THE
DUTIES OF THE WELDING INSPECTOR
VISUAL INSPECTION
At any point in the course
of welding, i.e. tacking, root pass, filler pass or capping pass, butparticularly
for the root and cap, a detailed inspection may be required. British Standard
5289: 1976 gives guidance on tools and responsibilities together with sketches
of typical defects.
The inspector at this point must :
a. Observe, identify and perhaps
record (measure) the features of the weld.
b. Decide whether the weld is
acceptable in terms of the particular levels that are permitted; defect levels
may be ‘in-house’ or national codes of practice.
When the defect size is in
excess of the permitted level then either a concession must be applied for (from a competent person), or the weld
rejected.
AIDS OF VISUAL INSPECTION
Illumination : Good lighting is essential.
Inspection Lenses : The magnification should not exceed 2 - 2.5
diameters. If higher magnification is required use a binocular microscope.
Optical viewing can progressively develop from eyesight, to use of a
hand torch and mirror, to the addition of a magnifier and light source.
In order to achieve accessibility, remote probe units are available
which must have the following properties.
a. Large field of vision
b. Freedom from distortion of image
c. Accurate preservation of colour values
d. Adequacy of illumination
CODE OF PRACTICE
A code of practice for an
inspection department should take the form outlined below. It is appreciated
that full implementation of the code would be extremely costly and therefore it
may be necessary to reduce the amount of inspection to less than is
theoretically required.
The inspector should be familiar with the following:
- All applicable documents
- Workmanship standards
- All phases of good workshop practice
- Tools and measuring devices
INSPECTION BEFORE WELDING
Before Assembly:
Check
·
All applicable documents.
·
Quality plan is authorised and endorsed with
signature, date and company stamp.
·
Application standard is up to date with the latest
edition, revision or amendment.
·
The drawings are clear, the issue number is marked
and the latest revision is used.
· Welding procedure sheets (specifications) are
available, have been approved and are employed in production.
·
Welder qualifications with identification and range
of approval are verified and that only approved welder as required are employed in production.
·
Calibration certificates, material certificates
(mill sheets) and consumer certificates are available and valid.
·
Parent material identification is verified against
documentation and markings.
·
Material composition, type and condition.
·
Correct methods are applied for cutting and
machining.
· Identification of welding consumables such as
electrodes, filler wire, fluxes, shielding and backing gases and any special requirements (e.g. drying) are met.
· Plant and equipment are in a safe condition and
adequate for the job.
·
Safety permits e.g. hot work permit, gas free
permit, enclosed space certificate are available
and valid.
After Assembly
Check
·
Dimensions, tolerances, preparation, fit-up and
alignment are in accordance with the Approved drawings and standards.
·
Tack welds, bridging pieces, clamping and type of
backing - if any used are correct.
·
Cleanliness of work area is maintained.
·
Preheat in accordance with procedure.
NOTE Good inspection prior to
welding can eliminate conditions that lead to the formation of defects.
INSPECTION DURING WELDING
Check
- The welding process must be monitored.
- Preheat and interpass temperatures must be monitored.
- Interpass cleaning - chipping, grinding, gouging, must be monitored.
- Root and subsequent run sequence.
- Essential variables such as current, voltage, travel speed to be monitored.
- Filler metals, fluxes and shielding gases are correct.
- Welding is in compliance with weld procedure sheet and application standard.
INSPECTION AFTER WELDING
Check
- Visual inspection to be carried out to ascertain acceptability of appearance of welds.
- Dimensional accuracy to be ascertained.
- Conformity with drawings and standards requirements.
- Post weld heat treatment, if any, monitored and recorded.
- NDT carried out and reports assessed.
- Assess defects as to either repairing, or application for concession.
- Carry out any necessary repairs.
- Control of distortion
REPAIRS
§
Repair procedure and welding code should be
authorised.
§
Defect area should be marked positively and clearly.
§
Check when partially removed and fully removed
(visual and NDT).
§
Re-welding should be monitored.
§
Re-inspect completed repair.
Collate all documents and reports. Pass the document package on to a
higher authority for final inspection, approval and storage.
THE WELDING INSPECTOR
RESPONSIBILITIES
Ensure
compliance with standard or code.
Ensure
workmanship.
Ensure
welding criteria by ‘policing’ work and documentation.
ATTRIBUTES
Honesty
and integrity.
Literacy.
Fitness -
physical and eyesight.
DUTIES
Observe.
Measure.
Identify.
