12” & 4.5” Pipeline End Termination (PLET)



PROJECT TITLE: Liwan Deepwater Project

CLIENT: Husky Oil China



YEAR: 2014

VESSEL: Pipe Lay Barge (PLB) Lewek Centurion

Lewek Centurion is a self-propelled DP2 S-lay pipeline installation vessel, The vessel measures 146.5m long by 30m wide (35m wide included the external thrusters), with mean operating draft of 7.8 m. The pipe lay ramp is located on the center of the barge and runs the entire length of the barge.

The vessel is equipped with one pipe transfer crane and one shipboard crane. The pipe transfer crane has a maximum capacity of 36MT at 30m radius, and the shipboard crane has a maximum capacity of 20MT at 25m knuckle boom. The main crane is a 300 MT Kenz crane at 15-16m radius.

LCE is also equipped with 300mT A-Frame and retractable Hang off Platform at port side with 300mT capacity at maximum retraction.

All of the vessel accommodation is located above the main deck, and is fully air conditioned with a mess hall and recreational facilities. A helideck is located over the bow superstructure and is capable of accommodating an S61 helicopter.


The scope of work for the PLET installation using pipelay installation vessel Lewek Centurion is described below:

  • Recover the pipeline to surface using 300mT A-Frame and cross haul to Main crane
  • Hang-off pipe in Hang-Off Platform
  • Cut-off the laydown head and prepare pipe end for welding
  • Transfer the PLET from the supply vessel to LCE, upend the PLET and position on to PLET support frame
  • Align PLET piping with pipeline and perform tie-in weld, NDT and Field Joint Coating
  • Deploy pipeline and PLET to seabed with crane and cross haul to A&R wire.
  • Perform PLET as built survey

PLET installation is for empty condition. Flooded condition is considered as a contingency plan.


I was on board LCE to install both 12” & 4.5” PLET


EMAS-AMC was subcontracted by Saipem to perform the installation of pipelines as part of Liwan 3-1 Area Facilities Development Project. The works involved installation of two (2) pipelines including its pipeline end terminals (PLET’s), four (4) in total, and lifting support of two (2) spools which will be installed offshore in South China Sea, approx. 300 km south from Hong Kong in a water depth range from 1100 to approx. 1400 meter. EMAS-AMC mobilized its pipelay vessel, the Lewek Centurion, end of March 2014 in Singapore for an arrival date of 28th April 2014 at latest in Shekou, China, for inward clearances and pipe load out. The installation activities were estimated to last approximately two (2) months.

PLET General Data

The PLET main components are piping, valves and its protecting procedure, the hub and its support, the mudmat and the yoke. 

12” PLET Data

ITEM 12” Pipeline
PLET 7 (P7) PLET 8 (P8)
Length Overall (LOA) 11.2 m
Height, Mudmat folded 3.33
Height, Mudmat open 3.13m 3.13
Width, Mudmat folded 3.0m
Width, Mudmat Open 8.194m
Nominal Pipe Size 12 inches
Pipe Grade API 5L X-65
Pipe material Carbon Steel 316L CRA –Clad Lined Carbon Steel
Weight, in Air 36.3 mT 36.5 mT
Weight, in Water 30.8 mT 30.5 mT

4.5” PLET Data

ITEM 4.5” Pipeline
PLET 6 (P6) PLET 9 (P9)
Length Overall (LOA) 7.89 m
Overal Height 2.25 m 2.15
Overall Width 3.0m
Nominal Pipe Size 4.5 inches
Pipe Grade API 5L X-65
Pipe material Carbon Steel
Weight, in Air 7.5mT 7.7mT
Weight, in Water 6.5mT 6.6mT

PLET Installation Target and Installation Tolerance

The target coordinate and tolerance for the PLET installation is provided in the following table:

ITEM Position Tolerance
EAST NORTH Heading Lateral Longitudinal Heading
PLET 6 337748.35 2205914.48 206.5 o ±3 m ±5 m ±2.5 o
PLET 7 337755.43 2205895.97 209.1 o
PLET 8 351846.97 2217132.30 168.5 o
PLET 9 351829.87 2217116.60 168.4 o ±2 m ±3 m




The PLET was fabricated in China yard


PLET Support Frame Stabbing Guide

The PLET Support frame was installed on Hang off platform. The main purpose is as a bumper and horizontal support of the PLET while upend and hold by crane prior tie-in to the pipeline.

