Need a reference for valves suitable for energy isolation (OSHA) 1

[JMichler]

I found the following definition from the semiconductor industry:

Definition of shutoff valve: A valve designed for and capable of positive closure to prevent flow within a piping system. Typical shutoff valves include, but are not limited to, manually-actuated, power-actuated, or spring-actuated fail-safe shutoff valves. Usually excluded are self-actuated valves, such as check valves, pressure regulators, flow controllers, and other devices that are not intended to provide positive shutoff for safety isolation. [SEMI F1-90]

Is there a similar definition in a ANSI, ASME, or BPV code?

I am working with our plant operators to ensure our LOTO program meets OSHA standards, and I keep getting asked the question why certain types of valves can't be used, specifically check valves. I have been able to find plenty of statements to not use them, but no engineering reference is provided. The closest document I found is "The Safe Isolation of Plant and Equipment" which I learned about in a post on this website. However, it doesn't reference an engineering spec either.

Is the SEMI F1-90 definition as close as I am going to get to an engineering reference?

 

[gerhardl]

I am afraid that my answer is only reinforcing what you have already stated, but do you actually need any more?

From common practice all over the world a 'positive shutoff' is a shutoff where the closing element is mecanically secured against accidental opening, eg. valves closing directly with mechanical devices and mechanical force and securly locked in the closed position, before mechanically operated to open position again.

And again by one sided closing pressure from springs or helping one-sided closing pressure from fluid, a positive closure can not be said to be given.

Exception on above list of constructions is globe-check valve with spindle (and handwheel) for shut off, and regulating valves constructed with (often protected or retarded, away from cavitation exposed areas) positive sealings with spindle and construction for drop-thigt closure.

Even those, especially the regulating valves, will in addition normally have mounted revision valves (positive closure valves) upstream.

 

[JMichler]

Thank you for the reply. I will probably go with what I have. I work in nuclear power and it has been my experience that unless I can provide to some hard requirement, the operator's are reluctant to accept my input.

I think what I have may be sufficient, I was hoping I was just overlooking another reference (preferably U.S.).

 

[vpl]

J Michler

If you work in a nuclear plant in the US, you can look at the Nuclear Regulatory Commission's Information Notices. There are more than a few that discuss check valves leaking. I think the worst case detailed was a plant where they had something like 9 different check valves in series leaked by (and caused problems). Look under the subject of "air entrainment in emergency core cooling piping."

Patricia Lougheed

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[JMichler]

Thanks. Checking the NRC Information Notices is an excellent suggestion. I'll do that.

I did find a prohibition against using check valves as an "energy source isolation" in MSS SP-92-1999, Valve User's Guide. I just wished it had been as helpful on the other type valves mentioned in the above definition.

 

[HEC]

There is another thread of similar content but a diferent question. If I am not mistaken JMichler you are looking for positive and verifiable isolation of the energy source. LOTO is Lock Out Tag Out? and would be for man entry or other work to access a service.

This is common in procesing industry and is generally a Double Block and Bleed isolation point. Simply this is two valves in series that provide a positive shut off. The cavity created between the two valves has a small bleed valve installed into it. The two main valves provide two points of isolation between the energy source and the LOTO point. The bleed valve is opened to vent/drain the cavity between the isolatino valves. This "bleed" valve provides a visual check that the primary isolation valve is holding and a relief point to ensure the secondary isolation valve is not over pressurised.

The style of valves generally used are ball, gate, or globe. Butterfly valves can be used but are not as secure (reliant on disc to seat pressure for seal), diaphragm valves are not ideal for the same reason. Check valves or line pressure activated valves are not at all suitable.


Mark Hutton

 

[JMichler]

HEC,

You are exactly right on what I am looking for. In fact, the information from previous threads that discussed the double block and bleed valves are what lead me to the information I have found so far.

The problem with the nuclear industry is it almost takes an act of god to make changes to the plant. Years of engineering design changes. So, basically we are working with what is installed in the plant. I find it very helpful to be able to refer to recognized industry standards when saying why or why not a certain valve or procedure can be used to comply with the OSHA standards. Unfortunately, for some of the valves, it looks like I will have to rely on tribal knowledge (or common practice as gerhardl stated above) to try to answer questions.

But in the meantime, I am still mining for that one nugget that leads me to the motherload of lock-out/tag-out information when it comes to fluid and steam systems.

 

[jte]

I am working with our plant operators to ensure our LOTO program meets OSHA standards, and I keep getting asked the question why certain types of valves can't be used, specifically check valves.

Well, I guess I’d ask the folks who think check valves could be used how they will lock or tag them shut?

"Double block and bleed" means the closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9797#1910.146(b)

jt

 

[JMichler]

jt,

I did ask...now I have to answer the "what tells me I can't use a check valve with 2,500# of water behind it holding it closed as an isolation point?"

I have also been told that in some cases there aren't two in-line valves and also in some cases there is not drain or vent valve in the line between the two closed valves.

So we are working on identifying alternative's that provide equal protection.

It's been an education.

 

[HEC]

Also need to look at the risks, isolation of potable water at low pressure is diferent to isolation of acid at low pressure, which is diferent to isolation of compressed air! What I am getting to is the DB&B set may not be required in all cases!

Mark Hutton

 

[jte]

JMichler-

But has the question about how one locks and tags out a check valve been answered? The OSHA rules are pretty clear on this.

If you don't have two valves with a bleeder to work with then slip blinds (line blanks) may be the way to go. They can get pretty thick at CL-2500. But consider that if you have one valve (locked and tagged out) on the process side, then a bleeder, then the slip blind... What pressure can the slip blind be exposed to? So, what is the design pressure of the slip blind in such a case? If you don't have a bleeder, the possibility exists to drill and tap a gate valve and install a bleeder downstream of the gate. See B16.34 Fig. 1 on page 13 of the 2004 edition. For a stem up gate valve you'd go with either location C or D.

jt

 

[JMichler]

I have what I need for check valves. As for the other valves of concerns (solenoid operated valves, air operated valves, etc.), I have decided that I'll have to rely on the concensus of opinion in various documents, especially those by the DOE, as they are closely related to the type of systems we have.

Thanks again, everyone, for your assistance.