Interpretation Response #07-0147R ([Fort Vale Engineering Limited] [Mr. Dave Bailey])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date: 07/23/2008

Company Name: Fort Vale Engineering Limited

Individual Name: Mr. Dave Bailey

Country: UK

View the Interpretation Document

Response text:

July 23, 2008

Mr. Dave Bailey, Chief Engineer

Fort Vale Engineering Ltd

Parkfield Works

Brunswick St

Nelson

Lancs

UK BB9 0SG

Ref. No. 07-0147R

Dear Mr. Bailey:

This serves as a retraction of our March 5, 2008 (Ref. No. 07-0147) letter responding to your request for clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to shear sections on IM101 and UN portable tanks. Upon further review, it is necessary to clarify our response to Q3. Your questions are paraphrased and answered below: We apologize for any inconvenience this may have caused.

Q1. You understand that the shear section or sacrificial device on UN portable tanks must break at no more than 70% of the load that would cause failure to the internal self closing stop valve in accordance with § 178.274(e)(1) . You ask if the removal of 30% of the wall section would result in a 70% stress reduction? If so, would this also satisfy the portable tank shear section requirement in § 178.270-12(d)?

A1. Reduction of the wall section by 30% may satisfy the 70% stress requirement specified in § 178.274(e)(1) provided an analysis of the shear section strength and expected performance shows that the shear section would break at no more than 70% of the load that would cause failure to the internal self closing stop valve. Section 178.270-12(d) requires a shear section to be located outboard of each internal discharge valve seat and within 10.2cm (4 inches) of the vessel. The shear section must break under strain without affecting the product retention capabilities of the tank and any attachments. It is the manufacturer"s responsibility to perform an analysis of the shear section design, dimensions, and expected performance to determine the orientation of the shear section installation required to meet the minimum requirements of §§ 178.274(e)(1) and 178.270-12(d).

Q2. As far as you can determine the only shear section calculation available is TTMA RP 86-98, "Emergency Valve Shear Section Strength Calculation". Is the use of the TTMA RP 86-98 calculation considered the best practice for calculating the valve shear section strength for portable tanks?

A2. The HMR requirement applicable to portable tank shear sections is a performance standard. Under the HMR, various methods of analysis or test may be used to evaluate the expected strength and performance of the shear section relative to the strength of internal self closing stop valve, and their configuration on the tank. The HMR do not specifically reference the TTMA RP 86-98 shear section strength calculation. However, it is the opinion of this office that the TTMA RP 86-98 shear section strength calculation is an acceptable method for calculating the expected performance of a shear section for compliance with the HMR.

Q3. In a Safety Advisory Notice (62 FR 37638), PHMSA clarified that internal discharge valves and shear sections are safety devices required on the bottom-outlets of IM portable tanks in hazardous material service to prevent significant release of lading when damage is sustained at the filling/discharge connection. Does the performance standard allow for some leakage of the tanks lading?

A3(a). For UN portable tanks, the shear section or sacrificial device must break at no more than 70% of the load that would cause failure of the internal self closing stop valve. Provided the shear section satisfies this performance requirement, some leakage may occur.

A3(b). For IM101 portable tanks, the performance requirement applicable to shear sections was previously specified in § 178.270-12(d) [Removed: 72 FR 55678 (HM-244); October 1, 2007] of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180). The requirement specifies that the shear section must break under strain without affecting the product retention capabilities of the tank and any attachments. Therefore, there may be no leakage of lading from an IM101 portable tank related to the performance of the shear section.



I hope this satisfies your inquiry. If we can be of further assistance, please contact us.

Sincerely,

Edward T. Mazzullo

Director, Office of Hazardous

Materials Standards

178.274(e)(1), 178.270-12(d)

Regulation Sections