Water Pipeline Monolithic Insulated Joints. Cathodic Protection/Isolation

 Monolithic insulated Joints are also known as "MIJs" are prefabricated Unions of butt-weld forged carbon steel construction that connect two ends of a pipe preventing metal-to-metal contact across the joint; so they increase pipeline resistivity, and this helps to mitigate corrosion by allowing electrical charges picked-up by the pipeline to travel only so far.   

IJs are an integral part of any corrosion control program because they block the flow of electrical or stray current on the pipeline. 

Stray current, of course, refers to current from another voltage source that has leaked out of its intended path and found the pipeline to use as its return path. Because the problem is, that these currents are picked up on the pipeline and discharged back into the soil at some distance down the pipeline wherever the protective coating is worn or thin or damaged in some way.

And it’s the process of discharging off the pipe that accelerates corrosion of the pipe wall at the discharge point. This corrosion is typically localized, but if left unattended, wall thickness can be compromised, and eventually, the load carrying capacity of the pipe is affected. 

CP is simply a way of mitigating corrosion electrically by supplying protection current to the external surface of the pipe. This protection current equalizes the pipe’s electrical potential, and this makes the surface of the pipe less reactive to soil conditions. 

Cathodic Protection current essentially passivates the pipe’s external surface by converting all anodic (or active) sites on the pipe’s surface to cathodic (or passive) sites

So that Protection current makes the pipe a net receiver of current rather than a net discharger of current; Because metal that discharges current corrodes; and metal that receives current is protected.

Sypris Tube Turns currently offers a size range of 48" - 120" Monolithic Isolation Joints for use in water pipelines (smaller sizes available as well). Joints currently come with 3' API 5L X52 pipe pups installed on each side of the joint offering easier installation and handling. Longer pipe pups available upon request. ASME Classes 150 to 900.

 MIJs are a BOLTLESS design and have no moving parts, so they’re maintenance-free. Nothing to adjust or maintain, and they’re LEAK PROOF.  In fact, there are no leak paths to the atmosphere because the IJ is sealed externally to the environment; and it’s sealed internally by two Viton/FKM O-rings.

MIJs are a great alternative to Flanged isolation Kits with bolts and washers which can be prone to leaks and operator error during the installation process with over-torquing the bolts. 

Flanged isolation kits are not resistant to bending, may not seal properly, and are not earthquake resistant. MIJs are designed to be stronger than the pipeline they’re installed in, MIJs have a resistance to mechanical and thermal stresses that’s at least equal to the pipeline

• Electrical Resistance (IR) Test – IJ is able to withstand an applied voltage of 1000 V DC across the test lugs The standard is > 25 megohm min resistance but an average IJ exhibits resistance > 2000 Megohms  

• Dielectric Withstand Test to 5KV  (optional)
•  Hydrostatic pressure test for leakage to 1.5x design pressure. 

All test reports are done in the factory and included along with your MTRs. 

High-performance two-part epoxy coatings are the first line of defense against external corrosion because they seal off the pipe from its environment, so they prevent contact between the pipe and electrolytes in the soil.  

Popular coatings include:

• Denso Protal 7200
• SPC 2-8888
• NSF 61 rated coatings for potable water service. 
• Any custom coating specified in the customer specs.