The purpose of hydrostatic testing (well worth discussing)
Thread Content
1. Test the strength and air tightness 2. Reduce or eliminate the peak stress in some parts 3. Short-term overpressure can blunt cracks and cause cracks to have a closing effect... Haha, this is the purpose of the hydraulic test... Generally speaking, everyone thinks it is just the first one... However, the reasons for the second and third items are not very clear, especially the third one, which is a modern mechanical theory after checking... I am not very clear either... Please ask experts to build the building
The second point I think is mainly because the internal pressure process causes the cylinder cross-section to change from non-circular to circular, which can redistribute stress on the main body and eliminate local stress. According to this statement, the third point should be the compressive stress generated on the defect. Only in this way can the cracks have a closing effect.
There should be more than these·····
For Article 2: During the hydraulic test, the maximum circumferential stress is allowed to reach 90% of the yield. At this time, the pressure vessel is in a state of elastic deformation, and there is a certain deformation to re-uniformly distribute the cylinder stress. For Article 3: I personally don’t know if this is my understanding: there is a high stress concentration area at the crack tip. The stress in this area is much higher than other places, which can easily cause crack expansion in future use. The hydraulic test uses overpressure load to cause strain at the crack tip (that is, let it expand in advance). In this way, the angle of the crack tip after strain also expands, the stress is released with the strain, and the stress concentration phenomenon is also alleviated. To put it bluntly, it is better to let the cracks expand first than to leave high-risk hidden dangers that will expand in the future. If this is not the explanation, then there is a practical question: Today’s containers basically pass RT testing levels 2 and 3. Such qualification standards do not allow the existence of cracks at all. Then Article 3 has no practical significance, right?
In addition to the heat treatment method that we all know, there is also a loading method to eliminate welding residual stress, including the mechanical stretching method. This method can be achieved through hydraulic testing. This paragraph is excerpted from the larger version of the book "Welding and Chemical Mechanical Structure". Passivation cracks should refer to surface cracks. When pressure is applied, it is in the elastic deformation stage. Once the pressure is released, it returns to its original state. The crack is still a crack after all. How can it close?
I have a question, where is the original quote from the poster?
Quoted from a relatively authoritative guidance book····