Blind flanges with openings

Procedure 3-3 Design of Blind Flanges with Openings [1,4]... 

If two or more jobs are being carried out on the same piece of equipment or in the same area, the chance for confusion as to which permit applies to which controls arises. Failure to control multiple permits was a major factor in the Piper Alpha incident—two permits were open on one compressor. When the first job was finished, its permit was closed and the compressor was started, even though the machine had a missing blind flange associated with the second job. 

At the evening shift changeover it was decided not to carry out the preventive maintenance work after all. Therefore, the only work to be done would the third task, the repair of the coupling—which did not require access to the pump itself, and so did not require that the pump be positively isolated. Due to a failure in commtmi-cations, information as to the status of the open work order to do with the relief valve had not been properly communicated to the incoming shift. In particular, the incoming crew did not know that the relief valve blind flanges had not been tightened up. 

Accoiding to the engineering drawings, a 6 in. (150 mm) diameter open nozzle was originally considered the tank vent. Over the seven years of operation, this 6 in. flange had been blinded and an unused 3 in. (75 mm) nozzle served as the vent. No one knew when this one-minute modification had occurred. Experience elsewhere in this plant with many similar products had established that a 3 in. vent hole could block sohd with this wax, but it was most likely that a 6 in. nozzle would not clog 18] (see Fig. 8.20). 

Flanges should be open a minimum length of time consistent with the safe installation of the blind. 

If a flange is to be routinely blinded, a spectacle blind (also known as a Figure 8, disk-and-donut, or spec blinds) can be installed. This type of blind looks like a pair of spectacles or the number 8, with one section closed and the other open. When the flange is broken and the line cleared, the blind can be rotated around the one bolt that is left in the flange. It is simple to ensure that the blind has been installed because the open part of the blind will be sticking out from the flange face. 

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