welding and installation of polyethylene pipelines under ... · uni 10779 september 98 iip...

The Total Quality

Welding and installationof polyethylenepipelinesunder pressure

DefinitionsWelder qualificationReference standards

Jointing systemsTransition systemsElectrofusion jointingButt fusion jointing

Inspection of weldedjointing

Installation of PE pipeline systemsPipeline testing

Defin

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Definitions

dn nominal diameter information about the nominal diameter, in millimeters,of a PE pipe or fitting

en nominal thickness information about the minimum nominal thickness,in millimeters, of a PE pipe or fitting

de outside diameter information about the outside diameter, in millimeters,measured at any point on the circumference ofa PE pipe or fitting

dem average outside diameter information about the average outside diameter,in millimeters

D nominal outside diameter information about the nominal outside diameter,steel pipe in inches, of a steel pipe

G gas thread diameter information about the dimension, in inches,of the threaded part

definitions

This publication, making reference to the ISO and EN standards, uses thefollowing geometric definitions:

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Welder qualification

welder qualification

Study Groups, who work on topics within the polyethylene fieldapplication, agree on the mainly importance, for the quality of weldings,not only the constant improvements in equipments but also, and above all,the training and qualification of welding personnel.Electrofusion welding systems, and those with butt fusion in particular, aresubject to human error that can compromise the result and the reliabilityof the jointing.Qualified Operators who follow standardized and consolidated proceduresmust guarantee perfect execution of jointings in order to achieve thehighest degree of safety in the pipeline system.With this end, in Italy, UNI 9737 Standard which is part of application ofLaw 46/90 (Official Gazzette 15.02.1992) claim for the qualification ofpolyethylene Welder, taking part to a theoretical-practical training. Thiscourse must be taken at a training center that is recognized by anauthorized Organization.

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ITALIAN STANDARDClassification and qualification of welders for plastic materialsWelders by the heated tool procedure, with mechanical equipment and by electrofusion forpolyethylene pipes and fittings for the supply of gaseous fuels, water and other fluids underpressureUNI 9737

ITALIAN STANDARDWelding of plastic materialsHeated tool butt weldingWelding of polyethylene pipes and/or fittings for gas, water and other pressure fluids pipelinesUNI 10520

ITALIAN STANDARDElectrofusion welding process of PE pipes and/or fittings for the supply of gaseous fuels,water and other fluids under pressureUNI 10521

ITALIAN STANDARDTrench work machines with heating elements by contact, used for buttfusion jointingsof PE pipes and/or fittings for the supply of gaseous fuels, water and otherfluids under pressureCharacteristics and requirements, testing, maintenance and documentsUNI 10565

ITALIAN STANDARDElectrofusion control units and auxiliary equipment for the jointing of PE pipesand/or fittings using e-fittings, for the supply of gaseous fuels, water and other fluids underpressureCharacteristics and requirements, testing, maintenance and documentsUNI 10566

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Training courses aimed to obtain the qualification of PE welderaccording to UNI 9737 are held in Tesero (TN) at the

Eurostandard Training Center

The instruction program is arranged by the Center’s Qualified Teachersaccording to the Standard. The following subjects, in particular, are dealtwith:

• theoretical information on polyethylene: chemical/physical characteristics

• characteristics of pipes and fittings

• jointing systems: electrofusion and butt fusion

• welding machines and ancillary equipment

• reference standard: installation

• hygiene and safety on work site

• practical training sessions.

The examination session is held at the end of the training part in thepresence of an Official from the Certifying Organization.The examination session includes:

• theory: written questionnaire and oral examination

• practice: welding of the test samples required by UNI 9737 Standard

The test samples welded by the Operators undergo destructiveexamination at the Certifying Organization.

If final results are positive the requested Qualification is issued to thebelonging Company, in the operator name, according to the UNI 9737Standard.

The qualification is valid for a three year period and can be renewed uponfurther examination.

training courses

class PE-2 qualification for butt fusion welding of PE pipe and/orfittings with outside diameter ≤ 315 mm

class PE-2-D qualification for butt fusion welding of PE pipe and/orfittings with outside diameter > 315 mm

class PE-3 qualification for electrofusion welding of PE pipes and/orfittings of any diameter

qualification types

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duration of courses

Qualifications can be obtained individually or in combination by applyingthe following minimum duration of training sessions:

The Operator, considering the subjects being dealt with, must have amiddle school certificate and at the end of the training session must be inthe position to pass the examinations requested by the standard.Otherwise it is the faculty of the Teacher to refuse his admission to theexamination sessions.

For other information and application contact:

TECHNICAL TRAINING CENTEREurostandard S.p.A - Course OfficeZona Industriale Lago - 38038 TESERO (TN)phone ++39 0462 811 211 - fax ++39 0462 811 200e-mail: [email protected]

pre-requisite

Type of qualification Total duration

PE-2 18 hours

PE-2-D 22 hours

PE-3 16 hours

PE-2 + PE-3 28 hours

PE-2-D + PE-3 32 hours

Upgrade from PE-2 a PE-2-D 4 hours

Qualification renewal (triennal) 8 hours

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Reference standards

UNIPLASTHigh density polyethylene pipes under pressure. Types, dimensions and requirementsUNI 7611 +FA-1

UNIPLASTHigh density polyethylene fittings for pipes under pressure. Types, dimensions and requirementsUNI 7612 + FA-1

UNIPLASTBuried polyethylene pipes for the supply of gaseous fuels. Metric series - SpecificationUNI ISO 4437

UNIPLASTPolyethylene fittings, for fusion with heated tools, for use with polyethylene pipes for the supply ofgaseous fuels. Types, dimensions and requirementsUNI 8849 + FA-1

UNIPLASTPolyethylene electrofusion fittings for the supply of gaseous fuels. Types, dimensions andrequirementsUNI 8850 + FA-1

UNIPLASTPE joints of pipes and fittings made with plastics or metal/PE for buried pipes for the supply ofgaseous fuels. Types, requirements and testsUNI 9736

CENPlastic pipeline systems for distribution of gaseous fuelspr EN 1555

CENPlastic pipeline systems for the supply of fluids under pressurepr EN 12201

CENWater supply requirements for system and components outside buildingspr EN 805

MINISTRY OF HEALTHSanitary discipline relating to plastics and rubber for pipelines and fittings suitable forpotable watern. 102 2 /12/1978

reference standards

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The references given below regard design, laying, management andinspection of pressurized PE pipeline systems. The standards,recommendations and requirements that are described are the workground of planners and installers.

production requirements

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testing methods

UNIPLASTHigh density polyethylene pipes. Testing methodsUNI 7615

UNIPLASTHigh density polyethylene fittings for pipes under pressure. Testing methodsUNI 7616 + FA90

welder qualificationand welding process

ITALIAN STANDARDClassification and qualification of welders for plastic materialsWelders by the heated tool procedure, with mechanical equipment and by electrofusion forpolyethylene pipes and fittings for the supply of gaseous fuels, water and other fluids underpressureUNI 9737

