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Chapter 4:

PE / PLASTIC PIPE

BKG3493 GAS SYSTEM MATERIALS &

COMPONENTS

BACKGROUND

Plastic pipe was introduced for gas distribution system more than 30 years ago

Now has permanently established itself as excellent alternatives to ferrous pipes – low pressure operation

Offer overall advantages as compared to ferrous piping in terms of

a) low investment cost

b) corrosion resistance

c) light in weight and easily coiled

d) easy to joint

e) reduce installation time

TYPE OF PLASTIC PIPE

Currently types of plastics that were widely being used for gas distribution are Polyethylene (PE), Polyvinylchloride (PVC) and Polyamide (Nylon/PA).

PE pipe is the most popular and at present being used in all parts of the world.

PA pipe has just recently being introduced in Australia was claimed to be more superior to PE pipe in many aspects.

List the advantages of PA compared to PE?

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CRITERIA/ ESSENTIAL CONSIDERATION

In years to come, there will be more new plastic pipe being introduced to the market for gas distribution.

Each type of pipe probably could be used, as long as it meets the following criteria:

a) Long term strength

b) Ageing resistance

c) Impact strength

d) Chemical resistance

e) Temperature resistance

f) Impermeability

g) Ability to – heat fuse for joining, coil for ease of handling, squeeze off pressure.

Advantage of PE Pipe

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Coil for ease handling

Squeeze of pressure

control

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Heat fuse ability

DESIGN OF PLASTIC PIPING As according to ANSI:

Provisions in ANSI B31.8 are intended to limit the use of plastic piping primarily to main and services lines in typical distribution system operating at pressure of 100 psi or less.

The design formula for plastic gas piping system or the nominal wall thickness for a given design pressure can be determined by the following formula:

P = 2S [t / (D – t)] x 0.32 where; P = design pressure S = long term hydrostatic strength t = specified wall thickness D = outside diameter

THERMOPLASTIC DESIGN LIMITATION

a) The design pressure shall not exceed 100 psig.

b) Thermoplastic, tubing and fitting shall not be used where the operating temperature of the material will be:

- below - 20°F

- above the temperature at which the long term hydrostatic strength used in the design formula

JOINTING REQUIREMENTS & TECHNIQUES

Joint Requirements for Plastic Pipe Pipe or tubing shall not be threaded Solvent cement joints, adhesive joint and heat

fusion join shall be made in accordance with qualified procedures which has been establish and proven

Joint methods of Plastic Pipe Heat fusion of mechanical joint shall be used

when joining PE pipe, tubing or fitting Heat fusion methods – butt fusion, socket fusion,

electro-fusion The joint performance is depend on pressure,

temperature and time.

BUTT FUSION

This is the earliest technique to joint PE pipe that gives satisfactory performances

Using this method the two ends of the pipe to be jointed is heated using hot plate and fused together by applying some pressure.

This technique rely heavily on skill and commitment of the operator in order to get better result.

Essential parameters are pressure, temperature and time.

BUTT FUSION

Failure to achieve the recommended specifications for one of the parameters may result in poor joint.

Other important factors in getting good joints are the melt flow index and pipe roundness.

A big difference in the value of MFI between pipes to be jointed will results in poor bonding.

While unsatisfactory roundness of pipe will make it difficult to be aligned during fusion operation.

BUTT FUSION

GF 160 Butt fusion machine with automatic heating element

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BUTT FUSION

A Standard Butt Fusion Joint

Process jointing PE pipe

The basic rule is that only similar materials can be fusion jointed, such as PE with PE.

This applies also for the jointing of PE80 with PE100.

For best results, only components which have a melt flow index in the range from MFR 190/5 0.3 to 1.7 g/10 min should be fusion jointed.

This requirement is met by PE butt fusion fittings from Georg Fischer product.

The components to be jointed must have the same wall thicknesses in the fusion area.

SOCKET FUSION

Two pipe ends are joint together by a socket made of the same compatible material

The external wall area of the two pipes and the internal wall area of socket are heated by using specially designed tool

Pipe roundness is not critical

Still depend on operator skill

Socket joint produces stronger joint as compared to butt joint

Experience showed that this type of joint is less exposed to environmental stress cracking due to reduction of stress riser points

SOCKET FUSION

Application of heating coil inside the coupler.

