VISAKH SPM REFINERY PROJECT

Transcription

1 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 :

2 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA TABLE OF CONTENTS 1. INTRODUCTION Objective DISCUSSION, CONCLUSION AND RECOMMENDATION Discussion Conclusion & Recommendation LONG TERM REMEDY General Remedial Action Piled Support for Pipeline... 5 ATTACHMENTS POST DREDGING SURVEY DATA REMEDIAL DETAILS SOIL BOREHOLES (BH-12/R13) DATA Pipeline Remedy Action.doc

3 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA 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. Pipeline Remedy Action.doc

4 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA 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 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. Pipeline Remedy Action.doc

5 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA 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. Pipeline Remedy Action.doc

6 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA 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 Pipeline Remedy Action.doc

7 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA 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 mm 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 Pipeline Remedy Action.doc

8 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL ACTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA POST DREDGING SURVEY DATA Pipeline Remedy Action.doc

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13 XYZ DATA EVERY 5m INTERVAL CHAINAGE EASTING NORTHING SEABED TOP OF PIPE

14 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL WORK OPTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA REMEDIAL OPTION DETAILS Pipeline Remedial Option - ITB.doc

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17 HPCL - VISAKH REFINERY SPM PROJECT LONG TERM REMEDIAL WORK OPTION PROPOSED FOR HPCL SUBSEA PIPELINE AT THE SAND TRAP AREA SOIL BOREHOLES (BH-12/R13) DATA Pipeline Remedial Option - ITB.doc

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