Comprehensive Quality Control Plan for Pressure Vessels: Working Guidelines
QUALITY PLAN FOR PRESSURE VESSELS: A STEP-BY-STEP WORKING GUIDELINES
Explore our detailed blog on implementing a robust Quality
Control Plan for pressure vessels. From design control to hydraulic pressure
testing, our step-by-step approach ensures every stage of the fabrication
process adheres to industry standards. Learn about material inspection, welding
procedures, in-process quality checks, post-weld heat treatment, and thorough
documentation practices. Ensure your pressure vessels meet safety and
compliance requirements with our comprehensive guidelines. Perfect for engineers,
quality control professionals, and manufacturers in the pressure vessel
industry. Stay compliant, enhance safety, and maintain the highest quality
standards in your pressure vessel projects.
"QUALITY IS NOT AN ACCIDENT IT IS THE RESULT OF AN
INTELLIGENT EFFORT" - John Ruskin
Prior to commencing any fabrication work, it is well to
bear in mind that manufacturing should be a planned exercise, and that no
experiments should be done on the job. A work procedure should be drawn out in
advance, detailing proposals for the method of work, for the method of
measurement thereof, expected or acceptable results, the proposed
documentation, and feedback for review. This is even more necessary for
pressure vessels and such equipment.
Accordingly, it is suggested that a Quality Plan detailing
design features, manufacturing controls and stage wise quality checks (in
sequence with the production stages) should be drawn out in advance. Based on
this inspection checklist indicating hold points for internal QC and for
third-party Authorized Inspector (AI) should be submitted for the approval of
AI before commencing manufacturing activities.
1.0 DESIGN CONTROL
1.1 Ensure latest revised and approved drawings are used
for inspection.
2.0 MATERIALS CONTROL (At Receipt Inspection Stage)
2.1 PLATES, PIPES & TUBES
2.2 FLANGES & FITTINGS
2.2.1 Shall be inspected along with their Test Certificates
and Purchase Order requirements and correlated with markings on flanges and
fittings.
2.2.2 Shall be inspected for their Rating and size -
Thickness, diameters, P.C.D., Number of holes, hole size, dimensions of mating
surfaces, bore diameter, height of hub. Also edge preparation, wall thickness
and I.D. at weld neck.
2.2.3 Surfaces shall be inspected for flaws or
irregularities.
2.2.4 All fittings shall be checked for hardness
properties.
2.3 FORMED ENDS
2.3.1 Template for form shall be checked on a layout as per
drawing.
2.3.2 Form shall be inspected by the pre-checked template.
Under crowning is not permitted. Over crowning is permitted to a maximum of
1.25% of inner diameter of dished end.
2.3.3 Check ovality. Maximum permissible is 1% of I.D.
2.3.4 Check circumference, inner/outer and note down.
Maximum permissible deviation is 1/4% of nominal circumference or up to 19 mm
maximum.
2.3.5 Check edges for laminations and weld preparation.
2.3.6 Check minimum thickness at S.F. knuckle and crown
(straight face).
2.3.7 Check straight face length and total height (depth)
of the dished end.
2.3.8 Inspect surface from the inside as well as the
outside, for blemishes if any.
2.3.9 Dye check or MPI on the prepared edge and the knuckle
area from the outside.
2.3.10 Scrutinize H.T. chart if heat treatment is called
for. Ensure that the requirements of UCS-79(d) of ASME VIII Division 1 or its
equivalent code are complied with.
2.3.11 If the dished end has a weld seam, the same has to
be radiographed and accepted prior to forming as well as after forming.
3.0 WELDING CONTROL
3.1 It is common to write down a comprehensive Welding
Procedure Specification conforming to applicable code of practice and general
good Engineering practices. In some cases, a mock-up test needs to be conducted
to prove that the proposed welding procedure will yield sound weldments.
3.2 Broadly speaking there are seven major welding
variables.
These are:
a) Welding Process/es
b) Parent Material Specifications (Weldability/Group/Type)
c) Parent Material Thickness (also diameter, Scantlings)
d) Welding consumables (Type, chemistry, compatibility)
e) Preheat, interpass, post heat etc., affecting weld
restraint, cooling rates
f) Post Weld Heat Treatment
g) Notch Toughness properties at reference temperature
Based on the above, applicable code of practice and
customer’s special requirements, suitable WPSs should be prepared and submitted
for approval of Authorised Inspector (AI).
3.3 Training of Personnel
Shall be undertaken at least six weeks prior to commencing
of actual fabrication on the job.
