Transcript Document

Inspection Criteria and Quality
Systems for Welded Steel Structures
13 December 2011
Dave Howse
Consultant Welding Engineer, TWI
Lead Assessor, TWI Certification Ltd
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Summary
1.
2.
3.
4.
Inspection techniques
Properties of welds
Common imperfections
Introduction to BS EN 1090/ISO 3834
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Background
• CE marking of fabricated structural
steelwork expected to become mandatory
in mid 2013.
• Requires steel fabrication to be carried out
in compliance with BS EN 1090:Execution
of steel structures and aluminium
structures Part 2: Technical requirements
for the execution of steel structures.
• Relates to public safety and enforcement
is by criminal prosecution.
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Inspection extent: BS EN 1090
Consequence Class
CC1
Service Categories
SC1
SC2
SC1
SC2
SC1
SC2
Production
Categories
EXC1
EXC2
EXC2
EXC3
EXC3
EXC3
EXC2
EXC2
EXC2
EXC3
EXC3
EXC4
PC1
CC2
CC3
PC2
Service category: loading type ie static or cyclic
Production category: steel strength etc.
Consequence class: high/medium/low consequence
for loss of human life
Gives Execution Class (EXC)
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Inspection technique
• 100% visual
• Supplementary according to Execution Class
and stress etc. varies from 10 to 100%.
• Radiography or ultrasonic testing for butt
welds
• Magnetic particle or penetrant applies to
fillets.
• New WPs requires twice as much
supplementary testing
• Qualification of inspectors except visual:
Level 2 as defined in EN 473.
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Weld acceptance criteria
• BS EN ISO 5817 applies:
• EXC1 quality level D;
• EXC2 generally quality level C except
quality level D for "Undercut", "Overlap“,
"Stray arc" and "End crater pipe";
• EXC3 quality level B;
• EXC4 quality level B+ which is quality
level B with defined additional
requirements.
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As-welded properties in structural steels
• Static Strength
• Fatigue strength
• Impact toughness
– Can’t be inspected for. Fundamental material
property tested in WPQR.
• Corrosion performance
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Static Strength
• Weld size
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Fillet throat
Cracks
Lack of fusion
Porosity
Presence of a weld!
• Weld fusion zone strength
– Fundamental property of the welding
consumable, welding process and parent:
established by Weld Procedure Qualification
testing
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Static Strength
• Weld Throat?
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Hydrogen Cracking
• Delayed in nature hence holding period
before inspection up to 48 hours
• Hydrogen present
– Welding process, rust etc., moisture
• Susceptible microstructure
– Cooling rate, Steel composition
• Residual Stresses
– Joint Design
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Subsurface porosity/inclusions
• Caused by poor
shielding (porosity)
• Pores in parent
(castings)
• Poor of inter-run
cleaning (slag)
• Too much can give a
strength reduction
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Lack of fusion
• Caused by too high deposition rate/cold
conditions/low current
• Poor placement/lack of weave
• Magnetic arc blow
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Surface breaking porosity/adhering slag
• Site of poor paint coverage
• Initiation site for corrosion
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Solidification or Hot cracking
Causes of hot cracking
•high level of impurities in weld/parent metal
•poor cleanliness on joint preparation
•high level of restraint
•insufficient weld bead size or shape
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Fatigue Strength
In service, few structures experience purely
static loads and most will be subjected to
some fluctuations in applied stresses and
may therefore be regarded as being fatigue
loaded.
If these loads are not accounted for in the
design, fatigue failure may occur in as few
as a couple of tens of cycles or several
million and the result may be catastrophic
when it does.
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Fatigue initiation
Stress flow
through toes
and roots
giving stress
concentration
at these sites
Cracks occur over time
in service but are
predictable if service
loading known.
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Stress raising defects
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•
•
•
•
•
•
Cracks
Undercut
Lack of fusion
Lack of penetration
Excess penetration
Lapping
Stray arcing/arc strikes
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Fatigue strength
Probable
crack sites
Develops faster due
to higher stress
concentration
Develops slower
here
Less throat
here
As above
Less throat,
less stiff,
higher stress
concentration
Less throat
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Flotation Chamber
Plane of
Failure
100m
Universal Joint
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Mooring Buoy Failure
Actual situation
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Mooring Buoy Failure
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Mooring Buoy Failure
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ISO 3834
ISO 3834:2005, Quality requirements for fusion
welding of metallic materials
Part 1: Criteria for the selection of the
appropriate level of quality requirements
Part 2: Comprehensive Quality Requirements
Part 3: Standard Quality Requirements
Part 4: Elementary Quality Requirements
Part 5: Documents…..
