First, find out first: What is the crane tube non-metallic compensator? — What role does it play in the loading arm pipeline?
To put it bluntly, the crane pipe (that is, the loading and unloading arm) is a pipeline system used to connect the tanker and the storage tank, and oil, chemicals and liquefied gas all go through it. But it wasn't a rigid one-piece — the car would shake, the pipes would expand and contract, and the pumps would vibrate. Without a "soft joint", the pipe connection cracks and leaks in minutes.
The crane tube non-metallic compensator, that's the soft joint. It is mounted between the riser and horizontal pipe of the crane tube, or near the rotary joint of the loading arm, and is used to absorb various displacements and stresses. Different from the metal corrugated compensator, its main body is made of non-metallic materials such as fabric, rubber or fluoroplastic, so it is softer, lighter and corrosion-resistant.
"Why don't you just put a piece of hose on?" Tsk, it's not that simple. Crane pipe has strict requirements for sealing performance, fatigue resistance life and pressure resistance, and ordinary hoses can't support frequent swinging and medium erosion. The non-metallic compensator is a solution specially tailored for this scenario-it must be flexible and carryable.
Second, its core functions are disassembled: absorbing displacement, isolating vibration, and carrying corrosion.
Let's start with absorption displacement. During the handling and unloading process of crane pipe, the tanker will be displaced due to uneven ground or change of loading weight, and the amplitude may reach tens of millimeters. If the metal pipe is hard, the stress will concentrate on the flange or weld, and accidents will occur over time. The non-metallic compensator easily absorbs axial, lateral and even angular displacement through elastic deformation of multiple layers of fabric or rubber. In the actual case, a loading crane pipe uses a fabric fiber non-metallic expansion joint, which has not been replaced for three years, and the displacement never exceeds 70% of the design value.
Let's talk about isolating vibration. During loading and unloading operations, the pump and pipeline will generate high-frequency vibration, which will be directly transmitted to the crane pipe base and valve, and the instrument will be affected. The damping coefficient of non-metallic materials itself is 5~10 times that of metals, which can convert vibration energy into heat and dissipate it. The petrochemical plant next door has done a test: after installing the rubber compensator, the vibration acceleration of the root of the crane tube dropped from 12m/s² to 2.3m/s².
Finally, carrying corrosion. The medium running in the crane tube often carries acid, alkali and solvent. Even if the metal compensator is made of stainless steel, it will be pitted and perforated if it is exposed to chloride ions or hydrofluoric acid for a long time. The layer of the non-metallic compensator in direct contact with the medium, which can be PTFE or special rubber, hardly reacts with any chemicals. Like PTFE compensators, except for molten alkali metals and fluorine, they are not afraid of anything else. This is not blowing. It is directly recommended in petrochemical industry standards for strong corrosion conditions.
Third, head-to-head with metal compensators: Why are non-metallic compensators more popular in the crane pipe scene?
"How many years have the metal corrugated compensator been used? The structure is strong. Why do you still use non-metal on the crane tube?" Come on, break, break, break.
The advantage of metal compensator is high pressure and high temperature resistance, but the working pressure of crane tube generally does not exceed 2.5MPa, and the temperature is often between-20°C and 200°C-this range can be completely covered by non-metals. The biggest shortcoming of the metal compensator is that the multi-layer corrugation is easy to produce stress corrosion and fatigue crack. The crane pipe swings frequently every day, and it is common for the metal bellows to be changed twice a year; As long as you choose the right material for the non-metallic compensator, you can use it for three to five years.
In addition, the weight of the metal compensator is heavy, and additional reinforcement brackets are required during installation; The weight of non-metallic expansion joints (fabric fiber expansion joints) is only 1/3 to 1/5 of the weight of metal parts of the same specification, and the installation cost is directly reduced. Two years ago, a customer replaced all the metal expansion joints on the crane pipe with non-metal ones, saving 120,000 yuan in the cost of the optical bracket.
Once the metal compensator leaks, it usually has to be replaced in the whole section; After the non-metallic compensator is damaged, in many cases, changing the sealing ring or mending a piece of fabric can be used for temporary emergency, and the downtime is reduced by half.
