Freight Container Tare Weight Reduction via High-Strength Steel
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Solution Overview
Problem
Conventional freight containers for pressurized fluids exceed weight limits due to their tare weight, leading to inefficient transport as they often need to be filled only partially to comply with load limits, especially in countries like Japan, where the maximum loaded weight is 53,000 lbs.
Innovation Solution
A novel freight container design with a tank constructed using high-strength steel, where the shell thickness is determined by the equation Ts = (Pw * R1) / (Su / Xa - Xb * Pw), with Xa > 1.5 and Xb between 0 and 1, reducing the tare weight by optimizing the scalar factors and material usage, while maintaining compliance with regulatory standards such as the ASME Boiler and Pressure Vessel Code.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional freight containers are designed according to ASME Division 1 code with standard joint efficiency, then they meet regulatory approval requirements, but their tare weight becomes excessively high causing transport inefficiency
Solution Approach 1:
The patent changes the joint efficiency parameter from conventional values (0.6-0.8) to a higher value (0.85-1.0) by implementing full radiography of all welded joints. This parameter change allows the use of thinner shell walls while maintaining regulatory compliance, directly reducing tare weight by approximately 2000 lbs compared to conventional containers
Solution Approach 2:
The patent replaces the conventional mechanical inspection method (visual inspection and spot testing) with a more advanced detection method (100% radiography of all welded joints). This substitution provides more reliable detection of joint quality, enabling higher joint efficiency values and thinner wall designs that still meet safety requirements
2Strength
If tank shell thickness is increased to meet pressure containment requirements, then structural strength is improved, but tare weight increases causing partial filling to comply with load limits
Solution Approach 1:
The patent optimizes the shell thickness parameter by using the thinnest possible wall thickness that still satisfies both the pressure containment requirement and the regulatory formula, enabled by the higher joint efficiency. This parameter optimization reduces material usage and tare weight while maintaining full structural strength for pressure containment
Solution Approach 2:
The patent employs composite construction principles by combining high-strength low-alloy steel material with optimized joint design and full radiography inspection. This composite approach (material + process + inspection) achieves superior strength-to-weight ratio compared to conventional single-parameter designs
3Weight of moving object
If joint efficiency is increased through full radiography, then manufacturing cost and inspection time increase, but tare weight is reduced improving transport efficiency
Solution Approach 1:
The patent implements a self-verifying manufacturing process where the manufacturing procedure itself (full radiography of all joints) automatically provides the verification needed to achieve high joint efficiency. This self-service approach eliminates the need for separate, complex quality assurance processes and makes the high inspection standard routine and manageable
Data Source
AI summary
A freight container for transporting a pressurized fluid at a design pressure P, including a tank and mounted within an ISO frame. The tank includes a vessel formed of a material having an ultimate tensile strength SU. The vessel has a cylindrical shell having an inside radius RI and a thickness Ts which is less than that of prior art freight containers and substantially equal to: (P*Ri) / ((Su / Xa) - (Xb*P)). Such a vessel conforms to ASME Boiler and Pressure Vessel Code, Section VIII, Division 2. The freight container may be mounted on a transport vehicle, before or after being filled with the pressurized fluid, and transported to a remote location.