ITALIAN STANDARDWelding of plastic materials. Heated tool butt welding. Welding of polyethylene pipes and/orfittings for gas, water and other pressure fluids pipelinesUNI 10520

ITALIAN STANDARDElectrofusion welding process of PE pipes and/or fittings for the supply of gaseous fuels, waterand other fluids under pressureUNI 10521

G.U. ITALIAN REP.Enactment of EEC Directive 80/778 regarding the quality of water destined for humanconsumption according to law dd. April 16, 1987 nr. 183DPR 236/88

G.U. ITALIAN REP.Quality of water destined for human consumptionDirection CEE 98/83

pipeline laying

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CIGGas distribution networks with maximum working pressures ≤ 5 barDesign, construction and testingUNI 9165

CIGGas distribution pipelines with maximum operating pressure ≤ 5 barMaterials and jointing systemsUNI 9034

CIGGas service pipes. Design, construction and serviceUNI 9860

CIGHome gas distribution systemsDesign, installation and maintenanceUNI 7129 edition 92

UNIFire extinguishing systems - hydrant systems. Design, installation and operationUNI 10779 september 98

IIPRecommendations for the installation of polyethylene PE buried pipelines for the supply ofgaseous fuels (according to the directions of D.M. 24.11.84)n. 7 may 93

IIPRecommendations for the installation of high density polyethylene PE pipelines for the supply of watern. 10 may 99

MINISTRY OF INTERIORFire-fighting safety rules for the transport, distribution, storage and use of natural gas with den-sity not higher than 0,8D.M. 24.11.1984

MINISTRY OF INTERIORModification to Ministerial Decree 24.11.1984:Fire-fighting safety rules for the transport, distribution, storage and use of natural gas with den-sity not higher than 0,8D.M. 16.11.1999

MINISTRY PUBLIC WORKSTechnical standards regarding pipelines. Regulation of design, construction and testingD.M. 12.12.1985

ITALIAN STANDARDCoordination of welding, pipe laying and test activities for polyethylene pipelines for the supply offuel gas, water and other fluids under pressure.Requirements for training, qualification and certification of personnelUNI 10761

STANDARD PROPOSALQuality requirements for the welding of polyethylene pipelines. for the supply of gaseous fuels, ofwater and other fluids under pressureSMP 90-99

STANDARD PROJECTWelding of polyethylene PE 100 pipes and/or fittings for the supply of gaseous fuels, of water andother fluids under pressureU28005960

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welding units

ITALIAN STANDARDTrench work machines with heating elements by contact, used for buttfusion jointings ofPE pipes and/or fittings for the supply of gaseous fuels, water and other fluids under pressureCharacteristics and requirements, testing, maintenance and documentsUNI 10565

ITALIAN STANDARDElectrofusion control units and auxiliary equipment for the jointing of PE pipes and/orfittings using e-fittings, for the supply of gaseous fuels, water and other fluids underpressureCharacteristics and requirements, testing, maintenance and documentsUNI 10566

safety

MINISTRY OF INTERIORStandards for plant safetyLegge 46 5 March 1990

G.U. ITALIAN REP.Standards for the precautionary measures of the accident at workDPR 547/55

G.U. ITALIAN REP.Direction of CEE 89/391 regarding the safety improvement for the workers health on thework siteDL 626/94

G.U. ITALIAN REP.Direction of CEE 92/57 regarding the minimum safety and health regulation to carry out ontemporary or mobile working siteDL 494/96

Jointing systems

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jointing systems

The FIXED SYSTEM includes butt fusion, socket fusion and electrofusionwelding.

BUTT FUSIONJOINTING

This process is used to weld pipesand/or fittings with equal thicknesswhere the surfaces to be welded areheated by contact with an heatingelement and subsequently jointedtogether.

SOCKET FUSIONJOINTING

This welding process uses specialfittings shaped so that they cancontain the pipe end to be welded.Pipes and fittings are heated byheating elements specific for eachdiameter.

ELECTROFUSIONJOINTING

This pipe and/or fitting weldingprocess works with the heating of theirsurfaces, suitable prepared, by contactwith an electric resistance (coil) fittedin a “special fitting”.

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fixed system

Welders making these jointings must be suitably trained and certifiedaccording to the UNI 9737 Standard.

The jointings of polyethylene pipes/fittings can be fixed and removable.

COMPRESSION FITTING

This is also called “quick joint” or“clamp fitting” and consists of amain body on which two bushesare screwed down. Tightness isguaranteed from the compressionof the body on the pipe through theexternal bushes.

This type of fitting is generally used in low pressure pipeline systems sinceoverpressure or hammering or ovalization can compromise tightness.

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STUB END AND BACKING FLANGE

Jointings with stub end, backingflange and gaskets are used toconnect polyethylene pipes withpipes made of other materials or toaccess to valves, branches, etc.It can be even chosen for thejointing of two PE pipelines, iftemporarily connected.

The stub end must be welded to the PE pipe using butt fusion system orwith electrofusion socket and forms the support base for the flange,normally made of steel or aluminium.The counterflange is connected by bolts. Tightness is achieved using a flatgasket. Gasket materials are different depending on the systemapplication (gas or water).

removable system

REMOVABLE SYSTEM includes all connections using stub end andbacking flanges as well compression fittings (quick release joints).These systems are used to connect different materials together (PE, PVC,steel or cast-iron) and to insert valves or when it may be necessary todisassemble the jointing.

Transition systems

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transition systems

The steel/PE couplings allow the connection of a polyethylene pipe with asteel one.

The range includes the following types:

• STEEL/PE MONOLITHIC COUPLING with thread metal part or to bewelded.It consists in a steel part on which has been overmoulded a PE tubularpart. This system allows high tightness guarantees. It is generally usedon gas branches.Connection to the PE part of the pipeline system uses electrofusion.

• STEEL/PE COUPLING FOR GAS ANDINDUSTRIAL PIPELINEIt consists of a monobloc, cold worked andcovered with epoxyvinilic painting, providedwith steel and polyethylene ends.

• STEEL/PE COUPLING THREE PART JOINTIt consists of female thread cast iron bush withflat gasket, union nut and polyethylene stubend.

• LONG COUPLING FOR GAS PIPELINE It isa special application of the steel/PE monolithiccoupling which has the metal sectionextended and bent to 90° in order to make adirect branch.

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• E-FUSION TRANSITION FITTINGIt consists of an electrofusion fitting arranged with nickel brass threadend - male or female - used to make transitions from polyethylene tometal materials.Types available: socket, 90° and 45° elbow.

• E-FUSION TRANSITION SADDLEThe upper saddle has a female thread brass insert to allow a directconnection with the metal pipe.

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Electrofusion jointing

electrofusionjointing

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Electrofusion welding system is now considered the most highlydeveloped and safest method for realizing polyethylene jointings. It can beused for diameters in the range from 20 mm up to 630 mm. Electrofusion,thanks to its versatility, can weld together pipes or fittings with differentthickness made both with polyethylene PE 80 and PE 100 in accordanceto the compatibility of melt flow index and raw material density.Today electrofusion is considered the most successful system both forin-line jointings and branches.

