Welding Inspection

Materials, Fabrication Stages

Material

All the materials used in the construction of a pressure vessel shall be identified to the relevant specification.

All the materials used in any pressure vessel shall conform to the specifications as given in drawing.

Material to a specification shall have a manufacturer’s test certificate and marking and/or stamping as mentioned in test certificate.

Carbon percentage shall be less than or equal to 0.25% for pressure parts.

No negative tolerance on plate thickness.

In the absence of mill test certificate, check testing shall be carried out in agreement with the inspecting authority. Check testing normally will be allowed only in the case of structural quality material and pipes and tubes of certain grades. Boiler quality material will be accepted only against mill marking and mill T.C.

Carbon steel Dished end material shall be of low sulfur (0.01% max.) if the dished is undergoing Spinning after Cold Pressing.

Fabrication

When plates are shaped by oxygen or arc cutting, the edges to be welded shall be free of all loose scale and slag accumulations before welding.

The surfaces to be welded and 25mm on both sides shall be clean free of scale, rust, oil, grease, slag, detrimental oxides and other deleterious foreign material.

End of nozzles or manhole necks which are to remain un welded in the completed vessel may be cut by shearing, but exposed inside edges shall be chamfered or rounded.

Tack welds used to secure alignment shall either be removed completely when they have served their purpose or their stopping and starting ends shall be properly prepared by grinding or other suitable means so that they may be satisfactorily incorporated into the final weld.

Butt-welded joints shall have complete penetration and full fusion.

All welded surfaces are acceptable provided the surface is free from coarse ripples, grooves, overlaps and ridges and valleys to permit proper interpretation of non destructive examinations.

In making fillet welds, the weld metal shall be deposited in such a way that adequate penetration into the base metal at the root of the weld is secured.

Fillet welds should have adequate root and side wall fusion. The legs of fillet welds should be equal and its profile somewhat concave rather than convex.

In butt welds root run should be chipped back to sound metal before welding on the reverse side. In multi pass welding de- slagging after each pass is necessary.

Butt welds should neither be under-flush nor with excessive reinforcement. Arc strikes, undercuts, porosity, slag and surface cracks are not acceptable.

Spatters should be avoided.

Longitudinal seams should be welded prior to circumferential seams, Run on and run off plates attached at both ends of long seams will avoid defective weldments at these ends.

All surfaces of parent metals should be dressed free from injury and blemishes.

Temporary welded hooks should be chipped off (not hammered out), and the area ground and DP checked for flaws.

All plates for shell sections and for heads shall be formed to the required shape by any process that will not unduly impair the physical properties of the material. Local hammering is not permitted.

If the plates are to be rolled, the adjoining edges of longitudinal joints of cylindrical vessels shall first be shaped to the proper curvature by preliminary rolling or forming in order to avoid having objectionable flat spots along the completed joints.

When non pressure parts such as lugs, bracket saddles, etc. extend over pressure refraining parts, such welds shall be ground flush and DP tested before further attachments. Or such parts shall be notched to clear those welds.

All Sharp edges shall be round off at the time of full welding, so as to take care of Aesthetics & to improve the life of applied coating

Welding inspector’s responsibilities

Interpret all welding drawings and specifications

Check PO to assure that the welding materials and consumables have been properly specified.

Check and identify materials as they are received against PO specs.

Ensure use of Calibrated Instrument during all Inspection.

During inspection insist on availability of following documents before Inspection

WTS/ Welder History Certificates & Process to be used

Purchase Order for the particular Job.

Requirements of Hold points, Extent of Inspection

Material Control Requirement

Drawing availability

Follow the Quality Assurance Plan Cum Route sheets / Quality Assurance Check Sheet for Further instructions & hold Points

Check the Chemical & Mechanical properties reported on the Mill TCs.

Investigate Base metals imperfections and deviations.

Check Storage of Filler metals.

Check equipment to be used

Check weld joint preparations

Check joint fit-up

Verify the application of approved & correct WPS

Verify the qualification of the welder/welding operator

Select production test samples

Evaluate the test results

Maintain records

Prepare reports

Intermediate Stress Relieving

To relieve stresses induced due to rolling.

To be done prior to longitudinal welding.

Shall be done if the ratio of plate thickness (t) to internal diameter (I.D) of shell [i.e. I.D/t ratio] is less than or equal to 20 for Carbon steel & 36 for Alloy steel.

Stage Offering

RAW MATERIALS

PLATES/PIPES/TUBES

Check surface visually for surface defects like pitting, dents, ditches etc.

Check original identification marking by the manufacturer.

Correlate markings with original Test Certificate.

Check thickness of plate/pipe (on all four sides for plates).

If original T.C. is not available then carry out check testing for physical and chemical properties in consultation with inspecting authority.

FORGED FLANGES

Correlate original marking with original Test Certificate.

Check for pressure rating as per Test Certificate and punching.

Check dimensions as per relevant standard

Check serration for any damages.

BEND/TEE/OTHER FITTINGS

Correlate original marking with original Test Certificate.

Check dimensions and thinning. Minimum thickness should be as per drawing.

HARDWARE

Inspect for original marking of manufacturer on each nut and bolt.

Check visually for cracks and dimensions.

