General
Quality control of the installation can be divided into three areas:
- Checking the material delivered to site for damage prior to use, checking the roll / panel identification number with factory QA and carrying out checks for the QA procedure.
- Inspection and continuous control of all welding including weld parameters and full testing of regular trial seams.
- Testing of the completed weld seams by destructive and non-destructive methods.
The on site welding of each material is carried out by special welding processes which are fully monitored and tested. This ensures consistent weld seam quality within a wide range of ambient conditions. Daily progress, weather and machinery set-ups and test welds, materials tests, panel sizes, faults and repairs are all recorded on our QA reporting sheets which form part of our contractor quality assurance procedure. A full report is provided following completion of contract works.
Inspection of Welding Seams
(a) Visual Inspection of Welding Seam
Visual inspection of the welding surfaces, the welding process and the completed weld is carried out to ensure consistency of weld.
(b) Destructive Mechanical Testing
The procedure is carried out on samples of completed trial welds under the requirements of the contract QA procedure. Each sample is subjected to tensile testing. At least two specimens are tested, one in the direct tensile mode and one in the peel mode. Once the test has been completed, the sample is viewed to establish where the break occurred and the weld classified by referring to industry standard charts.
(c) Non-Destructive Air Pressure Testing – for Wedge Welded Joints
The welds are tested for continuity by pneumatic pressurisation to the central void in the double weld. On completion of the weld, the channel is sealed at each end and attached to the air testing equipment. The air channel is charged to the correct pressure. It is then allowed to stabilise and is isolated from the air pressure source and monitored. A weld would have passed the test if the air pressure level had not altered by 10% of its initial stabilised value.
(d) Non-Destructive Spark Testing – for Extrusion Welded Joints
A copper wire is encapsulated within the weld. A high voltage electric spark is applied above the welded section. The spark will normally spread evenly across the surface of the weld, but will concentrate into any areas where a satisfactory welded seam has not been achieved, shorting to earth on the copper wire.
(e) Vacuum Box Testing – for Vulcanised Hot Air Joints
This method is used in areas of complex welding detail or where other methods are not feasible, and comprises treating the area of the liner to be tested with a soap solution and then using an open-based box producing a vacuum over the soaped area. Leaks are detected by the appearance of bubbles.
(f) Air Lance – for Vulcanised Hot Air Joints
This method involves forcing a high pressure jet of air along the weld edge and looking for signs of lifting or bubbling.
