Hi,

I am selecting and designing a customized threaded piece in regards to ASME B1.20 but have two questions and would be thankful if someone could help. The process condition is Gas with 120 MPa inside pipe pressure. I am going to attach a sensor to this pipe which requires a mechanism( i.e. fittings and sealing) in order to adjust the probe position axially while under pressure.

1 - I need to attach a fitting (Male-NPT 1/4"- OD 19 mm) to a threaded tube. The thread should be created on the tube. so the question is that what is the required tube OD and wall thickness? ASME B1.20 table A1 suggests drill diameter but it is confusing. The first column is DN Pipe size. Is this size the OD of required tube to create internal threads into it? If yes, then the ID of thread is smaller than the fitting body!?

2- In order to calculate the tight sealing thread length of engagement for the above mentioned thread and considering the pressure applied to the threads (12 MPa) is there any relevant formula or approach? I have found one approach for screws which is based on Cross section tensile area of the thread, but this formula is used for screws and not pipe threads.
Or can we use the same concept in this case too?

I appreciate your help.

Regards,

David