Welders must be suitably trained and certified according to UNI 9737Standard.

jointing preparation

The jointing quality depends directly on strictly compliance with thefollowing procedures:

• visually check that the pipes or fittings to be welded are free of defectssuch as cuts (maximum tolerable depth ≤ 10% en), abrasions, etc.All defects must be removed by cutting out the relative section of pipe.

• The pipes/fittings ends to be welded must be CUT AT RIGHT ANGLEusing proper pipe cutters.

• Using coiled pipes, take care to the RESIDUAL BENDING andOUT-OF-ROUND normally higher than those in bars.In any case maximum ovalization cannot exceed 1.5% calculated asfollows:

de max - de min

——————————— • 100 dn

where de = outside diameterdn = nominal diameter

Bending and ovality can be reduced by unrolling the pipe at least 24hours before its laying and using special re-rounders. In extreme casesa section of non-ovalized pipe can be butt welded to the end of the coilin order to facilitate subsequent work in site trench.

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scraping

• Clean all dust and dirt, etc. off the pipe and then scrape it. On thecontrary, the lack of this scraping will prevent the molecular penetrationnecessary for a successful welding, causing only superficial “sticking”and compromising the tightness of the jointing.

• The removal of the superficial oxidized layer (due to UV sun ray) mustbe done using the manual scraper furnished with the control unit or usingspecial mechanical pipe scrapers, being sure to perform UNIFORM ANDTOTAL SCRAPING of the welding areas for a length at least 10 mm fromthe mid-point of the socket and for a depth of approximately 0.1 mmfor dn ≤ 63 mm and 0.2 mm for dn ≥ 63 mm.

This operation, using pipe scrapers, must normally be done in a singlepass in order to avoid the excessive reduction of the pipe/fitting diameter.

Check the condition of the scraper whenever the result is not satisfactory.

Using a manual scraper, results are correct, when a consistent PE shavingis formed and remains attached to the pipe end. This is then removed byslightly rounding off (at 45° angle) the parts.

In case of branch saddles welding, the scraped area must correspond tothe width of the upper saddle or, in any case, to the welding zone.

AVOID ABSOLUTELY other scraping equipments such as abravisepaper, rasp, lapping wheels, sawblades, etc.

cleaning

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• Scraped surfaces must be cleaned using strong soft paper drenchedwith a suitable detergent to remove all traces of dust, grease, etc.

The DETERGENT must be compatible with polyethylene, quick toevaporate, sufficiently dry which will not leave traces of grease on thepipe/fitting. It is advisable to use Tangit Ks - isopropyl alcohol.

AVOID ABSOLUTELY DILUENT, TRICHLOROETHYLENE, BENZINE,DENATURED ALCOHOL.

Detergent cleaning must also be done on the inner surface of theelectrofusion fitting, which has to be removed from its protectivewrapping only at the moment of use.

Remember that the detergent does not improve the quality of the jointing,so avoid excessive use.

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positioning of socket andintegrated fitting

• The aligning clamp must be used for alldiameters to be welded. This eliminates jointstresses during the welding process and duringsubsequent cooling.Install reducing inserts to adapt the clamp todifferent diameters. Some models, thanks totheir design, make it easier to correctly centerthe fitting on the parts to be welded without thecentral stop system.

• Sign a mark, using a felt-tip marker, on the twoends to be welded that corresponds to thedepth of insertion, equal to half-way into thelength of the socket.

• Insert the socket up to the location mark.

• Fasten the pipe/fitting into the aligning clamp.

• Insert the other end of the socket up to itslocation mark and fasten it into the aligningclamp.Now the socket is centered on the two parts tobe welded.

Special aligning clamps are available forinstalling electrofusion integrated fittings. Thesehave adjustable joints for welding 90° and 45°elbows, 90° tees and reducing bushes. Alsohere we recommend using a felt-tip marker tosign the depth of insertion.It is recommended to mark the pipe afterpositioning it for at least 1/3 of theircircumference in the proximity of thesocket/fitting to make sure it has not movedwhen welding is completed.

electrofusion saddlepositioning

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• Cooling time must be strictly respected to prevent stress to the joint andit varies with welded diameter from 10 to 30 minutes.No forced cooling methods admitted (water, compressed air, etc.).The pipeline can be subjected to test after 2 hours from the last fittingjointing.

fusion

cooling

The welding area must always be sheltered fromadverse environmental conditions such as wind,rain, humidity, excessive sunlight.Electrofusion jointing is recommended workingin a dry site with ambient temperatures between-5°C and +40°C. In case of higher values protectthe location with suitable devices (tent andsimilar).

• Connect the plugs of the control unit to theterminals on the fitting.For a regular and successful working strictlyfollow the instructions equipped with the controlunit.

NOTE: If there is an accidental interruptionduring the welding cycle, operationcan only be repeated after theelectrofusion joint has totally cooled(minimum 1 hour). This operation canbe done only once.

• E-fusion saddle is furnished with specific assembly kit composed ofbolts, hexagonal nuts and washers.

• Insert the hexagonal nuts in the seats on the blank (or lower) saddle.

• Insert the bolts and washers in the upper saddle.

• The saddle must be clamped on the pipe by tightening the four couplingbolts. Tightening is done in a criss-cross pattern using an allen-headscrewdriver or wrench (depending on the type of bolt) until the saddle isfully tightened.

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e-fusion saddletesting

• Due to the special feature of the saddle (pre-perforated) the pressuretesting on the jointing can be carried out before the boring process.

This consists of a type 11.30 saddle equipped with a flow ON/OFF devicethat operates whenever the connection branch is damaged and causesviolent discharge of the fuel gas.The device stops the gas flow and permits the branch to be repaired.Gas-stop resets automatically or by introducing backpressure from anexternal source when the repair is completed.

e-fusion saddleboring

• The boring process can start only after thecooling of the jointing (about 20 minutes for alldiameters).

TAPPING SADDLEUnscrew the outlet cap and insert the hexagonalwrench into the built-in cutter.Screw clockwise till the pipe perforation. This isevidenced by a great decrease in screwing force.Tighten again for 2 - 3 turns and then retract thecutter back to its original position.Remove the hexagonal wrench and replace theoutlet cap which is provided with an O-ring gasket.SPIGOT SADDLEWelded using the same procedure as thetapping saddle. Boring is done using approvedholesaw.

WARNING: Pipe boring is not allowed before welding: this canseriously compromise the quality of the jointing.

tapping saddle with safetydevice (GAS-STOP®)

bar code

magnetic card

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The information necessary for operating the control unit, as an alternativeto the bar code label, can be contained in a magnetic card compatible withsome models of universal control units.

In this case the operator inserts the magnetic card furnished by the fittingmanufacturer and containing the welding parameters into the specialreader.

It is also possible to record data relative to the jointing on magnetic cards,when this is necessary to ensure traceability of the jointings.

The bar code is an universally recognized system to store up informationand to allow their reading by proper systems (light pen, scanner).For the electrofusion system of polyethylene, the BAR CODEINTERLEAVED 2.5 has been codified with 24 digits with control code.

