1. What is the procedure for application of wrapping and coating?
Procedure for application of coating and wrapping: –
A. Prior to application of wrapping & coating, the surface of pipe should be made free from all loose mill scale, dirt, rust, grease, moisture and other foreign material. This is achieved by blast cleaning to grade
Sa 2 ½ .
B. The pipe exterior surface or blast surface shall be coated with primer within four hours of shot blasting. The primer shall not be applied when the pipe surface temperature is below 7C and above 70C. When moisture is present on the surface, the same is heated for sufficient time to dry the surface.
C. The pipe after priming shall be coated with two-flood coat of hot enamel incorporating the simultaneous application of inner & outer wrapping.
2. What is the content of primer applied on the pipe surface before coating?
The primer consists of processed coal – tar pitch and refined coal – tar oil.
3. What is the enamel applied on the pipe surface for coating?
The enamel is plasticized coal tar pitch suitable for hot application and filled with inert mineral filler which have minimum tendency to settle down in fluid state.
4. Which material is used as inner and outer wrapping?
Fiber glass tissue consisting of a uniformly porous mat of chemically resistant boro – silicate glass containing not less then 5% B2O3 .
5. What should be the minimum thickness of enamel on any point on pipe?
The enamel shall have minimum thickness of 2.4 mm when measured on top of the weld with an overall thickness of 4 mm.
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6. How much should be the depth of pulling of inner fiber – glass tissue into the hot enamel?
The inner wrap of fiber – glass tissue pulled in such a manner that the same is imbedded half way into the enamel without touching the steel surface.
7. What should be the overlap between inner & outer wrap?
The inner and outer wraps shall be overlapped by 25 mm.
8. What should be the minimum staggering of inner & outer wraps?
The overlaps of the inner and outer wraps shall be staggered from each other by minimum distance of 100 mm.
9. What is cold type of wrapping?
PVC backed bituminous compound tape used for field wrapping is called cold wrapping.
10. What is the minimum overlap of field wrapping (cold Tape) on shop wrapping?
Wrapping shall start and finish to give a minimum 75 mm overlap onto the adjoining shop coating.
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