mp sem-8

44
CHAPTER - 1 QUALITY OF WELDMENTS 1.1 INTRODUCTION TO PROJECT For manufacturing of pressure vessel, there are main two part (1) fabrication (2) welding. But to control of dimension of vessel during the set up and after welding processes, it is very difficult. In same process, set up of nozzle on vessel within limited. It is very difficult and quality point of view and for customer satisfaction it is very important. Set up nozzle with special fixture can avoid some dimension problem and also some fixture can control distortion problem during and after welding of nozzle. Each testing of welded joint should start with the selection of a suitable testing method and determination of extent of testing. Repair and maintenance of parts and components is a major activity in any process industry. .Repair welding can be carried out as a logical procedure that ensures that part is usable and safe.

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Page 1: mp sem-8

CHAPTER - 1

QUALITY OF WELDMENTS

1.1 INTRODUCTION TO PROJECT

For manufacturing of pressure vessel, there are main two part (1) fabrication (2)

welding.

But to control of dimension of vessel during the set up and after welding processes, it

is very difficult.

In same process, set up of nozzle on vessel within limited. It is very difficult and

quality point of view and for customer satisfaction it is very important.

Set up nozzle with special fixture can avoid some dimension problem and also some

fixture can control distortion problem during and after welding of nozzle.

Each testing of welded joint should start with the selection of a suitable testing

method and determination of extent of testing.

Repair and maintenance of parts and components is a major activity in any process

industry.

.Repair welding can be carried out as a logical procedure that ensures that part is

usable and safe.

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1.2DESCRIPTION OF THE WORK PROJECT

Assembly of pipe or forging to flange is called nozzle.There are different type of set up nozzle.

• Radial nozzle• Offset nozzle• Tangential nozzle• Angular nozzle

(1) Radial nozzle: a nozzle, which is perpendicular to base of the shell or dished end lies on the orientation line is called radial nozzle.

(2) Offset nozzle: a nozzle, which is similar to radial nozzle but offset form orientation line, is called as offset nozzle.

(3) Tangential nozzle: a nozzle, which is on any tangential line of the shell, is called tangential nozzle.

(4) Angular nozzle: a nozzle, which is at an angle from the reference line, is called as angular nozzle.

Nozzle identification:-

If not specifically defined for the project, the nozzle on a vessel shell be identified as follows.

Process nozzles: N1, N2, N3 etc..Instrument nozzles: k1, k2, k3 etc.(Where multiple nozzles for a single instrument shall be identified K\A\B\C etc.)Manways: M1, M2 etc.Relief valves: RV1, RV2 etc.Vents: D1, D2 etc.Seam out connection: SOUtility connections: U

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Radial nozzles:-

Create and then position the nozzle to the correct-up coordination only p1 should point in the correct direction.i.e. E 45N.

Radial nozzle E 45N.

Create and then position in the nozzle at the correct-up coordinate and position it to an orthogonal distance the projection distance away from the equipment centreline.i.e. E 2’9. P1 should point in the orthogonal direction i.e.E

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Offset nozzle:-

If the angle option is selected in the off-set method drop down box specify the angle at which the nozzle intersects the cylinder in the nozzles offset angle(ADY) field.This value follows the left hand rule, so a negative angle rotates the nozzle about the +X axis.

1. Offset of nozzle by distance2. Offset of nozzle by angle

When the offset is 0, the nozzle is perpendicular to the vessel.

Offset of nozzle by distance offset of nozzle by angle

Angular nozzle:- By using a combination of X rotation and offset, a nozzle can be created with any

desired orientation.

(position of nozzle at angles a and b input int PV designer X rotation = a-b,

ADY=b)

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Angular nozzle

Manway

The size of a manway is usually 24”. Unless internal devices require larger size for

installation.

If the vessel diameter is 30” or less a flanged head may be considered instead of a

manway.

For mechanical reasons manway should be smaller than one half of the vessel inside

diameter.

As an alternative to manway, smaller vessels can be provide with an inspection hole,

which is normally 8”.

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Mesh density

The actual dimension of the transition region is adjusted to fit the mesh on the cylinder.

Fig. Transition mesh between nozzle and cylinder.

Key 1= nozzles on head 2=head on nozzle 3=nozzle on cylinder 4=optional raped on the cylinder 5=transition region on the cylinder

NY = distance between nozzle and end of transition region in the axial directionNX > =ratio cylinder diameterNT = distance between nozzle and end of transition region in the sweep direction.