The information stored in the code, and carried on the label, allow thesuitable control unit to understand automatically the characteristics of thefitting to be welded and to consequently work.The code stores all information necessary for the electrofusion cycle: typeof fitting, diameter, fusion time and cooling time, control character of acorrect reading, identification key.

The main characteristic of this system is to avoid any possibility of errorsin the fixing from the operator, who must only pass again and again thelight pen on the label.

The guarantee of correct code reading is determined from the controlcharacter carried on the label.Possible differences between the fitting connected to the control unit andthe wrong reading of the code are shown on the display, which does notproceed in the memorized sequence.

For a correct bar code reading we recommend using the light pen at anapprox. 45° inclination, moving it straight and continuously at constantspeed from left to right without exercising excessive pressure.

The monovalent control unit can only be used to weld PE e-fusion fittingsfrom a single manufacturer.No guaranteed results can be given for any use with other fittings.Generally the control unit allows the Operator to work at a welding safetyvoltage lower than 50 V and is manufactured in accordance to the UNI10566 standard and is furnished with CE mark.The heating power is automatically fixed according to the type anddiameter of the e-fitting, to the nominal pressure of the pipe/fitting to bewelded and to the ambient temperature.

The alphanumeric display guides the Operator when setting theparameters:• type of fitting to be welded - nominal diameter - PN (when required)

and consequently shows the following welding parameters:• ambient temperature• voltage• welding time• a progressive number of welding operations• alarm or malfunctioning messages.The control unit EURO M12 is designed to store the Operator code, thework site, the date/time of electrofusion and the welding parameters. Thememorized data can be subsequently transferred to paper or alternativelyto a PC by using suitable software.(Memory capacity: max 200 weldings)

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monovalent welding unit

EURO M12 UNIT CHARACTERISTICS

Supply voltage 220V AC ± 10% / 50 Hz ± 10%

Output voltage < 50V

Max power consumption 2500 W

Operating temperature from -5°C to +40°C

Printer output Serial RS 232

Protection IP 54

Dimensions cm 48x29x36

Weight Kg 25

welding units and equipment

The welding unit must undergo periodicoverhaul (biennal) according to UNI 10566standard.

The welding unit must undergo periodic overhaul (biennal) according toUNI 10566 standard.

universal welding unit

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EURO P40 UNIT CHARACTERISTICS

Supply voltage 220V AC ± 10% / 50 Hz ± 10%

Output voltage < 50V

Max power consumption 4000 W

Operating temperature from -5°C to +40°C

Set up system automatic with bar code reading

and/or manual setting

Printer output serial RS 232

Protection IP 54

Dimensions cm 50x29x36

Weight Kg 28

The universal control unit is used for welding of PE electrofusion fittingssupplied with bar code type Interleaved 2.5.• The unit is manufactured in accordance to UNI 10566 and ISO TC138 n.

153 standards and is furnished with the CE mark.• Welding parameters (time/voltage) can be set either reading the bar

code using the light pen or by manually setting based on data furnishedby the manufacturer.

• The unit is provided with serial connection to a printer, allowing thetransfer to paper of the memorized data, such as the welding cycles,Operator code, date/time/place and welding parameters.

• All memorized data can be also transferred to a PC using the suitableprogram.

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welding unit supplyusing power generators

Use of generators to supply power to welding units is permitted only underthe following conditions in order to prevent risk of damage:1. POWER not lower to real 3.5 kW for welding sockets with diameters up

to 315 mm

2. 50 Hz supply FREQUENCYWarning: some generators supply at 60 Hz. Avoid using this type ofgenerator.

3. Only AC CURRENT (50 Hz / 230 V)Do not use with DC or rectified voltage (present on some generators).

4. EXTENSION CABLES with 3 mm size cables up to 20 meters and 4mm size cables over 20 meters.

5. Generator HARMONIC DISTORTIONS between 18-20%.

6. VARIATIONS IN VOLTAGE from no-load to full load (with cycleunderway) not in excess of the machines setting limits: 180-270V.When values are outside tolerances the cause can be found in:- insufficient power- stated power not real power (stated, for example, at 60 Hz rather than

50 Hz),- poor maintenance of motor,- inefficient voltage regulator.

ancillary equipment

re-rounder

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• This has a shape similar to the aligning clamp but has wider jawsdesigned to exercise mechanical pressure on the pipe walls to correctovalization without damaging the pipe.

• It corrects ovalization higher than 1.5% as prescribed by UNI 10521Standard and required for correct welding. It is generally used fordiameters up to 110 mm which corresponds to the maximumrecommended limit for coil pipes.

• It can be manually powered or using hydraulic devices.

• Protects the jointing, either during theelectrofusion or the subsequent cooling, fromexternal mechanical stresses,

• allows to revise possible off-centering betweenboth ends to be welded and to recover theout-of-round of parts, if ovalized.

The aligning clamp is auxiliary to the control unit,its use is essential for the successfulelectrofusion jointing.

The clamp consists of a support frame with avariable number of jaws and reducing inserts toadapt the unit to the various diameters used. Italso generally includes a special accessory for45° and 90° welding.

A clamp version exists as alternative fordiameters ≤ 63 mm, offering great workingversatility.

Simultaneous use of multiple aligning clampswill affect the speed of installation.

aligning clamp

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pipe cutter

mechanical pipe scraper

Generally, for small diameter pipes/fittings (up to 63 mm) manual scraperswith interchangeable blades are used to remove the oxidized layer.

Mechanical pipe scrapers, that must be fastened to the pipe/fitting end,are available for larger diameters (larger than 63 mm). Removal of theoxidized layer is done using a special manual tool.

The use of these tools requires the perfect flatness of the pipe end,obtained by using a pipe cutter, and the periodic overhaul of the cuttingedge tool.

A square cut of the pipe to be welded is carried using a pipe cutter, withroller or with tool version. For a better choose of the type, it is important toconsider the wall thickness of the pipe.

Use of electrical cutters with high cutting speeds, such as disk grinders orthe like, is not recommended because the heat they generate couldcompromise the material characteristics.

Butt fusionjointing

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compatibility

welding preparation

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This technique can weld PE 80 or PE 100 polyethyelene pipes/fittings thathave the same wall thickness. In addition, it is the recommended methodfor diameters larger than 110 mm. Pipes and fittings, to be welded, musthave compatible melt flow index and density. In particular the MFR valueof the two components to be welded must be inside the range:

0,2 ÷ 1,4 g/10min (190°C - 5 Kg)

The guidelines in UNI 10520 standard are valid for all PE 80 pipes/fittingsand for PE 100 pipes/fittings ≤ 20 mm thickness. For PE 100 pipes/fittingswith thickness > 20 mm see the direction on page 55.Welders who carry out these jointings must be suitably trained andcertified according to UNI 9737 Standard.

It is good practice, before carrying out the welding, to check the materialswholeness and the equipment safety. The operator must position himselfin the way to keep the total visual control over all procedures and to haveenough space to work without restrictions, in a dry and, in so far aspossible, level site.