Part 6: Guidelines on implementing ISO 3834
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ISO 3834
• Wider quality level above Procedure and
Welder qualification.
• Compatible with, rather than conflicting with,
ISO 9001 but concentrates on welding as a
special process
• Level 2, 3 or 4 dependant on:
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Safety criticality
Complexity of manufacture
Range of products produced and material used
Likelihood of metallurgical problems
Extent of likely manufacturing problems
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Which level?
• BS EN 1090 execution class (EXC) which
in turn specifies which level of 3834
applies.
• EXC1: Part 4 "Elementary quality
requirements";
• EXC2: Part 3 "Standard quality
requirements";
• EXC3 and EXC4: Part 2 "Comprehensive
quality requirements
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ISO 3834 Part 2 Comprehensive
• Additional Inspection and testing: measures shall be
taken, as appropriate, to indicate, e.g. by marking of
the item or a routing card, the status of inspection
and test of the welded construction.
• After Welding:
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by visual inspection;
by non-destructive testing;
by destructive testing;
form, shape and dimensions of the construction;
results and records of post-weld operations (e.g. post-weld heat
treatment, ageing).
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ISO 3834 Part 2 Comprehensive
ALSO: Inspection and testing before welding:
– suitability and validity of welders’ and welding operators’
qualification certificates;
– suitability of welding-procedure specification (implies also
supporting WPQR);
– identity of parent material;
– identity of welding consumables;
– joint preparation (e.g. shape and dimensions);
– fit-up, jigging and tacking;
– any special requirements in the welding-procedure specification
(e.g. prevention of distortion);
– suitability of working conditions for welding, including
environment.
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ISO 3834 Part 2 Comprehensive
AND: Inspection and testing during welding: During
welding, the following shall be checked at suitable
intervals or by continuous monitoring:
– essential welding parameters (e.g. welding current, arc voltage
and travel speed);
– preheating/interpass temperature;
– cleaning and shape of runs and layers of weld metal;
– back gouging;
– welding sequence;
– correct use and handling of welding consumables;
– control of distortion;
– any intermediate examination (e.g. checking of dimensions).
Copyright © TWI Ltd 2011
EWF Database of certified companies
http://www.ewf.be
A Taylor & Sons (Leeds) Ltd
Russell Greenwood
29.Jul.2015
Structural steel in heavy plate
Atlas Ward Structures Ltd
B Overfield
19.Jul.2012
Structural Steelwork
Bourne Steel Ltd
Guy Roxby
17.Nov.2014
Design and fabrication of building structural steel in steel grades up to and
including 355 yield
Caunton Engineering Ltd
Martin Edwards
30.Oct.2013
Welded structural steelworks for buildings
Cleveland Bridge (UK) Ltd
A Smedley
3.Dec.2013
Structural Steelwork for civil and offshore structures
Fairfield-Mabey Ltd
William Ervig
24.May.2014
Bridges and heavy steelwork
Harry Peers Steelwork Ltd
D Eccles
21.Nov.2013
Structural Steelwork up to and including S355
James Killelea Ltd
Mr John Turner
9.Mar.2014
Structural steelwork and railway bridges
KRG Industries Ltd
David Crooks
1.Apr.2015
Steelwork for offshore applications: fabrication and overlay
Mabey & Johnson
Mr. G. Thomas
1.Nov.2010
A range of highway bridge systems and modular flotation
Mayflower Engineering Ltd
Jonathan A Bentley
8.Jul.2015
Etc
MTL Group Ltd
Adrian Goodwin
26.Jun.2015
Etc
RJD Engineering Ltd
Alan Powney
10.Dec.2014
Etc
Rowecord Engineering Ltd
Richard Thomas
18.May.2015
Etc
S. H. Structures Ltd
Ian Smith
8.Nov.2014
Etc
Serimax Ltd
Mr Malcolm Watt
20.Sep.2011
Etc
Severfield-Reeve Structures Ltd
J Krancioch
8.Nov.2010
Etc
Watson Steel Structures Ltd
D Swift
8.Nov.2010
Etc
William Hare Ltd
R Brandwood
17.Nov.2013
Etc
eg Company and
contact :
A Taylor & Sons
(Leeds) Ltd., RExpiration Date:
Greenwood
29 July 2015 Product:
Structural steel in
heavy plate
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Any Questions?
Contact for
welding enquiries
[email protected]
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