Pressure Vessel Fittings CNC Machining for Hydrogen Tanks

Switzerland CNC Turning is capable of producing complex boss fittings with threads, seal grooves, and hex features all in one setup within cycle times of 90 to 240 seconds. Airless and cut threads have a 30-50% difference in fatigue resistance. A rolled thread is significantly superior to cut threads. Thread rolling work/thread forming also thread seal grooves to a precision of ±0.002 in, which definitely tightens grooves to a compressed O-ring 10 to 25% seal. Multi-axis machining drills the gaps and 3D flow channels. The gaps are recessed hex broaches. The Recessed detent is broached in hex tools. Hex driving tools are broached. The Passivation is def as 2-3 and is a protective oxide and seal on the aluminum. Leak testing is helium mass spectrometry up to 10 to the negative 9 mbar liters per sec. Hydrostatic testing is pressure integrity at 1.5 times service pressure.

Stainless steel 316L and 316Ti give almost full hydrogen embrittlement resistance and hold weak interfaces stabilized, along with a strong microstructure, so embrittlement will not occur. Corrosion to the environment will be present. With weldable aluminum liners, it will assist in having tensile strength ranging from 500 to 700 MPa, and will support high-pressure sealing loads easily. Aluminum 6061-T6 and 7075-T6 will assist in providing superior specific strength, so tank mass can be reduced by 30 percent easily with lightweight boss fittings. With tensile strength ranging from 300 to 570 MPa will provide adequate strength, and will assist in thermal conductivity and aid with heat dissipation. Lastly, it will assist as a composite overwrap. Inconel 718 nickel-chromium will solve high stress problems, and the alloy provides 1200+ MPa of strength, overcomes compressive strength, thermal range 650°C, and overcomes hydrogen embrittlement. High-strength steel AISI 4340 provides ultimate tensile strength of 1100 to 1400 and allows to compress along help treat heat.

Switzerland CNC Turning is capable of producing complex boss fittings with threads, seal grooves, and hex features all in one setup within cycle times of 90 to 240 seconds. Airless and cut threads have a 30-50% difference in fatigue resistance. A rolled thread is significantly superior to cut threads. Thread rolling work/thread forming also thread seal grooves to a precision of ±0.002 in, which definitely tightens grooves to a compressed O-ring 10 to 25% seal. Multi-axis machining drills the gaps and 3D flow channels. The gaps are recessed hex broaches. The Recessed detent is broached in hex tools. Hex driving tools are broached. The Passivation is def as 2-3 and is a protective oxide and seal on the aluminum. Leak testing is helium mass spectrometry up to 10 to the negative 9 mbar liters per sec. Hydrostatic testing is pressure integrity at 1.5 times service pressure.

Absolutely! Zintilon does prototype design for hydrogen tanks and does almost all the work for prototype vehicles and industrial systems. Zintilon uses pressure cycling and performs a complete Finite Element Analysis to validate the design. Zintilon does low-volume production and works with integrated hydraulic circuits for industrial systems in the range of 50 to 2000 fittings. For commercial fuel cell vehicles, Zintilon does high-volume production of fittings with thousands to tens of thousands being produced each year. Zintilon does numerous quality checks to assure production integrity, including complete dimensional checks with CMM equipment, helium leak tests to a sensitivity of 1 x 10⁻⁹ mbar-liter per second, and numerous pressure cycles with hydrostatic testing to 1.5 times the working pressure. Zintilon performs pressure cycling, fatigue testing to ISO 11119, torque testing, and numerous other tests to validate all the components and hydrogen components to material certifications. Zintilon checks for hydrogen compatibility per ISO 11114, ASTM G142, and embrittlement testing.