Preparation of welding surfaces is of main importance for the quality of thefinal welding.

jointing withheating elements

butt fusion

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planing

The ends of the pipe/fitting must then be planed using a facer toolfurnished with the welding machine. First of all they must be cleaned of alldirt, mud or similar residue before planing in order to protect the cuttingedge of the blades. Blades must be sharpened or replaced when planingis difficult.

Bring pipe ends nearer to the electric facer tool only after starting up, setgradual pressure avoiding the facer stops during operation. If that, slightlyrelease pressure and quickly separate pipe ends avoiding to damage thefacer tool motor.

Planing is completed when the shavings are continuous and of equal sizeon both ends.

When planing is completed, remove the facer tool and bring the facedends together, checking that mismatch does not exceed specified valuesand that any detachment is lower than the values indicated in the followingtable. Planing must be repeated when these values are not achieved.

maximum off-centering

The ends of the parts to be welded must be positioned in the weldingmachine jaws so that any off-centering does not exceed the maximumtolerable value: off-centering beyond this tolerance can be adjusted byfurther tightening down the clamp bolts and/or turning the pipes until thebest condition as been reached.

Maximum off-centering ≤ 10 % en (not higher than 2 mm)

Diameter Max. distance

up to dn 200 mm 0,3 mm

over dn 200 up to dn 400 mm 0,5 mm

over dn 400 mm 1,0 mm

heating plate temperature

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When welding a PE 80 part with a PE 100 part with an en ≥ 20 mm, settemperature for PE 100.

working conditions

Welding must take place in a dry site, sheltered from adverseenvironmental conditions (humidity, rain, wind, etc.). Suitable measuresmust be taken to protect the welding operation. Ambient temperature mustalways be between:

- 5°C ÷ + 40°C

PE 80 PE 100

210° 10°C for en ≤ 12 mm 215° ± 5°C for en ≤ 20 mm200° 10°C for en > 12 mm 225° ÷ 240°C for en > 20 mm

The heating plate used to heat the parts must guarantee a constanttemperature over the whole surface within 20 minutes after it is turned on.The temperature, measured using a digital thermometer, must be inside a± 10°C tolerance with respect to the value set on the thermostat.Temperature values depend on the thickness en of the parts to be welded,on the type of polyethylene, on ambient conditions and are specified in thefollowing table:

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care measures

The Operator must make sure no external troubles interfere with correctexecution of the joint during the welding.It could happen that the heating element will be cooled because of airchanneled inside the pipelines. We recommend to close the pipeline endsand remove the protective caps only when welding is completed.The heating element must always be placed in its special support toprevent damages on the teflon coating. This one must be periodicallyreconditioned. It must be cleaned, when cold, with isopropyl alcoholwhenever it presents traces of grease, dust or PE residuals.

welding pressure

A 0.15 N/mm2 welding pressure is required for polyethylene.Special tables that give pressure values necessary for welding differentdiameters and thickness, must be supplied by the manufacturer of thewelding machine.Pressure can be adjusted using a distributor monitored by a pressuregauge.

drag pressure

Drag pressure is the minimum pressure necessary for the movable jawsof the welding machine to overcome friction. Its value mainly depends onthe weight of the pipes to be welded, but it also depends on the oiltemperature in the hydraulic circuit and on the jaws clamping force. Thisvalue must be checked for each welding and added to the welding andheating pressures given in the tables.

PE 80 welding cycle(and PE 100 with en ≤20mm)

49

The two ends are pushed against the heating plate with a pressure valuep1 that is the sum of p (from table) + pt (drag pressure).

The “heating with pressure” operation ends, after a t1 time as long as itforms a bead fused material, whose width A varies with the pipethickness:

A = (0,5 mm + 0,1 • en)

Ex. pipe dn 110/S5en 10 mmA 0,5 + 0,1 • 10 = 1,5 mm

The right value is given in the welding tables.

t1 phaseheating (with pressure)

pressure

N/mm2

time

50

In a relative short time it forms a bead of melted plastic, which shows thatthe material has started the fusion process.At this step, pressure is released avoiding the pushing out of meltedmaterial, which will lack for connection and will damage the good qualityof jointing (cold and fragile welding).The pressure is released to value p2 equal to 0,02 N/mm2.Whenever pressure p2 is not specified in the welding table furnished withthe control unit, we recommend setting the pressure gauge on a value thatis near to zero but never less than drag pressure.If the operation is correct, during this step which lasts for a time t2, thesurface heating continues without increasing the overthickness.

There is an approximate relationship that shows the value of heatingwithout pressure t2, expressed in seconds, equal to:

t2 = 12 • en ± en

where en = thickness in mmEx. pipe dn 110/S5

en 10 mmt2 12 • 10 = 120 sec ± 10

In any case the exact value is specified in the welding tables.

t2 phaseheating (without pressure)

t3 phaseremoval of the heating plate

51

At expiring of time t2, the ends are separated to allow the heating plateremoval and subsequently brought together for jointing.

This step is the most critical part of the jointing cycle. Correct performanceof this phase is essential for a successful welding. Separation speed mustbe as fast as possible to avoid cooling of the ends.

Smaller is the thickness of the pipes/fittings, faster must be the separationspeed. In any case it must be completed in a time t3 which means:

t3 = 4 + 0,3 • en


en 10 mmt3 4 + 0,3 • 10 = 7 sec

At the same time, when the two parts are brought together and during thewelding with pressure phase (to value p5), speed must be enough to avoidthat melted material may be pushed out and completed within the t4 time,expressed in seconds, equal to:

t4 = 4 + 0,4 • en


en 10 mmt4 4 + 0,4 • 10 = 8 sec

Whenever the stated pressure value p5 exceeds, avoid a following dropwhich will cause a decompression stress, damaging the jointing.

52

t4 phaseunder pressure ramp

53

the welding pressure must be kept for a time t5, at the end of which thetemperature in the welding area moves from the starting 220°C to about70°C.There is an approximate relationship for pressure welding time t5

expressed in minutes:

t5 = 3 min + en


en 10 mmt5 3 + 10 = 13 minutes

Welding pressure p5 is equal to “heating without pressure” value p1.When value p5 is achieved, a bead is formed whose width B must bewithin the range of values according to UNI 10520 standard point 11.1.2.For practical test on trench woks for en = 20 mm: bead width B must bebetween a minimum of 3 mm + 0,5 en and a maximum of 5 mm+ 0,75 en.

Ex. pipe dn 110/S5en 10 mmBmin 8 mmBmax 12,5 mm

It must also be uniform over the entire length of the circumference: thebead width B, at any point on the weld, must never vary more than 10%with respect to the average value:

B min + B max

Bm = ————————-2

where Bmin and Bmax are respectively the minimum and maximum valuesmeasured.

The maximum difference between the half-beads b1 and b2 must be at anypoint in the welding less than 10% of the width B of the bead forpipe-pipe jointing and 20% for pipe-fitting jointing.

t5 phasewelding with pressure

for PE 80

54

At the expiring of time t5, pressure is released and the joint removed fromclamps.

