Summary: Jiangsu, a company producing 10 type and 80 type rotary joint, in use, a small part of the breakdown. The main reason for the breakdown was much chamfered and chamfered parts just at 90 ° bend at sharp change in fluid flow here, chamfered step to produce fluid resistance, large particles of quartz sand in chamfering performed at the step Erosion produce breakdown. After identify the root cause of the breakdown, make the following improvements: the chamfered step into 10 °, and began chamfers WN bent sub 10 mm at import, try not to put at Elbow 90 °. After improvements, Swivel joint no longer produce breakdown.
Keywords: Swivel joint; breakdown; chamfered steps; improving
A company by the Jiangsu produced 10 type and 80 type Swivel joint is according to API Spec 16C standard production, a small number of products in the course of breakdown. After a comprehensive analysis of the samples was found breakdown: ① puncture site is basically the same, both in exterior ballistics WN bent at the joint; ② breakdown in third place outside the arc trajectory; ③ puncture site is not the weakest link, which is not the thinnest .
1 Sample Analysis Breakdown
1.1 raw materials
Swivel joint material used is 30CrMo round, round is made by rolling, perforation, bending and other processes. Breakdown sample of sample analysis results showed that the chemical composition within the normal range, in line with GB / T 3077 of the requirements.
1.2 quenching Biopsy
Swivel joint 30CrMo steel after quenching and tempering sorbite normal tissue, tempered sorbite plus a small amount of bainite, it is a normal tissue.
1.3 Mechanical properties
After the material by heat treatment quenching, in which the average hardness on three impact specimens were 239,245,253 HB, its hardness, mechanical performance in full compliance with the requirements of API Spec 16C in 75 K material. 30CrMo steel mechanical properties are shown in Table 1.
Table 1 30CrMo steel mechanical properties

1.4 parts breakdown
Changqing oilfield complex geological environment, relatively hard rock underground, pipeline fluid contains hard quartz sand, scouring effect is obvious. 10 type, 80 type Swivel joint breakdown parts are outside the arc portion of the circulating fluid at the inlet of the first bends, indicating the role of quartz sand erosion is one of the causes of the breakdown, but not the main reason, because not all Swivel joint has a breakdown.
2 Breakdown
Swivel joint breakdown is not thin wall thickness at while in office. After careful analysis of the assembly drawing found that the breakdown in the third outer arc of the trajectory. Here is a fluid inlet, a fluid direction along a 30 ° chamfer, the chamfered step to produce fluid resistance. The arrival of large particles of quartz sand chamfered step pause, then down to form a chamfered step scour pits, pits gradually expand to produce breakdown. Therefore, the breakdown of the main causes is much chamfered and chamfered parts just at 90 ° bend at sharp change in fluid flow here, chamfered step to produce fluid resistance, large particles of quartz sand in the chamfered steps It was produced at the erosion breakdown. In addition, the hole where irregular during molding, processing steps, some small, some of which is Swivel joint breakdown there's no reason for the breakdown.
3 improvements
After identifying the root causes of the breakdown, the following improvements: the chamfered step into 10 °, and began importing the joint chamfers WN bent at 10 mm, try not to put at Elbow 90 °. After taking the above improvements, Swivel joint no longer produce breakdown.
4 Recommendation
(1) The design pressure fluid control element, try not to have chamfered steps.
(2) oil fields in the daily construction process, high pressure fluid conduit arrangement, the corners better.
(3) Design high pressure fluid control element, if it exists chamfered step must try to design a small angle chamfered steps.