The support frame was equipped with hydraulic jack on top of the frame to adjust the angle of the PLET or adjust the alignment prior install the external clamp. The hydraulic jack had a max. Stroke length of 700mm with 8.2mT and 6.2mT push pull capacity respectively. This main function of this hydraulic jack is to push forward the PLET to ensure the cone insert the stabbing frame.

In order to ensure that PLET was aligned with the pipeline below, HOP was also provided with a stabbing guide. The stabbing guide can be adjusted to meet the required installation angle of the pipeline on HOP.

This stabbing guide vertical angle can be adjusted from range 0 – 4 deg. by changing pin location on the guide.

Buoyancy Modules

Buoyancy module was required to compensate the weight of the PLET during lowering it to seabed. The net buoyancy required to install the PLET is summarize in below table.

Item Net Buoyancy (mT)
12” PLET 27
4.5” PLET 5.5

Hang Off Platform (HOP) & Clamp

The main function of the Hang off Platform was to carry out full catenary of the pipeline once it is recovered in J-configuration with Max. Load capacity is 300mT.

The HOP came with a clamp for closing and locking the pipeline via hang off collar clamp. The Hang off collar clamp capacity is max. 300mT.

Shim plate was installed on top of hang-off collar to adjust the pipeline angle requirements.

External Line-Up Clamp

Subcontractor designed and fabricated external line up clamp to align pipeline and PLET pup piece prior welding.

Collar Protector

Subcontractor has been design and fabricated collar protector to protect pipe collar during abandon the pipeline in S-Lay mode. This protector was removed once the pipeline rise up on the surface and collar protector above the HOP.

PLET Upending Frame

PLET was transferred from Contractor supply vessel to LCE and landed on PLET upending Frame. PLET upending frame was installed on top of firing line of LCE Deck.

PLET mudmat opening, laydown rigging installation, hold back rigging installation and Buoyancy rigging installation to the Yoke was done when PLET sitting on the upending frame. Cutting of the pup piece for P6, P7 and P9 was also be done on this stage. Due to height of upending frame is about 4m above the top of the firing line, scaffolding was required as this was considered as a working at height which required full body harness for those people involved.


Pipe Cutting and Bevelling Machine

Prior to performing the cutting of the pipeline pup piece and PLET pup piece, project engineer and welding foreman on board the LCE confirmed the cut length on the pup piece. Cutting & Bevelling tool type

Item Cutting Type
P6 Hot Cutting
P7 Hot Cutting
P8 Cold Cutting
P9 Hot Cutting


Welding was performed in accordance with Pipeline Welding Procedure Specification

Subcontractor performed welding for carbon steel material (P7) and CONTRACTOR performed welding on CRA Carbon Steel (P8)

Weld Inspection

The tie-in weld was inspected with X-Ray for the CRA Pipe conducted by CONTRACTOR and AUT was used by SUBCONTRACTOR for Carbon Steel Pipe.

Field Joint Coating

After completion of the tie-in weld and NDT, the field joint coating was applied. SUBCONTRACTOR was responsible to commence FJC for Carbon Steel material (P6, P7 & P9) and CONTRACTOR performed FJC for CRA Pipe (P8).



PLET Installation covered following activities:

  1. LCE Preparation
  2. PLET Transfer and Preparation
  3. Pipeline Recovery
  4. Removal of Laydown head
  5. PLET Upending
  6. PLET Tie-In
  7. PLET Deployment

Initial Status Prior to Carrying Out Work

  • Identified specific work that has to be completed ahead of each task
  • Prepared a specific task plan for each major activity
  • Stage 2 HIRA has been conducted and approved
  • Stage 3 Toolbox talk has been conducted with all personnel involved in the operation

Lewek Centurion (LCE) Preparation

Step by step LCE preparation is outlined in table below.

