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Inspection And Testing

Inspection And Testing

 

In this article we will learn about inspection and Testing of the pressure vessels in detail as per IS 2825 set by the Bureau Of Indian Standard:

GENERAL:

 

  • The inspection shall be made at the various stages of construction depending on the type of the vessel.
  • The manufacturer shall keep the purchaser and/or the inspecting authority informed of the progress of the work and shall notify the inspector reasonably in advance when the vessel has reached the required stage for inspection.

1) Inspection During Manufacture

  • All materials to be utilized for pressure portions of vessels will be assessed before manufacture to identify absconds which may influence the safety of the vessel.
  • Special attention shall be paid to the cut edges and other parts of rolled material which may disclose the existence of serious laminations, shearing cracks, and other objectionable defects.
  • Defects shall not be repaired unless inspected and approved by the inspecting authority.
  • Material which in the inspecting authority sentiment can’t be sufficiently fixed will be esteemed not to agree to the necessities of this code.

Identification of Materials

  • The inspector will guarantee that all material before use is appropriately distinguished as agreeing to the code necessities.
  • Mill certificates or other test certificates to the satisfaction of the inspecting authority shall be produced to identify the material,
  • The manufacturer’s identification marks should not be obliterated during manufacture.

Where necessary the marks shall be transferred in the presence of the inspector.

Steel plate less than 7 mm thick or non-ferrous plate less than 12 mm thick shall not be deep die-stamped and the depth of stamping shall not exceed 0.5 mm.

  • The inspector shall witness the marking of, and place his stamp on portions of the parent plate intended to be used as test plates for seams.

The mark should be so located that it will not be cut out or obliterated during fabrication.

Inspection During Fabrication

Following are the important inspection aspects to be kept in mind while inspection:

i) The quality inspector will make examinations of every vessel at such phases of manufacture as he esteems important to guarantee himself that the creation is as indicated by code necessities.

ii) The edges of plates, openings, and fittings exposed during manufacture shall be examined for defects.

iii) Before getting together, all shell areas, closes, rings, and so on, will be analyzed for adjustment to endorsed shape and checked for thickness and measurements.

iv) The parts of the vessel shall be assembled and checked for alignment of matching edges.

Special attention shall be paid to the assembly of branches and their reinforcement.

v) When conditions permit entry into the vessel, as complete an examination as possible shall be made before the final closure.

 

Heat Treatment Check

– The inspector will fulfill himself that stress soothing procedure or other heat treatment, has been accurately completed.

Inspection of Completed Pressure Vessels

We will learn about the various methods of inspection of the Pressure Vessels:

1) Visual inspection

During the final inspection of the whole vessel, the surfaces of the welds are to be inspected visually and judged by the inspection authorities for final approval of quality.

If irregularities are found, rectification shall be carried out.

2) Records: of manufacturing details, inspection and tests shall be kept by the manufacturer and shall be available for the inspecting authority for examination, whenever required.

The manufacturer shall furnish a certificate of manufacture and production tests when requested.

3) Radiographic Examination

Radiographic examination of welded joints shall be carried out in the instances Where so required by the inspecting authority the results of the radiographic examination shall be made available to him at the manufacturer’s works.

All austenitic chromium-nickel alloy steel welds in vessels whose shell thickness exceeds 20 mm, shall be examined for cracks by a suitable fluid penetration method.

4) Pressure Test

The finished vessel shall, in the presence of the inspecting authority, pass satisfactorily such of the following pressure tests as may apply:

a) Standard hydrostatic test – This test is used for simple vessels where the thickness of all pressure parts can be calculated.

b) Proof hydrostatic tests

This test is carried out for complex vessels.

The thickness of which can’t be processed with a palatable confirmation of precision and for which the most extreme working pressure must be founded on the mutilation pressure.

c) Pneumatic tests

This test is used for vessels that are so designed and/ or supported that they cannot be safely filled with the testing liquid.

This type of test is used when vessels are to be used in services where even small traces of the testing liquid cannot be tolerated.

Pressure vessels in mellow or low-compound prepare intended for inward pressure will be exposed to a water-driven test pressure, which at each point in the vessel is in any event equivalent

D) to l-3 times the design pressure to be marked on the vessel multiplied by the lowest ratio of the allowable stress values f1 of the material of construction at the test temperature to the allowable stress value f2 at the design temperature.

Test pressure in kgf/cm2 = l.3 x design pressure

  • The test pressure specified includes the amount of any static head acting at the point under consideration.
  • If the weakest part of the vessel is not located at the lowest point of the vessel, it may be necessary to give special consideration to the effect of such an additional static head due to the test liquid.
  1. E) Vessels consisting of more than one independent pressure chamber operating at the same or different pressures and temperatures shall be so rested that each pressure chamber ( vessel ) receives the required hydraulic test with pressure in the others.

NOTE:

It is important in the interest of safety that the vessel is properly vented to prevent the formation of air pockets before the test pressure is applied. It is recommended that during the test the temperature of the water should not be below 15°C.

