edf-energy experience in the adoption of hdpe as the ...edf energy experience in the adoption of...

EDF-Energy Experience in theAdoption of HDPE as the Material ofChoice for Cooling Water Pipework.

David McKenzie, Fleet Lead Pressure Systems, Design Authority, EDF-Energy

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EDF Energy Experience in the Adoption of HDPE as the Material ofChoice for Cooling Water Pipework

Background

*EDF Energy is part of EDF Group*EDF Energy operates 8 Nuclear Power Stations in the UnitedKingdom.*The fleet consists of 7 Advanced Gas Cooled Reactors (AGR) and 1Pressurised Water Reactor (PWR) (Sizewell B).*The AGR's are cooled by C02 gas and are all twin Reactors witheach Reactor providing steam at 160 bar (2320 PSI) and 538degrees C (1000 F) to operate a 660MW Turbine.oThe nuclear stations are all sited on the coast and utilise sea wateras the final heat sink.*We have suffered extensively from corrosion in our cooling waterpipework systems at all stations

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Background

* Our first safety related installation was on one delivery line of the ESWsupply pipework and was designed in accordance with the principles ofASME B31.1 and installed under a category 2 Engineering Change (EC).

* The original pipework was designed to ASME III class 3 and was 750 mm(28") barrier coated carbon steel.

* This location was specifically selected to provide what we judged to be aa particularly onerous design where the arrangement would be subjectedto different loading mechanisms.

* The installed pipe was a 800mm o/d PE 100 SDR 11 to BS EN 12201.(16 barg @ 20 C for 50 years) based on a factor of safety of 1.25 againstits minimum required strength.

" We have a Technical Guidance document (TGN096) which provides thegeneric requirements for the use of HDPE within EDF Energy.

* We have a category 1 Engineering Change which justifies the change ofdesign code from ASME III Class 3 and to replace the existing barriercoated carbon steel pipework with HDPE.

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Sizewell B First ESW HDPE Installation

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TGN 096 WELDING/FABRICATION REQUIREMENTS

* Butt fusion welds in conjunction with stub flanges.* Fittings shall be injection moulded.* All butt fusion welds undertaken in the factory under a controlled environment.* Wherever practical weld beads are removed.* Weld beads are marked, visually inspected, given a bend back test and retained as

part of the lifetime records along with the printout from the computer controlledwelding machine.

" Electro fusion welding can only be adopted with specific approval. (generally smallbore 100mm and below is acceptable).Pipework layout is made up of "pre-fabricated spools" with a "make-up spool"which is measured, fabricated, tested and installed within 24 hours.

" Qualified Welders to BS EN 13607 and approved weld procedures. We adopt theWater Industries butt fusion weld procedures. These have been developed overtime and are use generically within the UK by all the water utilities.

" All pipework spools are hydrostatically pressure tested to 1.5 times designpressure.

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EDF Energy Experience in the Adoption of HDPE as the Materialof Choice for Cooling Water Pipework

TYPICAL FABRICATED SPOOL ASSEMBLY IN WORKSHOP

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• Stress analysis to ASME B31.1." Pipework is always modelled and analysed." Material PE 100 SDR 11 (16 bar @ 20 C for 50 years) to BS EN

12201" Pressure de-rating coefficient to be used for temperatures in

excess of 20 0 up to 40 0." A service coefficient (factor of safety) of 1.25 for water.• Damping factor of 5% used for seismic design.• Hydraulic analysis not normally required as we generally increase

pipe size to accommodate the thicker pipe.

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* Corrosion resistant flange backing rings bolts, washer studs &nuts.

* 3 mm thick Ethylene Propylene Diene Monomer (EPDM) gaskets.* Where rubber bellows have been utilised to accommodate the

higher thermal expansion movements associated with HDPE theconvolutions shall be filled.

" All spools suitably protected prior to transportation to station." Welded attachments to pressure boundary shall be avoided.* All weld beads (external) will be visually examined and wherever

practical both internal and external weld beads will be removedand a bend back test undertaken.

" Supports 120 degree contact angle by 1½ pipe diameter long with a3mm thick HDPE liner between the pipe and the support.

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DESIGN AND HAZARD CONSIDERATIONS

" Fire Loading and Penetration of Fire Barriers." Missile Impact" Dropped loads." Seismic Qualification." Extreme Ambient Temperatures." Biological Resistance.• Ultra-Violet Light." Erosion." Chemical Resistance

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DESIGN AND HAZARD CONSIDERATIONS (continued)

* Fatigue." Pressure Transients.* Mechanical Damage (10% rule).

* Qualification of Intumescent Fire Seals to provide a 3hour fire barrier.

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Current Scope of HDPE Installations within EDF Energy

Station Range of Pipe Sizes Meterage System

Heysham 2 550 mm nom size 1600 RSW & ACW

Torness 550 mm nom sizes 400 RSW & ACW

Sizewell B 750 mm nom size to 150 ESW & ACW1200mm

Hunterston B 400 to 630 mm nom size 600 RCW & ACW

Eggborough 660 mm nom size 5000 Fly Ash Slurry(Coal Fired Power Stationno longer part of EDFGroup)

Hinkley Point B 400 to 550 mm nom size 600 RCW & Towns Water

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Typical External to Buildings HDPE Installation(Hunterston B)

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* A technique to inspect HDPE butt welds using phased array technologyhas been developed. A water wedge housing was used to accommodatethe low longitudinal velocity of sound in HDPE.

* Test blocks have been supplied with a variety of implanted targets. Thosetargets within the weld volume that have been correctly inserted and donot protrude from inner or outer surfaces have been detected with asignal to noise ratio of 14dB or Greater. Additional to scope, the ability toresolve target edges was demonstrated, allowing measurement ofthrough wall defect size.

* We in conjunction with the Contractor consider that the capability ofdetection of lack of fusion defects greater than 6mm circumferential lengthby 2mm through wall within HDPE pipework using phased arraytechnology has been demonstrated.

* The acceptance criteria is currently "no discernable indications" Inpractice out of the - 100 butt fusion welds inspected by this technique wehave only rejected one weld based on this very onerous criteria.

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edf-energy experience in the adoption of hdpe as the ...edf energy experience in the adoption of...

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