  • HIRA  stage  2 was  read  and  understood  by  all  personnel involved in this operation. Carried out tool box talk (HIRA stage 3)
  • Ensured that PTW (with specific JHA) has been issued and signed off,
  • Cleared area on deck to receive the PLET from cargo barge/supply vessel (upending support frame)
  • The Welding/NDT/FJC Spread required performing the tie-in of the PLET and pipe alignment were brought to the hang off platform area and checked/tested functionally.
  • Checked that all PLET deployment rigging and Buoyancy module rigging installed and ensured that the arrangement as per drawing

PLET Transfer and Preparation

Step by step PLET transfer on to LCE is outlined in table below.

  • Brought the supply vessel alongside and secure mooring line to LCE
  • Transferred Riggers and Project Engineer from LCE to PLET supply vessel
  • Project engineer verified / re-confirmed the “as-left” status of the PLET from SIT yard. PE signed off checklist
  • Project Engineer visually checked that all ball valve are in closed position
  • Rigger inspected lift rigging to ensure no snag points or loose connection prior to lift and transfer PLET to LCE.
    Note: Lifting rigging was pre-installed by CONTRACTOR
  • Removed all sea fastening.
    Note: CONTRACTOR prepared sea fastening which did not need cutting tool to remove Seafastening.
  • Swung Main Block on top of PLET and lowered down the Hook
  • Connected the lifting rigging to LCE 300mT Crane Main Block. Ensured tag line on each corner of the PLET installed.
  • Lifted up PLET off the supply vessel deck and swung to top of PLET upending frame on top of firing line
  • Lowered PLET on to the upending frame.
  • Released PLET lifting up rigging from PLET lifting point.
    Note: Built up scaffolding to reach PLET for preparation work on upending frame
    : Preparatory work on PLET was considered working at height therefore, safety precaution need to be addressed prior start up the job.
  • Once rigging released, boom up and slew back to Supply vessel to return the rigging.
  • Ensured that PLET mudmat opened and secured back the lock pin
    Note: Ensured the area clear prior open PLET mudmat and used soft sling to control mudmat open up.
  • Cut-off and continued with pipe end preparation the pup piece on LCE once confirmation was received on distance required.
    Note: PE/FE confirmed the length of PLET pup piece to be cut off. No cutting was performed on P8 Pup piece
  • Once the pup piece bevelling completed, commenced NDT (MPI and UT Lamination Check).
  • Once completed, a protection cover over the pipe end was placed.
  • Installed PLET Lifting Rigging, PLET Tilt Rigging, Holding Back Rigging and Buoyancy Rigging to the PLET. 

Pipeline Recovery

When all PLET preparation is completed, the pipe recovery commenced. It was important to check before starting the pipeline recovery operation; ROV shall carry out the visual inspection along the pipeline axis and ensure that pipeline is clear from obstruction.

