المشاركة الأصلية كتبت بواسطة جصاني جصاني
السلام عليكم ورحمة الله وبركاته
يجب عزل هذه الخزانات عن كافة الانابيب ( فوق الارض وتحت الارض ) وذلك باستخدام فلنجات العزل:
كل المنشئات الحديدية المدفونة تحت والخاضعة للحماية الكاثودية لا بد أن تكون متصلة ببعضها البعض كهربيا سواء كانت أنابيبك أو الأنابيب الغريبة العابرة وذلك لتجنب مشاكل التيارات الشاردة
والفلنجات المدفونه لابد التأكد من عزلها كاثوديا حتي لا يخرج عندها تيار الحماية إلي التربة المحيطة
FLANGE INSULATING GASKET KITS
Flanges, the most common trouble area, need to be sealed properly to prevent leakage and must also be cathodically insulated to prevent stray currents which cause undo corrosion and eventual breakdown of the metal. Advance Products & Systems manufactures and maintains a supply of quality products and materials which help solve most flange sealing problems, therefore preventing subsequent corrosion and saving the integrity of the pipeline.
هذا الشكل يوضح أهمية وكيفية عزل المنشئات المدفونة والموضوعة تحت الحماية الكاثودية
b) Insulating Flanges :
عن المنشئات الموجودة فوق سطح الأرض
لأن تلك المنشئات معرضة للهواء (غير مدفونه في التربة أو مغمورة في ماء البحر) ويتم حمايتها بالدهانات والطلاءات فقط
If any portion of the pipe is above ground, then the same has to
be ‘Electrically Isolated’ from the under ground portion. This is required so as to prevent the flow of any other currents from sources outside and also the path of least resistance which the current may find through above ground pipe resting on steel or metal supports. (see fig. 8 on next page)
STRAY-CURRENT CORROSION is caused by an externally induced electrical current. Examples of this situation are commonly observed in rail transit systems, pipeline systems, and electric distribution systems (Ref, , ). Detailed technical presentations of stray current corrosion can be found in the literature (Ref, , ). Stray currents (or interference currents) are defined as those currents that follow paths other than their intended circuit. Unfortunately, nearly all stray current discharges are very local and concentrated, ensuring accelerated corrosion will occur. They leave their intended path because the current finds a path with lower resistance, such as a buried metal pipe, some other metal structure, or an electrolyte with low resistance such as salt water. The current then flows to and from that structure and causes accelerated corrosion whenever it leaves a metallic structure and flows into an electrolyte. For example, in a pipeline that is cathodically protected, if a foreign pipeline crosses or passes close to the protected pipeline, current from the cathodic protection system can gather onto the foreign pipeline and then be discharged from the foreign line when it crosses or comes close to the protected pipeline. This is particularly true in higher resistivity soil. Accelerated corrosion occurs on the foreign line at the point of current discharge. The location of the discharge can be detected because the pipe-to-soil potential is very low at that point. Likewise in an oil or gas field, where the flowline system or the well casings from several wells are being protected using a centrally located rectifier and ground bed, the path of lowest resistance is usually to the nearest well, down the well casing until a low-resistant formation containing salt water is encountered. The current then travels through the salt-water formation to the other more remote wells in the field where it travels up the well casing to the flowline and then returns to the rectifier. Accelerated corrosion occurs on the well casings of the close wells where current is discharged from the casing to the formation. This corrosion is extremely difficult to detect and is very expensive to correct. It can cause a blowout in the well to occur because of the corroded casing and can result in a fire or spill. Insulating flanges can cause corrosion from stray currents. Usually the insulating flange is separating pipes that have different ownership or different levels of cathodic protection. If current collects on the pipeline downstream of the protected pipeline, this current may flow back to the insulated flange, discharge into the earth on one side of the flange, and flow to the other side of the flange that is connected to the protected pipeline. Corrosion occurs where the current discharges from the unprotected, downstream pipeline.
From: ASM Handbook Volume 13A, Corrosion: Fundamentals, Testing, and Protection (ASM International)