Interpretation Response #07-0147 ([Fort Vale Engineering Ltd.] [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: 03/05/2008

Company Name: Fort Vale Engineering Ltd.

Individual Name: Mr. Dave Bailey

Country: UK

View the Interpretation Document

Response text:

March 5, 2008

Mr. Dave Bailey, Chief Engineer

Fort Vale Engineering Ltd

Parkfield Works

Brunswick St

Nelson

Lancs

UK BB9 0SG

Ref. No. 07-0147

Dear Mr. Bailey:

This is in response to your email on July 20, 2007 regarding the Hazardous Materials Regulations (HMR; 49 CFR 171-180) applicable to shear sections on IM101 and UN portable tanks. Your questions are summarized and answered as follows

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. You ask for confirmation that the performance standard does in fact allow for some leakage of the tanks lading, and that the groove is intended to protect the tank.

A3. Provided the shear section or sacrificial device breaks at no more than 70% of the load that would cause failure of the internal self closing stop valve, some leakage of lading may occur. The shear section is intended to protect the tank from catastrophic failure when damage to the filling/discharge connection is sustained.



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

Sincerely,

John A. Gale,

Chief, Standards Development

Office of Hazardous Materials Standards

178.270-12 178.274(e)(1)

Regulation Sections