Formed Head Inspection

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 β€œU” for pressure vessel.

  • Section VIII Div. 2 - Alternative Rules: Stamp for β€œU2” for pressure vessel.

  • Section VIII Div. 3 - Alternative Rules for Construction of High Pressure Vessels: stamp β€œU3” for High Pressure Vessels.

  • National Board Inspection Code - Stamp β€œR” 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.


Pressure vessel inspection

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Dimensional Inspection for Head

The inspection of head shall be performed in accordance with UG-32,79,81 / Sect. VIII,
Div.1 of ASME.

The thickness of the formed head shall be measured at the top and knuckle and shall
be meet the minimum required thickness.

Dimensional Inspection for Shell

All outward & inward dimensions specified on latest fabrication drawing shall be
measured and recorded within the allowable tolerance.

Actual wall thickness of pressure retaining part (One point per each ring/pipe), i.e.
shell, head and pipe(nozzle neck) shall be measured, and shall not be thinner than
the minimum design thickness.

Inside diameter of shell shall be measured in two(2) directions for each single shell at
about 100mm from circumference weld seam.

Before bundle insert to shell, gauge plate having the same diameter of baffle
composed of two spans of baffle pitch for out-of-roundness shall be done.

The shell length (TL–to-BL) shall be measured in two(2) directions.

All inside edges of nozzles and connections, whether flush or extended, shall be
rounded off to a radius of at least 6mm.

The flatness of gasket contact face for girth flange shall be checked within 1mm

The following dimensions shall be carefully checked:
(1). Related foundation such as Location, Pitch, Size, BCD of Saddles.
(2). Related connection such as Location, Orientation, Size of Nozzles
(3). Interface of Internal or External parts

Non-Destructive Examination

  • NDE shall be performed at that time in accordance with the project specification, and
    NDE plan.

Radiographic Examination (RT)

  • The butt weld where so specified in the relevant drawing shall be radiographic examined in
    accordance with ASME sec VIII, Div.1 UW-51/UW-52 and project specification.
  • If covering the longitudinal or circumferential weld by attachments is unavoidable, the seam to be covered shall be ground flush and 100% RT examined for the covered area plus a 50 mm length either side.
    RT for butt weld seam in shell in accordance with approved dwg.

Ultrasonic examination (UT)

  • When the UT of weld specified, The weld shall be examined by UT in accordance with ASME
    Sec VIII, Div.1, Appendix 12 and project specification.

Magnetic particle examination (MT) / Liquid penetrant examination (PT)

  • The MT shall be conducted in accordance with ASME Sec VIII, Div.1, appendix 6/8 and ASME
    Sec. V, article 7/6 and project specification.

  • Formed Head knuckle part surfaces

  • Pressure retaining welds.

  • Temporary attachment removed area & Arc strike removed area.

  • Attachment welds.(In/External).

Dear friend,
Regarding to formed head inspection as you are mentioning
"*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"
    Is there any reference in ASME sec VIII as to when NDE is to be carried out?

Thank you!

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Hello Anh @Thinh.seapts,

That are extract from specification to ITP and additional requirement to subcontractor who formed the head [UCS-79 (f)]

When vessel shell sections, heads, and other pres-
sure boundary parts of carbon and low alloy steel are cold
formed by other than the Manufacturer of the vessel, the
required certification for the part shall indicate if the part
has been heat treated per the requirements of UCS-79.