  • Checked with Pre-Pipeline recovery checklist that all recovery preparation tasks has completed.
  • Ensured that the Hang-off clamp has been installed including shim plate on the HOP.
    For 12” PLET required 3 deg departure angle. For 4.5” PLET required 2 deg departure angle.
  • Deployed ROV to temporary laydown head. Inspected recovery rigging to ensure no foul up of shackle, sling and flotation.
  • ROV visually inspected laydown head and hang off collar. No anomalies reported.
  • Prepared the A&R Wire including Rigging and ROV Hook.
  • Refer to Appendix 2 – 12” & 4.5” Recovery Rigging Arrangement for details.
  • Position the vessel A-Frame above the laydown head and lowering the A&R Wire
  • ROV to connect the recovery rigging to the ROV Hook
  • Once Recovery rigging connected to the ROV Hook, vessel commenced moving and keeping  the A&R wire slack. Completed vessel move where standoff distance from laydown head to the A-Frame
  • Following the recovery table, was brought to surface. The A&R centreline axis remained in the plane of the catenary / pipeline route.
  • ROV monitored TDP and proximity of pipeline to the existing facilities.
  • During ascent, A&R Operator monitored the weight of the pipe. If tension appears to be deviated from recovery table tension. Stop operation. Inform PE/FE and OM for investigation.
  • The ROV monitored the TDP during ascent
  • A&R brought the laydown head to the surface. Ensured that vessel Hang Off Platform centreline is in the axis with the pipe route. A&R Operator monitored the load closely.
  • Once the Triplate about 1m above the HOP level, held the A&R.
  • Slewed main crane with rigging to HOP level and connected transfer rigging on the Triplate to the shackle on Crane
  • Slowly hooked up the Crane until load transferred from A&R to the Main Crane.
  • Once the pipeline catenary taken by Main Hook, released A&R wire from the recovery rigging.
  • Crane brought in the pipeline in to the Toilet Sheet.
  • Rigger removed Collar protector from the pipeline.
  • Once vessel was all stop, Crane Operator lowered the pipeline in to the hang-off clamp. The hang off clamp (toilet sheet) is slightly higher above the HOP.
  • Prepared the hang off clamp (toilet sheet) stopper. Once the pipeline inside the hang of clamp, rigger shall close the stopper and lock.
    Note: Unauthorized personnel shall not be standing on the HOP during this operation.
  • Once the pin inserted, Main Hook slowly lowered the pipeline to sit on the hang off clamp (toilet sheet).
    Note: Crane wire was slack and did not disconnected from the laydown head.
    : Hang off clamp (toilet sheet) is provided with the shim plate to meet Catenary departure angle as                       
    required in the analysis.

Removal of Laydown Head

  • Reconfirmed pup piece extension above the hang off collar once the pipeline is hanged off.
  • Marked a distance 50mm below the laydown head girth weld and prepared fitter for cutting off the laydown head.
  • Attached taglines on the laydown head. Ensured that the Crane wire load had minimum tension to ensure the Laydown head did not fall on to the deck.
  • Using cutting tool type provided, fitter cut pipe circumferentially. Cut was 50mm below laydown head girth weld.
    Note:   cutting   operation   to   commence   circumferentially   from outboard end.
  • Fitter commenced cutting through pipe wall.
  • Pipe Fitter continued to commence pipe end bevelling.
  • Once  pipe  end  bevelling  completed,  commenced  NDT  (MPI  and  UT Lamination check)
  • After pipe end preparation completed, protection cover was placed over the end of the pipe to prevent object from getting in to pipeline or damage the pipe end.
  • Once laydown head was removed from pipeline, it was transferred to LCE deck (Production Deck)

PLET Upending

Prior to commence PLET upending; ensured that the External Line clamp was installed on the pipeline.

  • Rechecked all rigging connected to the PLET and ensured that was no snagging of the rigging on PLET
  • Connected PLET Lifting Rigging to Main Block of 300mT Crane
  • Tensioned the rigging. Ensured the PLET is not lift up.
  • Slowly boomed up and lifted the PLET until the aft of the PLET off the upending support frame.
  • Continued lifted up until PLET in vertical position.
  • Lifted up the PLET off upending support frame completely.
  • Slowly swung the boom to the HOP.
  • Using tag line, controlled the PLET squarely in front of the Support Frame.
  • Once PLET squarely, slowly hit the bumper on support frame and boomed up slowly to give an angle on PLET while resting on the bumper guide.
    For 12” – Stabbing guide set up at 3 degree angle
    For 4.5” – Stabbing guide set up at 2 degree angle 
  • Hydraulic stroke on support frame started working and push forward the PLET to ensure the cone insert the stabbing frame.
  • At the same time, ensured that PLET pup piece stabbing in to external clamp.
  • Once the cone was inserted the stabbing frame and the pup piece was inserted in the external line up clamp, slowly lowered down the PLET
  • Main Block will held the PLET load.
    Note: Crane Operator to maintain PLET Position all the time
  • Tied-up holding back rigging to the padeye on top of firing line and tensioned it