It is a good principle to wait for a further time t6 before stressing it. Thistime, expressed in minutes, must never be lower than 1,5 times thepipe/fitting thickness (safety time) and permits the joint to achieve atemperature of approximately 40°C.

t6 = 1,5 • en


en 10 mmt6 1,5 • 10 = 15 minutes

Absolutely avoid quick forced cooling methods like water, compressed airor other agents.

t6 phasecooling/safety time

PE 100 welding cycle(for en >20mm)

55

Once the ends are joined together, the welding pressure p5 0.15 N/mm2,must be maintained for a time t5 equal to 10 seconds and then reduced topressure value p6 of 0.05 N/mm2 and kept at this pressure for the time:

t6 = 3 min + en

where en = pipe in mmEx. pipe dn 110/S5

en 10 mmt6 3 + 10 = 13 minutes

When en > 20 mm, in addition to changing the temperature value, it is alsonecessary to apply the special “Dual Pressure” cycle which is the same asfor PE 80 except for the following phases:

t5 e t6 phaseswelding with pressure

for PE 100

Pressure

N/mm2

Time

56

t7 phasecooling/safety time

welding tables

The tables that give welding parameters (times and pressures relating tothickness and diameter) must be furnished by the manufacturer of thewelding machine and are specific for each model.

THEY CANNOT BE SUBSTITUTED FOR EACH OTHER.

They must always be available every time the welding machine is used. A copy should be filed.

At the expire of time t6, pressure will be released and the joint removedfrom clamps.

It is a good principle to wait for a further time t7 before stressing it. Thistime expressed in minutes, must never be lower than 1,5 times thepipe/fitting thickness (safety time) and permits the joint to achieve atemperature of approximately 40°C.

t7 = 1,5 • en

where en = thickness in mmEs. pipe dn 110/S5

en 10 mmt7 1,5 • 10 = 15 minutes

Absolutely avoid quick forced cooling methods like water, compressed airor other agents.

butt fusion machine

57

The butt fusion machine must be in accordance to UNI 10565 standardand with CE marking; it is also guaranteed to give:• a correct axial adjustment/movement of the pipes through the clamps;• a proper and true planing of the pipes/fittings through the facer tool;• a careful control of the welding pressure as well of the heating plate

temperature;• the conformity to the safety standards.Each machine can buttweld different diameters; according to the pipedimensions, the reducing insert are fitted into the standard clamps.The butt fusion machine consists of a supporting mounting with fixed andmovable clamps. Those movable, hydraulically driven with manual orelectrical control, are rolling on two guides.

The machine is provided with a facer tool (electrical or manual), anelectrically heating plate, an electro-hydraulic unit with distributor andmanometer pressure gauge.

The heating plate must guarantee uniform temperature on its wholesurface.The temperature control is carried out with an adjustable thermostat whichguarantees a maximal variation of ± 2°C of the stated temperature. On thelast up-to-date models, a thermometer is mounted on the heating elementwhich gives values with a precision equal to ± 10°C.

The welding unit must undergo periodic overhaul (biennal) according toUNI 10565 standard.

Inspection of weldedjointing

Insp

ectio

nof

wel

ded

join

ting

non-destructive testingsvisual testBUTT FUSION

61

DEFECT POSSIBLE ORIGINS

The bead is not rounded on the surface Normal when welding pipes producedof the pipe, but is raised up with bimodal PE 80 resins or PE 100 with

en ≤ 10 mm

In other cases it may be due to jointingperformed too quickly, too long“under pressure ramp”, too long removaltime of the heating element, insufficientheating

Irregular outline of the bead Non satisfactory preparation of the endson the pipe circumference to be welded (incomplete planing)

Bead dimension different to the foreseen value Bad setting of welding parameters(temperature, pressure, welding time)

Deep carving by the center of the bead Temperature values or welding pressure lowerthan the estimated ones

Surface inclusions by the bead Non satisfactory cleaning of the ends to be welded

Exceeding brightness of the bead surface Overheating during the welding cycle;exceeding temperature of the heating plate ortoo long heating time

Off-centering higher than 10% Wrong centering or exceeding out-of-roundof the pipe/fitting thickness of pipes

62

visual testELECTROFUSION


Lack of protrusion of fusion indicators The fitting has not completed the entire weldingcycleExceeding out-of-round or undersized pipesWrong positioning of the fittingWrong welding parameter settingsNot use of the aligning clamp

Off-centering of the welded parts Not use of the aligning clamp

Visible lack of scraping Insufficient scraping

Wrong insertion depth signed Wrong positioning of socketon the parts to be welded

Protrusion of melted material or damages Wrong welding parameters settingson the outside surfaces of the welded parts Times or voltages higher than requiredWelding cycle interrupted before completion Not use of aligning clamp

Off-centering, incorrect connection of the weldingmachine cables, defective welding machine,defective fittings, short circuit between coils

laboratory testBUTT FUSION

63

Non-destructive testing methods for polyethylene joints made by buttfusion are now under consideration for the achievement of reliableinstruments that permit fast on-site inspection.Good results have been obtained in the laboratory using X-ray andgamma-ray devices as well as using ultrasound techniques.

The following data gives the most typical defects that can be identified byradiological techniques:


Cold welding Low temperature of the heating plate, restricted heatingtimeToo high pressure with exceeding pushing out of material orjointing performed too fast

Crack inside Overheating or load application before the elapsing of the correct the reinforcement cooling timein the melting area

Shrinking cavity Defective jointing pressure or time too restrictedin the fusion area

Porosity Non satisfactory cleaning of the ends to be welded

Inclusions Dust, sand or metallic particles coming from ambient

Possible oil or grease inclusions cannot be noticed with the radiographic testing, for the littledifference of radiation absorption regarding polyethylene.

laboratory testELECTROFUSION

A non-destructive x-ray test technique for electrofusion jointings is understudy and presently carried out exclusively in specialized test laboratories,in the way to allow tests to be performed at the work site. Beingpolyethylene a poor electrical conductive material, these applicationsrequire special research to improve the sensitivity of test instruments.

64

wrong positioning wrong welding parameters setting

off-centering irregular welding bead

off-centering not rounded welding bead

destructive testingsBUTT FUSION

65

In consideration of the highly viscoelastic behaviour of polyethylene, thelast studies showed that the most significant testings in order to define thequality of a butt fusion welding, are “long term” testings whether these arepressure tests or high temperature tensile strength tests.

It has also verified that tensile strength tests carried out at ambienttemperature on test welded samples, after the planing of the bead can bea good choice (considering the mechanical strength) between good qualityweldings (test sample cracking after the overcoming of the yielding load ofthe raw material) and faulty weldings (fragile cracking at melted areabefore getting over this load).

UNI 9737 Standard require the following laboratory testings to beperformed in order to qualify Welders:

- TRAVERSE TENSILE TEST- TRAVERSE AND LATERAL BENDING TEST

Important experiences have been performed to evaluate the compatibilityof weldings between different resins using the CLT - Constant Load Test.

These consist in submitting different series of test samples, taken bothfrom welding parts and from the pipe alone, to different static loads whileimmersed in water at 80°C and 95°C additioned with tensioactiveingredients to speed up cracking. Results are positive if the welding factorand the ratio between the result from the entire pipe and that from thewelded pipe, is ≥ 0.8.

