Hydrogen Storage Tank Components CNC Machining for Energy Systems

Stainless Steel 316L is the most appropriate and cost-efficient option for the construction of hydrogen tanks and their components because of its remarkable resistance to hydrogen embrittlement. It enables cyclic pressure operation of 0 to 875 bar for 15,000 to 20,000 refueling cycles over a 15-year service life. It has a threshold stress intensity factor of over 25 megapascals square root meter and can withstand high cyclic hydrogen pressure. Stainless Steel 316L is also resistant to corrosion in humid and saline environments, which is necessary for underbody automotive installations. It has a yield strength of 170 to 310 megapascals, which is enough for the tanks to withstand burst pressures of 1050 to 1750 bar with a safety factor of 2.25 to 2.5 in accordance with ISO 19881 standards for pressure vessels. Lastly, the material has been qualified for use with hydrogen gas and numerous other tests per SAE J2579 standards, which include testing for slow strain rate and fatigue crack growth.
Because Aluminum 6061-T6 still gives a unique combination of strength over light weight, allowing for lightweight valve boss design,s reduces tank system weight by 2 to 5 kg per vehicle, improving fuel economy by 1 to 2 percent. With a yield strength of 276 megapascals and a density of 2.7 grams per cubic centimeter, 6061-T6 is still preferable to machining for complex geometries, including integrated pressure relief device pockets and receptacle mounting features. It suffices to say that hydrogen compatibility for limited stress applications under 200 megapascals is still of considerable importance. It provides remarkable thermal conductivity of 167 watts per meter Kelvin, allowing rapid refueling and cooling of valves that undergo adiabatic compression heating of gas to 85°C. There is considerable cooling to be done. Titanium Grade 5 Ti-6Al-4V provides the best strength-to-weight ratio; with a weight of 4.4 grams per cubic centimeter and a yield strength of 880 to 930 megapascals, it permits ultra-lightweight designs for aerospace and top-of-the-line cars. It is not embrittled by hydrogen and maintains weak high temperatures over 400 degrees for fire safety. It provides high corrosion resistance and allows designs to 350 to 700 bar.

Valve boss bodies are cylindrical parts that are made on CNC turning centers to a diameter accuracy of ±0.003 inches. The critical sealing surfaces, which range from 40 to 100 millimeters and have a bore diameter of ±0.002 inches within overlapping pressure gauges that reach from 20 to 50 millimeters. The sealing grooves of O-rings are finished to an Ra of 0.8 to 1.6 microns, achieving a leak rate of lower than 1×10⁻⁶ standard cubic centimeters per second of helium, which is equivalent to the permeation limits of the tease test SAE J2579. Complex port geometries on 5-axis CNC machining centers are made to positional accuracy of ±0.005 inches. The pressure relief device and receptacle mount surfaces are matched for perpendicular alignment of 0.010 millimeters to the main bore axis. This verifies road alignment during the refueling process. Cylinder head monocross and torso mount free flange patterns for tanks are also made. For the threads on pressure vessels to be rolled, the thread components must be cut. The rolled threads for cyclic pressure loading are also cut. These also adjust the surface finish to 0.4 to 0.8 microns. Surface hardening of the threads increases 10 to 20 percent when work hardening is applied, and adding 15 to 30 percent fatigue strength is given when threads are rolled.
We make all kinds of different screws using our CNC thread milling machine. These include 11/16-18 UNF SAE J2600 receptacle, and M12×1.5 to M30×2 MEtric pressure vessel thread corners and UNF. WE ALSO machine 1/4 to 3/4" NPT threads. WE do all these with 6g to 6H precision. WE also drill deep cavity PVD with slits of 3 to 10mm. WE do 10:1 to 20:1 L/Ds and hold a deviation of 0.010mm for every 100 mm of length. WE do electropolishing to reduce from to/4m to 0.4m. WE do this to minimize roughness and reduce hydrogen to 99.97% purity. This is to increase the hydrogen purity and to align with ISo 14687 for fuel quality. WE also do hard anodizing using Type-III. WE do 25 to 75 microns to increase wear resistance and insulate electrically.

