Is a PSV Always Required at a Spec Break? 1

[KernOily]

Hi guys. Been away for awhile. I trust you have all been well and busy with your fluid mechanicking.

A question. Is a PSV always required at a spec break? I know generally, yes, but I am thinking perhaps not always. I have a situation here where I think I don't need one but I want to hear a general discussion first. Thanks! Pete

 

[MortenA]

if your low pressure pipe class side dont have any options for blocking in and expels to atmosphere the fluid then i would say no.

Just an example. This could e.g. be a local open vent.

Best regards

Morten

 

[BigInch]

can get to the vent with the full flowrate from the source without building up additional pressure over the low pressure pipe's design limit then, ... no.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Latexman]

If the spec break is just for materials of construction; no pressure class change - no.

Good luck,
Latexman

 

[zdas04]

It comes down to engineering judgement. In another thread I described a spec break that I recently did that was made up a pair of check valves, a pair of block valves, and three test ports. No PSV. I've done spec breaks with an actuated trunnion ball valve. No PSV.

The design engineer just needs to demonstrate that he has a plan to prevent the high pressure side from damaging the low pressure side and that the plan has a reasonable chance of working in the scenarios that are credible.

David

 

[SNORGY]

Unfortunately, regardless of all of the credible scenarios and the soundness of the plan for overpressure protection, one is nonetheless often at the mercy of the Regulator, whose appointed Authorized Inspector or Design Survey Engineer can impose judgement that supersedes that of the Designer or Engineer Of Record.

Regards,

SNORGY.

 

[BigInch]

Ohooooo ... not the question.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[zdas04]

SNORGY,
I've had a few of those officious jerks try that crap. None successfully. A couple of times I requested a hearing and they backed off.

I've always believed that the regulations (and their interpretations) control in the absence of engineering judgement. If I do the calculations that say two check valves, two block valves, three test ports, and documented procedures for confirming that the low pressure line is protected over time then if some "Authorized Inspector" wants to prohibit it because he "doesn't think it feels right" then he, my lawyer, and I are going to visit a department head. If you get a reputation as someone ALWAYS willing to go to war and someone who's first shot is ALWAYS nuclear then the "Authorized Inspectors" tend to be less arbitrary.

I've been told that my approach is counter productive because there will be times that I need and authorized inspector to look the other way. I contend that I want to follow the code, it is there to define minimums. If an inspector sees something that I'm doing that fails to meet the letter of the code I want to know it. If the notice comes as a formal INC (incident of noncompliance) that becomes part of the public record, then so be it. I've fought several INC's over the years and won most of the fights. My position is that it is the rare government employee who knows my job better than I do.

At the end of the day they have zero authority to expand the code. The code says that at a spec break you need to protect the low pressure side. It doesn't say how to protect it. It leaves that up to engineers. If some bureaucrat wants to expand on the letter of the code, then I'll invite him to support his position in front of someone with the authority to write regulations.

David

 

[BarrySand]

I suppose that depends on what code you'll be designing your spec break to. We adhere to installing two forms of independant overpressure protection when doing a spec break which doesn't neccessarily involve a PSV.

 

[pennpiper]

The original poster did not define the reason for the Spec Break but implied it "always" had something to do with a High Pressure system. Pressure is not the only reason for a Spec Break.

Some Spec Breaks are due to a change in material but not a change in pressure.

 

[SNORGY]

David:

Points well taken. The acid test is always how well the designer or EOR can defend the design to the satisfaction of the A.I..

Unfortunately, in the jurisdiction where I work, you have to have a perfect record in all of your fights, because your competence is invariably judged by the one you lose, irrespective of the nine you win.

Regards,

SNORGY.

 

[zdas04]

I've heard that before. I get really angry at ad hominem arguments. If I've been wrong a hundred times in a row, and I bring in the 101st analysis it should be evaluated on its merit, not on my reputation.

When I'm talking to those guys, the very first time they bring up one my historical projects I stop the proceedings and ask that if past unrelated projects are germane I would appreciate it if they would provide detailed review with analysis of the project, please include the inspector's position, and my position so that we can fairly evaluate my past performance. Opinions are not allowed, just facts. The inspectors look really cute with their tails between their legs.

There are just too many people who feel that opinions should be averaged. For example, about 20 well respected, active eng-tips.com members are certain that pneumatic pressure tests are dangerous and irresponsible and make that point in some thread a couple of times a month. A half dozen of us say that with proper engineering design and controls they are quite safe and often the best answer. 20 against, 6 for, the nay's have it. Having done quite a few pneumatic tests safely in country where a hydrostatic test is just plain dangerous (with 3,000 ft of elevation change to do a 900 psig test at the bottom doesn't allow the top to be full and putting 900 psig at the top equates to 2200 psi on the bottom) I have to listen to my own council.

David

 

[SNORGY]

David:

I agree. My only point, really, is that if one is going to challenge an A.I. or a Regulator, one had better not lose the argument. As you suggest, armed with enough technical competence, there are engineers who can win such arguments. However, what people remember (sadly) are the ones they lose.

With respect to pneumatic tests, I have done a few in my time as well: 36" flare lines, steam/methane reformers, PSA units, hydrogen plant piping among them. Properly managed and engineered, they can be safe - contingent, of course, upon a corresponding level of quality having gone into the construction, fabrication and QA/QC that occurred prior to engineering the test.

Managing the risk inherent in the engineering of pneumatic testing is easy, but in so doing, one is not necessarily managing the risks inherent in the activities over which engineering may have had little or no control.

It's the wrong way to find a bad weld.

Regards,

SNORGY.