PLET Tie-In Weld

  • Removed protection cover from pipeline end
  • External line up clamp was installed to the pipeline prior PLET upending commence.
  • External Line Up Clamp was installed on to pipeline. Ensured the bolts are loose in to the maximum to give more gap between pipe and the inner side of the clamp. The required gap for welding purpose was 350mm, however, this gap was adjustable by tighten the vertical bolts.
    Note: Design was made to ensure there sufficient gap between pipe and internal line up clamp
  • Hydraulic Jack on top of Support frame was adjusted to align the PLET Pup piece to meet the angle of the PLET while Main Block was  holding the weight.
  • Slowly lowered main block and inserted the PLET pup piece in to external line up clamp.
  • Welder and Welding Engineer checked the line-up of the two pipe ends.
  • Once approved, tightened the bolt and nut of the external line up clamp.
    Note: Crane Operator maintained holding the PLET
  •  Once External clamp tightened, commenced tie-in welding.
  • Upon  completion  of  the  root  and  hot  pass,  welding  clamp  was removed.
  • NDT the girth weld using AUT or X-Ray
  • Upon acceptance of the weld, appled field joint coating
  • Carried out holiday testing after completion of field joint coating

PLET Deployment 

  • Once PLET tie-in was completed, removed all equipment used previously from HOP to ensure work space is clear.
  • The crane slightly hooks up to the PLET and gave tension on the crane wire.
    Note: Ensure that the PLET is not lift up
  • Slightly moved forward the main hook to give a slack on PLET tilt rigging while maintaining the tension on the holding back rigging to ensure PLET position is maintain.
  • Deployed Knuckle Boom with rigger on the working basket to the PLET Yoke.
  • Released and secured the Tilt Rigging on the yoke
  • Once the PLET tilt rigging released, restored back the main crane to initial position and released tension from the holding back rigging by slack the chain block on top of the firing line.
  • Retracted in the Hydraulic Stroke on support frame in to a normal position.
  • Secured the Buoy rigging to the HOP
  • Riggers commenced preparation to remove hang off clamp (toilet sheet) stopper.
  • Rigger slid out toilet sheet stopper
  • Once cleared, took up tension on the crane wire
  • Checked pipe movement on hang off clamp (toilet sheet)
  • Increased tension until the pipe collar is off the hang off clamp (toilet sheet).
  • Swung crane away from hang off clamp (toilet sheet) slowly until approx. 1.5m away from the HOP. Crane radius about 14-15m
  • Once the PLET cleared from the hang off platform, set-up the A-Frame to maximum radius as shown in figure below.
  • Lowered the A&R hook until reach HOP deck.
  • Slowly lowered the PLET until transfer rigging at the HOP deck level. Boat hook grabbed the rigging and connect to A&R socket.
  • Once connected, slowly tensioned the A&R by spooling in the wire.
  • Slowly lowered the main block until all load transferred to A&R wire.
  • Once the all load transferred to A&R, lowered the PLET main hook on to HOP.
  • Released the main block by disconnecting rigging on HOP
  • Once the main block released, boom up the crane and slewed to port side to lift up the Buoyancy module.
  • Once the Buoy rigged-up and lifedt up by the crane main block, slewed the crane with Buoyancy module back to HOP.
  • Connected the Buoy rigging at the Buoyancy module to buoy rigging which was secured to HOP
  • Slewed the crane in front on PLET. Maintain the Buoy rigging connected to Yoke is slack.
  • Continued lowered down the PLET using A&R Wire and lowered the Buoy with main Hook.
  • Once PLET and Buoy fully immersed, continued to lower down the PLET and the Buoyancy module until PLET at 150m WD. Held the A&R wire.
  • ROV cut off Yoke secured rigging and release Main Hook from Buoyancy module.
  • Recovered crane main block and continued lowering the PLET
  • Once PLET landed on seabed, ROV cut of rigging and release A&R Wire.
  • A&R Operator recovered the A&R Wire.
  • ROV continued cut the rigging at the Yoke and release the buoyancy module to surface.
  • ROV followed cutting sequence to release Buoyancy Module 
  • Once buoyancy module on the surface, recovered it using one of Contractor Supply vessel and connected to recovery rigging

As Laid Survey

The as-laid survey of the PLET was performed after completion of the above operation. The following data regarding the PLET was collected:

  • ROV Visual Inspection of the PLET
  • HUB Position
  • Heading
  • Inclination of the PLET
  • Video Survey

Comments are closed.