Orifice Flange
When engineering firms and manufacturing companies come into contact it is sometimes like trying to get a horse and a rabbit to communicate with each other. An engineer writes the specifications with the systems end-product needs in mind whether that be for custody transfer, boiler room steam flow pressure reduction, highly accurate small line size flows, etc… If the pressure is not very high the engineer makes an assumption that 150# will cover it for the orifice flanges and quickly writes “
150# orifice flanges with 1/2″ flange taps” into the specs, which sometimes end up getting pretty deep and irreversible into the department approval process. It is then approved to be sent out as an RFQ to the distributors, and then finally to the manufacturers. The manufacturer looks at the spec and sees a set of Carbon Steel 2″ 150# Orifice Flanges with 1/2″ taps needed for a Schedule 80 line and knows immediately that on a practical level, there is not enough room in the flange thickness of a 2″ 150# flange to fit a 1/2″ tap and still remain in compliance with standards. So, the manufacturer comes back with an alternate quote of 300# flanges with 1/2″ flange taps or 150# flanges with 1/4″ corner taps. The reason for these tap diameters and flange ratings is because standards say that there has to be at least 1/2″ thickness from the O.D. of the tap connection in order to maintain the ANSI flange standards. A 300# flange can be an orifice flange because the hub thickness is 1-1/2″ and the tap is 1/2″ leaving 1/2″ worth of hub thickness on each side of the tap. According to ASME standards, the centerpoint of the tap must be 1″ from the surface of the orifice plate including gasket. This extra flange thickness allows the tap to be where it should be for accurate measurement. The 150# flange is not thick enough for this thus the need for a 1/4″ corner tap is needed.
There are several disadvantages to corner-taps in 150# flanges:
1) They clog easily.
2) They may need bushings to connect to transmitters and manifolds.
3) They can be more labor-intensive to manufacture due to the non-standard nature.
4) Delivery time may be higher since 150# corner-tap flanges are not normally kept in stock by orifice flange manufacturers.
5) They do not meet ANSI standards.
Regarding 1/2″ flange taps in 300# flanges:
1) They can possibly be slightly more expensive due to extra hub thickness.
Any more disadvantages of flange taps? Not that I am sure of. Flange taps win this battle.
Posted in Flange Dimensions, Orifice Flanges, Tap connections
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Tagged 150#, 300#, ANSI B16.5, corner tap, cornertap, flange tap, flange taps, orifice, Orifice Flange, Orifice Flange Union
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When dealing with large end users that have thousands of products flowing into their plants everyday to be received, logged, inspected and installed, and used there has to be a close watch on the paperwork to make sure that safety standards are complied with. This is especially true in plants that deal with hazardous materials and environments for the workers and even whole societies surrounding them. The paperwork requirements, however, in their attempt to be thorough, sometimes overlap and cause a traffic jam in the smooth flow of project timelines and budgets. This overlap can cause grey areas in which large companies find it impossible to navigate and can be a bit tricky for smaller companies as well.
One specific grey area for example is a conflict between the demands from a client for material to have a certain origin of material and the requirement that the MTR shows the final product on it. The general orifice flange dimensions for a project may need to conform to ANSI B16.36 standards with the appropriate documentation reflecting this. However, at the same time, the written specifications also require that the Mill Test Reports (MTR’s) of the original material showing country of origin for each product be supplied. The contradiction in this is that the MTR needs to reflect an ANSI B16.36 orifice flange. The MTR from the original mill is for nominal pipe flanges, or forgings, or plate, barstock, etc… The documentation requires an MTR for a domestic orifice flange specifically, but the product before being manufactured into an orifice flange was from India, China, or Eastern Europe. So which requirement wins out? The domestic MTR for the actual supplied product that meets the ANSI standard to comply with the plant’s specifications, or the original MTR from the forging plant overseas that shows the origin of the original mill material, but does not reflect the final product on the purchase order?
