How to Prepare - Procedure for Vacuum Box Test of Storage Tank Bottoms

       

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Procedure for Vacuum Box Test of Storage Tank Bottoms

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                                                     Prepared by      Approved by        Client/Inspection Authority

Procedure for Vacuum Box Test of Storage Tank Bottoms

1.0  Scope

2.0  Reference Code and Specification:

        ASME Sec V, Article 10 Appendix-II

3.0  Equipment:

3.1  The vacuum box test shall be performed by using a box with visible window of plastic (e.g. 

       150mm wide by 750mm long metalic box with a glass acrylic at top 45͒ corner vacuum box shall

        be used for shell to bottom annular joints).

3.2  The open bottom scheme shall have suitable connections, necessary valves and calibrated 

        vacuum gauge.

3.3  The open bottom shall be sealed against the tank surface by suitable gasket.

3.4  Soap solution shall be used as a leak detection medium.

3.5  During testing, illumination shall be adequate for evaluation and interpretation of the test.

3.6  The test scheme shall be demonstrated with sample test block by application of soap solution at 

        site before conducting the test on job.

4.0 Personnel:

      The personnel shall be competent and familiar in performing this method.

5.0  Surface Preparation:

       

       The surface to be examined and all adjacent areas within at least 25mm should be dry and free

       from all dirt, grease, scales, welding flux, weld spatters, paint oil and other extraneous matter                that could obscure surface opening or otherwise interfere with examination. 

6.0  Procedure:

6.1  Visual examination of the bottom and weld shall be done before performing the vacuum box     

        test.

6.2  Metal surface temperature shall be in between 4 to 52 deg.centigrade.

6.3  The gauge shall be at least register a partial vacuum of 0.304Kg/cm square for inspection of the

        joints.Approximately 750mm length of seam under test is applied with the soap solution for 

       detecting leak. The foaming shall be minimized by means of uniform application of soap 

       solution. An overlap of 50mm for adjacent placement of the vacuum box shall be used foe each           subsequent examination.

7.0  Evaluation:

       Bubbles produced by air sucked through the weld seam can detect the presence of defects.Ensure

       that there is no quick bubbles or spiting response to large leaks if any. The tested areas are 

       accepted only when on continuous bubbles formation is absorbed. The require partial vacuum 

       shall be maintained at least 5 sec, for examination time/until proper inspection is over.

8.0  Repair/Retest:

       

       In case of repair, the position shall be marked and repaired with correct procedure and after 

       removal of defects that cause the leakage. After repaired, required examination shall also be

       carried out, in any case. Liquid Penetrant Examination and retest of vacuum box test shall be 

       carried out.

       Minimum 50mm length of weld or as required by actual weld repair whichever is greater shall             be deposited using the same production WPS.

9.0  After test the area shall be cleaned.

10.0  Report/Record:

       

         Upon satisfactory inspection a report shall be prepared as per below format.

         Prepared by                                 Approved by                        Client/Consultant

Vacuum Box Test Report for Vertical Storage Tank Bottom

             Cient                                                        Report No.                    Date

             Project                                                    Company Job Code No.

             Consultant                                             Tank description/No.

             Sub-Contractor                                     Drawing No./Revision No.

            -------------------------------------------------------------------------------------------------------

      1.  Test Description --------------------------------------------

      2.  Partial Vacuum ----------------  MM of Water ------------------- Kg/cm square or psi
     
      3.  Partial Vacuum holding duration -------------------------------------------

      4.  Test Temperature ----------------------------------------------------------------

      5.  Specific Requirement -----------------------------------------------------------

      6.  Pressure Gauge details -------------------------------------------------------
            Serial No.                         Range                       Calibrated Certificate No & Date




             Remarks:- 


          

           Sub-Contractor                       Principal Contractor              Client/Inspection Authority