establishing relieving capacities only...the required steam-relieving capacity, in pounds per hour...

Establishing Relieving Capacities

Prepared for Chief’s meeting October 9, 2019

By Joseph F. Ball, P. E.

Overview of Session

• Review of Section IV Pressure Relief Capacity Requirements• ASME Requirements• NBIC Installation Requirements

• Establishment of Relieving Capacity for Section IV Pressure Relief Valves

Section IV Capacity Requirements

The Basics:

Overpressure protection requirements are defined by boiler manufacturer.

Nameplate shall include:(HG-530.1(a)(3)) Safety or safety relief valve capacity (minimum) as determined according to HG-400.1(d) and HG-400.2(e)

Heating area must be marked


The Basics:

Same for cast iron or aluminum (HG-530.2(c)(3)) – depends upon number of sections


The Basics:

Modular Boilers

• Each module has its own nameplate with capacity required for that module

• Aggregate capacity (and heating area) is applied to a single nameplate for the combined unit


The Basics: HG-400.1

(d) The minimum valve capacity in pounds per hourshall be determined by dividing the maximum Btu/hr(kW) output at the boiler nozzle obtained by the firingof any fuel for which the unit is installed by 1,000(0.646). In every case, the requirement of (e) shall be met.(e) The safety valve capacity for each steam boiler shallbe such that with the fuel burning equipment installed,and operated at maximum capacity, the pressure cannotrise more than 5 psi (35 kPa) above the maximum allowableworking pressure.



(e) The required steam-relieving capacity, in poundsper hour (kg/hr), of the pressure-relieving device or devices on a boiler shall be determined by dividing the maximum output in Btu/hr (kW) at the boiler nozzle obtained by the firing of any fuel for which the unit is installed by 1,000 (0.646). In every case, the requirements of (g) shall be met.



(g) Safety relief valve capacity for each boiler with asingle safety relief valve shall be such that, with the fuel burning equipment installed and operated at maximum capacity, the pressure cannot rise more than 10% above the maximum allowable working pressure. When more than one safety relief valve is used, the overpressure shall be limited to 10% above the set pressure of the highest set valve allowed by (c).


The Basics:

Water Heaters and Storage Tanks

(HLW-602.1) Nameplate includes Maximum allowable input in Btu/hrElectric heaters may use kW or BTU/Hr. or both

Storage tanks are marked “Storage Only”


The Basics:

Capacity provided must be equal to or greater than unit output:

WProvided > WOutput


How do we know WOutput?

• Non-mandatory Appendix A gives a method for estimating capacity based on heating surface.

• HG-403 discusses calculation of heating surface• Boiler area outside of furnace measured

circumferentially• Waterwall and other surfaces done as projected

area

• Non-mandatory Appendix B gives a method based on fuel burned



NBIC Table 2.9.1.3 duplicates Sec. IV , Appendix A

• Additional data for copper finned watertubes• Additional corrections for BTU inputs above

8000 BTU/Hr for firetube boilers and 16,000 BTU/hr for watertube boilers

NBIC also mandates meeting maximum output (Table 2.9.1.3 may not supply adequate capacity)



Other than the 2 non-mandatory appendices, the method for determining Safety or safety relief valve capacity (minimum) is not specified.

Cautions:• Appendix A may under-estimate the required

capacity in some cases.• Appendix B uses 75% efficiency (output/input) -

some designs are better than this



How accurate are the manufacturer’s ratings?

• Effects if under-rated

• Effects if over-rated


Additional Verification Methods

• Accumulation test – pressure cannot exceed specified overpressure

• Measuring maximum fuel burned and calculating capacity based on fuel heating value

• Measure feedwater flow to get maximum evaporative capacity


How do we know WProvided?

• This is the certified capacity of the pressure relief valves provided and installed.

• Capacity is certified through the National Board Capacity Certification program.

• Certified capacities listed in NB-18


NB Capacity Certification Process

Design reviewed before testing begins Original design test (with steam) determines

capacity rating for the model being tested 3, 4, or 9 valves tested for performance and flow +/-5% consistency requirement must be met


NB Capacity Certification Process

2 production valves witnessed at factory by NB rep. and tested for performance and capacity

Each design recertified every 6 years Manufacturer’s Quality system audited every 3

years


Assurance of Adequate Capacity

• All valve designs include a 0.9 safety factor on capacity

• Very unlikely that capacity of the valve selected will equal the exact system output


Assurance of Adequate Capacity

Hot water heater valves are rated for thermal relief (AGA rating) and pressure relief rating at overpressure.

Application based upon the AGA rating is much more conservative.


Responsibility

ASME: Safety Relief Valves shall be installed by either the installer or the manufacturer (water heaters)

NBIC: The owner-user is responsible for ensuring that installations meet all the requirements of the Jurisdiction at the point of installation including licensing, registration, or certification of those performing installations.


Responsibility

Jurisdictional installation inspection (and periodic re-inspection) is the vital backstop assuring that adequate capacity has been supplied, and the

pressure relief valves are properly installed.


National Board “Opportunities”

NB-131: Recommended Boiler and Pressure Vessel Safety Legislation (2004)NB-132: Recommended Administrative Boiler and Pressure vessel Safety Rules and Regulations (2004)

Both need to be updated (applicable overpressure is included in NB-132)

Impact on NBIC will need to be assessedSection IV Capacity Requirements


10/7/19: Chief’s presentation establishing relieving capacities 10-19

establishing relieving capacities only...the required steam-relieving capacity, in pounds per hour...

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