Life Expectancy of

Polyethylene Pipe

Jan. 2014

Contents

• Overview

• MRS(Minimum Required Strength)

• MOP(Maximum Operating Pressure)

• Modification factor

• Conclusion

• Appendix

Overview

• Most common thermoplastic with chemical

formula of (C2H4)n

• Varies with crystallinity & molecular weight

– HDPE, MDPE, LDPE, LLDPE

Polyethylene

Overview

• Chemical

– Human safe & chemically stable

– Food container, bottle, pipe, toy etc.

• Physical

– Lightweight, impact resistance, very low moisture

absorption & high tensile strength

• Melting temperature(HDPE): 120~180℃

• Density(HDPE): >0.941g/cm3

• Elongation at break: >600%

Properties

• 1st(early 1950’s)

– PE32 for drinking water system, PE63 for low

pressure gas piping

• 2nd : PE80 for gas and water pipes

• 3rd(early 1990’s): High performance piping system

Generation Grade

1st generation raw materials PE32(LDPE), PE40(LDPE), PE63(HDPE)

2nd generation raw materials PE80(MDPE), PE80(HDPE)

3rd generation raw materials PE100(HDPE)

Overview Generation & grade

MRS

• means “long term hydrostatic strength”

– defined in ISO 12162 & tested by ISO 1167

– Hoop stress test⑴ for 10,000 hours at 20/60/80℃

• Criteria for PE grade classification

– based on calculated σLPL⑵ value by ISO 9080

– Static pressure rate for 50 years at 20℃

Minimum Required Strength

⑴ Hoop stress test is carried out by only certified organization/laboratory

⑵ σLPL: “Lower Confidence Limit” of the predicted hydrostatic strength

at 20℃ for 50 years, unit: MPa(MegaPascal)

• Example: outer diameter φ110mm 10bar pipe

– Higher MRS has thin wall at equal pressure level

– Economical with less material consumption

Rating σLPL(MPa) MRS(MPa) Remarks

PE63 6.3 ~ 8.0 6.3

PE80 8.0 ~ 10.0 8 Telecommunication etc.

PE100 10.0 ~ 10 Water pipe etc.

MRS Rating & meaning

MRS A typical plot of PE80 material

MOP

• Equation(ISO 4427-1)

MOP = (2 x MRS) / (C x (SDR – 1))

– C: overall service (design) coefficient

• PE: 1.25, PP: 1.6, PVC: 2.0

– SDR: Standard Dimension Ratio

• Tube outer diameter / wall thickness

• Meaning

– Maximum effective pressure allowed for

continuous use(@20℃, 50 years)

Maximum Operating Pressure

MOP

• 16/13 microtube

– SDR: 10.67 = 16/1.5

– C: 1.25(PE)

– MRS: 8MPa(PE80)

– MOP = (2 x 8) / (1.25 x ( 10.67 – 1))

= 1.32MPa = 13.2bar

• This pipe can endure 13.2bar pressure at 20℃

for more than 50years!

Calculation example

Modification factor

• MOP in higher service temperature

– @30℃: 13.2 x 0.87 = 11.48bar

– @40℃: 13.2 x 0.74 = 9.77bar

Pressure reduction coefficient

Temperature(℃) Coefficient

20 1.00

30 0.87

40 0.74

Conclusion

• Polyethylene pipe

– 16/13 microtube made of PE80 can withstand

13.2bar pressure at 20℃ for more than 50years!

– Microduct experiences short term pressure less

than 1 hour for blowing, so even longer utilization

is guaranteed

– PE is very stable against chemical attack

– PE is ductile material that adopts into installed

environment

Life expectancy

Appendix

• ISO 4427-1: Plastic piping systems – Polyethylene(PE)

pipes and fittings for water supply, part 1: General

• ISO 12162: Thermoplastics materials for pips and

fittings for pressure applications – Classification and

designation – overall service (design) coefficient

• ISO 9080: Plastics piping and ducting systems –

Determination of the long-term hydrostatic strength of

thermoplastics materials in pipe form by extrapolation

Standard and reference