What is the minimal pressure to use a safety relief valve 4

[JBO]

I have actually instaled a HF vaporizer operating at 24 Psig @ 150 ºF and actually we don´t use a safety relief valve, in a future the pressure to be 35 psig. The cuestion is what is the minimal pressure required to install a safety valve.

 

[JohnBreen]

Hello,

This is a question that should be asked of the juridiction in which the equipment is to be used. The ASME Code excludes equipment that contains less than a certain volume, but this does not necessarily exclude the equipment from the LAWS of the jurisdiction.

Regards, John.

 

[CHD01]

The minimum pressure for an ASME Code Section VIII vessel is 15 psig. There are exceptions if it is a small vessel or if it qualifies as "PIPE"; but generally speaking most vessels greater than 6-in diameter and 1-1/2 ft3 needs to be provided with a relief valve (check the code to be sure my memory is right - you need to check the code anyway!). The more you learn, the less you are certain of.

 

[whb]

For any closed vessel if the pressure exceeds the limit of 5bar the vessel should hv a safety valve
vj

 

[CHD01]

whb:

What are you trying to say? ANY enclosed vessel or tank MAY require a relief device (vent, relief valve, rupture disk, etc). There is nothing magical about 5 bar in the USA! If a VESSEL is over 15 psig a relief valve is usually required UNLESS it cannot be overpressured from an outside source (so long as state law permits application of the ASME Code Case). Below 15 psig a vent is usually used to limit maximum pressure. So 15 psig is a bit magical - but not 5 bar. The more you learn, the less you are certain of.

 

[juancito]

You still can sell these vessels without PSV´s as long as you state in the documents that the customer has to provide them. It is not mandatory that the PSV has to be installed stright onto the vessel. It can be located in the connected piping. But the vessel has to be protected always (in fact you can say that you protect in first place the people).

 

[davefitz]

The design code used plus additional rules by the local authority will govern.

In the case of HF, its toxic effects on persons probably imply special rules, such as using a bursting disc upstream of the relief valve . A seeping relief valve is not going to be accepted by the local authority. Tremendous damage was caused in 1945 in southwestern New Jersey by a Dupont HF facility leaking HF.

This is something that cannot be designed over the internet by amateurs. I would suggest finding someone that has experience with the chemical process .

 

[JAlton]

ASME Sec III, Nuclear Standards provide for an ASME "NV" Code Stamped Vacuum Service Relief Valve. ASME Sub-Committee Safety Valve Requirements, Sub-Group Testing is currently doing Task Group Work on an item intended to permit ASME Sec. VIII "UV" Code Stamping of PRVs under 15 psig. However, under current ASME Rules, a PRV is not required by ASME Sec. VIII for any pressure below 15 psig because there are no provisions for certification of such a device.
J. Alton Cox
President
DeLuca Test Equipment

http://www.delucatest,com

 

[tonycola]

ASME Section VIII vessels (15 psig or greater design pressure):
A relief device is required whenever there are credible scenarios that could cause the vessel pressure to exceed 110% of the design pressure.
A relief device is required to protect the vessel during an external fire if an external fire scenario is credible. In this case the device must be sized to prevent the pressure from increasing beyond 121% of the design pressure.
API 620 tanks(less than 15 psig design pressure):
Requirements are similar to ASME Section VIII.
API 650 tanks (less than 2.5 psig design pressure):
Relief device is required to prevent the pressure from exceeding the design pressure during normal and emergency situations.

Note: A relief device could be a relief valve, safety relief valve, conservation vent, rupture disk, etc.

 

[hacksaw]

JBO:

Does your vaporizer carry an ASME stamp and nameplate?

 

[TrevorP]

I've only just looked at this forum, so sorry for the delay in replying. Actually, by changing the operating pressure from 24 psig to 35 psig, you are changing nothing in relation to the need for pressure relief. To define if you need pressure relief (and to size it), consider this. You are using a vaporiser, right? So, you must have a heating element (Steam, electric, hot oil...). This has a maximum temperature associated with it - say steam at 300°F max. for the sake of argument. Then, the HF will have a certain vapour pressure at that temperature. If that vapour pressure exceeds the design pressure of the vessel, then you MUST have pressure relief, for the event that the normal outlet path is blocked, e.g. due to a closed valve. This is, however, just one contingency, consider the HF feed pump/system (unlikely to be the worst case scenario, but could be, e.g. if using N2 overpressure), fire case etc. etc. Make a list of every credible thing that can go wrong and design any relief for the worst case.... Also consider vacuum - what if the outlet is blocked, so the heating element goes off (Possibly due to a control system because the outlet is blocked)? HF vapours condense --> vacuum. If designed for full vac., no problems, but if not, you may need a vacuum breaker. If there is no credible case for any pressure or vacuum relief, then you don't need one (Unless specified by the vessel code - see above comments!).

 

[JAlton]

If you are looking for help with sizing regarding worst case scenarios or credible threats to pressure vessel integrity, you might try

http://www.digitalsolutions.com.

They offer PRV Sizing help. J. Alton Cox
President
DeLuca Test Equipment

http://www.delucatest,com