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1.2.1 The marking of the nozzle set up is done in following steps:-

First of all the orientation marking of the nozzle on the shell is done. The elevation is marked and the radius of the nozzle is measured and

marked on the shell. The marked line is punched. The cut out of the nozzle is done. Prepare the edges of the cut out section by grinding. Then the shell is leveled and the center of the cut out is found out.

Then the elevation of the center is matched. The nozzle is inserted in the cut out and then the elevation is maintained. The level is also maintained. The orientation elevation and level of the nozzle are rechecked. The plate supports are tacked with the nozzle. The seam number of the nozzle is punched.

1.3 TECHANICAL DATA FOR REPORT

NOZZLE SETUP STAGE INSPECTION REPORT:

Client: L&T Chiyoda LTD,

Job no: M-2152,

Drg no & Rev.no: M-2152 Rev-c,

Item No: v-101A,

Description: Stripper,

Inspection by: TUV/AEL.

NOZZELS ELEVATION PROJECTION

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Nozzle no.

Size/rating

Heat no.

Reqd. Actual Reqd.from shell C.L/OD

Actual

N1 50 - 345˚ 342˚ 500mm 554mmN2 70 - 0˚ 1˚ 0 0N3 70 - 180˚ 184˚ 0 0N4 60 - 30˚ 29˚ 524mm 522mmN5 50 - 0˚ - 0 0M 80 - 0˚ 1˚ 0 0

Some dimensions are not allowable. So rectify with acceptance to given requirement . The repair set up to keep the cleat(fixture) or plate support or the moon plate.

After the repairs set up the nozzle identification.

NDT OF Weld Edge: PT/ UT/ MPTWeld edge: Vee preprationWeld edge: root gap & offset

Sizing of nozzles:-

(1) Feed inlet nozzle(2) Vapour outlet nozzle(3) Liquid outlet nozzle(4) Manway(5) Vents and drains(6) Nozzle identification

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Various inlet devices are available to improve the vapour/liquid separation. Among others the following inlet devices may be installed.

• A deflector baffle• A slotted tee distributor• A half open pipe• A 90 elbow• A tangential inlet with annular ring• A schoepentoter

Dimension check of pressure vessel:-

Tolerance for formed heads Out of roundness of shell Nozzles and attachments orientation Nozzle and attachments projection Nozzle and attachment elevation Nozzles and attachments level less Weld mismatch weld reinforce ment.

APPLICATION TO THE NOZZLE:-

• Nozzle is used for inlet or outlet connection• Used for man way• Used for hand hole • Used as pressure, temperature, and level indication• For vent connection• Fire proofing cleats• Davit assembly• Farthing, lifting and tailing lug.• Name plate bracket & name plate

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EXPECTED OUTCOME

• Level the job and set the surface speed within specified range.

• Check mounting arrangement of the spool to ensure uniform feeding.

• The limit in order to get better alignment.

• To improve dimension stability &accuracy.

• To improve material mechanical properties.

• To relieve internal stress concentration.

• To improve product reliability.

• To determine acceptance to given requirement.

• To give information on repair criteria.

• For good look of component.

• Ensure cleanness of the surface to be overlaid.

Welding Procedure Qualification (WPQ) covers

The making and testing of a welded joint, and recording of welding parameters, to prove that the following are suitable for its intended use in production:

1. Welding processes.

2. Joint type, position and preparation.

3. Parent materials.

4. Welding consumables.

5. Run sequence.

6. Welding parameters (e.g. voltage, amps, polarity, travel speed).

7. Heat treatment (preheat & PWHT as applicable).

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Welding consultation:

1. To solve welding problems and failures. 2. To select suitable materials, processes equipment. 3. To reduce the rework, scrap and wastage. 4. To increase production. 5. To obtain the qualification you need. 6. To confront shortage of good welders. 7. To improve your bottom line.