66

electrofusion

The following tests to evaluate the quality of electrofusion jointings can beperformed exclusively at specialized laboratories and by qualifiedpersonnel in accordance with UNI 9737, pr EN 1555, pr EN 12201, ISO8085, ISO 4437 Standards:• 165 h - 80°C internal pressure strength test• cohesion strength test - peel test, crush test• tensile test• stress crack resistance on electrofusion saddles.

Cohesion strength tests are particularly meaningful. These consist of testssuch as the crush test for diameters between 20 and 63 mm and the peeltest for larger diameters.

peel test crush test

pressure test tensile test

Inst

alla

tion

of P

E pi

pelin

esy

stem

s

Installation of PE pipeline systems

SERIES SDR PIPELINE WORKING

S TYPE CONDITIONS

12,5 26 7a Max 0 ,04 bar

12,5 26 6a Max 0 ,5 bar

12,5 26 5a Max 1 ,0 bar

8 17 5a Max 1 ,5 bar

5 11 4a Max 5 ,0 bar

pipelineclassification

69

pr EN 12201

°C

working pressures of PEpipelines

carrying fluids

D.M. 24.11.1984 - D.M. 16.11.1999 - UNI CIG 9034-9165

working pressuresof PE pipelines

carrying fuel gas

20 6,0 8,0 10,0 12,5 16,0 20,0 25,0

30 5,2 7,0 8,7 10,9 13,9 17,4 21,8

40 4,4 5,9 7,4 9,3 11,8 14,8 18,5

MAX. WORKING PRESSUREACCORDING TO TEMPERATURE OF CARRIED FLUID

PRESSURE (bar)

70

depth

pipe laying bed

The bottom of the excavation must be flat, made of uniform materials andwithout elements that can origin mechanical stresses on the pipe.Pipelines must always be laid on a bed of sand or screened earth with aminimum thickness of 10 cm, protected around their entire circumferenceby same and well compacted material.

type of pipeline minimum depth

6th and 7th class gas pipeline 0,6 m4th and 5th class gas pipeline 0,9 mFire-fighting pipeline 0,8 mPotable water pipeline 1 mSewage pipeline 1,5 m

excavation

Excavations for PE pipes laying have to be made with straight sides witha minimum width at the bottom of the excavation at least 20 cm greaterthan the diameter of the pipe to be laid.

The minimum burial depth has to be measured from the upper generatrixof the pipe and depends on the use as specified in the following table thatsummarizes guidelines now given by the standards. Depth must also beevaluated in consideration of the road loads and freezing dangers.

Whenever these minimum depth values cannot be achieved, dependingon the type of ground and on the presence of other buried utilities, thepipeline must be protected by tubular sheathes, cement buildings orequivalent materials.

In case of smaller bending radii it is necessary use moulded elbows orsegment bends.

installation

pipes bending

71

Installation procedures must be performed by expert Operators.Pipes must be installed in the exact positions, both in height and in planlayout, as specified in project drawings unless otherwise ordered by theWorks Supervisor.

In any case the single pipelines, made outside the excavation, must belowered into the trench work by hemp or synthetic ropes, avoidingscraping them on the ground or on the edges of the excavation. Pipesections with surface cuts exceeding 10% of their thickness must beeliminated.

Pipe control components such as valves and gate valves that can exercisestress on the pipes due to their weights must be supported by independentsupports so that they do not transmit their stress to pipeline and joints.

class of pipe minimum bending radius

PN 4 - S 12,5 r = 50 de

PN 6 - S 8 r = 30 de

PN 10 - S 5 r = 20 de

PN 16 r = 20 de

To avoid excessively stress on the material, PE pipes can be bended atthe following bending radii (r) and at a temperature of 20°C. No type offorced heating must be employed.

72

refill

covering the excavation

signals

A continuous colored ribbon must be installed above the pipe, during thelaying, with the message “Attention Water Pipe” or “Attention Gas Pipe”.This ribbon must be at a level 30 cm higher than the upper generatrix ofthe pipe to indicate the presence of the pipe in case of subsequentexcavations. Whenever other utilities are being installed these must neverexcavate into the sand that covers the existing pipeline.

If pipeline detection systems are used, such as Ball Markers, these mustbe perfectly fixed on the pipeline by plastic bands in order to keep themaxially aligned.

For covering (at least for the first 50 cm above the pipe) can be usedexcavated material too, and it must be done for the entire pipeline in thesame ambient temperature conditions. We recommend covering duringthe coolest hours of the day, leaving one end of the pipeline free so it canrecover movements due to expansion or contraction until it settles downand adapts to the temperature of the ground.

Once pipes are placed in the excavation they must be covered by a layerof sand not lower than 10 cm measured from the upper pipe generatrix.Special care must be used when compacting the layer up to about 2/3rdsof the pipe height. Compacting must be manually done avoiding any pipemovement.

Compacted sand must have excellent consistence and good uniformity,covering both sides of the pipe.

parallelismand crossing

distance from buildings

73

Parallelism and crossing of railroad or tram lines are prescribed withinspecial rules issued by the Ministry of Transportation directly for the utilitysystem safeguard.

In case of aligning with urban tram lines, the minimum distance betweenthe outer surface of the pipeline and the nearest rail must never be lessthan 0.50 m.

When crossing tram lines, the pipeline depth must never be less than 1meter from the upper pipe generatrix and the rail track.

In addition the pipeline must be fitted in a protective pipe extended for atleast 1 m beyond each side of the crossing, starting from the external rail.

Preexisting buildings (bridges, underpasses, etc.) can be used whencrossing waterways, getting over differences in level, etc. If pipelines carryfuel gas they must always be buried in the roadbed.

The distance between surfaces, when passing over or under pipelines,must always permit maintenance on all utilities.The distances specified when running in-line or when crossing with gaspipelines must always be complied with the pipe type. These distancesvary from 0.2 to 1 m.

The following safety distances are required for PE pipelines used fordistribution of fuel gas and running aligned to buildings according toMinisterial Decree 24.11.1984 and Ministerial Decree 16.11.1999:

TYPE OF PIPELINE MINIMUM DISTANCE FROM BUILDING

6th and 7th class pipeline no distance

4th and 5th class pipeline with dn ≤ 50 mm no distance

4th and 5th class pipeline with dn > 50 mm laying class A : 2 m

laying class B : 1 m

Pipeline testing

Pipe

line

test

ing

pipelinetesting

water distribution

77

Pressure testings are carried out on the laid pipeline including all fittingsand control components as long as these are suitable for the estimatedpressure. On the contrary the fittings/accessories must be left out byinserting detection disks.On-site hydraulic testing of PE pipelines must be performed on sectionsno longer than 500 m to avoid problems whether during test (refilling withliquid, checking joints, presence of air bubbles) or in case of welding crack(total emptying and refill).

