A Weeping Safety Valve and Three Bad Ideas
A 150 psig, 30,000 lb/h steam boiler in a factory is protected by a single ASME-rated safety valve set at 150 psig with a certified capacity of 32,000 lb/h. For two weeks the valve has wept, and a plume is visible at the discharge head. Maintenance proposes three things: install a gag on the valve until the annual outage; swap in a spare ASME valve from the warehouse that is set at 125 psig with a nameplate capacity of 26,000 lb/h; or, if neither is acceptable, raise the setpoint so the valve seats harder. The state adopts the ASME code and requires an annual certificate inspection and a licensed operator for boilers over 15 psi. The last certificate inspection was 14 months ago. The operator on shift holds a license that expired two months ago; he says the chief engineer told him it is fine because renewal is pending. The burner was uprated two years ago to 34,000 lb/h output, and no one has rechecked the valve since.
1. Rule on each of the three proposed actions and state the correct course.
Read the worked answer
Gag the valve: no. A gag is a transport device and must never be in place on an operating boiler. Gagging a safety valve removes the boiler's final overpressure protection, and a weeping valve is telling you something is wrong with the seat, the disc, or the spring - dirt, scale, or wire drawing from years of simmering. If the valve will not hold, repair or replace it, and until then reduce firing rate or take the boiler off line. Do not simply keep operating.
Swap in the 125 psig spare: no, on capacity grounds. A safety valve's job is to relieve at least the boiler's maximum generating capacity. This spare is certified for 26,000 lb/h against a boiler now capable of 34,000 lb/h, so it is undersized by roughly a quarter. Its lower set pressure also cuts the operating margin between normal working pressure and relief. A valve can be set below the MAWP, but only if its certified capacity at that setting covers the boiler's maximum output; here it does not.
Raise the setpoint: no. The valve must be set at or below the boiler's maximum allowable working pressure, which is stamped at 150 psig. Setting higher is a rerating question, not an adjustment, and field-changing the set pressure on an ASME valve requires a certified shop and new capacity certification. It also does not fix a leaking seat - the valve would weep at the new setting too.
Correct course: replace with a valve set at or below 150 psig and certified for at least 34,000 lb/h at that setting, with discharge piping sized for the flow.
2. What does the two-year-old uprate mean for code compliance, and how would you verify the relief capacity is adequate?
Read the worked answer
It means the boiler may have been operating out of compliance for two years. Relief capacity must equal or exceed the maximum evaporating capacity of the boiler, and that capacity changed when the burner was uprated. Nobody re-ran the calculation, and the existing valve's 32,000 lb/h certification is now below the 34,000 lb/h the burner can deliver. Even if it had been adequate, ASME limits accumulation above the set pressure, and the discharge piping and vent must be sized so back pressure does not reduce certified capacity.
Verify in this order. Establish the actual maximum output from the burner nameplate and the gas train data, then confirm it against a firing-rate measurement - clock the gas meter over a timed interval at high fire, correct for heating value, and convert to steam output at the operating pressure. Compare that number with the valve's certified capacity at the set pressure, taken from the nameplate and the manufacturer's capacity tables, not from memory. Check the inlet and discharge piping sizes and the equivalent length against the valve manufacturer's requirements, and check that the discharge is piped to a safe location with no valve or restriction between the boiler and the valve. Then document the calculation and the valve data sheet in the boiler file, so the next person does not have to redo it.
If the numbers do not close, the options are a larger valve, a second valve, or derating the burner back to a capacity the existing valve can protect. Any of those is defensible; operating as-is is not.
3. What do you do about the lapsed certificate inspection and the expired operator license before the end of the shift?
Read the worked answer
Both are compliance failures, and the operator's intent to renew does not cure either. A certificate inspection 14 months old means the boiler is being operated outside the state's inspection requirement. An expired operator license means the person in charge is not currently licensed for a boiler over 15 psi. A verbal assurance from the chief engineer is not an authorization; the jurisdiction is the only body that can extend or waive these.
Before the end of the shift: notify the chief engineer and plant management in writing, stating the facts - inspection date, license expiry date, the weeping valve, and the undersized spare - and the recommendation. Record it in the boiler log; do not backdate or alter any entry. Contact the state inspection authority the same day to schedule the certificate inspection and to ask how they want an expired license handled, whether a temporary permit exists, and whether the boiler may continue to operate pending inspection. Have a currently licensed operator assigned if one is available.
If the jurisdiction does not authorize continued operation, the boiler comes off line at the end of the shift, and management is told the steam will stop. That is an uncomfortable conversation but a defensible one. Operating an uninspected boiler, with a defective safety valve, under an unlicensed operator, in a jurisdiction that requires all three, is the kind of decision that is examined closely after an incident and reads very poorly in a deposition.