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CHAPTER-2

LITERATURE SURVEY

2.1 ABSTRACT

Pressure vessels are typically designed, fabricated, installed, inspected, and testedIn accordance with the ASME Code Section VIII. Section VIII is divided into threeSeparate divisions. This course outlines the main differences among the divisions.It then concentrates on and presents an overview of Division I. This course alsoDiscusses several relevant items that are not included in Division I

A literature survey on Quality of Weldments in Pressure Vessels is shown with detailed

description and related figures as follows:

2.2 INSPECTION AND TEST RECORDS:

Test Records

Vendor shall submit to Owner the following records for each vessel:

Material mill test certificate

Hydrostatic and pneumatic test

Dimensional inspection

Non-destructive examination

Post weld heat treatment

Welding procedure qualification

Production weld test

Other inspection and tests, where specified

Vendor shall provide the following information in the first part of all the records of

Inspection and tests:

Name of Owner (end user)

Job No., Item No., and name of vessel

Name of Vendor

Date of manufacture and inspection

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Short specification of vessel

2.3 INSPECTION AND TEST ITEMS

General

Unless otherwise specified in the Owner’s specification or drawings, the

Application of the inspection and tests for each vessel shall be as shown in the

List of inspection and test items which are provided for each classification of vessel.

Where the application of any item in the list is considered impractical, the Vendor shall

submit a suggested alternative in detail to Purchaser/Owner for approval. Inspection and test

items specified in the codes and standards shall govern where applicable.

2.4 INSPECTION & TEST PROCEDURE AND ACCEPTANCE

STANDARDS :

2.4.1 Material Test

1. Vendor shall submit the mill test certificates for the followings:

Shell, head, nozzle

Tube sheet, channel cover, flange

Tube, tray made of alloy steel*

Pressure retaining bolt and nut, and alloy steel* bolt and nut.

Note: *Including high and low alloy steel such as C-Mo, Cr-Mo, 3.5 Ni

steel, etc.

2. Submittal of mill test certificates for materials may be exempted for any of the

Followings:

Materials conformed with ASTM A-36 Rolled Steel for General Structure

and their equivalent.

Stocked materials shall not be used in pressure retaining parts. Stocked

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materials used in pressure retaining parts, but not main parts, where their

mill test certificates are not readily obtainable. In such cases Vendor’s

certificates may be substituted for the original mill test certificates.

3. Vendor shall, prior to fabrication of the vessel, check the charge number and

the following items for the materials:

Chemical compositions

Mechanical properties

Heat treatment

Other items specified in the applicable codes and standards

4. Materials shall be free from injurious defects, such as surface flaw and

Lamination and these shall be visually inspected.

5. Material conformed with ANSI (Austenitic stainless steel containing

Molybdenum) or their ASTM equivalent not used in major parts of any vessel

and without mill test certificates shall be checked for molybdenum content by

Qualitative analysis.

6. As type 316 and 316L stainless steel (plate, pipe, forging material and welded

Deposit), examination for molybdenum detection shall be done.

2.4.2 Impact Test of Material for Low Temperature Service

Test procedure shall be in accordance with ASTM A370:

Test specimens of 2mmV (ASTM A379 Type A) shall be used.

Test temperature shall not be warmer than the minimum design temperature.

Acceptable impact energy are:

- Average for three specimens: 15 ft-lb and over

- Minimum for one specimen: 12 ft-lb

2.5 Welding Procedure Qualification :

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Test procedure and acceptable standards of the welding procedure qualification shall be in accordance with the applicable codes and standards.

Inspection and Tests of Welds :

1. Welders who participate in the welding operation of the main seams of vessels, such as

longitudinal and circumferential welding seams, nozzle-to-shell welds and other pressure

retaining welds, shall be checked for their qualification licenses. Purchaser/Owner may request

Vendor re-qualification of the welders, when necessary.

2. Prior to or during welding, the following items shall be inspected:

a. Dimension of welding groove

b. Alignment tolerances of plate edges

TABLE 2.1: ALIGNMENT TOLERANCES OF PLATE EDGES

Normal Plate Thickness t(mm) For Circumferential Joint t(mm)

t ≤ 45 1.0

4.5 < t ≤ 6 1.5

6 < t ≤ 20 t x 0.25

20 < t ≤ 38 5

38 < t t x 0.125, max.6

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Normal Plate Thickness

(mm)

For Longitudinal Joint

t (mm)

t ≤ 4.5 1.0

4.5 < t ≤ 6 1.5

6<tt x 0.25, max.3

Note: for clad steel, alignment tolerances of both longitudinal and circumferential joints shall be 1.0 mm.

c. Suitability of welding procedure, such as selection of welding rod or

electrode, pre-heating, etc.

d. First pass weld shall be back chipped and then inspected by magnetic

particle or liquid penetration method.

e. Neither slag inclusion or crack shall be found at the finish of each welding pass.

