§ 154.824 - Inerting, enriching, and diluting systems.

(a) A vapor control system which uses inerting, enriching, or diluting gas must be capable of inerting, enriching, or diluting the vapor collection line prior to receiving cargo vapor.

(b) Except as permitted by §154.820(a) of this subpart, a vapor control system which uses an inerting, enriching, or diluting system must be equipped with a gas injection and mixing arrangement located as close as practical but not more than 10 meters (32.8 ft.) from the facility vapor connection that ensures complete mixing of the gases within 20 pipe diameters of the injection point;

(c) A vapor control system that uses an inerting or enriching system may not be operated at a vacuum after the injection point unless:

(1) There are no sleeve-type pipe couplings, vacuum relief valves, or other devices which could allow air into the vapor collection system downstream of the injection point; or

(2) An additional analyzer is used to monitor the downstream vapor concentration and a means is provided to inject additional inerting or enriching gas.

(d) A vapor control system that uses analyzers to control the amount of inerting, enriching, or diluting gas injected into the vapor collection line must be equipped with at least 2 analyzers. The analyzers must be connected so that:

(1) When oxygen analyzers are used, the higher oxygen concentration reading controls the inerting or enriching system and activates the alarm and automatic shutdown system required by paragraph (h), (j) or (k)(2) of this section;

(2) When hydrocarbon analyzers are used, the lower hydrocarbon concentration reading controls the enriching system and activates the alarm and automatic shutdown system required by paragraph (i) or (k)(1) of this section; and

(3) When hydrocarbon analyzers are used, the higher hydrocarbon concentration reading controls the diluting system and activates the alarm and automatic shutdown system required by paragraph (l) of this section.

(e) A vapor control system that uses volumetric measurements to control the amount of inerting, enriching, or diluting gas injected into the vapor collection line must be equipped with at least one analyzer to activate the alarms and automatic shutdown systems required by this section.

(f) Each oxygen or hydrocarbon analyzer required by this section must:

(1) Be installed in accordance with API Recommended Practice 550 (incorporated by reference; see §154.106);

(2) Have a response time of not more than 30 seconds from the time the vapor is sampled; and

(3) Sample the vapor concentration continuously not more than 30 pipe diameters from the gas injection point.

(g) Oxygen analyzers which operate at elevated temperatures ( i.e. , zirconia oxide or thermomagnetic) must not be used.

(h) An inerting system must:

(1) Supply sufficient inert gas to the vapor stream to ensure that the oxygen concentration throughout the vapor collection system is maintained below 8.0 percent by volume;

(2) Activate an alarm when the oxygen concentration in the vapor collection line exceeds 8.0 percent by volume;

(3) Close the remotely operated cargo vapor shutoff valve required by §154.810(a) of this part when the oxygen concentration in the vapor collection line exceeds 9.0 percent by volume; and

(4) If a combustion device is used to produce the inert gas, have a hydraulic seal and non-return valve between the combustion device and the vapor collection line.

(i) An enriching system must:

(1) Supply sufficient compatible hydrocarbon vapor to the vapor stream to ensure that the hydrocarbon concentration throughout the vapor collection system is maintained above 170 percent by volume of the upper flammable limit;

(2) Activate an alarm when the hydrocarbon concentration in the vapor collection line falls below 170 percent by volume of the upper flammable limit; and

(3) Close the remotely operated cargo vapor shutoff valve required by §154.810(a) of this subpart when the hydrocarbon concentration in the vapor collection line falls below 150 percent by volume of the upper flammable limit.

(j) Oxygen analyzers may be used in lieu of hydrocarbon analyzers in an enriching system at a facility that receives cargo vapor only from a vessel with non-inerted cargo tanks, provided that the analyzers:

(1) Activate an alarm when the oxygen concentration in the vapor collection line exceeds 15.5 percent by volume; and

(2) Close the remotely operated cargo vapor shutoff valve required by §154.810(a) of this subpart when the oxygen concentration in the vapor collection line exceeds 16.5 percent by volume.

(k) An enriching system may be used in a vapor collection system that receives cargo vapor from a vessel with inerted cargo tanks if:

(1) Hydrocarbon analyzers are used to comply with paragraph (i)(2) and (i)(3) of this section; or

(2) If oxygen analyzers are used, the analyzers activate an alarm when the oxygen concentration in the vapor collection line exceeds 8 percent by volume, and close the remotely operated cargo vapor shutoff valve required by §154.810(a) of this subpart when the oxygen concentration exceeds 9 percent by volume.

(l) An air dilution system must:

(1) Supply sufficient additional air to the vapor stream to ensure that the hydrocarbon concentration throughout the vapor collection system is maintained below 30 percent by volume of the lower flammable limit;

(2) Activate an alarm when the hydrocarbon concentration in the vapor collection line exceeds 30 percent by volume of the lower flammable limit; and

(3) Close the remotely operated cargo vapor shutoff valve required by §154.810(a) of this subpart when the hydrocarbon concentration in the vapor collection line exceeds 50 percent by volume of the lower flammable limit.

[CGD 88–102, 55 FR 25429, June 21, 1990; 55 FR 39270, Sept. 26, 1990, as amended by USCG–2001–8661, 74 FR 45023, Aug. 31, 2009]