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Finding of Equivalence; Alternate Pressure Relief Valve Settings on Certain Vessels Carrying Liquefied Gases in Bulk

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Coast Guard, DHS.


Notice of availability.


The Coast Guard announces the availability of CG-ENG Policy Letter 04-12, “Alternative Pressure Relief Valve Settings on Vessels Carrying Liquefied Gases in Bulk in Independent Type B and Type C Tanks.” Existing Coast Guard regulations regarding the allowable stress factors for type B and type C independent cargo tanks are more stringent than the International Maritime Organization (IMO) standards for such cargo tanks. Materials, manufacturing, and inspections have advanced since the Coast Guard first promulgated regulations on allowable stress factors on May 3, 1979. CG-ENG Policy Letter 04-12 establishes that for certain type B and type C independent cargo tanks that are designed and manufactured using advanced techniques, the IMO standards for allowable stress factors provide a level of safety protection equivalent to the standards in 46 CFR 154.447 and 46 CFR 154.450.


CG-ENG Policy Letter 04-12 is effective as of September 27, 2012.


This notice and the documents referenced within are available in the docket and can be viewed by going to, and using “USCG-2012-0804” as your search term. CG-ENG Policy Letter 04-12 is also available at and can be viewed by clicking the link to the Office of Design and Engineering Standards (CG-ENG) under the “Units,” “USCG Headquarters Organization,” and “CG-5P” tabs, and scrolling down to “Policy Documents.”

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If you have questions on this notice, call or email Cynthia A. Znati, CG-ENG-5, U.S. Coast Guard; telephone (202) 372-1412, email Start Printed Page 59409If you have questions on viewing material in the docket, call Renee V. Wright, Program Manager, Docket Operations, telephone (202) 366-9826.

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Background and Purpose

The IMO first adopted the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) on November 12, 1975. The current version of the IGC Code is the 1993 Edition, as amended through December 5, 1996. On May 3, 1979, the Coast Guard promulgated regulations based largely on the IGC Code, but adopted the stricter standards of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section VIII with respect to allowable stress factors. Coast Guard regulations in 46 CFR 154.447 and 154.450 regarding allowable stress factors for type B and type C independent cargo tanks have remained unchanged since May 3, 1979.

Coast Guard regulations in 46 CFR 154.447 and 154.450 require that self-propelled ships carrying liquefied bulk gases in type B and type C tanks use stress factors that are higher than those in the IGC Code. The higher stress factors lead to lower maximum allowable relief valve settings (MARVS) than are allowed by the IGC code. Accordingly, ships with type B or type C tanks that travel from international waters to U.S. territorial waters must have two pressure relief valve (PRV) settings per tank, and they must switch PRV settings upon entering U.S. territorial waters. We believe that in many cases, switching between these two PRV settings is not necessary for safety purposes.

Finding of Equivalence

According to 46 CFR 154.32, vessels may meet an alternate standard if the Commandant determines that the alternate standard provides an equivalent or greater level of protection for the purpose of safety. We recognize that advances have been made with respect to materials, manufacturing, and inspection since we first promulgated 46 CFR 154.447 and 154.450. Therefore, as specified in CG-ENG Policy Letter 04-12 and below, we have determined that for tanks designed and manufactured with advanced techniques, the stress factors in the IGC Code provide a level of safety equivalent to current Coast Guard regulations.

Tanks manufactured consistent with certain conditions are considered to meet the level of safety required in 46 CFR 154.447 and 154.450. Tanks that meet the following two requirements may use the MARVS as determined by the IGC Code:

(1) The tank must be designed and built according to the IGC code, 1993 Edition, including all amendments through December 5, 1996; and

(2) The classification society that certified the tank must be authorized to issue an International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk (Certificate of Fitness) and must be authorized to participate in the Coast Guard's Alternate Compliance Program. See​hq/​cg5/​acp/​ for further information.

Tanks that do not meet both of these requirements must comply with current Coast Guard regulations in 46 CFR 154.447 or 154.450. Alternatively, persons may request approval from the Commandant (CG-ENG-5, formerly CG-522) to use an alternate pressure relief valve setting for such tanks. Equivalency requests must include the information required in 46 CFR 154.32(b) and should also include a copy of the Certificate of Fitness.

The guidance in this notice and CG-ENG Policy Letter 04-12 is not a substitute for applicable legal requirements, nor is in itself a regulation. It is not intended to nor does it impose legally-binding requirements on any party. It represents the Coast Guard's current thinking on this topic and may assist industry, mariners, the general public, and the Coast Guard, as well as other federal and state regulators, in applying U.S. statutory and regulatory requirements.

This notice is issued under authority of 46 U.S.C. 3703, 46 U.S.C. 9101, 5 U.S.C. 552(a), 46 CFR 154.32, and 33 CFR 1.05-1.

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Dated: September 13, 2012.

J.G. Lantz,

Director of Commercial Regulations and Standards, U.S. Coast Guard.

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[FR Doc. 2012-23772 Filed 9-26-12; 8:45 am]