The annealing furnace of the Company is in all process control, each pipes could check through computer system. The fuel of annealing furnace is blast furnace gas in the Company, the gas for the annealing not only reducing environmental pollution but also realizing energy recycle and  energy saving.
Spot check in each lots (batch) after annealing. 
In case that non-conforming is found in spot check, the whole lot shall be defined as non-conforming,and shall be returned for annealing and inspection.

Note: lot and group quantity refers to pieces of consecutive production of centrifugal machine.

Mechanical performance of ductile iron pipe after annealing should reach the following requirements

4. Inspection on zinc spraying thickness
 

The ductile iron pipe after annealing shall be sprayed with zinc. Zinc spraying machine sprays metal zinc onto the surface of ductile iron pipe by spray gun. The sprayed zinc coating could firmly attach to its pipe wall.
Zinc coating could prevent pipe rust effectively, prevent corrosion from salt and water, and is suitable for long-term external protection of ductile iron pipe.
Weight of sprayed zinc cooating is not less than 130g/m2.
Inspection method: weighing method or direct measurement method.

5. Roundness correction
 

Round correction refers to inspection and round correction on physical dimensions of ductile iron pipes to make it meeting the  standard requirements.

6. Hydraulic test

It is necessary to make hydraulic test as per ISO2531 to test whether there is leakage on each pipe in specified pressure and time. Qualified tubes without leakage will enter the following process. Those the leak pipe will be rejected, and returned back to the smelting process.

7. Inspection of coating and lining

Coating and lining are after qualified hydraulic test. Inspection are made on coating and lining quality and thickness. In measurement, it is advised to take the average of values on 4 points to make sure the accurate. 
Thickness standard of cement coating and lining of DI pipes: 

the cement lining requirements in the following form:

8. Inspection of curing and lining 

After coating of lining, it is necessary to make cement curing,  the curing time and temperature are depending on climate changes in the year.

9. Inspection of coating layer of anti-corrosion 

Ductile iron pipe after lining should be conducted with cement grinding on lining (over DN400) and externally sprayed with anti-corrosion paint .
Major technical indicators of painting films.

10. Final inspection

Before transfer to warehouse all the pipes should be tested by professional testes. Testing items cover: external surface quality, lining quality, marking identification etc. Qualified ductile iron pipes are transfer to warehoused wainting for delivery.

11. Delivery inspection

Before delivery, the quality control staff and logistics department should make final test on the products, generally testing whether there is damage on the pipes and the outside coating. In case of  pipes damaged, it could not allowed  delivery until the pipe qualified after repaire.