P91 pipe cap

Difficulties and common problems in P91 pipe cap and cylinder assembly

During the manufacturing process of pressure vessels such as heating buffer device, sewage buffer device and free water remover, the accuracy and quality control of P91 pipe cap and cylinder assembly has always been an important and difficult point in the manufacturing process of pressure vessels. Various quality problems often occur, such as excessive local clearance between the pipe cap and the cylinder assembly, deformation of the cylinder assembly, unconformity of ovality, unconformity of misalignment between the pipe cap and the cylinder, which directly affect the production progress and precision quality of the product. Through analysis, the influencing factors leading to such problems are as follows:

(1) During cylinder cutting and prefabrication, due to the deviation of the diagonal length of the plate (sizing) itself and the diagonal line during marking and blanking, and due to the influence of the accuracy of the cutting machine, the deviation between the circumference of the cylinder after rolling and welding and the outer circumference of the pipe cap is too large

(2) After the cylinder section is rolled and welded, the outer circumference of the cylinder shall be measured in time. When the cylinder section is assembled, the cylinder section with small deviation between the outer circumference of the outer circle and the outer circumference of the pipe cap shall be selected as the end cylinder section of the pipe cap, and the difference between the middle cylinder sections shall be found. The greater the circumference deviation between the tube section and the outer circle of the tube cap, the more difficult the accuracy control of the assembly is

(3) A packing frame may be set inside the barrel section near the pipe cap end. After the packing frame is welded with the barrel section, it is rigidly connected by full welding, and its welding stress affects the straightness deviation of the single barrel section. The overall expansion near the pipe cap end results in the size deviation of the pipe cap

(4) Due to the rigid constraint between the seasoning rack and the tube section, it is difficult to manually correct the tube section and the tube cap when they are assembled, which is time-consuming and laborious

(5) The assembly sequence of the pipe cap and the cylinder is unreasonable. The sequence of 0 ° → 90 ° → 180 ° → 270 ° → 0 ° is used for assembly, correction and welding. Between 270 ° → 0 °, the gap and misalignment between the pipe cap and the cylinder are obvious, and the correction is difficult