one Sandblasting pipe Thickness of

The key to the unevenness of the wall thickness of the sandblasting pipe is the position where the deformation of the sandblasting pipe is large. For example, the wall thickness of the back of the elbow is thicker than that of other positions; The thickness of branch pipe and sandblasting pipe body is different. According to the requirements of relevant laws, regulations and specifications, the thickness reduction of sandblasting pipe shall not exceed 12 and 5 of its nominal thickness. However, it is found in the field evaluation that some wall thickness reductions have reached 20-30. For the inspection of such problems, it is usually impossible to detect them with ordinary measuring instruments such as vernier calipers. At this time, only the ultrasonic coating thickness gauge can be used to measure them.

2. Strength exceeds the standard

The problem of strength exceeding the standard is mainly caused by the problem of heat treatment method after forming. The method of treatment is to carry out another heat treatment process with appropriate heat treatment method. This problem can generally be treated

3. Defects caused by raw materials and production process

This kind of problem will do great harm to the safety of the equipment and is inconvenient to check. There are many and complex factors that cause the defects. It has the disadvantages of raw materials, production, processing and manufacturing process problems, and the defects caused by the error of heat treatment methods. Then why did they cause safety damage, and how to prevent such problems? Now take the three links as an example to analyze the matter one by one.

3.1 Difficulties of raw materials

We know that the quality of raw materials will immediately endanger the quality of sandblasting pipes used to produce such sandblasting pipe fittings. For galvanized steel pipes, GB5310-85 Seamless Steel Tubes for High Pressure Boilers Raw materials of GB6479-86 High Pressure Seamless Steel Tubes for Fertilizer Equipment GB9448-88 Seamless Steel Tubes for Petroleum Cracking and GB8163-87 {Seamless Pipes for Liquid Transportation "and other standards. For this type of seamless steel tubes, steel mills solve the problem of carrying out pressure tests one by one. For large, medium and small steels, vortex or ultrasonic wave flaw detection (uT) is usually used The quality of pipe fittings can be ensured if the pressure inspection is replaced by strict inspection according to China and relevant specifications. However, sometimes it is inevitable that there will be missed inspection and false inspection, and even some pipe fittings suppliers are adulterated, and some are not approved at all

The raw materials come to the circulation industry. Therefore, in view of the fact that the pipe fittings after delivery are very right and wrong, the raw materials purchased immediately from the steel pipe factory in large quantities should be reviewed in an all-round way according to the specifications. In addition, the proportion of review should be increased, and even the inspection should be carried out one by one. From the research on the production and manufacturing of several sandblasting pipes with business scale that we have touched, Many manufacturers do not strictly check the recheck of purchased pipe fittings, blindly following the original quality certificate of raw materials (especially, the authenticity of some original quality certificates has problems), and the quality of sandblasting pipes made of such non critical pipe fittings can not be guaranteed only for the appearance inspection of double pier pipe fittings. In addition, the detection methods of many manufacturers at this stage are not perfect, so some unqualified sandblasting pipes are very easy to be regarded as qualified products. For example, such problems are encountered in the hydrofining equipment of Tianjin Petrochemical Enterprise Chemical Plant. In the whole process of pressure application after pipe installation, there are~pieces of 14mm × 7ram tee, when the working pressure rises to llMPa, the fixed head neck cracks and leaks, and the leakage position is shown as l in the figure.

Through accurate measurement, it is a through crack with a length of 21mm

For everyone Sandblasting pipe The cracks in this matter have been analyzed in the following ways:

a) Composition

According to composition analysis and litigation re inspection, it is clear that the composition of carbon element and manganese element is high (c0.26; Mn: 1.27, using carbon steel No. 2O);

b) Physical properties

All normal No. 2O seamless steel pipes are 410~550MPa, while that of evaluated products is 570MPa;

12) Alloy composition

According to the observation on the fracture surface of the tee and all normal positions of a part of the nozzle, it is found that the proportion of ferrite is significantly higher than that of 20 # steel, which is normal, and the carbon content between the two is relatively high. And its carbon content and manganese content are too high, which is bound to

3.2 Difficulties in manufacturing process

At present, Chinese manufacturers generally choose the following for production, processing and molding

Several methods: (1) cold stamping die forming;

(2) Hot stamping die forming; (a) ]] All normal positions (rolling direction) of 4ram pipe F-P (h)~1] 4mm pipe All normal positions (transverse+P (e)~61mm pipe crack fracture VI (transverse JF+P