How to calculate Plate thickness and weld thickness for hydro testing blind closure 2

[robinmech]

Hi Guys,

I want to calculate the plate thickness and weld thickness of a plate going to use for hydro testing.
We are planning to close the pipe end with the plate by using welding.

The details are as follows
Dia of Pipe 48"
Wall thickness 12.7 mm
Test Pressure 70 Psi
Plate material going to use S275JR


Deatil is attached in the sketch

Please help.

 

[EngDesServices]

Hey Robinmech,

If you have your test pressure (70psi), then you have your loading across the open area that you intend to close off with a welded plate. A flat head resists loading via pure bending and can be analyzed in that context.

You could approach the problem in various ways with varying complexity, namely:

[ul]
[li]You can throw the model in a design software and generate a finite element model and solve recursively for the plate thickness required for a required factor of safety.[/li]
[li]You have a uniform load on a symmetrical geometry therefore you can reduce the problem to any number of beam equations and determine the thickness of the beam required to minimize deflection to whatever deflection amount is considered safe in your circumstances. This will get you the thickness required for your plate and you can size the weld once you have the thicknesses of both plates being joined[/li]
[li]You have a 70psi pressure over a 48in diameter circle, or a static load of ~127,000 pounds. Analyzing for failure due to shear in the plate near the weld attachment would give a shear area of the plate thickness multiplied by the circumference. You can vary the thickness of your plate such that the shear area is sufficient (with a decent level of safety included) to withstand the load.[/li]
[/ul]

There are probably more methods to solving this problem, but those are a few I could think of off the top of my head.


Michael Hall, PE (TX) PMP - President
Engineering Design Services LLC

http://www.engdess.com

 

[MJCronin]

Your plan to use a flat plate head and secure it with a fillet weld will be a disaster.

The flat plate will flex and, when you test, you will be loading the "toe" (weakest part) of the fillet weld

Fillet/Socket welds are not permitted for large bore (greater than 2"NPS) piping in accordance with most piping codes, even for temporary hydro closures.

A better plan would be to install a "slip-on" type flange and bolt a flat plate to the head ...

A better question is "Why do you have a bizarre hydrotest termination at a plain pipe in the middle of a system somewhere ?" ..... Are there no permanent flanges in this system ??? ... That is where your hydrotest boundaries should be ....

Some companies rent properly sized paddle blinds, flanges test gear and services... they can answer your questions.

Paddle blind thickness calculation is covered in ASME B31.1 and B31.3

What is your code of construction and testing ?

https://www.google.com/imgres?imgur.../JTC8RNVCnUw/hqdefault.jpg&imgrefurl=https://

http://www.youtube.com/watch?v=JTC8...7DmAhXDG80KHVoQA1IQMwhLKAAwAA&iact=mrc&uact=8

Respect us ..... come back and complete this thread with your final plan ....

MJCronin
Sr. Process Engineer

 

[Geoff13]

I would use ASME Section VIII Division 1 clause UG-34, with a higher allowable stress to reflect that this cover is for hydrotest only. Read this section carefully for permitted weld details.

Your sketch appears to be only an outside fillet weld, like Figure UW-13.2(p), which is not a permitted detail for attaching a flat head. You could add an inside fillet weld to match Figure UW-13.2(g).

 

[robinmech]

@Michel Hall @Mjcronin

​

Thank you so much for the reply.

Actually I was trying to solve the problem with the formula dg*Sq.Rt(3*p/16*S*E)+C (From ASME 31.3). Is that the correct method.

The reason why we are terminating the pipe in the middle of a system is "These are pipe modules and the Continuation of this system is in a different module and the fabrication of the same is not in our scope. So we have to keep the pipe as open end with out any flange.

Do you to the cost impact we can't use any additional flange and the blind flange for the testing purpose. That's the reason why we are going with a temporary testing blind.

my code of construction is ASME B31.3.

Also help me to finalize the weld thickness.

Thanks in advance.

Robin

 

[mk3223]

For the piping module fabrication, one option is to weld the pipe cap welded to the open for the hydro testing. It can be part of the module fabrication procedure.