a training and certification standard for fusion welding of pe pipes 4s group conference stockholm...
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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
6
8
10
12
14
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