A CNG tanker in full definition is a Compressed Natural Gas tanker. The main application of a CNG tubes trailers is to transport compressed natural gas to a CNG sub-station. Many CNG stations don’t have the tubes underground, so the trailer is needed to transport CNG from the primary fueling station to its substation.
The CNG tanker has various design characteristics that enhance its function. Here, you will learn more about the different aspects that define this type of trailer. To help you understand more about this tanker, we will look into the following:
- The definition of the CNG tubes trailer
- The main applications of CNG tubes trailers
- Different types of CNG tubes
- The manufacturing process of a CNG-1 (type one) trailer
Here are the different kinds of tank trailers guide:
- Fuel Tank Trailer Guide – Diesel, Petrol, Oil Tanker Trailers Designs & Specs
- LNG & LPG tank trailer guide – Learn Tankers Specs & Design
- What is a bulk cement / powder pneumatic tank trailer?
- Asphalt / Bitumen Tank Trailer Ultimate Guide (Insulated Tank with Heating Device)
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1. What is a CNG (Compressed Natural Gas) Tubes Trailer?
The CNG trailer is an equipment of cargo transportation used in the transport of high-pressure gas. The CNG tanker is designed in different ways. First, it may have various seamless steel cylinders.
A gas valve and tube are used to connect every cylinder in the set up. The CNG tanker is also fitted with a safety device, a thermometer and a pressure gauge.
This type of tanker is largely used in stations for natural gas especially those located outside the CNG network. The structures of the CNG trailer have a bundling type and a frame type.
The bundling type usually consists of a framework, seamless steel cylinder and a pipeline operating system among other accessories.
All construction is made based on the set standards by the Supervision Regulation on Safety Technology for such machinery and equipment.
This is a Transportable Pressure Vessel and therefore, safety comes in first. Buyers are advised to assess the quality considerations that have been put in place to guarantee the safety of their CNG trailer during use.
The product model of a tune-bundle trailer is established based on the enterprise standards as provided for through the set regulations. A typical tube-bundle tanker is usually used along with a hydraulic CNG substation.
Here is a brief look into the use principle of this set up: high-pressure pump with pressure not exceeding 25MPa in the substation is used to fill up the liquid of a special nature into the gas cylinder of the CNG tube-bundle tanker in order to push out the already compressed natural gas in the steel cylinder.
After that, it is then used to fill the natural gas in high pressure into the car cylinder via a single-line double-gun dispenser for the CNG in the station. This helps achieve the use of the gas filling of the car. No extra supercharging equipment will be required.
The cylinders of the bundling type are fixed on trailer. This type of structure can reduce the quality of framework. Hence, you can assemble more cylinders. This type has a larger volume, higher efficiency, and lower costs.
The cylinders of the bundling type are fixed on trailer. This type of structure has one drawback in that it can reduce the quality of framework.
However, the construction can allow you to assemble more cylinders. With this type you can have benefits of a larger volume, higher efficiency, and lower costs.
With the purchase of CNG tankers, you have to be sure of what you are getting. Buyers are advised to get mechanical and structural drawings of the tankers to understand their construction prior to making a purchase.
Contact your supplier and get as many drawings as would help you understand what you are buying.
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2. Different Types of CNG Tubes
CNG tubes trailers use four major types of CNG Tubes. The types include CNG-1, CNG-2, CNG-3, and CNG-4. The quality and number of filaments vary across the four types.
The higher the number of CNG tube, the lighter the quality, the more the filament, and the harder the manufacturing process. Below is a description of the materials used to make each of these models of CNG tubes.
CNG-1 (Type one): This type consists of steel or aluminum alloy cylinders. The type one tubes are the heaviest tubes in the market. Weight is an important consideration when choosing a CNG cylinder for your trailer.
Despite the heavy weight, type one CNG tubes are the most cost-effective tubes you will find in the market. The outside part of the tube is usually painted using a protective coating.
CNG-2 (Type two): The model has filament wound composite gas cylinders. The inner part is made of steel or aluminum while the body the tube without the heads is wrapped using long fibers impregnated with a resin.
A composite material wrapper is in most cases to wrap the metal liner on the middle section of the cylinder. The composite material wrapper consists of woven carbon fiber or woven carbon fiber or both.
Type two cylinders use less metal and lighter composite materials. Hence, they are lighter than the type one cylinders. CNG-2 tubes are more expensive than CNG-1 tubes.
CNG-3 (Type three): This type also has filament wound composite gas cylinders. Similar to the type two cylinders, the inner part of the tube is made of steel or aluminum.
The tube body including the heads is wrapped but long fibers impregnated with resin. A CNG-3 tank is sometimes referred to as a fully wrapped or full wrapped tank.
The long fibers used to fully wrap the body and head of the type three tube may be woven carbon fiber or woven glass fiber. Type three CNG tubes are lighter than the type one and type two tubes.
Hence, they are more expensive than type one and two tubes. CGN-3 and the CNG-4 tubes described below are the best choices if you are looking for light CNG cylinders.
CNG -4 (Type four): This type consists of filament wound composite gas cylinders. Unlike the type two and type three models, the inner part is made of plastic. The body of the tube is wrapped using long fibers impregnated with a resin including the heads.
