Preparation to Blast Cleaning for Cement Mortar Lining  :

Prior to blast cleaning, the each pipe shall be inspected by the followings;

• Pipe identification control
  • Pipe shall be accepted as PE coated pipe condition

• The internal surface control
  • The pipe internal surface shall be inspected and cleaned to remove all traces of oil, grease and loose deposits. Any visible trace of oil or grease shall be removed using an appropriate non-oily and non-toxic product.

• If pipes have been in contact with marine or industrial atmosphere, they shall be cleaned before abrasive blasting to remove any contamination. Cleaning shall be carried out using an adapted process.

Surface Preparation :

The pipe surface shall be grit/shot blasted to ensure the SA 2 1/2 degree of cleanliness.

The finished pipe surface shall be completely removed all traces of rust and shall be provided a surface average roughness (R_Z) of  50 to 100 microns.

Pipes shall be heated to remove any surface moisture and to ensure more than 3^ºC above the ambient dew point. 

The ambient relative humidity shall not exceed 85 % as measured using a hydrometer and digital thermometer.

Immediately after abrasive blasting, all dust and traces of abrasives shall be removed from the pipe surface by brushing and vacuum cleaning.

Each cleaned pipe shall be inspected for surface defects. Any defect shall be removed.

Ambient Control :

The ambient temperature and ambient relative humidity shall be measured using 

a hydrometer  and digital thermometer.

The ambient relative humidity and ambient temperature shall be recorded to the shift report.

The grit-blasting is not permitted when the ambient relative humidity exceeds 85 %.

The metal temperature shall be 3ºC above the ambient dew point temperature.

Any pipe which has not been coated before degradation of its surface preparation shall be completely re-blasted before coating.

Surface Test and Inspection :

The below tests and inspections shall be performed on blast cleaned pipe:

• Surface profile :

Two methods can be used in measuring surface roughness measurements.          

                    Method 1- By visual comparison gauge,

                    Method 2- By a digital profile measuring device.

       Standard grid and shot comparator is compared to the pipe surface. The coinciding segment of the comparator shall be decided.

Surface roughness measured by a digital profile measurement device. Surface roughness shall comply with Rz=50-100 µm

The calibration of equipment shall be performed by reference blocks.         

• Surface cleaning degree :

Standard comparison pictures are used to decide the degree of the surface cleanliness. Surface quality degree shall be Sa 2 ½

• Dust  control :

Residual dust shall comply with acceptable categories of ISO 8502-3 and Specification. 

• Visual inspection :

The surface defects which appearance effect of grit-blasting or other reason shall be checked by visual inspection. In case of any grinding or mechanical reworks, the wall thickness shall be ultrasonically examined and remaining wall thickness shall be met minimum specified requirements.

Pipe external surface shall be cleaned of all dust and foreign matter using clean dry compressed air or vacuum cleaning. Residual dust shall comply with categories of ISO 8502-3 and specification.

Coating Application

Cement Mortar shall be composed of cement, sand and water well mixed and of proper consistency to obtain a dense, homogeneous lining that will adhere firmly to the pipe surface. Cement Mortar for lining shall consist of one part cement to not more than three parts fine aggregate by weight. Excessive amounts of batch mix water shall be avoided. Only enough water to obtain proper placement characteristics of the batched cement mortar shall be used. The water-soluble chloride-ion content of the cement-mortar lining mix, expressed as a percentage of the weight of cement shall not exceed 0.15 percent.

Mixing: The cement Mortar shall be mixed in batches. The amount of cement and sand entering into each batch shall be measured by weight. The quantity of water entering the mixer shall be measured automatically by an adjustable device, or it shall be otherwise measured to ensure that the correct quantity of water is being added.

Condition during application: The temperature of the substrate should be minimum 15°C and at least 3°C above the dew point of the air.

There is Centrifugal Process methods of lining.

The necessary amount of mortar for obtaining the required lining thickness is poured by boom-nozzle system along the pipe.

The boom is moved with constant speed inside the pipe from one end to the other end to provide evenly distribution of the mortar. 

Then the pipe is rotated.

The mortar is spread around internal pipe surface under centrifugal force. The mortar is compacted and residual water is drained at the end of the rotation.

Cement-Mortar Curing

Immediately after completion of spinning, the pipe sections may be moved to a curing area. Care shall be exercised at all times to prevent damage to the lining.

At the option of the manufacturer, linings shall be accelerated cured, moist cured, or cured by a combination of accelerated and moist curing.

Accelerated curing or moist curing may be used interchangeably on a time-ratio basis of 5 1/3 h of moist curing to 1 h of accelerated curing. In any case, the total curing period shall be equivalent to 96 h of moist cure and minimum curing period before applying the exterior coating shall be equivalent to 24 h of moist cure.

The lining shall be kept continually moist until completion of the minimum specified curing period.

Moist Curing may be used only if the minimum ambient temperature exceeds 5ºC continuously during the required minimum curing period. No credit shall be allowed for any time during which the temperature drops below 10ºC.

On arrival at the curing area, but not later than 30 min after completion after lining operation, pipe ends shall be covered with plastic cap. If a cement-mortar exterior coating is not specified, the lining shall be moist cured for 96 h before shipment.

After curing, the water shall be sprayed on the lining and wetting on the surface for seven days. 

Defective Lining :

General: All defects, including, but not restricted to, sand pockets voids, over sanded areas, blisters and cracking as a result of impacts, shall be cut out and replaced by hand or pneumatic placement to the same thickness as required for the cement mortar lining

Lining Cracks: Temperature and shrinkage cracks in the cement mortar lining less than 1,6 mm in width need not be repaired. Cracks wider than 1.6 mm need not be repaired if it can be demonstrated to the satisfaction of the purchaser that the cracks will be heal autogenously under continuous soaking in water. The autogenous healing process may be demonstrated by any procedure that keeps the lining of the pipe continually wet or moist. Pipe used in the demonstration shall be representative of the pipe to be supplied and water for the moistening of the pipe shall be chemically similar to the water to be carried in the pipeline.

Cement Mortar Lining Thickness :

Cement Mortar Coating Test  :

Surface Cleanliness Comparison

Surface Profile (Roughness)

Sand-Sieve Analysis

Lining Thickness Measurement

Curing

Visual Check