CODES AND STANDARDS
CLASS OF WORK
There are many types of work
which require engineering materials to be joined by welding, for example:
Pressure vessels Bridges
Oil rigs Earth
moving equipment
Aero-engines Ventilation
systems
Storage tanks Heavy
vehicle chassis
Car bodies Food
processing plant
The quality requirements of
the joints in these fabrications depend on their fitness-for-purpose and differ
significantly from one application to the next. Pressure vessels require welds,
which can withstand the stresses and high temperatures experienced in
operation. Oilrigs are designed to withstand the effect of wave formation and
wind loads. Earth moving equipment has to accommodate differences in terrain
and earth conditions and is subject to fatigue loading. Welds in food
processing plants must withstand corrosion by hot acidic liquors.
Below are listed some
typical codes of practice and standards which cover various types of
constructions fabricated by welding.
Code Class of Work
BS 5500 Unfired
fusion welded pressure vessels
ASME VIII American
boiler and pressure vessel code
BS 2633 Class
1 arc welding of ferritic steel pipe work for carrying fluids
BS 4515 Process
of welding steel pipelines on land and offshore
BS 5950 Structural
use of steelwork in building
AWS D1.1 Structural
welding code (American)
BS 5400 Steel,
concrete and composite bridges
BS 6235 Code
of practice for fixed offshore structure
API 1104 Standard
for welding pipelines and related structures
These documents can also
provide a useful source of data for applications where codes do not exist. It
should be remembered, however, that the principal criterion in the codes listed
is the quality of the joint in relation to the service conditions. There are
other applications where success is judged by different criteria, such as
dimensional accuracy.
Another jimportant
consideration is controlling the cost of welding. Variations in weld times and
quantities of consumables can readily result if the method of making a weld is
left to the welder to decide.
The continuous and
satisfactory performance of weldments made to various codes requires that
specific guidelines are laid down to cover all variables. These guidelines are
usually grouped under the general heading of a Weld Procedure.
CODE OF PRACTICE
A code of practice is a set of rules for manufacturing a specific
product. It should contain:
Design Requirements e.g. fit-up,
preparation and type of joints
Materials e.g.
types, thickness ranges
Manufacturer’s Working Practice
Inspection Criteria e.g.
100% visual, percentage other NDT
Acceptance Criteria e.g.
defect size, limits, etc.
Welding Process e.g.
type, consumables
Types Of Tooling e.g.
use of strongbacks
Contractual Information
The difference between a
code and a standard is that a code states how to do a specific job and does not
contain all relevant information, but refers to other standards for details.
A code or standard generally
mentions three parties - the customer or client, the manufacturer or producer
and the inspection authority. In a code the term ‘shall’ means mandatory - must
be done, and the term ‘should’ means recommended - not compulsory.
A concession ijs an
agreement between the contracting parties to deviate from the original code
requirements. (BS 5135)
THE WELDING PROCEDURE
A welding procedure is a way of controlling the welding operation.
Purpose of procedure:
1) To prove a joint can
meet design procedure - consistency
2) Instruction for welder
3) Ensure repeatability
Weld procedures are approved
to ensure they are functional and fulfil the physical and mechanical properties
necessary to reach the required standard (to establish the essential variables
for contractual obligations).
Welders are approved to
ensure a particular welder is capable of welding to a procedure and obtaining a
result that meets specification.
The task of collecting the
data and drafting the documentation is often referred to as ‘writing’ a weld
procedure. In many ways this is an unfortunate term as the writing of documents
is the last in a sequence of tasks.
Producing a weld procedure involves;
Planning the tasks
Collecting the data
Writing a procedure
for use or for trial
Making test welds
Evaluating the results
of the tests
Approving the
procedure of the relevant code
Preparing the
documentation
In each code reference is
made to how the procedures are to be devised and whether approval of these
procedures is required. In most codes approval is mandatory and tests to confirm
the skill of the welder are specified. Details are also given of acceptance
criteria for the finished joint.
The approach used depends on the code, for example:
BS 2633 (Class 1 arc welding
of ferritic steel pipe work for carrying fluids) provides general comments on
various aspects of a suitable weld procedure.
AWS D.1.1 (Structural
welding code - steel) favours more specific instructions for different joints
and processes that are, in effect, pre-qualified procedures.
Other codes do not deal
specifically with the details of the weld procedure but refer to published
documentation, e.g. BS 5135 ‘process of arc welding carbon and carbon manganese
steels’.
