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High Limit Control - Electric Boiler

High Limit Control - Electric Boiler

High Limit Control - Electric Boiler

Hello all,

I have a question regarding the requirement for high-limit pressure control in ASME Section I Power Boiler.
Where does this requirement come from?
What exactly needed?

Any information and reference will be great.

Thank you,

RE: High Limit Control - Electric Boiler

IdanPV: The code section (ASME Sect I) provides requirements for all methods of construction of power, electric, and miniature boilers; high temperature water boilers, heat recovery steam generators, and certain fired pressure vessels to be used in stationary service; and power boilers used in locomotive, portable, and traction service. Specifically, Section I Power Boilers include process boilers, power boilers, and high pressure boilers. It includes boilers in which steam or other vapor is generated at a pressures exceeding 15 psig (103.4 kPa) and high temperature water boilers intended for operation at pressures exceeding 160 psig (1103.1 kPa) and/or temperatures exceeding 250 degrees F (121 C).

Protection for pressure vessels is typically based on "above normal" conditions, to provide personnel and equipment safety. This means whoever is controlling the process wants to know when the pressure vessel is getting stressed (i.e., seeing elevated temperature and/or pressure). Hence the need for a "high limit" signal to trigger a control loop.

Converting energy to motion for more than half a century

RE: High Limit Control - Electric Boiler

Gr8blu, Thank you for your detailed response.
As far as I see, the code (ASME I) does not contain specific requirement for "manual reset, high-limit pressure control" as shown in ASME VII (which is only "Recommended Guidelines" , Figure 301.2-3 and 301.2-1 for example.

So, I wanted to know if there is any specific requirement for a "manual reset, high-limit pressure control" element in Electric power boilers which design and stamped per ASME I.


RE: High Limit Control - Electric Boiler

I was involved with limit controls for furnaces and ovens and it was the National Fire Protection Agency's NFPA 86 standard that covered control interlock requirements and used similar language.

NFPA 85 covered those topics for boilers.

RE: High Limit Control - Electric Boiler

The primary codes governing boiler controls are ASME CSD-1-2015, Controls & Safety Devices for Automatically Fired Boilers, and NFPA 85: Boiler and Combustion Systems Hazard Code. CSD-1 applies to boilers up to 12.5 million Btu/h. For boilers 12.5 million Btu/h and greater, NFPA-85 is the governing code.

The ASME is not a Nationally Recognized Testing Laboratory (NRTL), so they do not type certify devices like the "manual reset, high-limit pressure control" element,

RE: High Limit Control - Electric Boiler

Hello all and thank you very much for your answers.
As far as I see, neither CSD-1 nor NFPA 85 are referenced in ASME Section I.
Anyway, I went through CSD-1, but I couldn't find any mandatory requirement regarding a manual-reset, high-limit pressure control, but It might be a jurisdiction law, rule, or regulations which referenced to in NB-370?
Does the requirements of CSD-1 applies for the case of Electric Power Boilers up to 72kW?
If so, does the device have to be of the manual-reset type?

RE: High Limit Control - Electric Boiler

I'm a bit puzzled as to what you're trying to do here? Is it to not fit a recognised safety device?

A "manual reset high limit pressure control" sounds like an ESD high pressure switch to me. This normally has at least one if not two alarms set below this level and below the pressure relief valve level.

It sounds very much like a sensible and proportionate device to me. so I can't see why you don't want to fit it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: High Limit Control - Electric Boiler

Hi LittleInch,
Thanks for the comment.

Indeed, it is a very sensible and important device, and there are two of which in our boilers.
One is set at 10% of the operation pressure, the high-limit device is set at 21% of the operation pressure and below the set pressure of the PRV.

The thing is, I now need to justify and approve the reason why we need two and why one is not enough.

RE: High Limit Control - Electric Boiler

How does it work if the safety switch is at 21% of the operating pressure??

So your real question is Do I need two?

What does the lower switch do? Shut the system down or raise an alarm?
You need to have a good look at the Cause and effects or logic chart, but your data isn't making sense to me?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: High Limit Control - Electric Boiler

1st device - operating pressure control is at around 10% of the required operating pressure, it stops the heating element operating.

2nd device - high-limit manual reset control is at around 21% of the operating pressure, shut down the electrical system and need a manual reset in order to be back to work.

For example - MAWP is 420kPa, operating pressure 300kPa, 1st device set to 330kPa 2nd device is at 363kPa, PRV set pressure is 400kPa.

I know that I need 2 and I know that both of them are important.
I just wanted to know
a. where is it written (in the Code (ASME I) or CSD-1 or NB-370...)
b. Does the second one need to be of the manual-reset type or not.

RE: High Limit Control - Electric Boiler


You actually mean the first is 110% of operating pressure and the second 120% of operating....

I very much doubt the ASME code gets this specific if you can't find it in that CSD code.

This is simply good practice and whether the second one is an ESD type manual reset to restart is up to you I feel. Some are auto resetting, but if the boiler has gone 120% over the pressure it should have been controlled at this seems like a reasonable thing to do to enforce someone to come and look at it and try and find out why.

Still don't understand why you need to justify this when it is a fixture on the boiler at the moment??

Is a few dollars that important to you? Far harder would be justifying to anyone or a court of law for anyone who gets injured why you DIDN'T include that or have REMOVED it from your previous systems. Saying "The code didn't say I had to" isn't good enough. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: High Limit Control - Electric Boiler

How you get required to design to ASME B&PV Code, and either NFPA 85 or ASME CSD-1 is
  • Your jurisdictions boiler safety law.
  • Your insurance company.
  • Your sense of self preservation.
  • OSHA

  • RE: High Limit Control - Electric Boiler

    It is not about few dollars, the thing is we are having trouble with getting those elements currently, we can't find it anymore in the market.

    I totally understand the need of this element, but right now, it is a bit of a problem.

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