Passivation of stainless steel

This protocol is applicable for passivation of SS316L i.e., Passivation of stainless steel, This specification covers requirement for cleaning, and passivation of all SS316L. All welding flux and weld spatter shall be removed by passivation

Applicable Codes and Standards.

ASTM A 967- 01, Chemical Passivation Treatments for stainless steel parts.

ASTM A 380 – 99, Standard practice for Cleaning, Descaling, and Passivation of stainless steel parts, equipment and systems.

Initial Cleaning

Take 25-50% by volume of water in the storage tank. (Water quality –chlorine content shall be less than 5ppm), then circulate the water for 30 minutes.

Drain the water from the storage tank by opening the drain valve and system by lowest point valves.

Passivation of SS Vessels along with process pipelines and CIP (SS316L) with HNO3

Passivation with HNO3:

Calculation:

Volume: 3000 litre

Strength of HNO3: 5% v/v

HNO3 grade: 69%

Specific gravity: 1.41 g/ml

The composition of the passivating Bath shall be as follows

1% concentrated Nitric acid.

99% water with not more than 1-ppm chloride

1.5 times the hold-up volume of the distribution piping and 1.5 times the hold-up Volume of the equipment in the loop (Except tanks) OR 25% volume of the storage tank. Whichever is higher

Tanks, pipes and other equipment have to be filled with the solution.  The solution shall be held in the equipment or calculate for the following minimum period at the temperatures indicated.

35°C	15 Hrs
50°C	8 Hrs
65°C	4 Hrs
80°C	21/2 Hrs

Stop the circulation.

Drain the acid solution in the storage tank by opening the drain valve and system by opening the lowest point valves.

Flush the system with water (of the water quality –chlorine content less than 1ppm) till the whole acid solution is flushed out.

Note:

If Nitric Acid concentration is to maintain 3%, solutions have to hold in the equipment or calculate for the following minimum period at the temperatures indicated.

35°C	3 ½ hrs
50°C	2 Hrs
65°C	1 ¾ Hrs
80°C	1 hrs

If Nitric Acid concentration is to maintain 5%, solutions have to hold in the equipment or calculate for the following minimum period at the temperatures indicated.

35°C	2 hrs
50°C	1 ½ Hrs
65°C	1 hrs
80°C	¾ Hrs

If Nitric Acid concentration is to maintain 10%, solutions have to hold in the equipment or calculate for the following minimum period at the temperatures indicated

35°C	1 Hrs
50°C	¾ Hrs
65°C	½ Hrs
80°C	¼ Hrs

Final Cleaning

Take 25-50% by volume of water in the storage tank. (Water quality –chlorine content shall be less than 5ppm), circulate the water for the period of 30 minutes.

Drain the water in the storage tank by opening the drain valve and system

by the lowest point valves.

Repeat the above procedure till we observe the Conductivity

1.5 µs/cm.

This will end the cleaning cycle.

Water Quality Test During Flushing

Check Conductivity and HNO3 concentration of supply line water and return line water.

pH of the water should be between 5 to 7. Same pH to be maintaining for feed and drain water.