External Pressure Blind Flange

A. Para. 2-11 of Appendix 2 of ASME code, Section VIII, Division 1 deals with Flanges Subject to External Pressure's. The term flange in that Para. means: Loose Type Flanges, Integral Type Flanges, Optional Type Flanges, and Flanges With Nut Stops (see Figure 2-4 Types of Flanges), where no mention to the blind flanges. In that figure all of flanges can be subjected to internal pressure, external pressure or to the both.

B. But for blind flanges we have to use UG-34 which deals with Unstayed Flat Heads and Covers (our case). In this type of flanges, the design pressure shall be the max. pressure exerted on the flange from any side P1 or P2, or the absolute difference P1-P2 (where P1 is the design pressure from one side, and P2 is the design pressure from the other side).

The worst case in design of blind flange is when subjected to internal pressure, where strengthening of stud bolts. Using external pressure will give you "no need to stud bolts", where no load is exerted on the bolts.

Unfortunately I do not have access to the standard. I don't suppose there are any makeshift online resources to be had either, are there?

P.S. thanks for the note about the pipe, all that has already been worked out though.

Before I suggest any alternatives ............... what exactly are you doing / building?

I am designing an electronics casing to submerge in water (deep in water). The end must be flat for ease of connector mounting.

Alright - I can't see how anyone could get hurt if it failed. (unless you think otherwise - let me know)

Are you able to use any type of flange? Did you have a particular style in mind?

I would suggest going with a weld-neck - but it could work with a slip-on, or lap-joint, ..... or .......

Just for interests sake I am going to look into your pipe as well - how long is this unit? Are there any stiffeners on it?

Oh yeah - another thought:

Is this application in saltwater or freshwater? (I suspect saltwater due to that pressure)

Because the long-term corrosion resistance in stagnant saltwater for 316 ss is not very good and you may not get the service life for this 'vessel'. Or is this not a concern because it will only be used intermittently?

Already taken care of. You are correct. This is an ocean application, and in a saltwater environment, 316 ss would corrode on a relatively short timeframe. The client has selected 316L, an extra-low carbon content alloy of the 316, boasting improved resistance in saltwater applications, and quite possibly many other applications as well. The device will be fixed at the bottom of the ocean without removal. I am unaware of the client's intentions for operation lifetime, but can only assume it will be for the better part of a year.

Going the easy way, as Abdel offered - because, really, the codes do not apply here

You should be alright with a class 300 blind flange: they are rated for a maximum pressure of 600 psig. (Note that this is internal, and external loading will be slightly different) If you are confident in the code, and its safety factors, you should be alright.

However, if you can get your hands on them, you would be safer with class 400 flanges - rated to 800 psig.

If you really want to be safe, and money and/or weight isn't really an issue, you may want to go with class 600 - rated to 1200 psig.

In any case, even though the higher the external pressure, the greater the sealing force - make sure these flanges are properly torqued.

Lastly - be careful with your gasket choice, please see this article for an insight -

http://web.nace.org/content/publications/mp/2007/0710050.pdf

(Very lastly - I still recommend you go with a weld neck flange too)

Another thought - you mentioned you needed a flat surface to mount connectors.

Does that entail drilling holes through the blind flange (or otherwise removing material) - because that adds another twist to getting away with class 300 flanges.

Good Answer.

I disagree about no difference between internal and external pressure -

The amount of force on the edge of a class 300 flange is 44,000 lbs;

3.14159(15")(1.56")(600 psi) = 44,107.9 lbs

This lateral force will affect the buckling of the flat plate - even though some force will be taken up by the friction in the bolting and gaskets.

When you figure out which pressure rating and size you need, here's where you can buy them.

www.ticotitaniuminc.com

UFG

Reading the responses in this forum all sound like good advice,what I would like to add is this.In a application that calls for enginering qualifications and know how,not in any way given the advice from the well qualified answers is in any way wrong,I would suggest getting the anwers from the people directly involved with this project.Being a Business owner, I know that if anything were to go wrong the fine gentleman in this forum will not be accountable and shouldn't be in any regard.Do you not have qualified professionals that can give you the answers to your questions,the answers you receive I am very confidant will be of great help,also unfortunate in our society people would love to hang you if you make a critical error,and worse yet if people's lifes are in your hands I would suggest pay or find local professionals that can look at the sitiuation first hand and up close,jobsite,drawings,past history's.Good Luck and be careful,use caution.Don't be stupid.

Yes do not worry about that, I suppose I should have said this earlier. I am a 3rd year engineering student working in a firm, so people will look over my work. I am just looking around to see if any past studies or standards have already been established that may be available to me before i go and waste the time of the busy engineers around me. I will take these numbers and find references for them/work them out myself if i do use them, and I will catch any trouble spots in the process. The advice on this forum for the most part looks very promising though. Logically speaking, a flat flange seal should be theoretically better in compression than tension, making a better seal, so the B16.5 internal pressure flanges should more than suffice. I was just looking to see if i would be able to reduce weight or size in any way mostly.

P.S. I am glad to see you are showing concern, though, as I could have easily been a do-it-yourself kinda guy trying to do this out of my basement :P.

Thank you all for the advice, you have more than answered my question.

You made me proud,Good luck!

If I may ask something further, I was wondering how I would determine the safety factor used in the standardizing of these internal pressure flange classes?

Usually when dealing with external pressures, you are looking at vacuum systems. Check out vacuum chamber designs. Should have several details pertaining to what you are lookinf for. Flanges are very common on the sealing surfaces