A Training and Certification Standard for Fusion Welding of PE Pipes

4S Group Conference StockholmWednesday 15th October 2014

Edward Ingham (Exova Utilities)

Introduction

• Failure statistics for PE joints in the UK Water Industry

• Causes of failure of PE joints

• Auditing of the welding process

• On site assessment of weld integrity

Destructive testing

Non- Destructive Testing (NDT)

• Training and Development of a UK National Training Standard

UK National Mains Failure Database (NMFD)

• Analysis of UK NMFD indicates 3.5 failures/100km/year for PE

• Rates possibly higher as repairs made without reporting

• Failures of service pipes not included in database

• Observed failures are not always correctly reported

• Reporting protocols often adapted from those for metal pipes

Polyethylene Materials

• Lessons learnt from problems with early low toughness materials

• Early PE materials (service pipes water) suffered from poor slow crack growth resistance

• Continuous development of PE 80 and PE 100 materials since 1960s

• Current PE materials have exceptional SCG and RCP resistance

• PE 100 materials tested to requirements in excess of current standards

• PE 100+ Association encourages high performance and consistency

• Exova research indicates PE 100 lifetime >200 years

Standardisation for PE Pipes and Fittings

• EN 12201 series of standards for PE pipe/fittings are satisfactory

• Some UK WIS requirements covered in National Foreword

• Certain areas are not adequately addressed

• Fusion lengths specified for electrofusion are minimum

• No tolerances for ovality of coiled pipes

• No contamination test for electrofusion fittings (WIS 4-32-08)

• Fittings >630mm (e.g. stub flanges not covered)

• Important tests (e.g. AREL) not covered in standards for mechanical fittings

UK National Mains Water Failure Database (<300mm)

0

5

10

15

20

25

30

Asbes

tos C

emen

t

Ductile

Iron

Cast I

ron

Polyeth

ylene

PVC

Fai

lure

s/10

0km

/ Yea

r

UKWIR Report: Large PE Trunk Main Failures >300mm Diameter

Extremely variable performance - How can this be improved?

0

2

4

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8

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16

J I F K H E M D L

Bu

rst

Rat

e (F

ailu

res/

100k

m/Y

ear)

Company

These companies appear to have the correct approach

Methods of Jointing of PE Pipe Systems• Butt Fusion Welding (Above ground)

• Extremely reliable technique-historically extremely low number of failures

• Electrofusion Welding (In trench)

• More appropriate for installation in urban areas

• More sensitive to site conditions- disproportionate number of failures

• Failures due to misalignment, contamination, poor pipe surface preparation

• Jointing of coiled pipes significantly more difficult than straight lengths

• Mechanical Jointing (In trench)

• Reliable technique, but failures do occur due to poor assembly

UK National Mains Failure Database for Polyethylene

0

5

10

15

20

25

30

35

40

45

Circum

fere

ntia

l

Longi

tudin

al

Ferru

le

Gas

kets

Join

ts

Oth

er

Pinhol

ePip

e

Unkno

wn

Nu

mb

er o

f F

ailu

res

(%)

Butt Fusion Weld Failures

Extremely reliable technique

Failures extremely rare• Contamination• Pressure issues• Insufficient heating

Heat Affected Zone in Weld

Excessive pressure(single pressure)

Typical weld bead

Failure of Mechanical Fittings

Leakage

A B

C

Mechanical Fittings -Correct Assembly

Good all round access to clamp bands

Suppliers’ ‘Vision’ of a typical trench

On Site Welding Conditions

The reality!Manchester in Summertime

Causes of Failure – Misalignment

Causes of Electrofusion Failures –Scraping of Pipe

Poor scraping of pipe surface

Hand scraping can leave areas of pipe surface intact

Mechanical scraping ensure consistent/even removal of pipe surface

Causes of Electrofusion Failures -Contamination

Particulate contamination due to poor site hygiene

Incorrect use of welding wipes Correct use of welding wipes

Jointing of Coiled Pipes

Large forces required to straighten pipe

Pipe ovality causes gaps

Two joints of potentially poor integrity

Solutions for Jointing of Coiled Pipes

Reduce ovality at manufacture Inserts to correct ovality

Coil straightener to correct curvature

Assuring Good Workmanship

Train

Analyse Test

Audit

ContinuousImprovement

Structured PE Competence Programme

Awareness Training

Site Assessment On-site Joint Tests

Recommended frequency Every 3 years Every quarter Every quarter

Issues Addressed

Lack of awareness & competence

Use of incorrect equipment

Poor equipment maintenance

Commercial or time pressures

Pipe and fittings issues

PE competence programme containing three elements that together address the root causes of poor joint quality

On-Site Joint Testing

DemonstrateThe implications of deviations from best practice (misalignment, poor scraping, etc)

Give Immediate FeedbackProvide advice on equipment and procedures to ensure joint quality

Provide Positive FeedbackWhere correct equipment and procedure is used

WIS 4-32-08

ISO and Gas Geometry

Destructive Testing of Butt Fusion Welds

Force / Deflection Data: Ductile & Brittle Welds

Strength is equal, Energy (area under curve) is different

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35 40Displacement (mm)

Fo

rce

(kN

)

BrittleDuctile

Assessment of Electrofusion Joints

H

P

‘encourage’ cracking

P

Cold ZoneStarter Crack Side Grooves to

P

G

Shear Test – full or part samples!