COMPONENTS OF A WELD
PROCEDURE
Items to be included in the procedure can be some of the following:
Parent Metal
a. Type
b. Thickness (for pipe
this includes outside diameter)
c. Surface condition
d. Identifying marks
Welding Process
a. Type of process
(MMA, TIG, SAW etc.)
b. Equipment
c. Make, brand, type
of welding consumables
d. When appropriate,
the temperature and time adopted for drying and baking of electrodes
and / or consumables
Joint Design
a. Welding position
b. Edge preparation
c. Method of cleaning,
degreasing etc.
d. Fit up of joint
e. Jigging or tacking
procedure
f. Type of backing
Welding Position
a. Whether shop or
site weld
b. Arrangement of runs
and weld sequence
c. Filler material,
composition and size (diameter)
d. Welding variables -
voltage, current, travel speed
e. Weld size
f. Back gouging
g. Any specific features, e.g. heat input control,
run-out length
Thermal Treatment
a. Preheat and
interpass temperatures including method and control
b. Post weld treatment
including method and control
ESSENTIAL VARIABLES
An essential variable is a
variable that will influence or change the mechanical or metallurgical
properties of the welded joint - changes affecting the procedure approval. Any
change in an essential variable requires a new welding procedure specification
(WPS).
Essential variables include:
wall thickness, joint design, process, materials, consumables, welding
position, direction, heat input (voltage, amperage, travel speed), heat
treatment.
APPROVING THE PROCEDURE
When the data has been
collected, the procedure must be validated by producing and testing a trail
weld.
If the procedure is to be
used on a fabrication, which has been designed to meet the requirements of a
code, the test weld is done under the supervision of an independent witness.
The detailed arrangements for the test are subject to agreement between the
contracting parties.
A number of British
Standards make cross-reference to another standard which covers approval
testing. Other codes of practice include their own weld procedure / welder
approval information. In general they include a standard format, which can be
used to report the results of an approval test.
Range of approval. (extent of approval, scope of approval)
Provides a working range
over which certain variables may alter without requiring a new welding procedure
or welder approval.
Variables include thickness
(e.g. 1/2 down to 2x above), diameter (e.g. 1/2 down to 1/2 above) materials
(different materials can be covered), position, process, parent plate group,
and consumables.
Re-approval of a welding
procedure is necessary if there is a change of any of the essential variables
or considerable defect re-occurrence.
ABBREVIATIONS
WPS welding
procedure specification - an approved and accepted welding procedure; an
authorised
document.
PQR procedure qualification records
- proof the procedure works - record of tests undertaken to qualify procedure.
WAC welder approval certificate -
required to ensure a particular welder is capable of welding to a procedure.
WATC welder approval
test certificate.
WAR welder approval
record.
WPAR welding procedure
approval record.
WQT welder
qualification test.
pWPS preliminary WPS - unauthorised
(contains all essential variables and, after welding the test piece and all NDT
and destructive tests have been accepted, then the WPS can be approved).
WPS and WPAR give final WPS
(various WPS can derive from one pWPS).
DOCUMENTATION
The objectives of a procedure or welder approval test are:
a.
To prove the procedure meets the necessary
requirements with reference to feasibility, mechanical strength etc.
b.
To prove the welders are competent to work on a
particular job.
If a customer queries it, evidence can and would be supplied to prove
validity.
Approval Test Specifications call for a paper record, which can be
known as:
Procedure / welder
approval certificate
Procedure / welder
approval record
Procedure / welder
approval report
The following records should also be kept:
NDT reports
Records of visual
examination or mechanical testing
Test pieces from
destructive testing
Other records that are equally important are proof of regular employment on a job for scheduling re-tests to
avoid duplication on procedure approval.
WELDER APPROVAL
Welder approval tests are
used to determine the ability of a welder to produce welds of an acceptable
quality with the processes, materials and welding positions that are to be used
in production. Dependant on the requirements and administration the
manufacturer or contractor may choose to qualify their own welders or they may
employ outside personnel who can meet the requirements. These requirements
usually specify verification of the tests by an authorised inspector or
independent body. The requirements for the qualification of welders are usually
laid down in the governing code or specification or the contract specification.
Approval tests improve the
probability of obtaining satisfactory welds in production. However it is true
to say that approval test welds are made with special attention and effort and
so cannot show whether or not the welder can do so under every production
condition. For these reasons complete reliance should not be placed on these
qualifications - production welds should be inspected regularly to ensure that
the standard is being kept up.
Types Of Approval Tests.
