How to protect against oil and gas platform vertical pipe corrosion? What are the precautions?

Paint industry:
oil and gas extracted from offshore oil and gas fields are transported directly offshore, mostly through pipelines to on-land processing and to users separately. With the development of offshore oil and gas, the role of offshore pipelines is becoming more and more important. It is a pipeline that continuously transports large quantities of oil and gas to the seabed through closed pipelines, is a major component of offshore oil and gas field development and production systems, and is currently the fastest, safest and most economically reliable way of offshore oil and gas transportation . The vertical pipe is an important part of the connection between the submarine pipeline and the oil and gas platform, and the vertical pipe is more susceptible to corrosion than the flat pipe section of the undersea pipeline, so the corrosion protection of the vertical pipe is of great significance. In this paper, with the construction of the total assembly of the land construction of the standing pipe as the subject, the anti-corrosion protection of the opposite pipe is analyzed, and the rationalization proposal is put forward in order to improve the quality of the anti-corrosion protection of the vertical pipe, reduce the maintenance cost later, improve the safety and reliability.
anti-corrosion design of the
the anti-corrosion design method of the vertical tube is generally used to protect the joint anti-corrosion with the coating and cathode protection.
coating
vertical tube coating design according to the operating conditions, divided into the following:
(1) splash zone
due to the splash zone of the environment of dry and wet alternating, as well as ship docking, marine float collision and other special conditions, this part of the riser pipe The coating is usually neoprene, and the neoprene coating system is a typical offshore oil pipe splash zone coating system, usually based on a 0.5mm fused epoxy powder (FBE) coating and 12.4mm neoprene used to resist mechanical damage due to floating objects from ships and sea.
(2) atmospheric area, full immersion area
atmospheric area and full immersion area of the operating conditions are relatively single, corrosion is better than splash area, the use of the same coating system as the sea pipe flat pipe section. The common coating is 3 layers of polyethylene (3LPE). The system is divided into 3 parts: the bottom layer is FBE (melted epoxy powder), the thickness is minimum 300 m, play the role of corrosion protection, the middle layer is a high-concentration synthetic adhesive layer, the thickness is the smallest 200 m, play the role of intermediate sticky, the surface is polyethylene layer (PE), thickness is as small as 2,600 m, play the role of appearance protection.
(3) node repair
the entire vertical pipe system is composed of several single vertical tubes, which need to be patched with the coating of the welding channel position after welding connections between each other. Usually the standing tube node part of the three-layer structure in the form of a shrink belt for repair. The heat shrink belt in this form is generally composed of liquid epoxy paint with a minimum thickness of 150 m, a high shear strength hot melt with a thickness of 1.5mm, and a radiation crosslink high density polyethylene thermal shrink substrate with a minimum thickness of 1.0mm. The construction drawing of the node heat shrink belt is shown in Figure 1.
1 Heat shrink belt construction drawing
cathode protection
cathode protection system, usually using aluminum bracelet-type anode. The structure form is Shown in Figure 2.
Figure 2 Bracelet-type anode structure diagram
The material used in the sacrificial anode is mainly aluminum-zinc-indium, the anode is generally installed in the form of welding on the surface of the anti-corrosion layer outside the submarine pipeline, the coating damage at the welding site is mostly repaired by the method of shrinking the cladding, to prevent the seafloor pipeline metal from direct contact with the external media.
construction
(1) coating construction of the main part of the
pipe, usually in a professional pipe coating company to complete the coating. When built on land, only the coating of the opposite pipe weld position and the damage during the construction process are repaired. The damaged area of the coating is often patched with horseshoe esters. Melt the horseshoe ester with a roasting arm or hot air, fill the damaged area, and finally smooth it with a smear.
the position of the vertical pipe weld is repaired with a shrink belt. After the finished surface treatment, mix the two-part epoxy primer and apply it evenly to the tube body. Use a heating device to preheat the steel pipe coated with epoxy primer to the required temperature and start installing the shrink belt. During the installation of the heat shrink belt, the heating needs to be constantly used with a fire, and the heat shrink belt should be leveled with rollers, and the bubbles must be driven out, so that the shrink belt is firmly combined. Inspection and protection upon completion of construction.