CNG-4 are the lightest models in the market and hence the most expensive. The full wrapped method is used for these tubes. The composite material that wraps the tubes may be woven carbon fiber material or woven glass fiber.
The tubes rely on the composite material to reinforce the plastic inner lining. The composite reinforced wrapper supplies the strength of the CNG-4 Tubes.
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3. The manufacturing process of the CNG-1 (Type one )
We have mentioned above that the manufacturing process is different for the four types. Type four is harder to process than the type one model. In this section, we will outline different stages of the manufacturing process of the CNG-1 tubes.
Before we discuss the stages, it is important to note that CNG tank trailers are used to transport high-pressure gas. Hence, the cylinders should have no welds.
Instead, the cylinders should be unibody or integrated. Hence, there is no welding in this manufacturing process, as is the case with other types of heavy-duty trailers.
It is important to know the stages in the manufacturing process when shopping for CNG tank trailers. You need to buy a trailer who follows the full process to ensure that the trailers meet safety standards.
If any of the steps outlined below are skipped, the final product will be substandard and will not only be unsafe to use but will give you problems in your operations.
However, if the due procedure has been followed in their construction, it will meet the safety requirements in your state. Here now are the stages of the manufacturing process with illustrations:
- Steel tube inspection
The steel tubes are in most cases are purchased from other suppliers. Hence, the manufacturer has to inspect the tubes to ensure that they are made of high quality materials and have the right dimensions and specifications.
The quality of the steel tube determines the strength and safety of the finished CNG tube.
- Hot shell nosing
We have already mentioned that cylinders in CNG trailers require no welding. Hence, the hot shell nosing process does not involve any welding.
This is basically a hot forming process where the open end of the cylinder gets closed through axial pressing using a shaped die as shown below.
- Bottle neck cutting
The next stage is bottleneck cutting, which is a simple process as illustrated in the picture below. The process is necessary to simplify the process of loading the tubes with pressurized liquids.
One of the most important considerations in the bottleneck cutting process is to get the right dimensions to avoid leakages.
- Rough machining
The next process after cutting off the bottleneck is rough machining, which is illustrated in the picture below. All cut areas are carefully roughed-up to produce a good finish on them through this process.
- Quenching, heat treatment, and tempering
After the rough machining process comes quenching, heat treatment, and tempering of the CNG tubes. The heating and tempering processes are necessary to increase the strength or toughness of the tubes.
The processes also remove any excess hardness. The temperature applied to the tubes depends on the desired hardness level.
Quenching refers to the process of rapid cooling that is mostly used to harden steel and other metals. Quenching prevents any unwanted low-temperature processes during the hardening process.
Quenching, heating, and tempering work together to ensure that the finished tubes are hardened enough to handle pressurized liquid loads.
- Outside polishing
After assembling and heating the inner parts of the CGN tubes, the next step involves outside polishing. The purpose of this process is to improve their outlook and prevent the surface from rusting or corrosion.
- Hydrostatic testing
CNG tubes transport gas under high pressure. The hydrostatic test is one of the most important steps in the manufacturing process because the results determine the safety of the tube.
A hydrostatic test involves testing the cylinders for strength and leaks. A liquid is used to test the tubes for leaks. Many manufacturers add color or add to the water and use it to test the tubes to leaks.
The strength of the tube is tested by checking for any permanent deformation on the surface after filling it with a pressured liquid. Hydrostatic testing does not only ensure that the tubes meet the safety standards but also ensure that the tubes are durable.
- Steam drying
The next stage after the tubes pass the hydrostatic testing is steam drying. Typically, this process helps in providing a thorough drying of the tubes’ inside using steam.
- Inner Shot Peening
Shot peening refers to a cold working process that relieve stress and strengthens steel parts. The process in this case is necessary to strengthen the structure of the tank. In addition, inner shot peening gives the tube a muted finish.
- Inner tube inspection
The inspection at the beginning of the manufacturing process is not enough. The tubes must be inspected again after the processes outlined above, especially the inner parts.
During this inspection, a device is inserted in the tube that sends images of the inner structure. The manufacturer can see any flaws or defects on the screen and remove them before assembling all the parts.
- Non-destructive and air tight testing
Non-destructive testing procedures are used at this stage, which means that the process does not damage the materials of the tank body.
The air tight testing is necessary to ensure that the tank will not leak any gas out especially at high levels of pressure.
- Paint spraying and assembly
The last process involves assembling all the parts and paint spraying the outer surface. Paint spraying prevents corrosion and rust on the surface. The process also gives the tank body a polished outlook.
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You now know what a CNG (Compressed Natural Gas) tank trailer is. A lot goes in during its manufacturing and any buyer should understand what it all entails prior to making a purchase of their own tanker.
Just like is the case with other tank trailers, buyers are advised to consider the manufacturer’s reputation and whether they have followed due procedure when making their tankers.
Request for technical drawings of your tanker design to be sure you have the right product in place. CNG tank trailers are also made to suit different use and needs.
As discussed here, you will find both light and heavy-weight constructions in the market. Based on your needs, you can choose what suits you. Detailed here are some of the important checks to make, especially with the manufacturing process.
Disregard any CNG tank trailer with welds on it. That is not a standard CNG tank trailer construction. There are many sources to consult out there. Make use of them prior to settling on any one give supplier and/or manufacturer.