NM Boiler Operator cheat sheet

ASME BPVC Section I covers power boilers fired above 15 psig steam; Section IV covers heating boilers limited to 15 psig steam or 160 psig and 250°F water; Section VIII covers pressure vessels.

The ASME Code stamp and Manufacturer's Data Report are required for new construction; S stamp identifies a power boiler, H stamp a heating boiler, and U stamp a pressure vessel.

MAWP is the maximum allowable working pressure marked on the boiler; the lowest-rated pressure part or component establishes the assembly limit, and no safety valve may be set above MAWP.

Safety-valve capacity must equal or exceed the boiler's maximum steam-generating capacity; no shutoff valve is permitted between the boiler and its safety valve.

ASME I new-construction hydrostatic test pressure is 1.5 times MAWP; the test is held for at least 10 minutes before inspection for strength and tightness.

Corrosion allowance is added to the calculated minimum thickness; metal wasted below the minimum required thickness is not acceptable for continued service.

Welded repairs require a qualified welding procedure and welder; repairs to ASME-stamped boilers are commonly performed under an NBIC R stamp by a qualified repair organization.

A Section IV steam heating boiler relief valve is set at or below 15 psig; a hot-water heating boiler relief valve is set at or below 160 psig and 250°F.

The code edition and construction standard are identified on the Manufacturer's Data Report and code stamp; later adopted editions may govern new installations and repairs.

1 psi equals 2.31 ft of water; 1 in. of water column equals 0.0361 psi; draft gauges read in inches of water column.

Saturated-steam latent heat decreases as pressure rises and becomes zero at the critical point, about 3206 psia and 705°F.

One boiler horsepower equals 33,475 Btu/hr, roughly 34.5 lb of steam per hour evaporated from and at 212°F.

Pre-purge moves air through the furnace and flue before ignition to remove combustible gases; typical practice is four to eight furnace volume changes with proven airflow.

Startup sequence: establish normal water level, purge the furnace, prove ignition and pilot flame, open main fuel, increase firing gradually, and place controls in automatic.

Normal shutdown: reduce firing, stop the burner, keep feedwater available, and allow controlled cooldown; do not drain a hot boiler until pressure and temperature are safe.

On a low-water trip, fuel must shut off; do not add water to a hot, overheated boiler until it has cooled, and severe low water may require emergency shutdown.

Steam pressure gauges indicate gauge pressure; absolute pressure equals gauge pressure plus atmospheric pressure, about 14.7 psi at sea level.

Hot-water boiler return water is commonly kept above about 140°F to limit flue-gas condensation and corrosion on the fireside.

Natural gas flammable range is about 5 to 15 percent in air; propane is about 2.1 to 9.5 percent; concentrations inside these limits can ignite.

Stoichiometric air for natural gas is about 9.5 to 10 ft3 of air per ft3 of gas; for No. 2 fuel oil it is about 14.4 lb of air per lb of oil.

Typical excess air is 5 to 10 percent for gas, 10 to 15 percent for oil, and 15 to 25 percent for coal; higher excess air lowers combustion efficiency.

CO2 in flue gas reaches a maximum near stoichiometric combustion; rising CO indicates incomplete combustion from insufficient air, poor mixing, or flame impingement.

Draft systems include natural draft from stack height, forced draft with an upstream fan, induced draft with a downstream fan, and balanced draft using both fans.

On flame failure, the flame safeguard closes fuel valves within the safety shutoff time; trial-for-ignition time is limited by the burner control.

Heating values: natural gas about 1,000 Btu/ft3, No. 2 fuel oil about 140,000 Btu/gal, and propane about 91,500 Btu/gal.

Burner turndown is maximum firing rate divided by minimum stable firing rate; excess air, flame stability, and emissions set the achievable limit.

If ignition is not proven, fuel must be closed and the furnace purged before another attempt; retry only after the cause is corrected.

Feedwater pH is typically 8.5 to 10.5 and boiler water pH 10.5 to 12 for many industrial boilers; extremes promote corrosion.

Dissolved oxygen causes pitting; deaeration plus an oxygen scavenger such as sodium sulfite or hydrazine controls residual oxygen.

Hardness from calcium and magnesium forms scale; a softener replaces hardness with sodium, but it does not remove dissolved solids.

Blowdown controls dissolved solids and sludge; surface blowdown removes foam and high-TDS water, while bottom blowdown removes sludge and sediment.

Blowdown fraction of feedwater equals feedwater TDS divided by allowable boiler-water TDS; this sets the continuous blowdown rate.

Bottom blowdown uses two valves in series: open the boiler-side quick-opening valve first, control with the outer valve, then close the outer valve before the inner valve.

External care includes checking for leaks, corrosion under insulation, damaged supports, blocked vents, and deteriorated stack or breeching.

Waterside cleaning removes scale and sludge, and fireside cleaning removes soot and ash; both restore heat transfer and reduce tube overheating.

Water hammer is caused by steam-line condensate or sudden valve closure; traps, drains, and proper warm-up prevent it.

Required protective devices include the safety valve, low-water fuel cutoff, high-pressure limit, flame safeguard, pressure gauge, gauge glass, and feedwater check valve.

The low-water fuel cutoff must be tested under actual low-water conditions; a float or electrode chamber blocked by sludge can fail to trip.

Gauge glass must have protective shields and clear connections; blowdown confirms that the indicated water level is true.

A pressure gauge uses a siphon and three-way cock; its range is commonly 1.5 to 2 times operating pressure.

Safety valves must be tested at required intervals; after repair, set pressure and relieving capacity must be verified by a qualified organization.

Internal and external inspections check waterside, fireside, fittings, supports, and appurtenances; a hydrostatic test may be required after repairs.

New Mexico's Mechanical Safety Bureau administers boiler and pressure-vessel safety and adopts ASME BPVC and NBIC by reference.

NMAC 14.6.3 is the state boiler and pressure-vessel rule; operating without a required certificate is prohibited.

An explosion, rupture, or serious boiler accident must be reported immediately to the authority having jurisdiction, and equipment may not be altered before investigation.