Oxygen pipeline material issues
Thread Content
According to Clause 5.4.5 of JB/T12955-2016 \"Technical Requirements for Valves Used in Oxygen Systems\", \"the material used for the pipelines downstream of the bypass valve shall be an exempt material.\" May I ask: 1. What specific materials are considered \"exempt materials\"? Is there a corresponding material in Table A.1 of GB20801.2? 2. Why are there no such requirements for pipe valves without bypasses?
Hehe, it’s all new terms – exemption, obtaining diplomatic immunity: lol. It’s better to refer to the table regarding flow rates for metals.
Answer 2 first: since the bypass valve has a smaller diameter compared to the main valve, the flow velocity is generally high both in the bypass valve and in the bypass pipeline. Therefore, exempt materials must be used; in cases where there is no bypass system, this requirement does not apply. However, if the calculated flow velocity is high and the pressure is high as well, exempt materials must still be used.
Speaking of 1, as for the materials that are exempt from certain requirements, there are some materials for which it is not necessary to take oxygen flow rate into consideration at certain pressure levels. Monel material is currently the material with the highest allowable pressure among those that are exempt from such requirements. As the pressure and flow rate increase, the materials used change from carbon steel (very rarely) to stainless steel, then to copper, and finally to Monel; the safety level also increases gradually with these material choices.
Thank you for your reply. Should the exemption materials be selected from those listed in Table 3? Do the pipes of these materials have standard numbers? It doesn’t seem to be in Table A.1 of GB20801.2. If the main pipeline is made of 20# steel and Monel is used behind the valve, isn’t that a huge contrast? Can these 2 materials be welded directly? Incredible.
I’m not sure about welding carbon steel and Monel, but stainless steel and Monel are indeed very difficult to weld; we usually use flanges to connect them instead. As you mentioned, the main pipeline is made of carbon steel; I assume the pressure and flow rate in your system aren’t very high. It’s possible to estimate the requirements for the bypass valve, and stainless steel or copper would likely suffice – Monel isn’t necessarily necessary
Carbon steel and Monel are weldable; stainless steel and Monel are weldable
When selecting materials for pipes, it is first necessary to determine the relevant standards for those pipes. However, the exempted materials specified in these standards do not provide corresponding standards for the pipes themselves or for fittings such as flanges, which poses difficulties in choosing appropriate materials for pipe design.
Refer to GB 50030-2013 \"Code for Design of Oxygen Stations\" and GB 16912-2008 \"Safety Technical Regulations for the Production of Oxygen and Related Gases by Deep Freezing Method\"
Neither of these two standards requires “exemption materials”.
Thank you for your explanation. Please take the time to answer the question from the 9th floor when you have a chance