Procedure for Pickling and Passivation

https://www.hvacmepcontractors.com     Procedure for Pickling and Passivation, ASTM: A380–99,  Pre cleaning /Degreasing, pickling and passivation procedure for stainless steel, pickling and

1.    Purpose & Scope

 

2.    Reference Documents

 

3.    Process

 

4.    Inspection

 

5.    Extent of Examination

 

6.    Protection

 

7.    Sample report

 

 

Procedure for Pickling and Passivation

 1.    Purpose & Scope

 

This procedure covers pickling and passivation of stainless-steel vessel internal/external surface for cleaning, removal of surface contamination developed during fabrication, welding, handling or de- scaling or tight adherent oxide films etc.

2.    Reference Documents

 ASTM: A380–99

 3.    Process

 a.  Material

i.    For pickling use:HN03 6-25% concentration+ HF0.8 to 8% concentration, temperature of mixture 21-60 0C and soaking time shall be decided based on thickness of components such that there is No loss material.

ii.        For passivation use:HN03 having 20-50% concentration, temperature of mixture 50-70°C and soak time10-30minutes

iii.        Detergent Powder, NaOH & KMnO4.

 

b.  Pre cleaning /Degreasing

 

Surface to be pickled is cleaned of dust, spatters, grease, oil and other foreign parties by swabbing with emulsion or solvents, grinding (On fabricated components), etc.

Detergent powder Is used to clean oily or greasy surfaces.

 

c.  Acid Cleaning Mixture

 

A sufficient quantity of mixture of HF+HNO3 is prepared in proportion of 1:15 minimum or 1:3maximum and mixed preparation of pickling mixture separately just before use.

 

d.  Acid Cleaning

 

Pickling mixture prepared in Acid Cleaning mixture above shall then be applied on the surface to be picked by spraying, brushing, swabbing to give uniform and total coverage of the component / item, to be pickled. The applied mixture is left to react with the surface and time shall be determined based on thickness of components that are pickled as over exposure may lead to loss of material which is critical for thin walled components. taking into consideration the surface condition of the item. Under no circumstances shall the applied mixture be left on the surface for more than 30minutes.

 

e.   Cleaning After Pickling

 

The pickled surface shall then be rinsed with clean water then of chloride content less than 25ppm (PH values of water shall be between 6-8).jet of water or water with air pressure shall be used to remove any traces of pickling solution on the surface, crevices and

in accessible areas.

 

 f.    Precautions

 

During pickling operation proper ventilation, protective rubber gear, hand gloves, shoes, facemask, eye protector, rubber apron, or any other protective gear shall be used by the operator.

 

g.   Passivation

 

·  Passivation shall be carried out by swabbing using cotton cloth or brush

     ·  Passivation solution as follows Nitric Acid-20 to 50% by volume Water –Balance

       ·  Duration of application is 30-60 minutes to 20-40°C temperature.

       · Rinse the surface with plenty of water to remove any traces of acid or contamination. Water shall not have chloride contents exceeding 50 ppm and in the range of Ph value 6-8

 

4.   Extent of Examination

                   Pickling and Passivation to be carried out for accessible area of below SS Items-

 

·         Spin Vane Assembly

·         Waste gas connection SS items

 

5.  Inspection

             Visual inspection of surface shall be carried out to check for surface iron            contaminations. 

             Copper sulfate test to be carried out as per ASTM A380 to  ensure complete               removal  of iron contaminants.

 

6.  Protection

 

The pickled & passivated surface shall be suitably covered during storage & transportations.

 

6. SAMPLE REPORT