The dimensional inspection for vessel are included before/after welding activities.
Before welding: formed head inspection, shell inspection and opening hole inspection etc.
After welding: overall dimension, nozzle to nozzle, TL to TL, etc.
In addition of dimensional inspection after hydro-static test.
I recommend to learn more specified rules and follow it. It is a best way to understand and prepare your documents.
Understanding ASME BPVC Sec VIII
Section VIII Div. 1 - Pressure Vessels: Stamp “U” for pressure vessel.
Section VIII Div. 2 - Alternative Rules: Stamp for “U2” for pressure vessel.
Section VIII Div. 3 - Alternative Rules for Construction of High Pressure Vessels: stamp “U3” for High Pressure Vessels.
National Board Inspection Code - Stamp “R” for repair and alteration.
A qualified company have a ASME Manual as specified their qualification. I think it book is a better guide for you and follow up.
- Section VIII Division 1 up to 3,000 psi (20 MPa)
- Section VIII Division 2 up to 10,000 psi (70 MPa)
- Section VIII Division 3 over 10,000 psi
Inspection of the head sections to the specified shapes within the permissible tolerances UG-81.
Example: Internal diameter of shell vessel: D (ID) = 1960 mm.
Deviation outside of the specified shape ≤ 1 1/4% of D= 1960*1.25/100 = 24.5 mm.
Deviation inside of specified shape ≤ 5/8% of D = 19605/(8100) = 12.25 mm
So, Max. allowed deviation from template are: 24.5 +12.2 = 36.7 mm.
A Template Preparation
Next, we will prepare a template for checking.
Template for checking must be prepared with an offset at last 10 mm (from deviation inside of specified shape = 12.5 + 10 = 22.5 mm) for easy access during inspection due to knuckle of shape is not equally after forming.
If your template are not offset from min. deviation inside of shape, it may not insert into the inside of head.
Thickness of template should be greater 5mm to enough strong for inspection and minimize deformation and distortion.
Verification of Template
A template should cut by CNC machine to make sure the precisely arc length meet the design. The double verification the template must be manually verified this arc by drawn step by step length.
Formed Head Inspection
Preparation of the plates for forming head must offset (extra) a minimum of 25 mm, the offset area will discard after forming head and groove beveling.
Step to be checked:
- Groove beveling preparation must be done and meet the design drawing,
- Surface conduction must be checked without crack, peeling, flake off, lamination etc. after forming,
- Additional NDE for all surface or partial area (knucle areas) by MT or PT,
- Ultrasonic thickness measurement (UTM) must be done and available the UTM reports for reviewing.
How to check:
It is easy check by using template, put the template into the head, and align the template to the axial center and run it arround the circle of head.
NOTE: minimum and maximum gap must be recorded
As above example: Internal diameter of shell vessel: D (ID) = 1960 mm.
- Min. gap shall be 10 mm.
- Max. gap shall be 36.7 + 10 = 47.7 mm.
And then, you must record all values to inspection report.