(2) anode construction
after the anode of the vertical tube arrived, the site according to the anode structure map, layout and actual collision situation of the anode foot welding position positioning, stripping the coating. Welding installation is carried out after the coating has been peeled off to expose the tube body.
the anode is installed, all coating damaged areas can be repaired with polyethylene hot melt rods/polyethylene patches/polyethylene shrink belts as close as possible to the end of the anode side.
the specific installation process can be found in Figure 3.
Figure 3 Vertical Pipe Anode Installation Process
The influence factors of anti-corrosion protection of anti-corrosion pipes in land construction
(1) site node repair
The construction quality of the current standing pipe site node repair is not optimistic, mainly manifested in the following aspects:
Welding Road surface treatment problems
can not provide on-site blasting rust removal surface treatment equipment, more power tools to replace. The Sa2.5 rating, which causes the surface treatment level to fail to meet the construction requirements for the shrink belt.
heating of the heat shrink belt
can not provide medium frequency heating equipment, more use of roasting instead. When heating the heating, the preheating temperature is not as high as the medium frequency heating equipment, and the heat shrink belt is not uniform, often the heat shrink belt on both sides and the bottom of the heating is insufficient.
these two problems, it is easy to cause the shrink belt to fail during service, so that the vertical tube in the middle and late stages of service exposure to the risk of corrosion. Therefore, when the pipe construction, should be in accordance with strict heat shrink belt construction technology and quality requirements, equipped with portable removable blasting equipment and medium frequency heating equipment, the corrosion risk will be eliminated in the embryonic stage.
(2) Coating breakage rate
According to DNV-RP-B401, the demand for sacrificial anodes depends on the current required for cathode protection, and the current requirement is equal to the coating surface area, coating breakage rate, and average current demand. Where only the coating breakage rate is a variable value.
the value of coating breakage rate in the design stage is generally based on the relevant standards, but the standards for the vertical tube coating in the prefabriced, installation phase caused by the damage is not quantitative consideration. If the actual coating breakage rate is greater than the designed coating breakage rate, then the actual demand for anodes than the design of the anode, will cause the anode consumption during service period too fast, in the end of service cathode protection failure, so that the riser tube is at risk of corrosion.
the control of coating breakage rate in the construction process is particularly important. Reasonable construction arrangement, good site node construction quality, perfect coating protection, etc. are effective methods to reduce the rate of coating breakage. At the same time, it is suggested that the anti-tube prefabriced, the coating breakage in the installation process to track, which is very important reference for the future tube cathode protection design.
(3) cathode protection of insulated floran
seafloor pipelines (including vertical tube parts) and cathode protection of cathode frames are two separate cathode protection systems. At the same time, because the undersea pipeline sacrificing anode system's driving capacition is only about 0.25V, in order to avoid the interaction between different cathode protection systems, isolation of different facilities of the protection current, so in the submarine pipeline and land pipeline or platform process pipeline connection, all should be added insulated florans.
in the land construction process, it is important to ensure that the insulation of the frenchland before installation of proper storage, in the installation of the correct construction, after installation of insulation inspection. If it fails, an electrical connection occurs between the vertical tube and the catheter frame, resulting in a longer range of cathode protection, resulting in a large cathode anode state. The anode of the vertical tube will soon be lost and the cathode protection during the design life will not be maintained.
conclusion, with
development of offshore oil and gas fields, the use of submarine pipelines is becoming more and more extensive. As an important part of the connection between the submarine pipeline and the oil and gas platform, the anti-corrosion performance of the vertical pipe is particularly important. This requires construction workers, especially project managers, opposite pipe construction should invest more energy. Manufacturing, prefabriitation, installation should take into account the organic combination of environmental and construction factors, strict quality control, reduce unnecessary maintenance after the service of the pipe.