The heating coil is connected to the control box – an element of automation

Electrical current is used to heat the coil

The heat from the coil will melt the surrounding pipe

Less dependency to the skill of operator, but the cost is 20% higher than butt fusion.

ELECTROFUSION

ELECTROFUSION

STANDARDS DIMENSIONAL RATIO

Enable the user to select a number of different sizes of pipe

Same SDR, will have the same D.P.

SDR is the ratio of average specified outside diameter to the minimum specified wall thickness

HEAT FUSION PRINCIPLES

Butt fusion This technique consists of heating the squared ends of two pipes, a pipe and fitting, or two

fittings by holding them against a heated plate, removing the plate when the proper melt is

obtained, promptly bringing the ends together and allowing the joint to cool while

maintaining the appropriate applied force.

Electrofusion This technique used fittings with integral heating elements. Sockets are used to join mains

and service pipes and saddle fittings are used to connect services to mains. The pipe to be

joined must be prepared by removing the outer surface layer to a depth of around 0.2 mm,

then pipe and fitting are clamped together to prevent movement. A voltage is applied across

the fitting terminals via a control box. An electric current is passed through the wire which

heats the wire and melts the polymer, fusing the fitting to the pipe. After welding, the joint

is allowed to cool before removing the restraining clamps.

Socket fusion This technique involves simultaneously heating the outside surface of a pipe end and the

inside of a fitting socket, which is sized to be smaller than the smallest outside diameter of

the pipe. After the proper melt has been generated at each face to be mated, the two

components are joined by inserting one component into the other. The fusion is formed at

the interface resulting from the interference fit. The melts from the two components flow

together and fuse as the joint cools.

MELT FLOW INDEX (MFI)

A measure of the ease of flow of the melt of a thermoplastic polymer.

Defined as the mass of polymer in grams flowing in 10 minutes through a capillary of specific diameter and length by a pressure applied (subject to gravimetric weights & temperatures) -ASTM D1238 and ISO 1133 (similar).

Indirect measure of molecular weight, high melt flow rate corresponding to low molecular weight.

A measure of the ability of the material's melt to flow under pressure.

Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, though it should be bear in mind that the viscosity for any such material depends on the applied force.

Ratios between two melt flow rate values for one material at different gravimetric weights are often used as a measure for the broadness of the molecular weight distribution. Melt flow rate is very commonly used for polyolefins, polyethylene being measured at 190°C and polypropylene at 230°C. The plastics converter should choose a material with a melt index so high that he can easily form the polymer in the molten state into the article intended, but on the other hand so low that the mechanical strength of the final article will be sufficient for its use.

MEASUREMENT OF MFI The procedure for determining MFI is as follows:

1. A small amount of the polymer sample (around 4 to 5 grams) is taken in the

specially designed MFI apparatus which is nothing but a miniature extruder.

The apparatus consists of a small die inserted into the extruder, with the

diameter of the die generally being around 2 mm.

2. The material is packed properly inside the extruder barrel to avoid formation

of air pockets.

3. A piston is introduced which acts as the medium that causes extrusion of the

molten polymer.

4. The sample is preheated for a specified amount of time: 5 min at 190°C for

polyethylene and 6 min at 230°C for polypropylene.

5. After the preheating a specified weight is introduced onto the piston.

Examples of standard weights are 2.16 kg, 5 kg, etc.

6. On account of the weight shear is exerted on the molten polymer and it

immediately starts flowing through the die.

7. A sample of the melt is taken after desired period of time and is weighed

accurately.

8. MFI is expressed as grams of polymer/10 minutes of flow time.

POLYVINYLIDENE FLUORIDE (PVDF) Highly non-reactive and pure thermoplastic fluoropolymer - used in applications requiring the highest purity, strength, and resistance to solvents, acids, bases and heat and low smoke generation during a fire event.

Compared to other fluoropolymers - easier melt process due to relatively low melting point of around 177°C , low density (1.78) and low cost compared to the other fluoropolymers.

Available as piping products, sheet, tubing, films, plate and an insulator for premium wire. Can be injected, molded or welded and is commonly used in the chemical, semiconductor, medical and defense industries, as well as in lithium ion batteries.

Fine powder grade, KYNAR 500 PVDF or HYLAR 5000 PVDF used as the principal ingredient of high-end paints for metals - extremely good gloss and color retention-use on many prominent buildings around the world, e.g. the Petronas Towers in Malaysia and Taipei 101 in Taiwan

THANK YOU

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