Blind Flange w/ Tapped Hole Hydrotest Pressure

[BGinOG]

We have a 12" SPO blind flange (duplex SS) with a small hole in it that was used for a hydrotesting connection. We need to determine if it will be acceptable for a 15,000 psi hydrotest with a plug in that threaded hole (3/4" threaded, the rest of the hole is 4-5/16" w/o threads). The thickness of the blind is adequate for this on its own. But if we install a plug is it still ok for the 15,000 psi hydrotest? Is there a code out there that considers this where I can do some calculations to determine this?

Thanks,

BG

 

[Duwe6]

Sketch please; 4-5/16" diameter hole?

 

[BigInch]

you're going to thread the hole?

Learn from the mistakes of others. You don't have time to make them all yourself.

 

[LittleInch]

As I'm sure you're aware this is a bespoke flange produced by Vector. I would just ask them. Norsok L-005 has some formulas and calculations, but 15000psi is not to be trifled with and you need some official back-up.

Why are you taking the risk for the cost of a blind flange? Would you stand in front of the plug with 15,000 psi behind it? Ask the same thing to anyone else who tells you it is "Ok" and to try and save a very minor amount.

Threaded connections and plugs like this have failed, especially if screwed in and out, possibly with damage you can't see, galling, over tightening to stop a minor leak. I think you get the drift.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BGinOG]

@Duwe6 - It is a 1" diameter hole. The threading (NPT) is 3/4" long, the rest of the hole (unthreaded) is 4-5/16" long.

@BigInch - The hole in it is already threaded as described above, it was used to hydrotest 5,000 psi for a different application.

@LittleInch - Yes I am aware that this is a bespoke flange produced by Vector. I will consult our contact there to see about this, that is a good suggestion. The reason for avoiding purchasing a new blind flange is because of our own reasons specific to the project schedule, and we want to explore all options before making a decision.

Thank you all for your insight!

BG

 

[LittleInch]

This 1" diameter plug has 5,300 kg force on it at 15kpsi. All resisted by a 3/4 " long thread?? Makes you think a bit.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

"This 1" diameter plug has 5,300 kg force on it at 15kpsi"

11,660# at 1" dia. requires a 1/4" fillet weld [all around]; disregarding the threads. Weld the plug in to keep from buying a new blind.

 

[BGinOG]

@Duew6 - Thank you for your advice, where are you getting this requirement from ("...requires a 1/4" fillet weld..."), so that I can see it for myself and educate myself?

Thanks,

BG

 

[Duwe6]

Fillet strength calc;
928* x weld length in inches x weld leg size in 1/16's, thus

928 x [1" dia. x 3.14] x 4/16's = 11,655#

*928 is a combined constant from the fillet leg size-to-throat ratio, 70ksi weld strength, and a safety factor. This is published in AISC Structural Handbook. Pretty handy.

 

[MJCronin]

BGinOG...

You have a piping system that operates and will be tested at very high pressure.

The system has at least some 12"NPS piping in it.

You are asking questions phrased as "is there some kind of code out there".....

I am not getting a big feeling of confidence here

To what piping code was this system designed, inspected and tested to ?

What is the maximum diameter pipe and it's wall thickness and material ?

What is the flange class/rating of the flange that mates to the blind flange ?

MJCronin
Sr. Process Engineer

 

[BGinOG]

@MJCronin,

ASME B31.3 Chapter IX, this is a duplex stainless steel API 10,000 piping system. You are correct it will be operating at a high pressure (normally 3-4,000 psig) and tested at a high pressure (15,000 psig since it is a 10,000 psig design pressure).

The system does have some 12" NPS (mostly at the riser section, but I don't want to get too specific into what my project is).

Yes I am asking a question is there some kind of code out there because as far as I know there isn't one for calculating if a blind flange with a tapped hole and plug and is able to withstand XYZ pressure. No one has showed me one yet is all...

You are correct in questioning my confidence, and that is exactly why I came to this board, because I am a young engineer, trying to help solve a problem, and yet have no code to do a calculation to in this unique situation. We are trying to exhaust all of our resources, and I thought I'd give this one a shot without criticism for asking a question.

BG

 

[DekDee]

BG
Your intentions may be admirable but trying to find out if something is acceptable over an internet forum is not a good idea.
It is obvious your company is looking for a cost cutting "short cut" and you are trying to find a way to justify it.
If you cannot access a duplex blind (w/o hole) why not use a C/S blind flange as long as it is insulated from the duplex W/N flange ?

