Interpretation Response #10-0195 ([National Oilwell Varco] [Jianke Wang, Ph.D., P.E.])
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: National Oilwell Varco
Individual Name: Jianke Wang, Ph.D., P.E.
Location State: TX Country: US
View the Interpretation Document
Response text:
June 29, 2011
Jianke Wang, Ph.D., P.E.
Senior Project Engineer
National Oilwell Varco
2800 N Frazier St.
Conroe, TX 77303
Reference No. 10-0195
Dear Dr. Wang:
This is in response to your e-mail requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR) applicable to UN portable tank design criteria. Specifically, you ask for the definition of "design margin of 1.5" as it is used for determining the safety factor in § 178.274(c)(2). You state that it is your understanding that a design margin of 1.5 could result in a safety factor of 2.5 (1.5+1=2.5).
Sections 178.274(c)(2)(i) and (c)(2)(ii) state that the safety factor under each of the forces specified in paragraph § 178.274(c)(1) must be:
(i) For metals having a clearly defined yield point, a design margin of 1.5 in relation to the guaranteed yield strength; or (ii) For metals with no clearly defined yield point, a design margin of 1.5 in relation to the guaranteed 0.2% proof strength and, for austenitic steels, the 1% proof strength.
The term "design margin of 1.5" is the safety factor to which the UN Specification portable tank must be designed by calculating the stresses resulting from acceleration loads applied to the tank. The two terms are used interchangeably in the HMR (design margin § 178.274 (c)(2)) and UN Model Regulations (Volume 1 Section 6.7.3.2.10) to determine the minimum ratio between the yield strength of the material and the design stress. In § 178.274 (c)(2) the design margin is equal to 1.5; therefore, the minimum ratio is 1.5. Additionally, please note that an approval agent must evaluate the design and calculations for UN Specification portable tank as required by § 178.273(b).
I hope this information is helpful. Please contact this office should you have additional questions.
Sincerely,
T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division
178.274(2)(2), 178.273(b)