"Step-by-Step Guide to Inspecting Pressure Vessels: Ensuring Safety and Compliance"

Overview of inspection requirements for pressure vessels.

PRESSURE VESSELS - CODED

 

This specification includes inspection requirements for vessels under internal or external pressure. For vessels constructed to the requirements of a particular code, the details shall be obtained from the specified code of construction.

 In this blog we will cover Stages of inspection.

Following is a list of applicable National / International Standards: 

• ASME Section VIII Div. 1 - Boiler & Pr. vessel code
• ASME Section II
• Part A - Ferrous materials
• Part B - Non-Ferrous materials
• Part C - Filler Materials
• ASME Section V - Non-destructive examination
• ASME Section IX - Welding and brazing qualification
• BS 5500 - Design of pressure vessels
• AD Merkblatter - Technical rules for pressure vessels
• Swedish pressure vessel code
• Swedish boiler code
• IS 2825 - Code for unfired pressure vessels

This document outlines the scope of inspection and the relevant standards that apply to the construction and inspection of pressure vessels. If you need further details or specific sections explained, please let me know!

 

Detailed stages of inspection for a pressure vessel. 

 

1.      Material Identification

·         All materials used in the construction of a pressure vessel must be identified according to specific notes on materials identification and stamping.

 

2.      Procedure and Welder Qualification

·         Before fabrication begins, the vendor must submit a welding procedure specification (WPS), which must be tested according to ASME Section IX.

·         All welders working on the vessel must be qualified according to WPS, PQR, and welder qualification standards.

 

3.      Shell Longitudinal Seam Setup (L/Seam)

·         Check 'V' dimensions.

·         Ensure joint alignment.

·         Measure circumference at both ends.

·         Check length and shell curvature using a template.

·         Verify ovality and material identification stamping.

·         Pre-pinching at edges.

·         Back chip the longitudinal seam weld to sound metal, and conduct a dye penetrant examination to check the soundness of the chipped back surface.

 

4.      Shell Circumferential Seam Setup (C/Seam)

·         Verify dimensions. Check 'V' dimensions

·         Ensure joint alignment.

·         Check total shell alignment (straightness).

·         Ensure NDT clearance of longitudinal weld seams and stagger long seams.

·         Back chip the circumferential seam as mentioned in the longitudinal seam process.

 

5.      Dished End Blank Setup

·         Check 'V' dimensions and blank diameter.

·         Perform back chipping and necessary examinations.

 

6.      Dished End Inspection at Source ( at Vendor )

·         Crown radius Template Checks.

·         knuckle radius using templates.

·         Height and straight face.

·         Over crowning using templates.

·         Maximum and minimum diameter (ovality) checked at four points uniformly divided along perimeter

·         Check the circumference of dish with matching shell circumference.

·         D.P. Check:

·         Dye penetrant check on knuckle portion (inner and outer surfaces).

·         Thickness:

·         Ensure minimum thickness meets requirements of UDS 79(d) of ASME VIII-1.

 

7.      Dish to shell Setup:

·         Verify 'V' dimensions and

·         joint alignment.

  

8.      Dish to shell back chip (as per previous processes).

·         After completing welding from one side, the back side of the weld shall be chipped to sound metal. A dye penetrant examination shall be carried out to check the soundness of the chipped back surface.

 

9.      Nozzle Orientation and Marking

·         Verify nozzle orientation and elevation per drawing.

·         Nozzles should not be on or near any weld joint; if they are, the weld joint's soundness must be checked by radiography to a length over three times the diameter of the opening with hole center at mid length..

 

10.  Nozzle Setup

·         Pipe to Flange: Check nozzle schedule, flange rating, and weld preparation.

·         Nozzle to Shell: Check squareness, weld preparation, and height.

·         Back Chip & D.P.: Perform back chipping and dye penetrant examination.

  

11.  Pad Testing

·         Nozzle reinforcing pads must be soap-leak tested with air at 1.5 kg/cm².

  

12.  Internal Coils

·         Heating and cooling coils should only be cold-bent. Check for ovality, thinning, passage area, wrinkles, and dents in a sample tube piece bent over the smallest radius.

·         Ensure correct 'V' dimensions,

·         pitch,

·         pitch circle, and

·         coil alignment over entire length

It is advised to use TIG welding for root run, when radiography quality weld is required.

13.  Non-Destructive Testing (NDT)

·         For weld joint efficiency of 0.85, subject all butt welds to 10% spot radiography.

·         For joint efficiency of 1, perform 100% radiography.

·         Dished end welds must be fully radiographed in the case vessel has 10% radiography.

·         All nozzle welds examined by dye penetrant.

  

14.  Stress Relieving

·         Follow rules for loading temperature, heating rate, soaking temperature, soaking time, and cooling rate as per the applicable code.

 

 15.  Hydrostatic Test

·         Conduct a hydrostatic test at 1.5 times the maximum allowable working pressure.

·         Inspect all joints and connections at not less than two-thirds of the test pressure.

·         Galvanized or lead-lined vessels may be tested before or after galvanizing/lead lining.

 

·         Preparation for Hydrotest

·         Dress or grind all weld joints as required.

·         Remove all tack marks, temporary clamps, or supports before the hydrotest.

·         Provide vents at high points to purge air pockets during filling.

·         Connect an indicating pressure gauge to the vessel, calibrated before testing. The test gauge used shall have the dial graduated over a range of double the intended test pressure, but in no case the range be less than 1.5 times test pressure.  

·         Use rust inhibitors during hydrotesting.

·         After testing, drain and dry the vessel, apply a rust preventive coating inside, and paint the outside with two coats of red oxide primer.

 

 Final Inspection

Check and record overall dimensions against drawings.

Ensure compliance with documentation and stamping requirements.

 

These procedures, steps ensure the pressure vessel's structural integrity , safety and quality standards through rigorous inspection at each stage of fabrication and testing procedures. If you need more detailed information on any specific section, feel free to ask!

Thanks for reading!