report

Chemical Requirements

Sulphur is originally present but is extracted in the plant. Typically

<10-50 ppm. So other odorants are needed.

Also conditioning agents (e.g., odorants, moisture removers at

cast iron joints – mono/di/trielthylene glycol in yarns)

Protective coatings

• Cast iron pipes need liners for

corrosion protection.

• Corrosion on inner surface produces

roughness that increases pressure

drops

• PE pipes have no problem.

ENVIRONMENTAL EFFECTS

• O2 • UV light

• Oxidation – Extruder barrel

– Solidification

– Joining

– Long term exposure

OXIDATION

Oxygen reacts and produces carbonyl groups.

Oxidation depends on availability of oxygen which

comes from the surface by diffusion – thermally

activated ; time at temperature plays a role.

Oxidation is autocatalytic

It is prevented by antioxidants

Oxygen diffusion

OXIDATION REACTIONS

Antioxidants

~0.1 w/o

There is antioxidant

loss that needs to be

checked.

With and without antioxidants

Induction period lengthens with

antioxidants, which are

consumed with time...

Carbonyls break by

hv to create radicals

a surface effect

Weathering

The effect is similar in PE –

Note that storage is mostly outside.

Assume that you are in charge of the installation

of a PE natural gas pipe network.

Propose a detailed plan for the evaluation of the

oxidation state of polyethylene pipe during:

- PROCESSING

- STORAGE

- FUSION

- USAGE

Be specific – comment on everything:

- instrumentation, cost, time, availability, etc.

QUESTION TO PREPARE FOR NEXT WEEK

JOINTING AND INSTALLATION

• The most obvious difference with steel is

FLEXIBILITY

• Critical difference between PE and PCV

• Jointing also advantageous for leakage

“BUTT” JOINTS OF PE PIPES

alignment trimming

Hot plate in contact

Bead formation pressure

Weld line

Low pressure OK High pressure

WHAT IS THE

Shoulder of the road

"We will need newer, cleaner and safer pipes to

move larger quantities of natural gas - up to

38,000 new miles of pipe, and 263,000 miles of

[new] distribution lines."

President George W. Bush

May 17, 2001

REPAIR OR MODIFICATION?

SQUEEZE OFF !

Does it pose any problems?

Local yielding

Can be “undone”

Not a problem if not repeated

on the same spot

Do this with a iron pipe

if you dare!

Replacement is “easy”

Use a “bullet” to cut off the old pipe and

pull in the new one.

R

What is the safe limit for bending of the pipe?

 

22

22

22/2

min

DE SR

R

D ES

ES

R

D

R

RDR

Y

FYF

YF

 





 





 



Requirements

• Should “resist” pressure of 2 bar

• High ductility factor > pipe thickness????

• Yellow color

• Range of sizes

• Range of sockets

• Negligible gas loss

• Resists UV and oxidative degradation

• Can be fusion welded

• Can be bent for insertion

• Cost and availability

• Optimum mechanical properties to minimize wall thickness

• Can be extruded at suitable rate