X70 pipeline welding quality control points and control methods

- May 22, 2019-

X70 pipeline welding quality control points and control methods

(1) attach importance to the control of welding process evaluationWelding process evaluation is the premise to ensure the quality of pipeline welding. Its significance is to evaluate whether the designed welding process can meet the quality requirements of pipeline design.Generally speaking, the welding process of pipeline engineering requires at least the welding process of main pipe line, repair welding process, station pipe welding process, etc., or the welding process developed separately according to the change of important factors in the standard requirements, such as butt joint of pipes with different wall thickness and welding process with joint.In order to ensure that the welding quality meets the requirements of the standard specification, the welding procedure must be evaluated.According to the above requirements, in the process of welding process assessment, the following must be able to ensure the purpose of assessment:

A must be tested with the ordered steel tubes used in the project.Because although be, X70 steel tube level, in fact, each manufacturer meet grade X70 steel chemical composition and processing in a different way, delivery condition is different, so using someone else's welding procedure qualification, and the engineering use of steel tube test, the test results are difficult to prove the engineering use of welding process meets the quality requirements of this project.

B shall use welding materials of stable quality and specified gradeA number of welding material manufacturer can conform to the required standard models of welding materials production, by the same token, the formula of raw materials and production methods in each manufacturer is different, so if used in the welding procedure qualification welding materials manufacturers and actual project when using different welding material manufacturer, the actual performance of girth and technology evaluation performance may be different, so you can't prove welding procedure qualification results must be used.Even the materials provided by the same manufacturer may have quality problems due to different batches.The problem is that in the acceptance of welding materials generally, the acceptance method agreed by the customer and the welding material manufacturer is in accordance with the welding material production standard test and acceptance, especially the welding process performance does not have a suitable method for pipeline welding evaluation, so the acceptance of welding materials does not necessarily mean that the pipeline can be welded.In order to control the quality, welding materials consistent with the project should be used as far as possible.Welding materials should be selected from mature manufacturers as far as possible. For welding materials of different batches, the acceptance method for welding process performance of pipelines should be formulated.

C welding procedure qualification shall be carried out by the team participating in the construction of the project. The welders participating in the qualification shall be selected from the welders of the project team and the welders with this level shall have at least one crew member.In fact, another purpose of welding process assessment is to check whether the construction team can master the corresponding welding skills, so as to ensure the overall welding quality of the whole construction team.

D most importantly, the project must have standards for welding quality control and acceptance methods.The welding standards of domestic long-distance pipelines are generally modified in accordance with API 1104 standards of American petroleum institute. The purpose of the improvement is to make the adopted methods and indicators meet the requirements of engineering construction and use conditions.

(2) control of welder qualificationAny pipeline project is completed by people, so the fundamental guarantee of project quality lies in the skill level of the people involved in the project and the overall construction management level of the team.Pipeline girth seam welding is to master qualified technology to complete, so how to determine the welding workers really master this skill, and can faithfully implement the specified welding process, is to be determined by the welder qualification examination.Depending on the specification, different locations and types of welds require different welder skills.The qualification of on-site pipeline welders is generally divided into two categories:One is the qualification of normal pipeline pipeline welding, which can be divided into 5G position and 6G position.Because it is an assembly line operation, it can even be qualified according to each level.The other category is the qualification of the repair welding joint, which requires the welder to be able to conduct independent welding cutting, group welding and repair welding according to the repair process.

The welder shall be qualified to weld at least 6G of the main line welds.The site management task of the construction team is basically: qualified people do the corresponding qualification;To ensure that personnel with such qualifications are in normal working conditions;Take responsibility for the work done;And make sure the records are traceable.According to China's national conditions, welding quality problems mainly occur in the following three aspects:A. Use unqualified persons to do the work that needs qualified persons, so the welding quality cannot be guaranteed;Although B has the corresponding qualification, it is in an abnormal working state, such as working with excessive fatigue or illness, and its work cannot guarantee the welding quality;C. Subjectively and intentionally not implementing the process discipline, such as in order to meet the deadline or schedule, etc., this is intentional damage to quality.Therefore, the main content of field management is that its management system should be reasonable and sound, to avoid the occurrence of artificial reasons for the advantages and disadvantages of welding quality control and damage.

(3) control of welding equipment and materialsThe welding equipment used shall be in good condition and the welding parameter indicating instrument shall be within qualified error.However, although the welding equipment is in good condition before the project, it is necessary to check and debug before the daily work. The purpose of this is to confirm the continuous integrity of the equipment, and to prevent unexpected parameter changes that may affect the welding quality.In fact, the welder is very sensitive to whether the output of the welding equipment is normal when welding, when there is a disagreement, the application of another qualified current and voltage clamp table or other instruments for verification.The welding materials must be inspected and accepted in accordance with the standards or the contract, and the inspection and acceptance shall be carried out in batches.The distribution, on-site storage and invalidity of welding materials shall be carried out according to the manufacturer's Suggestions to ensure the welding quality.Of course, the quality of steel pipe is more important, but its on-site quality control and management methods do not belong to the content of this paper.It will not be repeated here.

(4) appearance inspection standards for welding jointsIn the welding specification, the corresponding acceptance standards are established for the welding seam after completion of welding, which can be executed according to the standards.However, there are several principles to note in the implementation:The residual height control of A weld can be polished to the standard range immediately after welding.B a small number of surface pores can also be removed by polishing on the remaining upper layer, but it must be done immediately after welding and smooth transition is carried out, and the remaining height is still within the standard range after removal.C the undercut defect cannot be removed by polishing and smooth transition.D. Serious attention must be paid to the occurrence of cracks and defects, and repair or rewelding of incisions shall be carried out according to the standard provisions.

(5) on-site review of objections in X-ray inspectionX-ray inspection of the film will often show false defects, when the defect standards exceed the standard, may appear false defects of the film, must go to the scene to review, in order to avoid the wrong repair.From the safety evaluation point of view of the whole pipeline, the current standard is more and more inclined to avoid repairing and cutting as much as possible, because most experience has proved that the quality and performance of repaired welding joints are often inferior to that of the welding joints with defects.Because of the complexity of the methods for evaluating the impact of defect size on safety, the old acceptance criteria are still used in the standards despite such experience.

(6) spot check of welding joints shall be completedAlthough there is welding process assessment to ensure the performance of the welding joint, but the welding process assessment is carried out in the laboratory conditions of simulation, so the actual engineering welding quality and performance, must be cut on the site of the project flow welding joint to conduct damage inspection to know.Now some pipelines are carried out a certain proportion of the destructive spot inspection of the pipe mouth in the construction stage.There is a precedent that the entire nearly completed pipeline was excavated and rewelded due to unqualified pipe mouth spot check and further unqualified welding materials.

7 summary

(1) the combination process of using cellulose electrode as the base and flux cored wire for self-shielded welding to fill the cover of X70 pipeline is a relatively mature process, which has the characteristics of high qualification rate, high efficiency and good applicability and has been accepted by most pipeline construction teams.

(2) the guarantee of the welding quality of pipeline construction site mainly depends on the control of the quality of materials and equipment, the qualification of construction personnel and the on-site quality management.

(3) the defects that need to be repaired or cut should be carefully treated, and the on-site pseudo-work should be carried out.

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