Fourth, don't step on pits in model selection: according to temperature, medium and pressure, choose the most correct one from our product library
When it comes to selection, remember three elements first: what the medium is, how high the temperature is, and how high the pressure is. For example, when concentrated sulfuric acid is transported, the temperature is 80°C and the pressure is 0.6MPa. The rubber PTFE compensator is the first choice-the PTFE lining is corrosion-resistant, and the rubber outer layer absorbs displacement. If it is high-temperature flue gas or dust medium, such as crane pipe for dry dust removal pipeline, fabric fiber non-metallic expansion joint must be used, and the temperature resistance can be above 1000°C (plus ceramic fiber layer).
-rubber compensator: Suitable for normal temperature, low pressure, weakly corrosive media, with the lowest cost, but the upper temperature resistance limit is only about 120°C.
-Rubber PTFE compensator: Lined with PTFE, acid and alkali resistant, suitable for chemical crane pipe, temperature range-20°C ~200°C, pressure can reach 1.6MPa.
-Non-metallic expansion joint (fabric fiber expansion joint): Multi-layer structure, high temperature resistance, wear resistance, used for power plant desulfurization, cement industry crane pipe, can also customize guide tube.
In actual selection, we have to pay attention to the compensation amount. The conventional displacement of the crane tube is within ±30mm, but if it is an LNG loading and unloading arm, the low-temperature shrinkage may reach more than 50mm, so it is necessary to choose a fabric fiber non-metallic expansion joint with large compensation amount or install a tie rod.
Stress. Don't be fooled by the word non-metal. The working pressure of fabric fiber non-metal expansion joint can reach 2.5MPa or even higher through multi-layer reinforced cloth and steel wire ring. However, if the rubber compensator exceeds 1.0MPa, flange limit bolts must be added to prevent blasting.
5. Those "hidden rules" in installation and maintenance: Don't let a screw destroy the whole crane pipe
Install a non-metal compensator, and the easiest place to roll over is pre-stretching. Metal compensators should be stretched before installation, while non-metals do the opposite: a compression margin needs to be allowed. What's the meaning? When the crane pipe is installed, if the two pipes are just right, there is no room for deformation when the compensator is installed, and it will be overloaded and torn as soon as the construction starts. The correct way is to let the compensator butt the flange in the free state, and then tighten it slowly with bolts to control the excess compression within 10% of the design value.
Direction of the guide tube. Many fabric fiber non-metallic expansion joints have a guide tube inside, and its arrow direction must be consistent with the flow direction of the medium. Installed backwards, the medium directly impacts the fabric layer and perforates in three months.
In terms of maintenance, non-metallic compensators are most afraid of mechanical damage. In the daily operation of crane pipe, the outer fabric may be scratched if the tanker driver collides and the tool falls. Regular visual inspection is recommended. If the surface is found to be worn or fluffed, repair it immediately with patch glue. Don't wait for a leak before replacing it. Last month, there was a chemical plant because the workers didn't check it, and the compensator broke a small hole, and the acid dropped on the grounding wire, which almost caused a big accident.
VI. Common cognitive misunderstandings and practical cases in the industry: Why did some people miss it after two or three months?
"Non-metallic compensators are cheap. Just buy one." Wrong! There is a cheap oil depot diagram, so I bought a non-standard rubber compensator and installed it on a 0.8MPa gasoline crane tube. As a result, the aromatics in the medium swelled the rubber, and two months later, gasoline leaked all over the floor. Regular rubber compensators have special formulas for different media. Nitrile rubber is oil-resistant, neoprene is weather-resistant, and EPDM is acid-and alkali-resistant. Buying indiscriminately is equal to laying mines.
"Non-metallic expansion joints do not require brackets." Not too. While it is lighter than metal, its own weight plus pipe stress allows the compensator to be elongated or squashed if there is no bracket support on either side of the flange. A refinery installed the fabric fiber non-metallic expansion joint directly in the air. After half a year, the flange gasket was displaced and the seal failed. Later, the bracket was added, and the problem was resolved.
Last year, a liquefied hydrocarbon terminal was equipped with three DN200 rubber PTFE compensators, the medium is propylene, and the design temperature is-45°C. The manufacturer suggested using the woven reinforcement layer to thicken the type, but the on-site installation master was too difficult to install, so he secretly replaced it with the standard type. Results after the cooling medium, the rubber layer was brittle and cracked at low temperature, and it leaked after two weeks of use. After replacing it back to the correct model, it runs for one year with zero failures. Therefore, the selection can't be patted on the head by experience, but depends on the actual parameters.
With so many words, the core is one sentence: whether the crane tube non-metallic compensator functions well or not depends on whether the materials are selected correctly and whether the installation specifications are not. Next time you encounter a leak accident, don't just scold poor quality, check these details first.