F F

Double Cantilever Beam (DCB) Hydrostatic Pressure Tests

Failure Modes of Electrofusion Couplers DCB Test

Ductile Mixed

Brittle Voiding

Destructive Testing of Electrofusion Joints

Site Audit Data

All joints made specifically for audit purposesWelders were aware the joints would be tested

Destructive Testing of Electrofusion Joints

Production Joint Data

All joints taken at random from installed system prior to commissioning

NDT Testing of BF Welds (Very simple form)

Twist bead an inspect for signs of splitting

NDT Testing- Microwave (MW) Imaging

• Material under inspection is bathed in microwave energy of an essentially constant frequency (≈ 25GHz)

• Energy is reflected from each interface of differing dielectric constants within specimen

• The reflected energy creates a resulting signal measured in volts

• The resulting voltage is sampled at discreet locations across sample to create an image

• Volumetric inspection technology: will view the entire thickness of the piece at once

Channel A & B are a ¼ wavelength apart

General Probe Configuration

NDT (Microwave) Evaluation of PE joints

• State of the art NDT methods available to inspect plastic joints in the field

• NDT techniques has been verified by mechanical testing

• Removes the need to cut out and destructively test joints.

• Immediate feed back regarding quality of joint.

• Testing can be done on new or in-service pipelines.

• The system can be used in conjunction with current site auditing practices to further improve the reliability and quality assurance of PE joints in the field.

• Fast assessment of joints

NDT microwave results of butt fusion joints

PASS

FAIL

Assessment of Weld Quality using Voltage Threshold

NDT Phased Array Results for Butt Fusion Joints

PA-UT Field equipment

Well fused region of EF joint

Lack of fusion observed in EF joint

Issues with Current Training and Certification• Some training courses based on UK WIS 4-32-08

• Lack of National standard causes inconsistencies in training and hence competence

• Training is classroom based rather than under true site conditions

• All practical assessments use relatively small diameter pipes

• Practical assessments are on straight pipe and not coils

• Theory examinations too easy (everyone passes)

• No time limit before re-training/refresher training is required

• No system to address poor workmanship/or ensure corrective training is taken

Stakeholders

• Water UK

• Water Utilities

• PE pipe and fittings manufacturers

• Welding equipment suppliers

• Installation contractors of PE pipes

• Training companies

• Engineering Contractors

Administration of Standard and Qualification

• Expert group to be set up by Water UK

• Will review effectiveness of training and make change if necessary

• National database holding qualifications- held by UKAS accredited body

• Accreditation body to be appointed by Water UK

Structure of Specification

TrainingArea

EF1

(20-180mm)

EF2

(200-315mm)EF3

(≥355mm to 710mm)

BF1

(63-355mm)BF2

(>355mm to 900mm)

Electrofusion - -

Butt Fusion - - -

Service Pipes - - - -

Distribution Pipes

Straight Pipe

Coiled Pipe - - -

Skinned Pipe

Barrier Pipe - - -

Co-extruded Pipes

Branch Saddles - - -

Range of Qualification

• Standard will be for welding personnel and supervisors of welding personnel

• Aim to make personnel self supervising

• Supervisors retain status by continuous record of competency and on site welding every 6 months

• 3 Qualifications for electrofusion and 2 for butt Fusion

• Qualification will be modular (i.e. to gain EF3 a welder must hold a current version of EF1 and EF2)

• For EF>710mm and BF >900mm specialist training from the fitting/equipment supplier and certificate of competence required

• Qualification valid for a period 3 years

•

Training for Electrofusion WeldingIntroduction Health and safety relevant to the welding process and working in the field Relevant standards (WIS 4-32-08) Pressure rating and SDR rating for pipes and fittings Correct storage for pipes and fittings The consequences of producing a poor quality weld The different types of PE (PE 80 and PE 100) and how these materials differ from Polypropylene and Polyvinylchloride (PVC) The effect of ovality and pipe end reversion Techniques for destructive and non-destructive testing (NDT) of welds Pupped bends and fittings (potential issues regarding clamping) The commissioning pressure tests and pressure tests for electrofusion top tee and saddles Importance of machine calibration and periodic checks on pipe surface preparation tools Welding Equipment Generator and use of power ratings relevant to the procedure being undertaken Control box Pipe surface preparation tools for conventional pipes, pipes with a peelable skin, barrier pipes and coextruded pipes. Pipe clamps for re-rounding and restraining pipes and positioning electrofusion tapping tees and saddles Ancillary Equipment Welding shelter, pipe support Rollers, coil straightening equipment. Techniques for lifting of pipes, pipe cutters, PI tape, marker pen (for marking insertion depths) Isopropanol cleaning wipes and pipe end plugs Checking of pipe/ fittings (markings, damage or ovality)

