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Swagelok Rl4 Proportional Relief Valves And As1271 - Compliant?


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#1 black friday

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Posted 24 September 2013 - 08:59 PM

Hi All,

I'm on a site right now which has poorly managed it's PSV inventory and has a the whole lot due for recertification at once. The site has a number of swagelok RL4 proportional relief devices installed, in a very one size fits all manner. We've had incidents where secondary devices have discharged (bursting discs) under a relief scenario as the swagelok product is inadequate for the relieving flow rate.

Would anyone more conversant than I with the Australian PSV standard, AS1271, be able to advise whether these valves, assuming they are adequately sized, are compliant? I'm currently reviewing all installed valves and doing calcs to ensure they're adequately sized. But even if one of these valves was big enough, as I read AS1271 a proportional relief device is not a safety relief device. However I don't want to replace them with different models if not necessary.

And help would be much appreciated.

Cheers,

Sackrace.



#2 ChemEng01

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Posted 26 September 2013 - 01:28 AM

Hey

 

It does say in the Swagelok catalogue that these RVs shouldn't be used as safety relief devices, and R series relief valves are proportional relief valves that open gradually as the pressure increases. Consequently,they do not have a capacity rating at a given pressure rise (accumulation), and they are not certified to ASME or any other codes”

 

However. They are typically used on chemical injection systems. 

 

Stating a required  size is meaningless for these valves. As can be seen from the catalogue there are only a few types. Each type is a standard size and can be set at different set pressures for different services. Calculating a required size using API equations or similar can not be done for these valves as they are proportional. 

 

If you look at the graphs in the catalogue, the proportional RVs will relieve more at a higher upstream pressure.

 

When checking the suitability of the valve use the standard % allowable overpressure (generally 10%) and ensure that this valve is capable of relieving the relief load at allowable % overpressure. 

 

In your case I bet if you check the graphs in the catalogue your valves may be able to relieve the required relief rate but the overpressure required to relieve this rate will be higher than your bursting disk set pressure

 

Using the graphs in the catalogue. Draw a line for your set pressure using same gradient as the line below (unless you have your RV set at one of the set pressures outlined in the catalogue). Check what your valve can relieve at the allowable overpressure. 

 

If you look at the graph for the RL4 type valve the upstream pressure needs to be approx 20% above set pressure to relieve the max flow shown on the graph. Check what the required over pressure is at your required relief rate and see if this is above the set pressure of the bursting disk. 

 

Hope this clears it up.



#3 black friday

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Posted 29 September 2013 - 09:20 PM

I'll admit I don't entirely follow your post without the catalog in front of me, but I'll take the time and see if it makes sense. Thanks for taking the time.

If I'm not entirely mistaken the gist of your post is that they aren't code compliant but may have the necessary capacity? In which case I would still have to replace them correct?

Cheers, black friday.



#4 ChemEng01

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Posted 30 September 2013 - 10:49 PM

Hey

 

Please follow this link for catalogue http://www.swagelok....N/MS-01-141.pdf

 

I think they are not compliant with regards to hydrocarbon service. They are ok for chemical injection systems (methanol / CI /PPD).

 

Check out the catalogue an d see what you think.

 

cheers



#5 astro

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Posted 11 August 2014 - 08:51 PM

Hey

 

Please follow this link for catalogue http://www.swagelok....N/MS-01-141.pdf

 

I think they are not compliant with regards to hydrocarbon service. They are ok for chemical injection systems (methanol / CI /PPD).

 

Check out the catalogue an d see what you think.

 

cheers

 

To clarify, the issue is that the valves are not capacity certified so that they do not comply with the ASME BPVC and you won't find them listed in NB-18 over at the National Board of BPVI:

http://www.nationalb....aspx?pageID=64

where orifice diameters and coefficients are documented. When doing a rating or final design relief calc, this is the data source I refer to rather than any other basis.

 

So, if you use one of these non-code compliant relief valves then you need to understand the limitations of what you've got. API STD 520 Part 1 (referring to the 9th ed at 5.9) has a methodology for liquid relief of non-capacity certified relief valves but not gas.

 

All this style of relief valve are (as best as I can make out), in effect, a sprung loaded control valve. So, for sizing, the current technical data from Swagelok does not provide sufficient useful information, in my opinion. I say this because I'm dealing with the exact same issue. What I want to know is the flow characteristic or flow resistance of the valve at full lift, i.e. conditions relevant to sizing when a capacity check is involved. All Swagelok give you in their current catalogue is an orifice diameter. This is of little use without its associated orifice coefficient.

 

I did find some old 1994 catalogue data here:

http://50.244.15.10/...lief Valves.pdf

Unfortunately, it's for an R4 not an RL4, but it does show that at higher inlet pressures the flow rate that the valve will pass reduces. The problem with the current Swagelok data is that if you chose to extrapolate the flow curve, then you'll end up with the wrong result. Given that I've got nothing better, I'm using the quoted Cv for my work on the expectation that the key difference between the R4 and RL4 is around the installed spring. I'd be happy to get better data if anyone can offer it up.

 

If it helps, I also found the RL3 data sheet here:

http://50.244.15.10/...lief Valves.pdf

 

 

I'd also suggest that when working with uncertain data sources such as this, that the approach offered by API STD 520 Part 1 at 5.12 is a sensible strategy and that is to work to a relieving capacity at a reduced flow factor.






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