Use of High Density Polyethylene for Repairs/Replacements ... · Use of High Density Polyethylene...

Use of High Density Polyethylene for

Repairs/Replacements of Buried Pipe

Alex Summe/Doug Munson

Project Managers

IAEA/EPRI Technical Meeting on Ageing Management of Buried

and Underground Piping and Tanks for NPPs

October 13-15, 2014 Charlotte, NC

2 © 2014 Electric Power Research Institute, Inc. All rights reserved.

Introduction

• HDPE is an attractive option for low pressure/low

temperature piping systems containing raw water

– Repairs and replacements of degraded buried pipe in

existing plants

– New plant construction

• Applicable US codes

– ASME B31.1 for non safety service water

– ASME Section III for new construction

– ASME Section XI for repairs/replacements

– NFPA for fire protection piping

• ASME is developing a new code for nonmetallic piping (non

safety)


High Density Polyethylene

Safety Related Service Water at Callaway


Cooling Tower Blowdown Piping at Callaway (non safety related)


Above Ground Applications

HDPE has also been used in

above ground applications

• Service Water piping at

Catawba (US - non safety)

• Essential Service Water Piping

at Sizewell B (UK - safety)

• Heysham 2 (UK)

• Torness (UK)

• Hunterston 2 (UK)

• Hinkley Point B (UK)


HDPE is Tough


HDPE is Ductile

Bend Back Test of a Butt-Fused Joint


HDPE (continued)

• Advantages

– No tendency to foul, corrode or host tubercles

– No need to line/coat or install Cathodic Protection

– Very resistant to seismic and pressure transients (e.g.,

water hammer)

– With additives: UV and chlorine resistance

– High abrasion resistance

– Material cost ~same as carbon steel, but much less than

for stainless alloys

– Joining costs ~1/10 that of metal

– Other fabrication and installation costs (e.g., handling

and rigging) much less


HDPE (continued)

• Disadvantages

– Material is not as well understood as metal

– Code rules still evolving: B31.1 rules are needed, new thermoplastic code in development

– Creeps, even at low temperatures

– Coefficient of thermal expansion much greater than metal (more thermal growth)

– Modulus of elasticity much less than metal (more hangers needed for above-ground)

– Is more easily damaged than metal

– Only 1 supplier with NQA program

– Cannot withstand extended operation at high temperatures (> ~140°F)

– Vendors have not standardized the product (e.g., fitting dimensions)


Material Cost Comparison

Material Carbon Steel

316L Duplex 2205

AL6XN HDPE

10”

(250 mm)

$60/ft $275/ft $900/ft $1230/ft -------

12”

(300 mm)

$70/ft $325/ft $940/ft $1460/ft $22/ft

24”

(600 mm)

$100/ft $700/ft $1900/ft $2850/ft $78/ft

36”

(900 mm)

$150/ft $800/ft $2850/ft $4300/ft $158/ft

Notes: 1. Costs are for materials only, HDPE also much less expensive to install

2. Data courtesy of Duke Energy


Joining

• HDPE pipes and fittings are joined by:

– Butt fusion

– Flanges

– Side wall fusion

– Electrofusion couplings


Flanged Joints

• HDPE creeps under load so flanged joints need to be retorqued

Metallic Backing Ring

PE Flange Adapter

Gasket if required

BoltingMetallic Flange

Metallic Pipe

CL Pipe

Washers

CL Pipe

PE Flange

Adapter

Metallic Backing Ring

Washers

Bolting

Gasket not used

PE Flange

Adapter

Typical Detail – HDPE to Steel Pipe

Typical Detail – HDPE to HDPE


Fittings

• Stress indices and stress

intensification factors have been

developed for common fittings

– Mitered elbows

– Molded elbows

– Mitered tees

– Molded tees

– Electrofusion couplings

– Flanges

– Reducers

– Mitered wyes

– Sidewall fusion branches

– Saddle branch

Strength Test of Flanged Joint

Fatigue Test of Elbow


Degradation Mechanisms

• Primary failure mechanism is slow crack growth

– Over many years, a surface scratch or a flaw in a

butt-fusion joint propagates through wall in a

brittle manner

– Local leakage, not catastrophic rupture

• A PENT test is used in the US to measure the

comparative resistance of resins

– A sharp razor notch is placed in a specimen and

the specimen is pulled until it fails

– Early HDPE resins had a PENT resistance of a

few hours

– Resins used in safety related applications in the

US are required to have a PENT resistance of >

2000 hours


Degradation Mechanisms (con’t)

• Early resins were also

susceptible to Rapid Crack

Propagation (current bimodal

resins are very resistant)

• Susceptible to oxidation in

high chloride environments

• Material properties need to be

downgraded if carrying

hydrocarbons

• Will form a “parrot beak” when

subject to extreme over

pressure


Fusing Procedure Qualification

• Fusing procedures are required in

the US for butt fusion joints

– Requirements provided by

Subsection QF of ASME

Section IX

• Rules not yet developed for

electrofusion

• Both the procedure and the fuser

must be qualified

• Procedure must cover the range

of “Essential Variables”

• Joints tested until failure

– Failure must be ductile

High Speed Tensile Impact Test


Inspection

• The critical area of HDPE to inspect is the joints

– Voids

– “Cold Fusion”

– Particulate contamination

• Several of the ultrasonic techniques have been found to

detect voids (planar flaws).

– Two techniques that have been found to work well are

Time-of-Flight Diffraction (TOFD) and Phased Array

• EPRI is starting a round robin project to evaluate various

NDE methods for their ability to detect cold fusion and

particulate contamination


Time-of-Flight Diffraction

TOFD Examination Concept

Screen Capture of TOFD Examination of HDPE


Linear Phased Array

Linear Phased Array Beam Coverage

Typical Ultrasonic Response

from Inside Geometry


Current ASME Code and US Regulatory Status

• ASME is bringing rules into main body of code

– Section III for design, Section IX for fusing, Section V for NDE

• Appendix nn to Section III will replace Code Case N-755-2

– NRC voted to approve but will place additional restrictions on Owner

• Provision for 10 year hydro testing

• Design consideration of modulus as a function of time, stress, &

temperature (new EPRI data should resolve)

• Adequacy of high speed tensile impact testing to qualify fusion

procedure specification (work underway to resolve)

• Code actions not complete

• Once code actions are complete, minimum of 2 years to incorporate

into 10CFR to allow unrestricted use

• Current path to approval is a Relief Request


Together…Shaping the Future of

Electricity

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