3.4 Test Plates for W.P.S. & W.P.Q’s:
Raw material (plates & pipes of required thickness,
diameter schedule and material specifications) shall be procured on top
priority receipt of order in anticipation of obtaining the order. M.T.O.s
(Material Take off) by Engineering and Design Department should ensure this for
guidance of Material Department.
3.5 Welding Consumables
Approved consumables shall be ordered on top priority
basis. Where batch testing is required, AI/QC shall be involved at Consumable
Manufacturer’s Works in such testing.
3.6 Welding Procedure Specifications
WPSs approved by Customer or his Consultant shall be
submitted for A.I.'s approval.
3.7 Approval of PQR’S and WPQ's
Shall be obtained from A.I. after satisfactory conclusion
of relevant tests duly Witnessed and results found acceptable by A.I.
3.8 Only approved WPS's and WPQ's shall be employed on
respective jobs. This shall be monitored by patrolling QC and Welding
Engineers.
3.9 Records
Records of approved PQRs shall be available on shopfloor
and at sites.
4.0 IN PROCESS QUALITY CONTROL:
4.1 Longitudinal Seam Set up
4.1.1 Check identification mark and A.I.'s stamp.
4.1.2 Check misalignment, if any, at the welding edges.
4.1.3 Check circumference and length of shell. Check
whether circumference matches with corresponding shell or dished end.
4.1.4 Check ovality of shell
((𝐷𝑚𝑎𝑥−𝐷𝑚𝑖𝑛)/(Dnim))
x 100 is less than 1%
Dmax−Dmin / D nom x 100 < 1%
4.1.5 Check edge preparation for bevel angle, root gap, and
cleanliness of preparation and plate surfaces approximately 50 mm either side.
4.1.6 Check all edges for laminations.
4.1.7 Check shell surfaces for flaws.
4.1.8 Ensure run-in and run-out plates are attached along
the length of long seams.
4.1.9 Ensure production coupon plates are attached, if
called for.
4.1.10 Inspect tack welds.
4.1.11 Mark 90-degree orientation around the circumference
of the shell and elevation reference marks 100 mm from each edge.
4.2 Circumferential Seam Setup:
4.2.1 Same as longitudinal seam except for:
4.2.2 Check production coupon plate is tested and accepted.
4.2.3 Check straightness (alignment) of shell courses at 0
degrees, 120 degrees, and 240 degrees orientation.
4.2.4 Check staggering of longitudinal weld seams as per
drawing.
4.2.5 Check orientation of degree markings.
4.2.6 Check long seam radiography is completed and cleared.
4.3 Back Chips at Root of the Weld on the
Opposite Side:
4.3.1 Check that the grinding is smooth.
4.3.2 Inspect for slag inclusions, cracks, porosity, etc.
4.3.3 Check included angle.
4.3.4 Check D.P./M.P.I. is carried out in the required
manner.
4.4 Markings on Vessel for Cutting:
4.4.1 All markings on the shell are to be checked by the
Q.C. inspector prior to cutting.
4.4.2 Check orientation of shell markings i.e., 0 degrees,
90 degrees, 180 degrees, and 270 degrees.
4.4.3 Check orientation of nozzle opening markings with
reference to markings on the shell.
4.4.4 Check elevation of nozzle openings from Tanline or
reference mark from one end of the vessel.
4.4.5 Check diameters of openings.
4.5 Nozzle Sub-Assembly Fit-Up:
4.5.1 Check material specifications, size, schedule, etc.
as per drawing.
4.5.2 Check identification on pipe and check flange size
and rating as per drawing.
4.5.3 Check weld geometry.
4.5.4 Ensure that the gasket faces are protected against
damage.
4.5.5 Check trueness of pipe with respect to flange. (This
is also to be checked after full welding).
4.6 Nozzle Fit-Up on Shell:
4.6.1 Edges of all openings cut in the vessel shall be
inspected for laminations prior to nozzle setup. If D.P. is called for, then
this has to be witnessed and approved by A.I.
4.6.2 Check weld geometry as per drawing.
4.6.3 Ensure reinforcing pads are in place, where called
for. Check that tell-tale hole is drilled and tapped on reinforcing pad. Check
width and thickness, and material specification of the reinforcing pad are as
per approved drawing.
4.6.4 Check orientation, elevation, and stand-off height
with reference to shell markings.
4.6.5 Check for cleanliness of the edges.
4.6.6 Check that the bolt holes of flanges are straddling
main centre lines of vessel.
