Friday, June 15, 2012

Welding Inspector Duties


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:
  1. All applicable documents
  2. Workmanship standards
  3. All phases of good workshop practice
  4. 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.

  1. 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).

  1. 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.

  1. 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.

  1. 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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