B16.5 Flange Modified with Dual NPT Threaded Holes

[WDSeng]

Hello Everyone,

I have a request from a customer for a various B16.5 flanges with dual NPT threaded openings. One example is an 8” 150# B16.5 A182 F316/F316L flange modified with dual 1-1/2” NPT threaded openings that are 4.50” apart (each are offset 2.5” from center, see attached). The threaded openings will be used to install instrumentation used for process control.

Sketch of Flange

My interpretation of ASME B16.5-2013 Table II-6 (reducing flanges) is that a single opening is allowed on center not multiple openings. Whether or not the reducing flange requires a hub is governed by the table. It doesn’t state anything about comparing the material removed from a single opening versus a dual opening configuration. Based on this, it would not be acceptable to say that a dual opening configuration is acceptable just because less total material is removed than from a single opening configuration (dual 1-1/2” NPT removes less material a single 2-1/2” NPT).

B16.5 flanges are pre-engineered so any modification not allowed by code will result in a flange that no longer can be called B16.5. It is also known that B16.5 flanges may fail ASME BPVC Section VIII Div. 1 Appendix 2 calculations because they are over bolted.

How should one go about properly analyzing a B16.5 flange that has been modified and can no longer be called a B16.5 flange? I believe it will need analyzed per ASME BPVC Section VIII Div.1 but would like to receive feedback on whether my approach below is the correct. If not correct or complete I would appreciate any feedback to help me get on the correct path.

Step 1: Calculate the required thickness of the flange per ASME BPVC Section VIII Div. 1 UG-34(c)(2) equation (2) for bolted blind flanges.

Step 2: Calculate the reinforcement required for the openings in the flange per ASME BPVC Section VIII Div. 1 UG-39(b).

Step 3: Compare the required thickness to the actual thickness and determine if the flange is adequately reinforced.

In cases where a B16.5 flange is purchased and modified to no longer meet B16.5 how should the markings on the flange be handled? Should the diameter of the flange be machined just enough to remove the markings? What information is required to be engraved back into the flange (ie. heat number, max pressure, etc.)?

Thank you.

 

[XL83NL]

Id say your path is pretty good. That would be my way to. Not sure if VIII-1 app 2 is for flanges with openings.
This topic may come in handy for you, albeit the topic is slightly, it does answer (parts of) your question.

Not sure what to do on the marking though, see what others have to say bout that.

 

[WDSeng]

Thanks XL83NL for the feedback and the topic link. I am familiar with that topic but it does have recent additions that I was unaware of and will need a more thorough review. I have done a somewhat exhaustive search on this forum but was never able to narrow down a definitive approach for this task.

 

[WDSeng]

For future reference here is an update to this topic.

Original Post:
Step 1: Calculate the required thickness of the flange per ASME BPVC Section VIII Div. 1 UG-34(c)(2) equation (2) for bolted blind flanges.

Step 2: Calculate the reinforcement required for the openings in the flange per ASME BPVC Section VIII Div. 1 UG-39(b).

Step 3: Compare the required thickness to the actual thickness and determine if the flange is adequately reinforced.
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I have confirmed with a few ASME Committee members that the method listed in my original posting is the approach to take.



Original Post:
In cases where a B16.5 flange is purchased and modified to no longer meet B16.5 how should the markings on the flange be handled? Should the diameter of the flange be machined just enough to remove the markings? What information is required to be engraved back into the flange (ie. heat number, max pressure, etc.)?

Yes all markings need removed from the flange. This includes the manufacturer marking as well since they are not the manufacturer of the end product (modified flange). There is no requirement to engrave information on the modified flange because it is must meet the vessel requirements.