There are some very knowledgeable members who have stated for high pressure piping what you are proposing is not recommended - that is why there is no reference given to "some kind of code out there",
Regards,
DD

 

[BGinOG]

@DekDee I thought an engineering message board was a place where we could ask questions and get advice from other engineers, but apparently "trying to find out if something is acceptable over an internet forum is not a good idea". I was never going to make a decision based on what someone told me here, I was just looking for guidance. This is one of many avenues I have working on this issue, I just thought it couldn't hurt. I will just stick to just reading the board and not asking anymore, thanks for your advice.

BG

 

[LittleInch]

BG - you're going to have to get a bit of a thicker skin in this industry if you've got the hump over a couple of comments like this.... There are a lot of posts from people who want answers to everything and justifications without acknowledging that they don't know very much or what they're going to do with the information. Next time you post, try to add as much details of what you have, what you've found so far and what it is you've been asked to do.

There is a wealth of past posts here if you search tapped holes or tapping holes in flanges. Many codes do allow this up to a certain size. If you look at B16.5, they have a minimum depth of 0.68" for a 1" tapped hole - see figure II-11 in appendix II. However the max rating is #2500.

One suggestion is to maybe weld on an additional boss to the outside and then tap that to increase the length of the screwed part - say double the length of what have now. Not all engineering can be calculated and sometimes you would spend much more trying to calculate something than just adding some more metal.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DekDee]

BG,
My apologies if my post came across as harsh.
There are too many people posting on this forum (and others I frequent) who cannot bother to do their own research and just post the question on here and hope someone else will save them the time, do the research for them and give them the answer.
You talk about the implacations to your project schedule - I have spent my whole working career in Quality being pushed by "project schedules".
I refuse to budge - do it right or don't do it at all !
You have had responses from some very experienced engineers (myself not included) and it appears nobody thinks your scenario of testing of high pressure piping with a blind flange with a threaded hole is an acceptable solution.
Hope you resolve your problem,
Cheers,
DD

 

[Duwe6]

". . . it appears nobody thinks your scenario of testing of high pressure piping with a blind flange with a threaded hole is an acceptable solution"

The calc's show that with a 1/4" weld around it, that 1-inch threaded plug will comfortably withstand the proposed hydro pressure. Threads alone, of course not!

 

[DekDee]

Sorry Duwe6, I have got my clients / owners hat on and I am saying I will not accept what you (and/or BG) are proposing without calcs proving it is safe to do sitting on my desk (not calcs given by an unknown poster on an internet forum who gives no reference to any codes/standards).
If I, as the client am going to approve the use of a blind flange with a threaded plug in it (especially for high pressure applications) when it is the norm to supply an untainted blind flange then I need to be pretty damn sure it is safe.
If it was me as the clients rep I would reject straight away (unless compelling evidence was provided) and demand the required blind flange was provided.
Regards,
DD

 

[Duwe6]

RULE #1: The customer is always right [if his checkbook is open]
RULE #2: If the customer's requirements seem onerous, excessive or odd, please refer to Rule #1.

 

[jte]

Duwe6-

Well, speaking as an owner/user/client I'd day that your rule #2 is a bit harsh. However, I realize that there is substantial truth in what you say. I suppose it comes down to how the message is delivered and how confident the owner's engineer is: An engineer lacking confidence in their understanding of the basics is more likely to toe the line when it comes to enforcing spec requirements. Generally when a deviation request is presented to me there's a better than 50-50 chance it will be accepted. But come to me with a request which indicates to me that this is a "we always do it this way" rather than a request with knowlegable engineering behind it and persuasively presented and the odds are that I'll recommend rejecting the request. Another way of pushing me towards "reject" is when an outside request is made directly to me rather than working through my company's project engineers. I've had some contact with an E&C firm which somehow seems to think that I'm the project's vessel specialist... Not the case, but they keep asking me questions directly anyway. I keep sending them to the project engineers.

I'm with DD on this one. As one colleague used to say, "Show me the numbers." This particular case should be fairly easy, and based on some of the weld strength discussions (referring to AISC) are persuasive since this loading will be at ambient conditions. In a non-hydrotest case the only thing I'd look for in those is to verify that the AISC values are not used directly, but are adjusted for temperature. After all, most structural engineers I've met seem to be of the opinion that steel vaporizes at around 200 deg. F, and so there is no point in discussing strengths at higher temperatures.

 

[Duwe6]

"Show me the numbers." Yep. If you can't calculate it, it's not engineering. It is an opinion [or a guess].