Technical Requirements for Boiler Forging Valves
1. Forging raw material should be accompanied by quality certificates (also known as quality assurance certificates). Supplementary inspection should be carried out when there is no quality assurance certificate. Only those who are qualified can be put into production.
2. Forging pieces (referring to raw materials for forging) may be rolled (e.g. round steel) or ingots. If the forged blank is rolled, its surface quality and chemical properties will be improved.
Chemical composition and mechanical properties shall conform to GB/T 699, GB/T 1220 and GB/T 3077. ASTM A276 and other ASTM standard.
3. When steel chain forging is used, the head and tail defects must be thoroughly removed. After the removal, there should be no visible shrinkage holes, looseness, cracks and other defects affecting the forging quality. Whether ingot or rolling is used for forging, the defects affecting forging quality on the surface of forged billet must be completely eliminated.
4. In order to ensure good performance and structure of forgings, when ingots are used as forging blanks, there should be sufficient forging ratio.
5. The material, shape and dimension tolerances of forgings shall meet the requirements of design drawings or process documents.
6. There should be no cracks, folding and overlapping defects on the surface of forgings. The above defects should be treated in accordance with the following provisions.
A Defects existing on non-machined surfaces should be removed, and the depth of removal should not exceed the negative deviation of the nominal size.
B exists on the surface which needs to be machined. When the depth is less than 2/3 of the nominal machining allowance and the removal is guaranteed, no special treatment is necessary.
C Defects exceeding the specified are generally not allowed to be repaired. Special cases should be determined after joint analysis by design, process, inspection department and production workshop. If it is a purchased part, the supplier’s repair welding plan shall be approved by the buyer. The repair welding shall be carried out according to the qualified welding procedure rules. The welder shall hold the qualification certificate and shall be re-heat treated after the repair welding.