We achieved tolerances within ±0.002 inches for O-ring grooves between 2 and 6 mm wide and 1.5 to 4 mm deep, ensuring a squeeze of 10 to 25 percent and protecting against extrusion for pressure seals with 350 to 700 bar. Flat sealing surfaces were produced with a tolerance of 0.002 inches over 30 to 100 mm diameters while maintaining a leak rate of 1×10⁻⁶ standard cc/sec. The defined porous areas and threaded connections were produced with class 6g external and 6H internal screw threads according to ISO 965; pitch diameter control within ±0.025 mm for the screw threads of pressure vessel connections. Bore diameter tolerance is ±0.002 inches for pressure regulator cartridge fits 20 to 50 mm with interference fits of 0.010 to 0.030 inches to prevent loosening during cycling from -40°C to +85°C. Port position control within ±0.005 inches for pressure relief devices, maintaining 438 to 875 bar of actuator pressure. Perpendicularity of sealing surfaces and mounting features within 0.010 mm between control of assembly features was achieved. Surface finish ranging between Ra 0.8 to 1.6 microns for the critical sealing interfaces was achieved to reduce leak paths. Additionally, formed threads were finished to a Ra of 0.4 to 0.8 microns and provide fatigue strength to withstand pressure cycles between 15,000 and 20,000.

Yes, Zintilon provides rapid prototyping services and produces between 5 and 25 functional components within time frames of 3 to 5 weeks for pressure vessel testing. This includes the following: hydrostatic burst testing to 1.5 to 3.5 times working pressure, leak testing using helium mass spectrometry with a sensitivity of 1×10⁻⁶ standard cubic centimeters per second, and cycling hydrogen testing (0 to 875 bar for 500 to 1,000 cycles) to validate fatigue resistance. Zintilon also performs low-volume production of 100 to 1,000 components for pilot fuel cell vehicle programs and demonstration systems with first article inspection, including documentation of hydrogen compatibility, and high-volume production exceeding 10,000 components per year for commercial hydrogen vehicle production. This production for commercial hydrogen vehicles utilizes automated CNC turning cells with a cycle time for each valve boss of 3 to 8 minutes and statistical process control with process capability indices Cpk greater than 1.67 for critical sealing dimensions.
Every production phase involves extensive cross-checking. It involves coordinate measuring machines, O-ring groove specifications, touch-triggered probes, optical comparators, leak testing to SAE J2579 performed at room temperature and -40°C, and pressure cycling performance and hydrogen embrittlement testing to measure cracks and ductility referenced in ASME Article KD-10.

All the hydrogen storage tank parts are designed and made in accordance with the ISO 9001:2015 standards, and there is full traceability from the raw materials to the final product, so there is proof of all the testing and the pressure vessel code compliance. All the hydrogen storage parts designed by us and documentation stored by us have met all the SAE J2579 standards about fuel system-mounted components in fuel cell vehicles about materials of construction, component-level design, testing, and all gas 5 to 875 bar pressure hydrogen handling requirements. Also, ISO 19881 and ISO 19882 standards with land vehicle fuel containers about gaseous hydrogen and 2.25 times nominal working pressure burst tests, 45 hydraulic cycles, and 45,000 cycles without leakage, and UA ECE R134 standards about uniform provisions and fuel-powered vehicles with special attention to pressure relief devices, minimum standards about crash safety, and hydrogen vehicle provisions.
Manufacturing processes include gathering certifications verifying materials and documenting chemical compositions with sulfur and phosphorous values that define hydrogen compatibility, verifying the mechanical properties such as tensile strength, yield strength, and elongation, verifying the properties against minimum values, hydrogen embrittlement testing by slow strain rate testing under 100 megapascal hydrogen and measuring ductility reduction factors, dimensional inspection reports with measurement uncertainty analysis, leak testing documentation validating hermetic sealing performance under 1×10⁻⁶ standard cubic centimeters per second helium equivalent, and pressure testing certificates documenting hydrostatic proof testing and burst testing sample components with 1.5 times working pressure, 2.25 times working pressure, and additional sample components verifying 15 years service life and 15,000 to 20,000 refueling cycles.

