If the hydrostatic test is replaced with a pneumatic test, what changes are required in terms of design and manufacturing?

If the design pressure of the container is greater than 0.6 MPa, a pressure test is generally not carried out; there are no changes in equipment manufacturing

The change is too significant; at the very least, the welding joint factor should be 1, which would mean that 100% of the welds need to be inspected using non-destructive testing methods, with a grade of two required for acceptance. The test pressure should be 1.15 times the design pressure.

I agree with the opinion above: pressure testing should be accompanied by 100% radiographic inspection, with a grade 2 pass standard; the test pressure should be 1.15 times the design pressure. Meanwhile, the relevant pressure testing equipment and inspection methods also need to be modified

In addition to what was mentioned above, the following should be added: 1. Requirements for the surface quality of welded joints: There shall be no undercuts on the surface of the welds； 2. The pressure test shall verify that the circumferential membrane stress in the shell does not exceed the product of 80% of the material’s yield strength at the test temperature and the welding joint factor of the cylinder. 3. The test gas should be dry and clean air, nitrogen, or other inert gases. This post was last edited by sfg6630 on 2009-3-18 22:11]

The weld joint factor is set at 1, with 100% non-destructive testing

Additional notes for the 3rd and 5th floors: ① Consider whether it is necessary to improve the quality of materials (e.g., by adding UT tests, re-inspections, etc.)； ② The structure should avoid sudden changes as much as possible to minimize stress concentration.

If hydrostatic testing is not performed, the requirements for the proportion of welds to be inspected vary

According to the relevant regulations, unless there are structural or other reasons, pressure vessels should generally undergo a hydrostatic test; therefore, it is recommended to avoid making any changes to them as much as possible. If it must be changed to a pneumatic test, the changes that should be made, as far as I know, are as follows. The welding joint coefficient must be 1; the strength test pressure shall be 1.15 times the design pressure. The requirement regarding the percentage of radiographic inspection in the technical specifications should be 100%, and the acceptance level should be Grade II. The description related to the strength test also needs to be changed.

1) If the hydrostatic test is replaced by a pneumatic test, there are two design changes involved: 1. If the previous welding coefficient was 0.85, this coefficient needs to be adjusted, and 100% RT testing is required; as for what value the welding coefficient should ultimately take, it also depends on the material used. 2. The calculation coefficient for the test pressure value needs to be changed from 1.25 to 1.15. The changes in manufacturing involve only differences in the procedures for pressure testing. 1. Change the design pressure, from a coefficient of 1.25 to 1.15. 2. The gas used in experiments is dry and clean air, nitrogen, or other inert gases. 3. The welded joint adopts a full weld head structure. 4. Welded joints of categories A and B must undergo 100% non-destructive testing (radiographic or ultrasonic). 5. The welding joint coefficient is taken as 1.0. If the original weld joint coefficient is not 1.0, then the calculations for the 6. cylinder and the head must be done anew. 7. Reconsider whether heat treatment is necessary in the case of a change in thickness. 8. Reconsider whether the plate is over-inspected in the case of a change in thickness. 9. Attention must be paid to manufacturing and inspection related to thickness.

In addition to the welding and calculation changes mentioned by the above, gas seals and liquid seals are not exactly the same either, and the sealing components also require appropriate adjustments.

