5 replies to this topic

[xyz168]

There are many relief devices in a plant. I believe they are not all come from the same manufacturer. Also, I am pretty sure they are not all purchased and installed at the same time. Looking at this situation, isn't there supposed to be some kind of general standard? Some numbers that cannot be violated and whatnot? When we size a PSV, we don't really know who we'll purchase it from. So, there must be some kind of rule of thumb.

My other question is... some people design a relief device per API. Others use ASME as their standard. Does it matter which one we follow?

[pleckner]

Both of your questions actually go hand-in-hand so I'll address them both at once. Also, my response will assume we are discussing pressure vessels only.

ASME (American Society of Mechanical Engineers) produces a series of documents. API (American Petroleum Industry) also produces a series of documents. I don't know where in this small world of ours you are located but in the United States, all states except for two have adopted ASME as Code or law. This means that the facilities located in these states must comply with what is in those ASME documents. These documents describe how a pressure vessel is to be constructed and what must be done to that vessel to prevent a catastrophic failure caused by over pressure. They also tell you the types of devices that are acceptable to use to accomplish this.

Being that ASME dictates what your facility must comply with, API documents tell you how to achieve compliance. The three most common of those documents are API RP520 Parts 1 and 2 (RP stands for Recommended Practices) and API Standard 521. Note that these API documents are not law but only packages of standards and recommendations (by the way, "RP" or "standard" makes no difference, they both cary the same weight as being nothing more than standards). So these (API) documents give you all the details you need (well, almost) to comply with the law (ASME). In other words, API provides those "rules of thumb" you are looking for.

Be aware that many of these "rules of thumb" may not be good for every relief device you have. For instance, the effective coefficient of discharge for a gas/vapor/steam relief valve is given as 0.975 as a "rule of thumb" but Farris PSVs use 0.953! So you can use API documents as a first approximation but must eventually check your design against the true values for the device you eventually purchase.

OK, even though the API documents are "just" standards and recommended practices, in the United States they are basically considered to be "good engineering practice" and you would be very foolish not to follow them as a minimum. You can be more conservative than what these documents say but you should not be any less.

So you see, you are using both sets of documents at the same time.

OK, so how does this affect your facility? If your local government has also adopted ASME as Code (law), then everything I've said pertains to you as well. In my experience, most other countries have adopted ASME or some equivalent, such as the PED in Europe. Even if your local government has not adopted ASME, or equivalent, as Code, these documents are proven so it would be in your best interest to follow them nevertheless.

[xyz168]

Phil, what are the two states?

Both of your questions actually go hand-in-hand so I'll address them both at once. Also, my response will assume we are discussing pressure vessels only.

ASME (American Society of Mechanical Engineers) produces a series of documents. API (American Petroleum Industry) also produces a series of documents. I don't know where in this small world of ours you are located but in the United States, all states except for two have adopted ASME as Code or law. This means that the facilities located in these states must comply with what is in those ASME documents. These documents describe how a pressure vessel is to be constructed and what must be done to that vessel to prevent a catastrophic failure caused by over pressure. They also tell you the types of devices that are acceptable to use to accomplish this.

Being that ASME dictates what your facility must comply with, API documents tell you how to achieve compliance. The three most common of those documents are API RP520 Parts 1 and 2 (RP stands for Recommended Practices) and API Standard 521. Note that these API documents are not law but only packages of standards and recommendations (by the way, "RP" or "standard" makes no difference, they both cary the same weight as being nothing more than standards). So these (API) documents give you all the details you need (well, almost) to comply with the law (ASME). In other words, API provides those "rules of thumb" you are looking for.

Be aware that many of these "rules of thumb" may not be good for every relief device you have. For instance, the effective coefficient of discharge for a gas/vapor/steam relief valve is given as 0.975 as a "rule of thumb" but Farris PSVs use 0.953! So you can use API documents as a first approximation but must eventually check your design against the true values for the device you eventually purchase.

OK, even though the API documents are "just" standards and recommended practices, in the United States they are basically considered to be "good engineering practice" and you would be very foolish not to follow them as a minimum. You can be more conservative than what these documents say but you should not be any less.

So you see, you are using both sets of documents at the same time.

OK, so how does this affect your facility? If your local government has also adopted ASME as Code (law), then everything I've said pertains to you as well. In my experience, most other countries have adopted ASME or some equivalent, such as the PED in Europe. Even if your local government has not adopted ASME, or equivalent, as Code, these documents are proven so it would be in your best interest to follow them nevertheless.

[pleckner]

Aha, a Jeopardy question! Now I'm going to get in trouble because I always blame Lousiana and can't remember if it is really the "other" one. But up to now, no one has corrected me so...Texas IS one and the other I THINK is Louisiana.

[JoeWong]

Aha, a Jeopardy question! Now I'm going to get in trouble because I always blame Lousiana and can't remember if it is really the "other" one. But up to now, no one has correcte me so...Texas IS one and the other I THINK is Louisiana.

Phil,

TEXAS !!! HOUSTAN as well ?! Aha...interesting ! Anymore elaboration on what they commonly applied ? Love to hear more...

[pleckner]

They commonly apply API and at least some of ASME BPVC but these aren't mandatory. Perhaps someone from those states will write in and enlighten us on just what they do follow and what the state law says.