Cement Lined Carbon Steel Pipe Fittings

What’s Cement Lining?

The cement lined carbon steel pipe fittings are usually factory-wrought butt welding pipe fittings made to ASME B16.9, which are furnished with cement-mortar or concrete linings. The cement mortar is a mixture of cement, fine aggregate (sand) and water. The concrete is a mixture of cement, fine aggregate (sand), coarse aggregate (gravel) and water. The cement lining, either cement-mortar lining or concrete lining, shall be applied to the internal surface of the pipe fittings by a proper placing method. Cement-mortar lining is generally applied to carbon steel pipe fittings in sizes up to 20″, while more stronger concrete lining is used for sizes 24″ and larger. However, the selection of specific lining is at the discretion of the user.

Cement-mortar lined 90° elbows, long radius, 4″ SCH40 ASME B16.9.

It has been known that cement-mortar and concrete provide considerable protection to embedded ferrous materials against the corrosive effects of soil and water. The cement-mortar and concrete linings have become the most common protective measure used for pipes and fittings in water and wastewater service. They are very economical and provide superior corrosion protection. The cement-lined carbon steel butt welding pipe fitting covers a variety of product forms such as elbow (90° & 45°), tee (straight & lateral), reducer (concentric & eccentric), cross (equal & reduced), end cap, bend (3D & 5D), 180° return, and saddle.

Function & Applications

Cement mortar or concrete linings protect carbon steel by three interrelated processes: (1) Cement linings form a barrier coating which works to prevent physical damage to the metal surface. They passivate the metal surface. (2) Hydrated cement is highly alkaline, with a PH of about 12.5. At that PH, a passivating oxide film forms and is maintained on the metal surface, preventing corrosion. (3) Chemical reactions can occur in the mortar or concrete lining which can make infiltrating corrodents harmless, or they can form compounds that physically block further infiltration of corrodents.

The cement-lined carbon steel pipe fittings protect the interior steel surface from being attacked and damaged by corrosion, which in turn can lead to the formation of leaks, scale, or tuberculation or a combination of these defects. They are found highly effective and economical for the transmission of fluids such as raw fresh water, potable water, raw sewage, treated sewage, seawater, and power plant cooling water.

Manufacture & Fabrication

Workers applying cement mortar to the internal surface of the elbow.

The carbon steel pipe fittings, seamless or welded, shall be made by a wrought process such as extruding, bending, pressing, forming, rolling, or forging, etc. Due to the irregularity of shape and passage of the fittings, the cement-mortar or concrete linings are generally hand-placed, sometimes with the assistance of pneumatic tools. The thickness of the lining shall be determined by the designer or user. The lining surface shall be compact and smooth. The mortar is mixed using 1 part cement to 3 parts fine aggregate (sand), with enough water added to obtain the necessary workability. After the application of cement lining to the internal surface, the carbon steel pipe fittings shall be moved to a curing area. Care shall be exercised at all times to prevent damage to the lining. The curing methods include accelerated curing and moist curing. After the cement lining is cured, the external surface of the fitting shall be coated with black paint.