18 replies to this topic

[chemks2012]

Hi

 

I have a bursting discs [BD] with below specs

 

1) BD01: 3barg +0  and -10% at 200 deg C and the design pressure for a vessel to be protected is 6barg.

2) BD02: 3barg +10%  and -10% at 200 deg C and the design pressure for a vessel to be protected is 6barg.

 

My query

1) what is the relieving pressure in both the cases? I believe it is 2.7barg. Please correct me if i am wrong.

 

Thanks in advance

KS

 

 

[Bobby Strain]

You really only care about the pressure that is the allowable accumulation pressure for the vessel.

 

Bobby

[chemks2012]

Thanks Bobby,

 

In my case, the vessel being, an accumulation of 10% is allowed.

 

From your post, I gathered that I need to consider physical properties of material being released at 6.6barg and not at 2.7barg. If my understanding is correct, I would beg to differ as the material will be relieved way before the pressure reaches to 6.6barg? 

 

Or am I missing anything here?

 

Thanks

[Bobby Strain]

Your interest is to protect the vessel against overpressure. So you should design the relieving device to do this. Unless you want to do something different.

 

Bobby

[chemks2012]

As per company’s policy and original design limitations on process [confidential to share here], I am not allowed to change the set pressure of bursting disc.

As this is the case, I believe, relieving pressure is 2.7barg and NOT 6.6barg?

 

Input from other members?

Thanks

KS

[fallah]

 

I have a bursting discs [BD] with below specs

 

1) BD01: 3barg +0  and -10% at 200 deg C and the design pressure for a vessel to be protected is 6barg.

2) BD02: 3barg +10%  and -10% at 200 deg C and the design pressure for a vessel to be protected is 6barg.

 

My query

1) what is the relieving pressure in both the cases? I believe it is 2.7barg. Please correct me if i am wrong. 

 

 

KS,

 

Are the -10%/0% and -10%/+10% manufacturing ranges? If so, then 3 barg seems to be the specified burst pressure, the first range is negative and the second range is positive and negative manufacturing range. Am i right?

 

Please specify the burst tolerance range of each BD. Then the maximum and minimum burst pressures could be specified. Obviously, the marked burst pressure would be within the manufacturing range.

Edited by fallah, 03 March 2014 - 04:03 AM.

[aroon]

KS,

 

You will have to study the system thoroughly to find out why the set pressure is so low. There are ample of reasons:

1. To protect the downstream systems, see liquid and vapor outlet downstream to find out limiting set pressure basis.

2. To avoid thermal decomposition of valuable fluid inside vessel. Sometime at elevated pressure, temperature may cross thermal decomposition limit.

3. To avoid run away reactions in case of vessel if a reactor.

4. To capture the spontaneous high relief rate relief scenario, which can lead to raise inside pressure above overpressure limits in a fraction of time.

 

and some more reasons.

 

You can check the vendor's supplied rupture disc datasheet and to study limiting scenario calculation and to figure out the issue (if available).

 

- Aroon

[chemks2012]

Fallah,

 

Those are tolerances and NOT manufacturing ranges. Do I need to know manufacturing range?

 

Aroon,

 

Yes, you are right but the reason we have low set pressure is probably to avoid thermal decomposition of product.

 

Thanks

[fallah]

Fallah,

 

Those are tolerances and NOT manufacturing ranges. Do I need to know manufacturing range?

 

KS,

 

Tolerances are normally indicated by +/- value percent and rarely wider than +/-5%. Please recheck again...

 

Yes, you need to know manufacturing range also...

[chemks2012]

Thanks Fallah,

 

As I understand, tolerance will give me minimum and maximum pressure range for a given bursting disc. Please confirm.

 

I will request manufacturing range but not sure what is the significance of manufacturing range?

[fallah]

 KS,

 

My answers in red color are as follows:

 

 

 

As I understand, tolerance will give me minimum and maximum pressure range for a given bursting disc. Please confirm.

It is deviation range from minimum and maximum marked burst pressure. 

I will request manufacturing range but not sure what is the significance of manufacturing range?

It will specify minimum and maximum marked burst pressure based on specified burst pressure...

[chemks2012]

Thanks Fallah,

 

Supplier confirmed that manufacturing range is zero.

As this is the case, the minimum burst pressure would be 2.7barg and max 3barg if I understood your last post correctly?

Thanks,

[fallah]

 

Supplier confirmed that manufacturing range is zero.

As this is the case, the minimum burst pressure would be 2.7barg and max 3barg if I understood your last post correctly?

 

KS,

 

Then marked burst pressure is equal to specified one...

 

For the marked burst pressure above 40 psig, same as your case, the burst tolerance is normally +/-5%...Anyway as per the tolerances you submitted:

 

For RD1: The minimum/maximum burst pressures would be 2.7/3 barg... 

 

For RD2: The minimum/maximum burst pressures would be 2.7/3.3 barg...

[chemks2012]

Thanks Fallah,

 

This means that, for relief calcs, I need to consider 2.7barg for both, RD1 and  RD2?

 

Thanks

[chemks2012]

 

 

Supplier confirmed that manufacturing range is zero.

As this is the case, the minimum burst pressure would be 2.7barg and max 3barg if I understood your last post correctly?

 

KS,

 

Then marked burst pressure is equal to specified one...

 

For the marked burst pressure above 40 psig, same as your case, the burst tolerance is normally +/-5%...Anyway as per the tolerances you submitted:

 

For RD1: The minimum/maximum burst pressures would be 2.7/3 barg... 

 

For RD2: The minimum/maximum burst pressures would be 2.7/3.3 barg...

 

Hi Fallah,

 

Is my understanding correct that my relief calcs should be based on 2.7barg for both bursting discs?

 

Thanks

KS

[fallah]

 

Is my understanding correct that my relief calcs should be based on 2.7barg for both bursting discs?

  

 

KS,

 

You should use marked burst pressure of 3 barg, as set pressure for relief calculation of both bursting discs...

[chemks2012]

Thanks Fallah... much appreciated.

 

I am sizing these bursting discs for two phase flow release using HEM model and not sure if I should allow 10% overpressure to arrive at relieving pressure? i.e.

 

Set pressure: 3barg

Relieving pressure: 3barg + 10% over pressure = 3.3barg

 

Also, I think I need to use physical/thermodynamic properties of released materials at relieving pressure and not at set pressures?

Edited by chemks2012, 05 March 2014 - 09:35 AM.

[fallah]

KS,

 

Relieving pressure would be 3.3 barg and physical/thermodynamic properties of the released material at relieving pressure should be used...

[chemks2012]

Thanks Fallah for all your help,

You are a star!!