Training for Electrofusion Welding

Site Preparation Erecting the shelter, preparing the excavation, siting of equipment Appropriate ambient temperature for welding and control of ambient temperature Checks for generator, control box and tooling Production of Electrofusion Welds (Straight Lengths) Importance of site hygiene, Cleaning/preparation of pipe surface (conventional pipes) Cleaning/preparation of pipe surface (pipes with protective skin) Clamping, re-rounding of pipe and dealing with end reversion Operation of the control box, Making the weld Production of Electrofusion Welds (Coiled Pipes) All of the elements for straight lengths plus the following Understanding of difficulty and safety issues with coiled pipes Specialist equipment (coil straighteners) for welding of coiled pipes Techniques for welding of coiled pipes, Making the weld, Rejection of unsuitable welds Assessment of Weld Quality Alignment of weld and evidence of gaps, check for axial movement of pipe relative to fittings Observation of melt indicators. Maintenance Maintenance of equipment, servicing and calibration of equipment Records Welding records, job supervision records and certification information for welding personnel

Training for Butt Fusion WeldingIntroduction Health and safety relevant to the welding process and working in the field Relevant standards (WIS 4-32-08) Differences between manual, semi automatic and automatic machines Pressure rating and SDR rating for pipes and fittings Correct storage for pipes and fittings The consequences of producing a poor quality weld The different types of PE (PE 80 and PE 100) and how these materials differ from Polypropylene and Polyvinylchloride (PVC) The effect of ovality and pipe end reversion Techniques for destructive and non-destructive testing (NDT) of welds Pupped bends and fittings (potential issues regarding clamping) The commissioning pressure tests and pressure tests for electrofusion top tee and saddles Importance of machine calibration and periodic checks on pipe surface preparation tools Welding Equipment Generator and use of power ratings relevant to the procedure being undertaken Control box, machine chassis and clamps, hydraulic unit/control box, trimming tool and heater plate Ancillary Equipment Welding shelter, pipe support rollers, coil straightening equipment, techniques for lifting of pipes, pipe cutters, PI tape, marker pen, Isopropanol cleaning wipes, digital thermometer and probe, timer, bead measurement gauge, pipe end plugs, tools for de-beading the weld Site Preparation Preparing the excavation, erecting the shelter, siting of equipment, checking the equipment use of ground sheets or baseboards Appropriate ambient temperature for welding and control of ambient temperature

Training for Butt Fusion WeldingPreparation for welding Cleaning the trimming tool, cleaning/washing the heater plate Checking the pipe (for damage and excessive ovality) Production of Butt Fusion Welds 1. Clamping Positioning of the pipe, clamping of the pipes 2. Trimming Using the trimming tool, Removing the pipe shavings from the machine Checking the pipe ends (misalignment and mismatch) 3. Making the Weld Dummy welds, Single pressure and dual pressure welding Applying the heater plate, initial bead-up pressure and heater plate removal Rejection of unsuitable welds Assessment of Weld Quality Removal and identification of internal and external weld beads and applying the twist test to weld beads Maintenance Maintenance of equipment and servicing and calibration of equipment Records Welding records, job supervision records, certification information for welding personnel Calibration records, databases for recording welding production and location of welds

Theory Exam

• To ensure knowledge safe working/ production of high quality welds

• Separate exam for each qualification

• Exam will be 1 hour in duration with 20 multiple choice questions

• Failure to answer key questions will result in failure of whole exam

• Score of 80% required to proceed to the practical exam

Practical Test

• Carried out under site rather than classroom conditions

• Welding area set up in accordance with best safety and site practice

• Test to include welding of different pipe diameters

• Demonstrate ability to weld coils and handle long pipe lengths

• Welder and joints will be visually assessed

• Joints produced will be destructively tested

Welding Test Certificate

• Details of qualifications held on National database

• Welder provided with identity card containing qualification information

Retention of qualification provided:

• Welding undertaken with regular frequency (no inactivity>1 year)

• No issue regarding knowledge or practical ability of the welder

• Employer shall establish the competency of the welder on an annual basis

Conclusions• Draft specification well advanced. Publication hopefully in 2014

• Strong basis on practical competency under site conditions

• Theoretical exam will be more demanding that at present

• Practical test ensures competency in joining coiled pipe

• Welders must show competency in welding large diameters before they are permitted to install these pipes on site

• Utilities can ensure competency of workforce by specifying the training standard in their procurement documents

• Standard will improve quality of installation and reduce leakage