Control of samples, tolerance joints, control joints
acceptance joint – a welded joint performed during the certification of welding technology;
tolerance joint – a joint performed during tolerance tests of welders;
· control joint – a joint cut out of a welded pipeline string for testing in the scope provided for by current standards;
· guarantee joint – a joint that connects sections of the pipeline subjected to test pressure. The guarantee joint is not subjected to test pressure and requires a larger (in comparison with the overlap) volume of non-destructive testing, for example, duplication of radiographic testing by ultrasonic testing.
Acceptance testing of welders
The purpose of acceptance testing of welders or operators of welding machines is to determine the welder’s ability to make a quality weld using the welding process.
All welders involved by the contractor to perform work at the facility must be certified in accordance with the current Certification Rules.
Tolerance tests of welders are carried out by welding tolerance joints immediately before the start of welding work at the facility.
A welder may be certified to perform the entire joint as a whole or a specific layer (s) of the weld.
During tolerance tests using the technology of manual arc or semi-automatic welding of fixed joints of pipes with a diameter of less than 1020 mm, the welder must weld 100% of the joint perimeter (the entire seam or a specific layer). For joints with a diameter of 1020 mm or more, it is allowed to weld one of the halves of the joint perimeter (relative to the vertical axis).
A welder-operator certified for automatic welding must perform the entire set of operations associated with welding the entire joint as a whole, or those layers for which he is certified.
A welder or welders who have welded a joint recognized as fit during the certification of welding technology are considered to have passed the tests and may not perform welding of a tolerance joint.
In the process of tolerance testing, the welder must comply with all the requirements of the technological instruction and operational flow chart, use equipment, observe the welding technique and the speed of all operations that will be used in the future when welding or repairing welded joints of the oil pipeline.
Pipe coils prepared for welding of tolerance joints must be made from the same pipes, i.e. have the same strength class, wall thickness and groove as the pipes used for the construction of the facility. The length of the coil for tolerance tests for manual and semi-automatic welding must be at least 125 mm. To carry out tolerance tests for automatic welding, the length of the coil is set based on the possibility of meeting all the requirements of the technological instruction and technological map.
The tolerance joint must be carried out in the presence of a representative of the Customer’s technical supervision service, while ensuring continuous operational control and consistent assessment of the quality of operations.
Repeated admission tests of a welder, including when working as part of a team, are prescribed in cases where:
he had a break in his work for more than three months;
· the content of the technological instruction and the technological map has been amended, listed in clause 2.1.6.3. However, welders may be allowed to work at the facility without repeated admission tests, provided that the practical examination during the certification of welders in accordance with the current Rules was carried out in full accordance with the technological map for the welding process, which was certified and is used at this facility.
Tolerance tests of welders for repair work are carried out for each type of repair, regulated by the technological instruction. The length of the seam section for each type of repair must be at least 200 mm.
The tolerance joint is subjected to:
· step-by-step control in the course of welding;
visual inspection with the determination of the geometric parameters of the welded joint;
radiographic control;
· control of weld sizes and the presence of unacceptable defects in macrosections (in the case of double-sided automatic submerged arc welding);
· mechanical tests for static bending (only for semi-automatic welding in shielding gases).
A weld is considered acceptable if it meets the requirements for visual and radiographic inspection. In this case, the welder is recognized as having passed the test, which must be confirmed by the Acceptance Test Protocol, and receives a permit to work on welding the oil pipeline (object).
If the test results do not meet the requirements for tolerance joints, then it is allowed to perform welding and control of two other tolerance joints. If satisfactory results are obtained during the repeated control at least at one of the joints, the welder is recognized as having failed the test. The welder may be allowed to re-test only after additional training.
Based on the results of the tolerance tests, a Permit Sheet is issued for each welder, and a list of welders is compiled to perform work at the facility.
The period of validity of the Tolerance List is determined for the time the welder performs the work for which he passed the tolerance tests, if the break in his work does not exceed three months.
As part of the certification of welding technology, it is necessary to perform one or more pipe joints of standard length under conditions identical to those of the route, in compliance with all the provisions of the technological instruction, technological maps and this Instruction.
The number of acceptance joints should be sufficient to identify all the features of the technology and register the process parameters, conduct step-by-step, visual and non-destructive testing by physical methods, as well as mechanical tests of welded joints.
Welding should be carried out using pipes, materials and equipment that are specified in the PPR, technological instructions and can be further used for the construction of the facility. In the absence of full-size pipes, it is allowed to use “coils” of pipes intended for the construction of the facility. The length of the coils must be at least one nominal pipe diameter.
Production certification of welding technology is carried out by each contractor before starting work at the facility, subject to positive results of the initial certification. The contractor who has successfully completed the first certification is exempted from conducting production certification of welding technology at this facility for 1 year. Welders of the contracting organization, who performed welding in the process of primary certification, are allowed to perform the corresponding type of work at the facility without passing the procedure for additional tests (welding of tolerance joints).
RD 153-006-02 Instructions for welding technology during the construction and overhaul of oil trunk pipelines