VISUAL INSPECTION
At any point in the course of welding, i.e. tacking, root pass, filler pass or capping pass, but particularly 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:
a) All applicable documents
b) Workmanship standards
c) All phases of good workshop practice
d) 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 welders 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.
* 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.