4.6.7 If nozzle is inclined as per drawing, the inclination
of the nozzle shall be checked by template, which in turn shall be checked on
layout.
4.6.8 Chip back to sound metal if necessary prior to
welding on the opposite side.
5.0 INSPECTION PRIOR TO HEAT TREATMENT (P.W.H.T)
5.1 Ensure that welding is completed in all respects on the vessel.
5.2 Check all weld for imperfections, notches,
reinforcements, under-cuts etc.
5.3 Check all fillet welds for sizes as per drawing.
5.4 Carryout complete dimensional check of the vessel
including orientations.
5.5 Ensure that all N.D.T. has been previously completed
and cleared by A.I.
5.6 All nozzles which are required to be flush ground from
the inside, shall have their edges rounded off to a radius of 3 mm.
5.7 All such flush ground nozzles should be Dye checked
from the inside.
5.8 All nozzle reinforcing pads should be air tested.
5.9 Internal and external surfaces are to be inspected for
arc strikes, indentations, spatter, lifting cleat marks etc. as well as
undercuts and under flush of Welds. Check and ensure fillet weld sizes are
correct.
5.10 Repairs/rectifications if any, are to be completed to
A.I.’s satisfaction.
6.0 POST WELD HEAT TREATMENT:
6.1 PWHT should meet all the requirements set forth in
UCS-56 of ASME Sec. VIII Div.1/ or applicable code of practice.
6.2 Check that the thermocouples and the recorders are
calibrated to A.I.'s satisfaction.
6.3 Ensure that the parameters like rate of heating,
Soaking temperature, Soaking time and the rate of cooling are as per the PQR,
and approved by A.I.
6.4 Prior to P.W.H.T ensure that A.I. has signed the Heat
Treatment Chart. Ensure that the equipment is properly supported, and
(previously calibrated) thermocouples are firmly attached to the skin of the
vessel.
6.5 The Heat Treatment chart shall be signed and approved
by the A.I. after heat treatment is completed.
7.0 HYDRAULIC PRESSURE TEST
7.1 Hydraulic Pressure test shall be witnessed and approved
by the A.I.
7.2 Ensure that the vessel /equipment is adequately
supported. If necessary, spacing of supports shall be verified with Engineering and
Design Department.
7.3 Pressure gauges shall preferably have dials graduated
over a range of double the intended test pressure but in no case shall the
range be less than 1.5 times nor over 2.5 times that pressure.
7.4 Vents shall be provided at all high points of the
vessel in the position in which it is to be tested to purge possible air
pockets while the vessel is being filled. Leakages at flanges, gaskets, socket
plugs, etc., shall be eliminated prior to commencing pressure test.
7.5 The hydrostatic test pressure shall be as per the
drawing. (Usually 1.5 times the Design pressure) The pressure shall be
maintained for approximately 30 minutes.
7.6 Following the application of the hydrostatic test
pressure an examination shall be made of all weld seams, joints and
connections, to look for leakages if any. Drop in pressure shall merit further
purging of air, or detection of possible leakage/s. Increase in pressure owing
to warming up to ambient temperature is not uncommon and may be considered a
healthier sign.
7.7 In case of leakage/s detected, rectification thereof
and Retest are the next course of action.
8.0 STAMPING FOR IDENTIFICATION
All Vessels shall be hard stamped for permanent
identification on one of the manway rims (preferably) by the QC and approved
flanges the specified code by the third party Authorized Inspector as per requirements.
9.0 DOCUMENTATION
9.1 Final documentation of the vessel/equipment shall be
furnished by QC and approved by the A.I. ( Authorized Inspector) for submission to the client.
9.2 Documentation shall consist of, but not limited to, the
following:
a) Design features
b) Material Chart / Material history chart (item-wise)
c) Statement that "Under noted qualified WPSs (Welding Procedure Specification) and WPQs (Welder Performance Qualification) were
used"
d) Copies of approved POR's (Procedure Qualification
Record) and WPQ's
e) A sketch of the vessel, highlighting the heat numbers of
the materials used in the fabrication of the equipment for all parts, and the
weld seams subjected to NDT.
f) Copies of test certificates of all materials used in
construction.
g) A "Rub off" of the stamping details after the
A.I. stamps it for acceptance.
h) Report of hydrostatic test signed by A.I.
i) Heat Treatment Certificates with charts.
j) NDT Report in detail.
k) Final Inspection Report and Release Note signed by the
A.I.
Thanks for Reading !
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