Cement Mortar Lined (CML) piping is the industry-standard solution for protecting steel and ductile iron pipes in a wide range of water services. By providing a durable, protective barrier, the cement lining prevents corrosion, maintains water quality, and significantly extends the service life of the pipeline.
Key Applications:
CML piping is ideally suited for transporting:
* Raw & Potable Water
* Sewage & Wastewater
* Sea Water
* Cooling Water (both once-through and recirculating systems)
1. The Lining: Standards and Specifications
The application and quality of cement mortar linings are governed by strict industry standards to ensure consistency and performance.
* Primary Standard: Shop-applied linings typically conform to AWWA C205, which defines the composition, application, and thickness requirements.
* Lining Thickness: Standard thicknesses are specified by diameter in AWWA C205. However, for highly aggressive environments (e.g., high sulphate content), manufacturers can provide thicker linings upon request.
* Consideration: Increased lining thickness adds to the overall pipe weight, which can impact handling, transportation costs, and maximum shipping lengths.
2. Application Methods: Shop vs. Field
The method of applying the cement lining depends on the pipe diameter and project requirements.
* Shop Application (Up to ~120″ Diameter): This is the preferred method for quality control and efficiency. Straight pipe sections are lined using a high-speed centrifugal process:
1. Spraying: A pre-mixed cement mortar is sprayed uniformly onto the inner pipe wall.
2. Spinning: The pipe is centrifugally spun at high speed, compacting the mortar to create a dense, non-porous lining with a smooth surface finish.
3. Curing: The lined pipe is cured under controlled conditions to achieve its required compressive strength.
* Field Application (Large Diameters): For diameters larger than what shops can handle, linings can be applied in-situ according to ANSI/AWWA C602.
* Fittings and Flanges: These components are lined using specialized techniques such as hand trowelling or spray application to ensure complete coverage of complex geometries.
3. Reinforcement for Structural Integrity
For larger diameter pipes and fittings, the cement lining is often reinforced with welded wire fabric.
* Purpose: Reinforcement controls cracking caused by thermal expansion, shrinkage, and handling stresses.
* Placement: The wire fabric covers the entire surface to be lined and is tack-welded in place with specified overlaps.
* Joints: Extra reinforcement is typically applied at field joint locations to ensure continuity and strength.
4. Jointing Methodologies
A critical aspect of a CML system is maintaining the integrity of the lining at the joints. The two primary joint types are:
A) Butt-Weld Joints
* Process: Pipes are aligned and welded together in the field.
* Lining Restoration: After welding, the heat-affected lining must be restored by hand.
1. The exposed steel is sealed with a synthetic resin-based primer.
2. A ready-mixed mortar is troweled into the joint, finished flush with the existing lining, and cured.
* Note: Pressure testing must be delayed until the field-applied mortar reaches its minimum compressive strength.
B) Sleeve (Carrier-Ring) Joints
* Process: A pre-welded sleeve connects two pipe ends. For pipes over 24 inches, a two-piece half-sleeve is commonly used.
* Advantage: Simplifies field assembly.
* Key Consideration: Welding procedures must be controlled to prevent heat damage to the adjacent cement lining. Internal welds are ground flush to maintain a smooth bore.
5. Critical Installation & Design Details
* Butterfly Valve Installation: When installing wafer-style butterfly valves, the valve disc must have clear clearance from the cement lining. The lining should be chamfered at the flange face if necessary to prevent contact and binding.
* Flange Gaskets:
* ≤ 10 bar(g): Reinforced chloroprene rubber gaskets (3mm thick, 70 Shore A).
* > 10 bar(g): Compressed Asbestos-Free (CAF) gaskets are recommended.
* The gasket’s inside diameter must match the lining’s ID to prevent turbulence and erosion.
* Handling & Storage: CML pipes and fittings are susceptible to impact damage and cracking if flexed. Always use padded slings and provide adequate, continuous support during storage and handling to prevent bending.
6. Applicable Codes and Standards
Cement Lined Piping systems are manufactured and installed in compliance with a comprehensive set of international and national standards, including:
| Category | Standard | Title / Purpose |
|---|---|---|
| Lining | AWWA C205 | Shop-Applied Cement-Mortar Lining |
| AWWA C602 | Field-Applied Cement-Mortar Lining | |
| Piping | ASME B31.3 | Process Piping Design & Construction |
| Materials | IS: 12330 / ASTM C150 | Sulphate Resisting Portland Cement |
| IS: 383 / ASTM C33 | Concrete Aggregates | |
| ASTM A82 / A185 | Steel Wire & Welded Fabric for Reinforcement |
By understanding the specifications, application methods, and critical installation details of cement mortar lined piping, engineers and project managers can ensure the successful implementation of a durable and long-lasting pipeline system.