ASME Section I - Ligament Efficiency 1

[ITmecheng]

Hello everybody,

I am trying to calculate the ligament efficiency of a steam drum of a d-type watertube boiler.
However I am not sure how to calculate the ligament efficiency in the below marked-up area since the two of the 3" holes are closer to each other than the rest 3" holes.
d=77mm
(dimensions in mm)

I would be incredibly grateful for any feedback, suggestions, or help you can provide.

Thank you in advance for your time and assistance!



I would be incredibly grateful for any feedback, suggestions, or help you can provide.

Thank you in advance for your time and assistance!

 

[r6155]

Read the PG-52 slowly and try to understand it.
It's easy.

Regards

 

[goutam_freelance]

Since there is no definite pattern of holes, PG-53 should be applicable

 

[r6155]

@ goutam What is the edition of your ASME 1?​

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[r6155]

@ goutam
You are wrong.
Read again PG-52 and the drawing of OP.

I Insist what is the edition of your ASME 1?

 

[goutam_freelance]

I am correct as per ASME I, 2015.

 

[goutam_freelance]

@r6165

I do not know your background, but it seems you are a nuisance.
You never properly explain your points but always confronting others. You act like you own this portal, which you do not.
You should accept that all points of view must be expressed, including seemingly wrong ones.
As I explained to you old codes are not wrong altogether, in fact, one is legally permitted to follow old codes with proper declaration.
You should not believe that only you are right and others are wrong.

I request you not to abuse me and others through posts but refer to admins if you have any problem with my posts.

 

[ITmecheng]

Read the PG-52 slowly and try to understand it.
It's easy.

Regards

I have read it and I have calculated ligament efficiency for all groups with different definite patterns except the area which I have marked up. How would you calculate it?

Since there is no definite pattern of holes, PG-53 should be applicable

I have thought about it, but how would you calculate it?

 

[r6155]

@ ITmecheng
The governing DEFINITE pattern is with distance 101, as per PG-52.

 

[ITmecheng]

@ ITmecheng
The governing DEFINITE pattern is with distance 101, as per PG-52.

So would I take the equation from PG-52.2.1 -> E=(p-d)/p in order to calculate the longitudinal efficiency (two 2F holes) ? => E=(p-d)/p=(101-77)/101=0.238 ?

and then equation of PG-52.3 2*(pc-d)/pc in order to calculate the equivalent longitudinal efficiency of the circumferential ligament (hole 1 and 2F). This results in =2*(115-77)/115=0.661

and then also the equivalent longitudinal efficiency of the diagonal ligaments (1 and 2f) and finally take the lowest value?
Is there any mistake in my considerations?

If I calculate the efficiency as above the lowest ligament efficiency of the whole drum is the value 0.238 (the longitudinal efficiency of the holes 2F).

However my concern in all these calculations is following:
The steam drum already exists and the boiler is being operated for 25 years. We want to manufacture a new steam drum and mud rum (+ tubes of course) and I am going over the design in order to verify the calculations before proceeding with the manufacture. We noticed, that in the initial mechanical calculation the efficiency of the holes 2F was never calculated. with the above calculation I would need a steam drum that be 50% thicker than the existing. If the above calculation are correct, how does our existing boiler even operate without any failure?

 

[goutam_freelance]

I have thought about it, but how would you calculate it?

Refer
https://www.eng-tips.com/threads/ligament-efficiency-reg.371379/

If you still have issues please let me know.

 

[goutam_freelance]

In Cl 53.2.2, there is a relaxed provision for short length of asymmetry.

My interpretation is that if you calculate as above the min ligament efficiency as 0.238 you have to calculate MAWP of drum with max E as 0.238/0.8=0.2975.

But in case even this may become uneconomical for you, you can try to convince the inspector, citing that the drum design is already proof-tested. Alternative FEA analysis may be conducted to satisfy the inspector if required. Alternative analysis and/or proof testing may be acceptable as per PG 16, depending on the inspector.

But please try to consult a reputed boiler drum designer.