  • A hydraulic test based on a calculated pressure may be used by agreement between the purchaser and the manufacturer.
  • The vessel shall be maintained at the specified test pressure for a sufficient length of time to permit a thorough examination to be made of all seams and joints but in no case less than 10 minutes.

Whilst under pressure, the vessel to be well hammered on both sides of and close to the welded seams.

A Hammer test is not required for vessels fabricated from materials which will be deleteriously affected by hammering and where the longitudinal and circumferential seams have been radiographed.

Single wall vessels and chambers of multi-chamber vessels designed for vacuum or partial vacuum only shall be subject to an internal hydraulic test.

Pressure should not be less than l-3 times the difference between normal atmospheric pressure and the minimum design internal absolute pressure but in no case less than l.5 kg/cm2.

In the case of jacketed vessels when the inner vessel is designed to operate at atmospheric pressure or under vacuum conditions, the test pressure need only be applied to the jacket space.

5) Pneumatic Tests

  • Pressure testing with air or gas may be carried out in place of the standard hydraulic test in the following cases:a) Vessels that are so designed, constructed, or supported that they cannot safely be filled with water or liquid.b) Vessels that are to be used in services where even small traces of water cannot be tolerated.

Such a pneumatic pressure test shall be carried out under close supervision by the inspecting authority.

Adequate precautions, such as blast walls or pits and means for remote observation are essential.

The pneumatic test pressure shall not be less than the design pressure but need not exceed test pressure in a hydraulic test.

Procedure

  • The pressure will bit by bit be expanded to not in excess of 50 percent of the test pressure.
  • From that point, the pressure will be expanded in steps of roughly 10 percent of the test pressure till the necessary test pressure is reached.
  • At that point, the pressure will be decreased to the estimation of the comparable design pressure and held at the pressure for adequate time to allow inspection of the vessel.

Combined Hydrostatic Pneumatic Test

In some cases, it may be desirable to pneumatically test a vessel partially filled with liquid.

In such cases a pneumatic test may be applied to space above the liquid level, the pneumatic test pressure is as required by the purchaser. Less will be the pressure due to the static head of the liquid contained.

  • When pressure testing of small, mass-produced pressure vessels, the length of time for which the test pressure is to be maintained may be reduced upon agreement with the inspecting authority in each case.
6) Mechanical Tests of Fusion Welded Seams

Fusion-welded seams shall satisfy the following mechanical tests:

 

  • Vessels exposed to extreme obligation or with a weld joint efficiency factor J = 0.9 to 1.0 will be given two test plates to speak to the welding of all the longitudinal creases of the initial six shells or part thereof.
  • Vessels with in excess of six shells will have a test plate for each third extra shell or part thereof.
  • No test plate need be provided for circumferential seams except in cases where a pressure vessel has circumferential seams only.
  • If the welding process, procedure, and technique are different in that case two test plates are to be provided, each having a joint as far as possible duplication of the circumferential seam.

5.1.1) Test plates shall be attached at one end of the longitudinal seam in such a manner that the edges to be welded are in continuation and duplication of the corresponding edges of the seam.

Welding shall be effected in one reasonably continuous operation by the same process and the operator or operators.

The location of test plates shall be as agreed to between the inspecting authority and the manufacturer.

5.1.2)

Test plates shall be of a size sufficient for the preparation of all the production test specimens and should include provisions for re-tests if any tests fail.

5.1.3) Welding test plates will make provisions for the following:

a) One all-weld metal tensile test.

b) One reduced section tensile test specimen cut transversely to the weld or as many specimens as are necessary to investigate the tensile strength over the whole thickness of the joint.

c) Two bend test specimens, one for direct and one for reverse bending, to be taken transversely to the weld, and where the thickness of the plate permits, one shall be above the other.

When the thickness of the plate exceeds 30 mm, face bend and root bend tests may be substituted by side bend tests.

When welds are made from one side only, one bend test may be a side bend test but at least one shall be a normal bend test with the root of the weld in tension.

d) Three notched bar impact test specimens, to be taken transversely to the weld as near as possible to the face side of the last pass of the weld on the outer and inner plate surface.

5.2)  Vessels exposed to medium obligation or with a weld joint efficiency factor J = 0.8 to 0.85 will be given two test plates.

5.2.1)   Test plates shall make provision for the following:

a) One reduced section tensile test specimen cut transversely to the weld or as many specimens as are necessary to investigate the tensile strength over the whole thickness of the joint.

b) Two bend test specimens, one for direct and one for reverse bending to be taken transversely to the weld, and where the thickness of the plate permits, one shall be above the other.

Where the plate thickness exceeds 30 mm, face bend and root bend tests may be substituted by side bend tests.

When welds are made from one side only, one bend test may be a side bend test but at least one shall be a normal bend test with the root of the weld in tension.

c) One nick break test specimen shall be cut transversely to the welded seam. It shall be the full thickness of the plate.

5.3) All conditions for the actual workpiece and test plate shall be similar.

5.3.1) The material of the welded production test plate shall be of the same specification and the same nominal thickness as that of the workpiece.

