We need to store, handle and transport higher quantity of gas in containers that are manageable. Higher the pressure, larger is the quantity of gas contained in same cylinder volume. Lighter the cylinder, more convenient and economical it is to handle it and transport it.Larger cylinders banks offer less joints to make leak proof. There are certain requirements which just cannot be serviced by liquefied gases.
Why not Liquefied Gases?
Usually the liquefied gases containing, conveying and transportation is full of limitations which have so far kept them away from being universal solutions. They call for specialized cryogenic vessels which need to be continuously monitored. They also need special care while handling, unlike gas cylinder. This calls for persons with special training and skills If the off take of gas from cryo vessel is lower than the gas being generated due to heat seepage then the gas has to be released with resultant wastage. Such release is not possible for flammable gases. So, there are majority of applications where only compressed gas cylinders are suitable.
The word Efficiency is used in cylinder industry for the amount of gas content for unit weight of cylinder. So, cylinders which can contain higher pressure for lower weight are more efficient. They reduce the transportation costs substantially. Permanent gases follow the Gas Equation
So, for higher gas content in fixed volume of cylinder, you need to get higher pressure in cylinder. For this the cylinders have to be with materials with higher strength to get higher efficiency.
Technical Efficiency of Gas Cylinder:
Ratio of cylinder: Gas Volume / Cylinder Weight
From the derivation given in the handout it would be clear that for a given diameter and length of cylinder, the Gas Volume is proportional to the pressure ,Cylinder weight is also proportional to the pressure But The cylinder weight depends on wall thickness which is inversely proportional to cylinder steel strength
Conclusion : For a given water capacity and diameter of cylinder, the ratio of gas volume / cylinder weight i. e. technical efficiency remains constant and shall only be affected by material properties and density.
So, to improve the technical efficiency of cylinders high strength steels have to be employed, with their limitation of intolerance for embittering gases and stress corrosion cracking.
Advancements have come as a result of constant human desire to do things in a better way. As far as gas cylinders are concerned it meant filling more gas in a cylinder. Since the gases follow the Gas Equation, it means the cylinder has to be filled at increasingly higher pressures. This gives rise to two challenges
The development has been slow due to interdependence of the above two challenges
Advancement in related fields is another driver for technology development. Aerospace imposed more exacting specifications for weight per unit volume of gas. Another important driver is the Oil Crisis in 1970. Rising fuel costs required lighter cylinders with higher technical efficiency i.e. Free Volume of Gas / Weight of Cylinders.
Cylinders designs mainly depend on the capability of manufacturing of the Seamless Steel Tubes. The minimum thickness which could be produced. Secondly they depend on the development of suitable steels. The evolution was as below:
Material of Cylinders Working Pressure Heat Treatment Year
Carbon Steel 70 to100 Bar Normalized 1910
Carbon Moly Steel 100 to 150 Bar Normalized 1935-60
Chrome Moly Steel 150 to 200 Bar Normalized 1960
Chrome Moly Steel 200 to 300 Bar Normalized 1990
High Strength Steel 200 to 300 Bar Normalized 1985
High Strength Steel 300 to 400 Bar Normalized 1985
Heat treatment choice depends on the minimum thickness available and working pressure required. Even now, normalized cylinders are popular in small sizes because hot rolled tubes of lower thickness are not available and for the thickness, normalized steel can sustain the pressures particularly for Co2. It makes cylinder more economical too.
Maneuverability is a consideration which drives the move to higher strength steels and / or different heat treatment.50 liter 300 bar cylinder with standard CrMo steel would weight 95 kg against 67 kg of high strength steels. At present the Indian standards for cylinders cover maximum tensile strength only up to 1100 MPa.
50Liter 200 Bar Cylinders are very economical as compared to 46.7 Liter 150 Bar cylinders. We get 10 m3 gas as against 7 m3 (based on what gas we fill).Each bundle contains 12 cylinders so 120 m3 gas. (In case of 46.7 liter x 150 bar we get only 84 m3 i.e. 43% more. Ease of filling – 12 cylinders with single connection No frequent cylinder changing by user
When two or more cylinders are held together in a frame and are also interconnected and connected to the outlet through manifold piping they are called Bundles, Quads, Cascades, and Skids. They offer following advantages.
Cylinders valve or cylinder will not get damaged
Cylinders tracking/accounting will be easy and cylinders will not be lost
Cylinders can be easily identified for next test due date.
In transport, you need to be confident that the integrity of your product will be protected.
ATDM offers a wide selection of cylinders those standards for transportation of chemicals. These cylinders feature consistent wall thickness, smooth internal neck transitions for easy cleaning, and heavy-wall connections that resist flaring.
Single- and double-ended and miniature styles
Sizes from 10 to 3785 cm³ (1 gal)
304L, 316, 316L, and Alloy 400
Working pressures up to 5000 psig (344 bar)
Variety of options including integral valves, outage tubes, and specialty coatings
Transport low volumes of fluids and hazardous materials safely
Are suited particularly well for lab use and other specialty applications due to the smaller size
Have consistent wall thickness, size, and capacity
Allow easy cleaning and minimizes trapped fluids with a smooth internal neck transition
|Pressure Rating||1000 psig (68.9 bar)|
|Materials||316 stainless steel|
|Sizes||10, 25, and 50 cm3 capabilities|
|End Connections||3/8 in.|