Tests that are prescribed by
most codes and standards are in the main similar. Common tests are:
a. Plate and structural
members.
b. Pipe welding.
c. Positions of welding.
d. Testing of approval
testpieces.
e. Re-tests.
- Plate and structural members.
The requirements for welders
of plate and structural parts (including pressure vessels) usually require the
welder to make one or more test welds on plate or pipe assemblies with the
qualified welding procedure. Each weld is tested in a specific manner, often
both destructively and non-destructively. The requirements normally state the
applicability of material thickness and welding positions that will qualify for
production work. Other details will cover joint type and direction of welding
when depositing vertical welds (vertically up or vertically down).
- Pipe welding.
The requirements for the
approval of welders for pipe welding differs from those for welding plate and
structural members chiefly in the type of test assemblies and test positions.
As a rule the welds must be made on pipe and not plate. In some cases the space
within which the test piece must be welded may be restricted if the production
work involves welding in cramped conditions. As a general rule welders who
qualify for certain joints on pipe need not qualify for plate work, but
qualifications on plate do not apply to pipework.
- Position of welding.
Approval tests are normally
expected to be made in the most difficult positions that will be encountered in
production welding. For example qualification in the vertical, horizontal and
overhead positions usually qualifies for welding in the flat position.
- Testing of welder approval test pieces.
All codes and specifications
will have definite rules for the testing of approval welds to determine
compliance. Most frequently this involves the removal of specimens for
mechanical tests, such as bend tests, and specimens for macro examination from
specific locations in the test pieces. Non-destructive testing may be required
in conjunction with the mechanical tests.
Other properties required of
the procedure qualification welds such as tensile strength, hardness, etc. are
not generally specified in welder approval tests since these properties depend
primarily on the parent and filler materials used on procedure details that are
beyond the individual welder's control.
Welders whose test welds
meet the requirements are qualified to use the process and to weld with the
filler metals and procedures similar to those used in testing. It should be mentioned
that a welder who has successfully welded a procedure test specimen is not
required to undergo an approval test, unless the requirements of production
welding are different from those of the procedure in which he has qualified.
e. Re-tests.
The circumstances for the re-testing of a welder include the following:
1. Failure of the initial
test welds.
2. A significant change in
welding procedure.
3. A welder has not been
engaged in welding for an extended period. (Usually three months.)
4. There is reason to
question the welder's ability.
5. Change of employment
without the transfer of his approval certificates.
CHECK LIST FOR WELDER AND
PROCEDURE APPROVAL
1. The test being carried
out is the correct one required.
2. Welders are in
possession of all relevant information concerning the test.
3. Test materials confirm
in all respects to requirements.
4. Joint configuration and
tolerances are correct.
5. Welding plant and
consumables.
6. The welder's
identification is clearly marked on the test piece.
7. Where it is specified
for a root run to be stopped and restarted in a certain position, that this
position is clearly
marked.
8. In the case of joints welded in fixed positions the test
piece is so fixed that it cannot be moved.
9. All ancillary tools such as chipping hammers, wire brushes,
grinders, etc. are available.
The tests should be carried
out without interruption but with sufficient supervision to ensure that the
requirements are being complied with. Where welder approval is carried out in
accordance with ASME section IX it states that the person supervising the test
may, if in his opinion he considers that the welder will not meet the required
standard, terminate the test at any time. If it is necessary to apply this
ruling, it is suggested that full reasons for termination be recorded. It is
further recommended that the testpiece should also be kept for a short period
as a means of backing up written statement.
If the test is to be
supervised by a representative of an independent authority he should be given
all the relevant details of the testing required.
Where British standards are
involved, they generally state that if the welder is of the opinion that his
first attempt may not pass any subsequent testing, he may withhold it and weld
a second. In this case it is the second testpiece that is submitted for
examination and the first one must be scrapped.
TEST CERTIFICATE
Should state clearly that it is a welder approval and not a procedure
approval, and, depending on the particular standard, should contain the
following:
a. welder’s name and
identity number
b. date of test
c. standard of code in
full, e.g. British Standard 4872 PT 1: 1982
d. test piece details
including material specification
e. equipment and
consumable details
f. extent of approval
g. sketch of run
sequence, preparation and dimensions
h. other factors,
operating parameters etc.
i. the test results
(visual, NDT, DT etc.)
j. remarks
k. witnessed by
l. test supervisor
m. location
Most standards give an example of a test certificate.
Signatures on certificates must be endorsed by company stamp.
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