The pipeline must be anchored to avoid movements by pressurized pipes.We recommend to proceed with partial trench covering leaving thejointings uncovered for further inspection.This allows an uniform temperature of the pipe, avoiding any variationduring the different hours of the day and the night. It also permits greateraccuracy in calculating the water quantity added during test period.The pipeline filling is carried out with water starting from the lowest pointof the pipeline system. At this same point the following equiment must beinstalled:- a pressure gauge- a pressure and time parameter recorder- a volumetric meter.

Special care is necessary for allowing air to exit from the suitably installedbleeds.Tests normally performed are the standard or the up-to-date typeaccording to EN European Standards projects. Both methods can beselected by the Customer or by the Works Supervisor; verify here belowdescription.

Before final covering of pipe excavation it is always good practice toperform a tightness test of the jointings and a pressure test of thecomplete pipeline, even if it is not specifically required by specifications orby the customer. Tests can be performed according to the guidelinescontained in the IIP Recommendations: Publication No. 10 for water andPublication No. 7 for gas PE pipelines.

Generally these tests are performed by sectioning parts of suitable lengththat must be closed by safe systems.These systems can be, for example blank flanges with connections forpressure gauges, pumps, breathers, etc.

78

standard testingpreliminary test - 6 hours

approval test - 6 hours

Approval test begins at the end of the preliminary one: it takes 6 hoursand is developed by reducing the internal pressure to a value of:

P of test = 1,3 • PN where PN is the nominal pressure of the pipeline

In any case the test pressure must not exceed the value: PN + 3 bar

The internal pressure must be measured every hour, as it may generallydrop of 0.3 bar/h. Pressure must NOT be restored up until the end of thetest.Test results are positive when the ∆p (difference between initial and finalpressure) is ≤ 1.8 bar.A test report is drawn up at the end of test and must be undersigned bythe Contractor and by the Works Supervisor.

The preliminary pressure test begins once completed the filling andbleeding operations. No leakage must be checked during this test. Thetest pressure must be kept for 6 hours and its value must be:



The pump must be started every hour to restore test pressure. The meterin the pressurization unit must calculate the fluid volume that is added, asthese data must be recorded in the test report.Due to internal pressure the pipe expands during all the 6 hours test andit can loose up to a 0.8 bar/h pressure. With 20°C temperature the volumecan expand up to 3%. Expansion may be less if temperature is lower than20°C (during the night for example).During the preliminary test it is necessary cyclically inspect all weldedjointings and check the tightness of flanged joints. The operator shouldtake necessary measures for self-protection performing these proceduresin order to prevent risks generated by sudden leaks or breakage.

up-to-date test

79

This method checks the pipeline tightness using a particularly fast“Contraction Method”.

The principle behind this method utilizes the PE viscous-elasticcharacteristic by which the pressure lowering inside the pipeline origins itscontraction and this keeps the pressure at the same level for a shortperiod.

Necessary test equipment includes a motor pump, a storage tank for refillliquid, bleed and adjustment valves, pressure recorder, pressure gauge,thermometer and graduated liter meter or recovery tank to monitor thedischarged volume (≤ 5% subdivision of the required volume).

The tested pipeline length must be kept buried in order it does not exceeda maximum 20°C temperature.

1 Pressure recorder time/pressure2 Pressure gauge3 Adjustment valve4 Liter meter5 Bleed valves6 PE pipeline7 Hydraulic test unit8 Thermometer

Pressure test layout

80

preliminary test

The pipeline is filled with water at a temperature lower than 20°C and witha speed higher than 1 m/s, bleeding the pipe to prevent air bubbles. Thenthe water supply valve is closed and the pipeline settled for at least 1 h(settling phase).Subsequently the pipeline is pressurized at the test pressure:



Test pressure is maintained for 0.5 h restoring the pressure drop back upto the P(of test) (maintenance phase).

Pressure variations with respect to P(of test) are monitored during thesubsequent hour (expansion phase). These must not be greater than30%.

If the pressure drop is greater than 30%, the test is interrupted and theorigin of pressure drop must be eliminated. After 1 hour the testing canstart up again.

To proceed with the approval test this preliminary must be passed.

Pressure curve diagram

test pressurePcoll = 1,5 PNmax PN+5 bar pressure

lowering

approvaltest

settling phase

pressurization

maintenancephase

expansionphase

contractionphase

preliminary test

Time

Pre

ssur

e (b

ar)

approval test

81

n 1 1 n dVamm = 0,1 • F • [ ∑ (Ai • Li)] • Pabb • [-------- + -------- • ∑ (---------) ] [ml]

i=1 EA ET i=1 s i

PN

2,5

4

6

10

16

Pabb

0,4 bar

0,7 bar

1,0 bar

2,0 bar

3,0 bar

When the preliminary test is successfully completed, pressure is loweredto the Pabb value given in the table and depending on the pipeline PN; justregulating the adjustment valve for a few minutes. Pressure is thenmonitored during the subsequent half-hour (monitoring can be extendedup to an hour and a half to obtain a more reliable result).

Relationship between pressure lowering (Pabb)in function of the pipeline PN

If the pressure drop monitored after 0.5 hours is ≤ 0.25 bar against themaximum value measured during this phase, proceed to check this resultby calculating the water volume discharged during the pressure lowering.Test results are positive if the liquid quantity is less than the maximumdischargeable water volume Vamm (ml) calculated using the followingformula:

where:

Vamm = maximum dischargeable water volume (ml)Pabb = pressure drop according to table (bar)d = inside pipeline diameter (mm)EA = 2000 N/mm2 - water compression modulus ET = 800 N/mm2 - short term modulus of PE elasticitys = pipeline thickness (mm)L = pipeline length (m)F = 1.2 - correction coefficient for the air presence in the pipelineA = internal section of the pipeline (mm2)

Examples of positive/negative pressure drop

Positivetest

Negativetest

TimeTime

pres

sure

(ba

r)

pres

sure

(ba

r)

82

gas distribution

joint tightness

pipeline test

The whole network pressure test is performed on buried pipeline.Generally it is hydraulically carried out using air or inert gas, but only aftertaking all necessary measures to guarantee testing in total safety.The test pressure must be:- 1,5 • Pes for 4th and 5th class pipes- 1 bar for 6th and 7th class pipeswhere Pes = maximum working pressure.

These values must be kept unchanged for at least 24 hours. They must bemonitored by instruments, such as a pressure/temperature graph, that candetect the following values: time, temperature and pressure.The only acceptable pressure variations are those due to ambienttemperature (during the night time for example), calculated on the groundof the expansion coefficient of the used gas.

This test can be performed outside the excavation after a suitable closingof the pipeline ends to be tested. These are then filled with air at apressure of:- 1 bar for 4th and 5th Class pipes- 0.2 bar for 6th and 7th Class pipes

Pressure is kept at these values for at least 1 hour and leaks are checkedusing a soapy water solution or other leak-detection substances.

Up-to-date standards require pipeline test and joint tightness for gasnetworks laying too.

The Total Quality

PE/PP fittings for pressure pipes gas and water

Zona Industriale Lago - 38038 Tesero (Trento) ItalyPhone ++39 0462 811 211 - Fax ++39 0462 811 200

E-mail: [email protected] - Website: www.eurostandard.it

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