We provide a variety of surface finishing constructions on aluminum of hard anodization Type III with 25 to 75 microns thickness for 820-970 microns of anodized wear damping for valve seat interfaces to provide 1000+ hours of corrosion protection in salt spray environments exceeding ASTM B117, electrical insulation against galvanic corrosion with carbon fiber composite tank structures, stainless steel electropolishing of internal flow passages surface roughness decreasement from Ra 1.6 to Ra 0.4 microns for minimization of particles generation for ISO 14687 hydrogen purity requirements in flow passages to be less than 0.2 milligrams per kilogram total hydrocarbons for facilitated cleaning, passivation ASTM A967 chrome oxide layer forming stainless steel with nitric acid or citric acid treatment, chromium liner of polymer conduits to stop hydrogen galvanic incursion, chrome plating on brass components thickness 5 to 15 microns providing hydrogen diffusion barrier and wear resistance for threaded connections, nickel plating 3 to 10 microns thickness providing corrosion protection and preventing galling on assembly of stainless steel threaded joints with torques 50 to 200 Newton-meters. O-ring sealing surfaces are kept as machined to Ra 0.8 to 1.6 microns for leak rates under 1×10⁻⁶ standard cubic centimeters per second, maintaining critical conservation of dimensional accuracy.
Every surface treatment undergoes hydrogen compatibility testing. These tests verify adherence to SAE J2579 hydrogen material qualification. Specifically for coating adhesion, the testing assesses for surface porosity (less than 1%) and for cracking after 1,000 cycles of pressure cycling (0 to 700 bar). Lastly, permeation and embrittlement susceptibility testing assesses porosity to ensure no cracking.

When it comes to standard designs for valve boss assemblies made of aluminum and pressure regulator blocks made of stainless steel for Type III and Type IV 350 bar or 700 bar working pressure tanks, the lead time is 8 to 12 weeks. This includes the time for procurement of hydrogen service compliant raw materials, CNC turning and milling, thread rolling, surface finishing, quality inspection, and leak and pressure testing. This is with the production lot sizes of 200 to 2000 machined components. For other custom and more complex designs for heavy-duty vehicle tanks that store hydrogen in the range of 30 to 50 kilograms, or stationary storage systems with 100 to 1000 kilograms capacity, the lead time is 10 to 16 weeks again depending on the materials, required pressure rating, and hydrogen cycling validation testing at operational pressure and temperature.
You can get high-quality prototypes for the development of hydrogen fuel tanks in just 4 to 6 weeks. The prototypes are made using hydrogen-compatible materials. Additional efforts for expedited machining and basic pressure testing allow you to integrate systems and validate safety in record time. For high-volume production orders of more than 10,000 pieces a year, the setup time is about 14 to 20 weeks. This includes the optimization of CNC turning cells with automated part handling, thread rolling setup and validation, leak testing integration with helium mass spectrometry, and completion of production part approval processes in which the parts are hydrostatically proof tested and checked for dimensional accuracy and material certification. This is all in alignment with your phased delivery schedules that are intended for the manufacture of tanks and the assembly of vehicles. This supports your production of fuel cell vehicles in the range of 5,000 to 50,000 annually.

Indeed, we create ultra-high-pressure valve bosses for 875 bar storage systems, allowing 10-12 kg of hydrogen to be stored in the same volume as 700 bar systems, increasing the range of the vehicle by 15-20%. Integrated sensor bosses joining the valve body with pressure, temperature, and hydrogen quality sensors into one assembly reduces the part count by 30-40% and enhances system reliability. We design lightweight titanium end caps for Type IV polymer-lined tanks, reducing the tank system mass by 3-8 kg compared to aluminum end caps, which improves vehicle efficiency and allows for larger hydrogen capacity under mass constraints. We develop robust components for commercial vehicle tanks storing 30-80 kg hydrogen designed to operate on buses and trucks with a range of 400-600 km, featuring enhanced fatigue resistance for 30,000-50,000 refueling cycles over a 1,000,000 km service life. We also create specialty configurations, including cryogenic-compatible components for liquid hydrogen storage at -253°C, which requires austenitic stainless steels or aluminum alloys with maintained ductility at cryogenic temperatures. Modular manifold systems which distribute hydrogen among 2-8 tanks with integrated shut-off valves to isolate individual tanks for maintenance. Maritime-rated components with enhanced corrosion protection for hydrogen-powered ships and submarines have been developed to meet DNV-GL classification society requirements. We also design aerospace components for hydrogen fuel cell aircraft using titanium or high-strength aluminum, achieving power-to-weight ratios of 1-3 kW/kg with the target to reach 1-3 kW/kg.
Custom designs use finite element analysis to ensure safe designs with stress distribution analysis under internal pressure loading with safety factors of 2.25 to 3.5 per pressure vessel codes, then use computational fluid dynamics to optimize flow passages internally to minimize pressure drop during refueling at mass flow rates of 50 to 200 grams per second at 0.1 to 0.5 bar. Testing for hydrogen compatibility is also performed to allow use of the material for the assessment of slow strain rate testing, fatigue crack growth testing, permeation testing, and material performance over 15 to 25 years. The design life is assessed.

