ITB.doc

SOIL BOREHOLES (BH-12/R13) DATA

Documents

Document Number and Title - HPCLtenders.hpcl.co.in/tenders/tender_prog/TenderFiles/3710/Tender/SPM... · Point) and onshore section from LFP to ISPRL is 1.2 km. 1.1 Objective This