DISHED ENDS

DISHED END BLANK SETUP AND WELDING

Blank diameter

Joint dimensions

Back chipping and P.T. and R.T. of complete weld

DISHED END - INSPECTION AT SOURCE

Check template on layout.

Check crown radius, knuckle radius, over crowning with template.

Check dimensions (OD/ID, Straight face and Height).

Check circumference. Circumference shall match with shell circumference.

Check for minimum thickness.

Knuckle radius shall not be less than specified.

Carry out P.T. test on inside and outside of knuckle area to ensure freedom from cracks.

Review H.T. chart.

For IBR review form III A.

TUBE PLATES

Check for dimensions (Diameter, Thickness) and No. of holes.

Check hole dimensions with ‘GO/NO GO’ gauge.

Tube hole groove dimensions.

Check Min. ligament width as per drawing.

SHELL LONGITUDINAL SEAM SETUP AND WELDING

Check welds edge/bevel preparation.

In setup check root gap and offset.

Profile using template Circumference at two ends

Long seam back chip P.T

Check for NDT reports for rework & documents for same

Check for Punching on Shell at all the Stages of inspection

Check for Run-in, Run-off Plate Dress-up

Check for Stress Reliving of Pressure Part as per Code & accordingly send test plate for Stress Reliving/Testing.

SHELL CIRCUMFERENTIAL SEAM SETUP AND WELDING

Check welds edge/bevel preparation.

Joint alignment

Total shell alignment (straightness).

Staggering of longitudinal weld seams & Orientation of Long Seam

NDT clearance of Long seams

Visual Inspection of Tack welds

Cir. seam back chip P.T

DISHED END TO SHELL SETUP AND WELDING

Check welds preparation.

Joint alignment

Dished end to shell back chip P.T

NOZZLES

Nozzle marking - Check orientation and elevation as per drawing

Nozzle setup - Check nozzle schedule, flange rating and weld preparation, PT of Tack welds.

Check Nozzle setup for Squareness.

NOZZLES TO SHELL SETUP AND WELDING

Check Squareness and height.

Check welds preparation.

Nozzle to shell back chip P.T. when both side welded

Check for back chipping of Nozzle from i/s for full penetration Nozzles

Check for Nozzle Radius & Flush grinding for Safety Valve Nozzle, Air Vent &

Blow down Connection

Check for Plumb of Nozzle, including the Mobrey & Gauge glass connection in CGG.

Check for all Stiffeners for Distortion & are at place.

TUBE TO TUBE PLATE SETUP AND WELDING

First conduct a mock-up test to establish torque for expansion and welding parameters.

Tube to Tube plate fit up and Tube projection

Tube to Tube plate joint preparation

Tube Expansion verification, Inspection of tube bunch for Undercuts, Tube Cuts, Burnout edges etc.

TUBE PLATE TO SHELL SETUP AND WELDING

Check welds groove dimensions.

Check fit up and alignment and orientation.

Tube insertion - to verify alignment of tube plates

Penetration of weld

Check the Gusset Setups & Check for Punching & Inspector’s stamp on that

Check for Tube plate distortion after welding

Check for Inspector’s Stamp & Punching on Tube Plate.

COMPENSATING PADS

Check curvature of pads to conform reasonably to the curvature of the shell or surface to which they are attached.

Pads shall be provided with a Tell-Tale hole.

Pneumatic testing of pads at 1.25 kg/cm2

Verify Pad Thickness as per requirement

Verify Pad for Punching Details & Inspector’s Stamp

Non Destructive Testing

All NDE Shall be Carried Out as per Relevant Code of Manufacturing.

Stress Relieving

Before Sending to Stress Reliving Check the Pressure part for Welding sufficiency like fillet weld size, weld reinforcement size etc. using templates for Correct Fillet Gauge Use & Details

When the vessel requires stress relieving, rules regarding loading temp., heating rate, soaking temp. And soaking time and cooling rate as per the applicable code shall be observed.

The Pressure part will be water leveled to check the plumb of Pressure part in all direction and at various places like Nozzle Connection, Top & Bottom Line.

Pressure Testing

Hydro test shall be conducted after all fabrication has been completed.

Hydro test shall be conducted at a pressure equal to 1.5times maximum allowable working pressure or as specified in relevant Code of Manufacturing.

The pressure shall be maintained for a period of 30mins. When pressurized.

Pressure gauges shall be with valid calibration status and checked for accuracy after the tests.

Pneumatic test in lieu of Hydro test may be carried out when the vessels are so designed and/or supported that they cannot be filled safely with water or in services where traces of the testing liquid cannot be tolerated.

The Pneumatic test pressure shall be at least equal to 1.25 times the maximum allowable working pressure. Safety precaution shall be taken while carrying out pneumatic test.

Final Inspection

After completion of Hydro test the vessel shall be drained and inside surfaces shall be dried (with compressed air if possible).

The outside surfaces shall be painted as per painting manual.

The overall dimensions of the vessel shall be checked and recorded.

Before dispatch, check for all loose items which are available and to be send loose.

Chemical shall be incorporated so as to avoid future Rusting inside the vessel.

All documents shall be reviewed and placed in the Folder and store it safe for Next 03 years or as per Specific Code requirement.

Check for Center line marking on Pressure part (if not Insulated).

Do the mock up assembly of external attachments on pressure part, so as to check & rectify the miss-alignment.