What should be considered when changing from a hydrostatic test to a pneumatic test? Original content by Vcad: Pressure vessels are not easy to handle. When a hydrostatic test is difficult to carry out, it is generally safer than a pneumatic test, as the level of destruction in case of an accident is lower. So, hydrostatic testing is used most of the time. The tolerance specifications also list some situations in which a pneumatic test can be conducted. For example, in pressure vessels where residual test liquid is not allowed due to structural or supporting reasons, or because of operating conditions, pneumatic testing or a gas-liquid mixed testing method can be chosen. As equipment sizes increase and deadlines become tighter, hydraulic testing often presents many difficulties. For example, in the hydrostatic testing of large thin-walled equipment, it may be necessary to retain supporting fixtures inside the equipment, and the time required to fill and drain water is long, which affects the project timeline ； Lack of water or high requirements for water quality result in high costs for pressure testing ； After being filled with water, the device becomes too heavy, causing the device itself to deform ； In the north, where winter temperatures are low, there is a risk of freezing when using production water as the medium for pressure testing ； Or the bearing capacity of the site may not meet the requirements for hydraulic testing, and so on. At this point, the manufacturing unit often wonders whether the hydrostatic test can be replaced with a pneumatic test. Who will take responsibility? There are mainly three types of testing methods currently: hydraulic testing, pneumatic testing, and combined gas-liquid testing. Among them, the hydraulic test is safe, relatively easy to operate, and cost-effective, though it has certain limitations; it is the most common testing method. Pneumatic testing involves higher risks, but it is cost-effective and easy to operate. As a constraint, it is an alternative approach when limitations are present in the hydrostatic test acceptance or when the conditions are not met to carry it out. Stabilizing pressure during gas-liquid combined tests is difficult; the constraints are the same as those for hydraulic testing. The risks are intermediate between those of hydraulic and gas testing, the economic efficiency is average, and such tests are used less frequently. Several pressure testing methods are technically mature with well-defined risks; the choice of a pressure testing method is not really a matter of technology selection, but rather a matter of risk preference. Some organizations are more aggressive; they aim to carry out pressure tests at lower costs and in less time, and are willing to control risks and mitigate their consequences, which leads them to opt for pneumatic testing, although it is more cost-effective but also involves higher risks. Some organizations are relatively conservative and reluctant to take excessive risks; they prefer to opt for pressure testing, which involves lower risks, even if it means delaying progress and incurring additional costs. If experiments are conducted using high-risk methods, then who should bear the risks? Generally, based on the principle of equal risk and reward: those who benefit make the decisions, and they are also those who bear the responsibilities. The manufacturing unit is generally the biggest beneficiary, as it reduces the costs and duration of pressure testing; therefore, when it proposes to replace hydraulic testing with pneumatic testing, it should bear primary responsibility. Design institutes or engineering companies generally prioritize safety and do not actively request the use of pressure testing. By changing water pressure to air pressure, there are no benefits to be gained, yet one still has to decide whether to agree to the change, taking on risks for nothing. This is also why, in many cases, design institutes or engineering companies are reluctant to approve pressure tests. The necessary requirements that must be met for pressure testing: Gases are compressible, and compressed gases can store energy. Gas is used for pressure testing, especially in situations where high pressures and large volumes are involved. In the event of a leak or rupture, the consequences can be as severe as those of a super bomb, leading to catastrophic outcomes. The larger the volume, the greater the potential for explosion, and the risk level is much higher than that of hydraulic testing. Therefore, extra care must be taken when conducting pressure tests. Of course, most companies apply to conduct pressure tests; generally, they should first meet the requirements of relevant standards and satisfy the essential basic conditions for carrying out such tests. Class A and Class B welded joints are subject to full radiographic or ultrasonic testing, with a welded joint factor of 1. (GB/T150.4 10.3.1) The weld surfaces of the containers must be free from undercuts. (GB/T 150.4 7.3.4(g)) The joint design between the nozzle (flange) and the shell, as well as the joint design for jacketed pressure vessels, shall adopt a fully welded-through structure. (TSG21-2016 3.2.2.2(2)) It complies with the provisions of GB150.4 11.4.10. Safety distance for pressure testing: Due to the large amount of energy stored in compressed air, it is generally necessary to maintain a certain safety distance from the equipment under pressure during testing. In ASME PCC-2, Mandatory Appendix 501-II, there are calculations for the amount of stored energy in pressure tests. When the pressure medium is air or nitrogen, its energy E and the T*T equivalent are given by the following formulas: In Appendix 501-III, the distance from an explosive shock wave is determined based on energy and the T*T equivalent; the distance between personnel and equipment must be greater than the shock wave distance R. When the explosion fragments from a container pose a threat to personnel safety, the distance between all personnel and the container under test must comply with Table 501-III-2-1. As can be seen from this table, the safe distance for pressure testing starts at 50 meters. In many companies, it is not possible to achieve this due to space constraints. If it is difficult to achieve the above two distances, the table below can be used to assess the impact and select an appropriate Rscaled value to recalculate the safety distance R. Assume the test pressure is 0.9 MPa, the absolute pressure is 1 MPa, and the volume of the equipment is 10 cubic meters. Using the formula mentioned above: the energy of the gas during the experiment is 12,180,427 joules, which is equivalent to 2.85 kg·T². The safety distance should be maintained at 38 to 50 meters. Pressure test safety devices: For pressure tests, it can sometimes be dangerous to observe them up close. For equipment with a high PV product or a high equivalent T*T, it is possible to consider connecting a buffer tank to the test vessel. The pressurization is achieved using an air pump, a pressure storage tank, and N2 gas cylinders; however, these gas sources must be connected to a buffer tank to balance the pressure before it is introduced into the testing container ； The length of the high-pressure hose connecting the buffer tank to the container can be determined with reference to the safety distance R specified in PCC-2. The personnel carrying out the pressure testing must stay away from the container under test and monitor the changes in the pressure gauge installed on the buffer tank. The site for the pressure test should be located in an open outdoor area with no people present, and the minimum distance between the isolation line and the test vessel must be at least the safety distance R specified in PCC-2. When the weight of the pressure testing vessel exceeds the lifting capacity of outdoor cranes, or when the outdoor temperature cannot be guaranteed to prevent brittle fracture, testing may be carried out in a workshop, but stricter conditions must be met, such as greater margin for safety in the equipment, additional safety measures, and procedures for evacuating personnel. In summary, when changing from water pressure to air pressure, the following aspects should be paid attention to: clarifying responsibilities, identifying risks, and avoiding them. It fully meets the requirements for pressure testing as specified. Maintain a certain safety distance during the test. When the risk is high, appropriate test supporting equipment should be used.