It may be taken from any part of one or more plates of the same lot of material that is used in the fabrication of the welded vessel.

5.4) The test plate shall be supported or reinforced during welding to prevent undue wrapping and distortion during welding.

Non-destructive Examination and Repairs of Welded Seams

The following are the non-destructive tests which can be performed:

1) Radiography

It covers the radiographic assessment of all longitudinal and circumferential butt welds in drums, shells, and headers all through their entire length incorporating purposes of crossing point with different joints.

1.1) For circumferential butt welds in extruded connections, pipes, tubes, headers, and other tubular parts:

a) No radiographic examination is required where the thickness does not exceed 6 mm.

b) No radiographic examination is required where the thickness is greater than 6 mm but does not exceed 12 mm and the outside diameter does not exceed 102 mm.

1.2) If the results of the examination of check radiographs of the selected welds are not satisfactory, the cause shall be investigated and, if considered necessary, the percentage of radiographic inspection increased by agreement between the manufacturer and the inspecting authority.

1.3) Protection of personnel

All persons exposed to X or gamma rays and engaged in radiographic work shall be suitably shielded against direct and scattered radiations.

Other Non-destructive Testing  –

When special conditions make it expedient, radiography, as specified in standard code, may be replaced by other non-destructive testing methods, for example,

  • dye penetrant,
  • Magnetic or ultrasonic testing techniques upon past assent of the investigating authority and on the condition that such testing methods may be considered to render an equally safe evaluation of the quality of the welding work.
  • Magnetic or ultrasonic testing techniques upon past assent of the investigating authority,
  • Magnetic or ultrasonic testing techniques upon past assent of the investigating authority,
  • Such non-damaging testing strategies may likewise be utilized to determine the nature of welds, where radiography can’t be effortlessly utilized as on account of fillet and butt welds on branches and fittings.
2) Re-examination of repaired joints

 

a) Welded joints or parts thereof, which do not show the quality required, shall be repaired.

After such repairs, the parts in the question of the welded joints shall be subjected to renewed radiographic examination and shall meet the requirements.

b) If any part of a welded joint, which has been subjected to Radiography, or which has been examined at the points of intersection with other joints does not show the quality required, an additional radiographic examination shall be carried out in the following manner:

-On each side of and in immediate extension of that part of the welded joint, where the radiograph was previously located, one additional radiograph shall be made.

These radiographs should be no shorter than 250 mm unless this is necessitated by the shape of the joint.

If the first radiograph has been made at a point of intersection or on a welded joint ending in this point, only one radiograph is to be made in the extension of the first one.

Should special conditions make it expedient, the inspecting authority has the right to modify the location of such additional radiographs.

  • All parts of the welded joints, which do not meet the requirements stated under shall be repaired and re-examined after repair.
  •  No repairs shall be carried out after the radiographic examination without the prior consent of the inspecting authority.
  •  Radiographic films shall be preserved by the manufacturer for at least five years after the acceptance of the films.
3) MARKING AND RECORDS

1) All vessels built under this code shall conform to the provisions of this code in every detail and shall be distinctly stamped and certified.

A) Marking:

A.1) Each pressure vessel shall have stamped upon its front plate in a conspicuous position the following particulars:

Manufacturer’s name

Manufacturer’s Serial No

Year built

Max W.P . . . . . . . . . . . . . . . . . . . at Temp . . . . . . . . . . . . . . . . degree Celcius.

IS 2825                                        FR/PR/SR

Hydraulic pneumatic test pressure

Date of test

Inspecting authority’s official stamp

A.2) The figures and letters of the stamping shall be at least 8 mm high when stamped directly on the vessel or 4 mm high when stamped on a permanently attached name-plate.

The figures and letters shall be legible and stamped fully into the plate.

Deep stamping shall be avoided when stamped directly on the vessel.

A.3) Stamping of vessels may be made directly on the vessel or may be stamped on a permanently attached name-plate so fixed as not to be covered by lagging or insulation.

Permanently attached name-plates shall be used on all vessels of steel plate less than 7 mm thick.

4) The Following are the two arrangements that can be used in marking vessels having two or more independent pressure chambers designed for the same or different operating conditions.

  • Each detachable chamber shall be marked to identify it positively with the combined unit:

a) The marking may be grouped in one location on the vessel, provided it is arranged to indicate the data applicable to each chamber.

b) The complete required marking may be applied to each independent pressure chamber, provided additional marking, such as stock space, jacket, tube-nest, or channel box is used to indicate clearly to which chamber the data apply.

4.2) Removable pressure parts shall be permanently marked in a manner to identify them with the vessel or chamber of which they form a part. This does not apply to manhole covers, handhole covers, etc.

Certificate of Manufacture and Test
  • A certificate of manufacture and test in the form shall be filled out by the manufacturer and signed by the manufacturer or a responsible representative of the manufacturer and shall be complete with all the enclosure as per the standards.
  • The manufacturer shall issue such a certificate for every vessel fabricated by him.
Inspection And Testing

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