Welding enthusiasts must keep it! Total rework for weld repair? There are only 4 differences in standards between domestic and international standards, so don't fall into the trap after thoroughly understanding
The four major standards of domestic GB, international ISO, European EN, and American AWS D1.1 have significantly different requirements for repair, which directly affects how to do it on site.
Choose the core differences below and provide some practical suggestions.
1、 The core difference of the four major standards is 1 Repair frequency: GB card is strict, and there are strict rules for domestic GB in Europe and America: the same part can be repaired up to 2 times at most.
If it exceeds the limit, the owner/supervisor needs to sign and come up with a special plan - afraid that multiple repairs will make the steel brittle.
ISO, EN, AWS do not limit the number of repairs, but there is a prerequisite: the process of each repair must be qualified, and the final weld quality must meet the standard. AWS also requires additional impact testing after multiple repairs to ensure that the toughness of the steel does not decrease.
2. Preheating and welding materials: GB needs to be "upgraded", and other aspects depend on the matching. GB is particularly strict with preheating: during repair, the temperature must be 30-50 ℃ higher than normal welding, and low hydrogen welding materials (such as E5015 welding rods) must be used - mainly for Q355 and Q460 steel commonly used in China, which are afraid of cracking.
ISO and EN did not mention raising the temperature, but they require that the repair process should match the original process (preheating to 150 ℃ in the original process, and the repair should also be within this range).
AWS, regardless of whether the temperature is raised or not, requires low hydrogen welding materials to be hard, and the minimum preheating temperature must be calculated based on the thickness of the steel (for example, for 25mm thick Q345 steel, preheating cannot be lower than 100 ℃).
3. Defect removal: GB prevents crack extension, and GB for European and American base materials has the finest crack treatment: not only does it require magnetic particle/penetrant testing to confirm cleanliness, but high-risk structures (such as pressure vessel connections) also need to drill 6-8mm crack arrest holes at both ends of the crack to prevent the crack from becoming longer as it becomes clearer;
The groove can only be machined or polished, and cannot be cut with fire.
EN is similar to GB, which also requires drilling anti cracking holes and recording the clearance path (such as drawing it for comparison). AWS is afraid of grinding the base material too thin, and stipulates that the removal depth cannot exceed 10% of the design thickness. If it exceeds, it must be repaired by welding.
4. Personnel and records: GB requires "same qualification", and European and American heavy traceability GB requires that the repair welder must be the original welder or of the same qualification; EN and AWS rely on certificates - welders must have corresponding standard certificates (such as EN's ISO 9606 certificate).
In terms of records, GB needs to fill in repair records and inspection reports; EN needs to write a dedicated 'Weld Repair Record' with photos before and after the defect; AWS does not have a fixed format, but it must be able to find out who soldered and what parameters were used.
5、 Practical key: Regardless of which standard is used, these 4 things must not forget that the crack must be thoroughly cleaned: first use magnetic powder/ultrasound to find the crack head and tail, mechanically polish and remove it, drill crack stopping holes at both ends, and after cleaning, check again to ensure there is no residue.
Preheating should not be lazy: The preheating range should be sufficient (3 times the thickness of the steel on both sides of the weld), and the temperature should be measured in real time. Low hydrogen welding materials should be dried and placed in insulation tubes to prevent moisture.
Don't blindly repair: If possible, do not exceed 2 times. If it exceeds the limit, conduct mechanical tests to confirm that the steel is not welded brittle.
The records are complete: where the defects are, how they were cleared, who welded them, and what the test results were like, all written clearly and stored together with the engineering files, at least until the end of the engineering design life.
To be honest, there's no need to worry about which standard is better. The key is to consider the contract requirements (EN/AWS for exports and GB for domestic pressure vessels);
Reliable craftsmanship (regardless of which standard is used, the repair process must be tested first); People must be qualified (welders and inspectors must have corresponding certificates).
Repair is not about patching up loopholes, it is about ensuring safety again, following the rules and paying attention to details, in order to be as strong as the original weld seam.