The precision machining of hydrogen storage tanks' components ensures optimal pressure containment, which maintains O-ring groove dimensions of ±0.002 inches, achieving proper squeeze of 15 to 20 percent, and preventing extrusion at pressures of 350 to 700 bar. The leak rates are below 1×10⁻⁶ standard cubic centimeters per second, which meet the SAE J2579 permeation limits, preventing hydrogen loss of over 0.5 normal liters per hour, which is a reduction of the driving range by 5 to 10 kilometers over 8 8-hour parking duration. Pressure vessels with accurate thread dimensions made under class 6g/6G tolerances provide the proper engagement length of 1.5 to 2 times the thread diameter, which gives the joint strength that supports burst pressures of 875 to 1750 bar with a minimum safety factor of 2.25 per ISO 19881 over 15 vehicle service life years or 15,000 to 20,000 pressure cycles of 0 to 700 bar, preventing catastrophic failure of the vehicle. Sealing surface flatness within 0.002 inches eliminates the need for elastomeric seal compression or metal-to-metal sealing. This flatness maintains hermetic seal containment during thermal cycling from minus 40°C ambient to plus 85°C storage temperature and 40°C refueling. It prevents seal degradation during low-temperature storage, which would increase leak rates 10 to 100 times over baseline, resulting in thermal cycling seal degradation.
When different components are installed, the proper pressure regulator cartridge installation is designed to have a pressure bore tolerance of less than (±)0.002 inches. This ensures an appropriate interference fit of (0.015 to 0.025) millimeters to keep it secure since vibration exposure of 5 to 20g, and pressure pulsations during operation of the fuel cell at power levels of 80 to 120 kilowatts, may loosen it. Proper port alignment of less than (±)0.005 inches maintains the correct sequence of operation during relief device activation at the set pressure. This is critical to prevent over pressure conditions during exposure of the fuel cell of 110 to 120 degrees centigrade ambient temperature which may activate thermal relief devices at set venting rate of 60 grams per second, leaving the controlled venting of 60 grams per second to prevent tank rupture with a blast radius of 20 to 50 meters, and over pressure of 438 to 875 bar. Increased fatigue strength of 20 to 30 percent compared with cut threads enables threaded components to withstand cyclic pressure loading and cracking during 15,000 to 20,000 refueling events. Excellent surface finish Ra 0.4 to 0.8 microns on internal passages minimizes the fuel cell catalyst contamination. Particulates above 5 microns fuel cell catalyst's contamination performance is 10 to 20 percent over 2,000 hours of operational time, with degradation of 1-2 % performance per hour of operation time. Particles above 5 microns fuel cell cradle catalyst is a 10 to 20 percent performance degradation over 2,000 hours of operation time.
Well-built and maintained manufacturing facilities permit the safe storage of hydrogen in fuel-cell cars. These cars hold between 4 and 10 kg of hydrogen at a pressure of 350 to 700 bar. They allow a distance of 400 to 650 km to be traveled with a 3 to 5 minute refueling time, comparable to gasoline cars. These vehicles have a hydrogen storage efficiency of 4.5 to 5.5 percent storage mass and a service life of 15 years, which is around 15,000 to 20,000 refueling cycles. They can lose only 1 to 2 percent of hydrogen every year, which is very economically efficient. Additionally, every cargo handling equipment and stationary energy systems with 5 to 1000 kg hydrogen storage can safely withstand frontal and side crash and rollover tests without the venting of hydrogen, hemorrhaging, or rupturing of tanks.