A cut-off valve cannot be equipped with a bypass
Thread Content
Help, does anyone know which standard this requirement comes from? Thank you!
There’s no need for any standards to regulate this; I really haven’t seen any standards requiring it. However, from a technical perspective, there’s no need to add a bypass to the cut-off valve; it’s pointless. The cut-off valve itself operates in abnormal situations to ensure interlocking or safety; then why is a bypass valve needed?
This is specified in the instrument guidelines, and it is required that the isolation valve not have a handwheel
HG/T20570-2014 11.9.7 For the control valves of process production safety interlocks used in emergency shut-off valves, a handwheel mechanism shall not be provided.
A bypass can be used, but it must be labeled and locked; moreover, there should be corresponding management procedures in place when using the bypass, such as specific approval processes when it is necessary to shut off the isolation valve. This is the content of the investigation report regarding the unauthorized use of the bypass valve, from an investigation into a safety incident that occurred last year: Huabang Company failed to properly manage the steam bypass valves; it neither took measures such as locking them to prevent their use nor installed warning signs on those valves. When workers used the steam bypass route in violation of regulations, the company failed to detect and correct this behavior, as a result of which the temperature control system in the reaction vessel and the steam interlock shutdown device lost their effectiveness.
Which standard is this from? Could you let me know?
There are no detailed regulations for this; it is all governed by the company’s management policies. Generally, emergency shut-off valves are equipped with actuators. In the past, most of them were of domestic manufacture; the quality of these domestic shut-off valves was poor. The purpose of installing a bypass is to test whether the shut-off valve can operate properly. Later, many companies began importing valves from abroad, as their quality was higher. As a result, some design institutes decided to eliminate the bypass systems, since foreigners claimed that it was possible to achieve 100% reliability