US DOT Approval - Opening new markets for international manufacturers
US DOT approval can open larger international markets for non-American composite cylinder manufacturers. An additional benefit is that DOT certification creates strong evidence of excellence and reliability to customers and government safety agencies.
Hansho Composites provides design and engineering services to help manufacturers gain US DOT approvals, with more than 30 years’ experience in this area.
US DOT’s Focus: Transportable Cylinders
US DOT approval is regulated by its Pipeline and Hazardous Materials Safety Agency (PHMSA). The cylinders which are approved by PHMSA are those which are transportable or are used in gas transportation. Examples of composite cylinders regulated by PHMSA include
US DOT’s Regulations per 49 CFR Code of Federal Regulations:
US DOT’s regulations for composite cylinder approval are defined in the USA’s Code of Federal Regulations, 49 CFR paragraphs:
105.40; Designated agents for non-resident manufacturers and re-testers
107.105; Application for Special Permit
178.70; Approval of UN Pressure Receptacles
178.71; Specifications for UN Pressure Receptacles
178.74; Approval of MEGC’s
178.75; Specifications for MEGC’s
These regulations can be found on PHMSA’s internet site at www.phmsa.dot.gov/phmsa-regulations
DECISION TIME: ISO-11119 (-1), (-2), (-3) or DOT Special Permit?
The DOT allows two paths of specifications for design approvals: UN ISO standard or DOT Special Permit. These are defined as:
UN ISO-11119-X specifications provide faster, direct recognition and approval by DOT.
Type 2 composite cylinders: ISO-11119-1:2012, Gas Cylinders – Refillable composite gas cylinders and tubes – Design, construction and testing – Part 1: Hoop wrapped fiber reinforced composite gas cylinders and tubes up to 450 liters.
Type 3 composite cylinders:ISO-11119-2:2012, Gas Cylinders – Refillable composite gas cylinders and tubes – Design, construction and testing – Part 2: Fully-wrapped fiber reinforced composite gas cylinders and tubes up to 450 liters with load sharing metallic liners
Type 4 composite cylinders: ISO-11119-3:2013, Gas Cylinders – Refillable composite gas cylinders and tubes – Design, construction and testing – Part 3: Fully-wrapped fiber reinforced composite gas cylinders and tubes up to 450 liters with non-load sharing metallic or non-metallic liners.
DOT Special Permits allow more design freedom and cost reduction to deviate from the ISO-11119-X family of specifications. The DOT Special Permit approval procedure often takes 6 or 12 months (approximately) to process. And yet there are good reasons to go with Special Permits, deviating from ISO-11119-X. These reasons include:
Larger size than 450 liters. Alternate ISO specifications for larger composite tubes, such as ISO11515 are not yet approved in the UN Specifications section 49 CFR 178.71
Lower, more economical burst strength requirements. Many DOT Special Permits for composite pressure vessels specify lower burst strengths of 1.6 x Test Pressure rather than ISO11119’s 2.0 x Test Pressure. This results in 20% lower material costs and competitive selling position.
Different, faster qualification test requirements. Many DOT Special Permits allow variations from ISO11119 and ISO11515 testing requirements. Pneumatic gas cycle testing, long term creep testing, impact testing, leak testing are some examples where DOT Special Permits are different from their ISO11119 and ISO11515 counterparts.
Better retest and service life extension methods. DOT Special Permits allow the use of Modal Acoustic Emission (MAE) testing and other methods to do periodic requalification and service life extensions.
In short; ISO11119-X specifications are faster for approval – faster by 6 months to 1 year (approximately). DOT Special Permits allow more design freedom and capability to reduce product costs.
DOT’S APPROVAL PROCESS
DOT’s approval process follows the following flow-chart.
Independent Inspection Agencies (IIA)
US DOT requires that an Independent Inspection Agency (IIA) shall inspect and verify composite cylinder factories and the composite cylinders during qualification testing and production.