Limitations for reinforcement Pad

[vinothsvk]

Hi ALL,

I have confusion on reinforcement pad limitations. I had evaluated that Nozzle RF Pad thickness is higher than the shell thickness due to Nozzle WRC Loads, but my client Specification says, the RF pad thickness should not exceed than the shell thickness. But in dennis moss page no.96 of 825 (4th edition), maximum limitation of reinforcement pad thickness shall be 1.5 times of shell thickness and width limitation is 2inch.

And my question is, ASME BPVC SEC VIII DIV-I have any limitations for Reinforcement pad?

 

[DSB123]

Normally thickness is limited to 1.5 times the vessel thickness. The 2" width limitation is not correct.This should be the minimum width not the maximum. Width is limited by the Code you are dealing with

 

[SnTMan]

No Code limits in pad thickness (other than limits of reinforcement) that I am aware of.

1 1/2 t max pad thickness is generally considered good practice, but if your client limits this then, given the loadings you may have to ask for a deviation, either the loadings or pad thickness.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Trestala]

The reasoning for having that requirement in the specification is because of the lap weld between pad and shell. If you have a thicker reinforcing pad, it is good engineering practice to limit the weld leg size equal to the thinner part. Then any excess thickness of the reinforcing pad beyond the shell thickness wouldn't be attributed for its strength.

 

[SnTMan]

Then any excess thickness of the reinforcing pad beyond the shell thickness wouldn't be attributed for its strength.

Well, per UG-37 calculations, this is just not true.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[DSB123]

SnTMan,
So I am wrong in what I said then - "Normally thickness is limited to 1.5 times the vessel thickness." ?

 

[TGS4]

DSB123 - the rationale for that limit is that beyond there you basically are creating a hard spot in your vessel at the nozzle (it will have a stiffness much in excess of the generally-existing stiffness) and that has a history of causing problems.

Personally, I would limit it to 1x wall thickness.

 

[Trestala]

Well, per UG-37 calculations, this is just not true.

Typical good practice is limiting the weld leg size for lap welds equal to the thickness of the thinner part. If you have a 1.5t pad on a 1.0t shell, your fillet weld leg size between the 1.5t pad and 1.0t shell should be limited to 1.0t. That is only considered as good practice and ASME Code is silent on that. Strength path across that fillet weld would then be limited to 1.0t (see UG-41). Though, you are free to do whatever you like.

I also agree with what TGS4 mentioned.

 

[r6155]

In ASME VIII Div 1 the only limit is the engineering judgement.
I disagree with pad thickness greater than shell thickness. Out of this my good engineering practice is integral nozzle.

In PD-5500: The thickness of a pad shall not exceed 40 mm or the as-built shell
thickness, whichever is the lesser.

Regards
r6155

 

[SnTMan]

Again,

No Code limits in pad thickness (other than limits of reinforcement) that I am aware of.
1 1/2 t max pad thickness is generally considered good practice...

The OP's question referred to both good practice and Code requirements. I addressed both.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Shashvat]

Hi vinothsvk,

I think that the clause UG-40 of the code, Limits of Reinforcement, will be applicable to the dimension of the reinforcing pad that will contribute to the reinforcement. A reinforcing pad designed as per this will work satisfactorily as far as the code is concerned.

However, the client may set his own standard that should lie within the UG-40 limitations. In such case, if possible, you can persuade the client for an exception( to his standard, not the ASME), or else follow the client standard.

 

[r6155]

Client specification is mandatory, unless be impossible to comply.

Regards
r6155