ISO 9001 quality management systems and hydrogen storage standards give building codes and construction standards, body standards, and comprehensive standards. Pressure vessel construction ASME Section VIII protects against leak rates of 1x10⁻⁶ mbar-liter per second and ensures structural integrity and 15-year service life, fatigue resistance exceeding 100,000 pressure cycles, and beyond structural compliance for pressure vessels up to 15 years service life. Other construction standards, such as CSA B51 for pressure vessels, ISO 19881 for Type III and Type IV containers, and integration of portable fuel cell systems, vehicles, and compliance with fuel system standards SAE J2579.

Finishes include electropolishing on stainless steel achieving Ra below 0.4 microns on seal contiguous surfaces for leak-tight performance, enhanced passivation, and hydrogen induced stress corrosion, passivation per ASTM A967 and A962 for dark oxide film, hard anodizing on aluminum achieving 25 to 50 microns coating provides wear resistance, corrosion protection and 1000 HV surface, and shot peening increase surface compressive residual stress and fatigue life by 40%. Other surface finishing options include nickel-PTFE coating, silver plating on threads, and shot peening.

For standard stainless steel boss fittings for Type IV hydrogen tanks, it takes about 12 to 18 business days, including machining, thread rolling, passivation, and leak testing. More complex, multi-port manifolds take 8 to 12 weeks, which includes assembly and certification testing. Rapid tank development and safety validation are made possible when prototype fittings for pressure testing are completed within 10 to 14 days.

Absolutely! We create ultra-high-pressure fittings for 1000 bar research systems with extremely low leak rates and lightweight aluminum boss fittings to reduce tank mass by 2 to 5 kilograms for extended vehicle range. We also design cryogenic fittings for liquid hydrogen tanks that operate at -253°C and integrated instrumentation bosses with pressure transducers and thermocouples. We create redundant seal designs that meet SIL-3 safety integrity and integrate quick-disconnect couplings that allow tank removal for maintenance in 30 seconds. We also design anti-rotation features, smart fittings with RFID tags that track fill history and certification dates, and fitting loose seal designs to thermal cycle and vibration.

Threads machined to within ±0.003 inch will lock down to a preset torque, and leakage will not occur while attaining 200 to 800 Newton-meters. A A0.010-inchh deviation will compromise the seal, and the leakage rate will exceed 1 x 10⁻⁴ mbar-liter per second. Hydrogen builds up to within the flammable limit of 4 percent in a confined space. Seal groove dimensions within ±0.002 inch will control the O-ring compression to within acceptable limits of 10 to 25 percent. We will attain leakage rates above 1 x 10⁻⁶ mbar-liter per second and will be in line with SAE J2579. Seal grooves not within the stated limits will result in compression, causing extrusion failure, unbalanced O-ring sealing, and insufficient seal. Threads that will be formed will have grain flow and will improve residual compressive stresses. This will improve fatigue strength by 30 to 50 percent from 100,000 pressure cycles from ambient to 700 bar. Concentricity within 0.003 inches will eliminate eccentric loading and unbalanced stress over 1000 MPa at the thread roots. Smooth sealing surfaces, Ra less than 0.4 microns, will provide reliable true sealing or an elastomer seal. Well-defined stress concentration will limit fatigue crack growth. Adequate strength and suitable alloys will prevent embrittlement. After 700 bar, susceptible alloys will reduce ductility by 50 percent, sustained exposure, as the other alloys will retain ductility. Proper passivation will allow the formation of a passive layer of chromium that will prevent hydrogen-induced stress corrosion cracking.
Properly designed systems can store enough hydrogen to power a fuel cell system. This system has a fuel tank pressure of between 350 and 700 bars and can store between 4 and 7 kilograms of hydrogen. The system can provide a driving range of 400 to 650 kilometers. The system can be refueled in 3 to 5 minutes and can fill hydrogen capsules at a flow rate of 60 grams per second. The system has a 15-year service life and can withstand more than 100,000 pressure cycles. Hydrogen storage systems are used in fuel cell electric vehicles, hydrogen tube trailers of 200 to 1000 kg capacity, stationary backup power systems, and industrial gas storage. These systems store conventional gas and serve the automotive, energy, aerospace, and material handling industries.