Volume-II of IV - GAIL

8.13.4 The CONTRACTOR shall check that the concentration for the chemical pretreatment
solution remains within the range recommended by the chemical
manufacturer for the pipe coating process. The concentration shall be checked at
the make up of each fresh solution and once per hour, using a method approved
by the chemical manufacturer. The CONTRACTOR shall also ensure that the
chemical pre-treatment solution remains free from contamination at all times.
Recycling of chemical pre-treatment solution is not permitted.
8.13.5 The CONTRACTOR shall ensure that the temperature of the substrate is
maintained between 40°C and 80°C and the chromate solution temperature does
not exceed 60° or as recommended by the manufacturer.
8.13.6 The chromate coating shall be smooth, even, free from runs, drips or excessive
application and lightly adherent with no flaking of the coating. The chromate
coated steel must be thoroughly dried immediately after application and shall be
achieved by boiling off any residual solution on the surface.
8.14 The total allowable elapsed time between completion of the blasting operations
and commencement of the pre-coating and heating operations shall be such that
no detectable oxidation of the surface occurs. Relative humidity readings shall
be recorded every half on hour during the blasting operations in the immediate
vicinity of the operations. The maximum elapsed time shall not exceed the
duration given below :
Relative Humidity % Maximum elapsed time
> 80 2 hours
70 to 80 3 hours
< 70 4 hours
Any pipe not processed within the above time-humidity requirement shall be
completely re-blasted. Any pipe showing flash rusting shall be re-blasted even if
the above conditions have not been exceeded.
8.15 Pipe handling between abrasive blasting and pipe coating shall not damage the
surface profile achieved during blasting. Any pipe affected by the damage to the
surface exceeding 200mm 2 in area/ or having contamination of steel surface shall
be rejected and sent for re-blasting.
9.0 COATING APPLICATION
The external surface of the cleaned pipe conforming to clause 8.0 of this
specification shall be immediately coated with 3-layer extruded polyethylene
coating in accordance with the procedures approved by COMPANY, relevant
standards and this specification. In general, the procedure shall be as follows :
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