3. After completion of welding, the following items shall be visually inspected to be within the acceptance criteria:

Crack Not permitted, remove if any

Overlap Not to exceed 1.5 mm

Undercut Not to exceed 0.3 mm

Bead with uniformity Not to exceed 5 mm

Bead height un-uniformity Not to exceed 1.5 mm

Incomplete penetration Not permitted and lack of fusion

Insufficient toe Add welding length of fillet weld

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Crater Remove

Bead dripping Remove

Spatter Remove

2.6 References

Site of References:

Reference-1: www.scribd.com

Reference-2: the ASME code simplified By Robert Chuse, Bryce E. Carson

Book of References:

1. J.F. Porter. Residual Stress Evaluation of HMCS ONANDAGA

Pressure Hull Weldments, Canadian Forces/CRAD

Meeting, DREA – Halifax, May 1985.

2. J.F. Porter, M.F. Brauss, and J. Pineault. X-ray diffraction

determination of residential strain for marine platforms, 2nd

Canadian Forces/CRAD Meeting on Naval Applications of

Materials Technology, DREA-Halifax, May 1985.

3. M. Brauss, H. Wong, R. Holt, and P, Fryzuk. Non-destructive

evaluation of oberon submarine pressure hull residual

stress. 2nd Canadian Forces/CRAD Meeting on Research In

Fabrication and Inspection of Submarine Pressure Hulls,

DREA-Halifax, May 1987.

4. C. Adams and D. Corrigan. Mechanical and metallurgical

behaviour of restrained welds in submarine steels. MIT

Welding Lab, Defence Technical Information Centre,

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AD0634747, May 1966.

5. S. Khan, D. Saunders, J. Baldwin, and D. Sanford. Exp.

Mech. 37, 264 (1997). doi:10.1007/BF02317417

CHAPTER-3

3.0 Inspection and Welding Repairs of Pressure Vessels

3.1 ABSTRACTS

Repairs are required for pressure vessels in order to restore its original / intended operating condition, safe operation and to prolong trouble free service life. The vessel condition deteriorate due to various factors mainly Mechanical Problems, Process Related Problems and Corrosion Problems. Repairs are required to be planned and carried out under the strict supervision and control of a competent Inspector.

The paper briefs the various steps involved in:

Decision making for the repairs depending on location and nature of defect within the pressure vessel as per ASME as well as API 510 code.

Welding procedure qualifications. Materials and Welding consumables to be used for procedure qualification. Requirements and limitations of controlled deposition welding as an alternative to

PWHT, or where Impact testing is a requirement. By using preheating methods where Impact testing is not a requirement. Method of "Temper bead techniques". Method of "Half bead technique". NDT that can be employed before, during and after welding. Necessity of PWHT and Hydrostatic tests. Repairs and precautions during overlay weld repairs.

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Methods and precautions to be taken during alterations and re-rating of pressure vessels. Aspects of reporting and re-inspection.

The Paper aims to brief the interested audience involved in welding inspection and repairs of pressure vessels that can be conducted in Shut downs within Chemical, Refinery, Petrochemicals and Fertilizer industries; various methods of weld repairs and related activities such as testing after welding.

Key Words:

Owner user : Owner or a user organization of the equipment.

Repairer: The agency or organization, appointed by the owner user for repairs of the

equipment.

Inspector: A competent inspection engineer having full knowledge of the pressure vessel

construction, in-service inspection welding etc. Designer : A competent Pressure Vessel Design Engineer.Code : Code or standard used for design / construction and Inspection of Pressure vessel.NDT inspector

: A competent NDT inspector having thorough knowledge and experience of NDT techniques involved in Construction and repairs.

PWHT: Post Weld Heat Treatment given to the Pressure vessel during construction or

repairs.

3.2Introduction: Repair and maintenance of parts and components is a major activity in any process industry. Repair welding can be carried out as a logical procedure that ensures the part is usable and safe. If repairs are done with proper care or precautions, it can avoid premature failures, large warranty claims, safety of property and personnel and result in satisfied customers. Failures of pressure vessels are still observed, which result in a costly down time of production and product losses also sometimes it results in environmental hazards and unsafe working conditions or disasters. Every owner user wants to extract highest possible safe service life from equipment.The pressure vessel repairs also cannot be an exception this philosophy. Modern pressure vessels are constructed in accordance to a recognized code and established fabrication and welding practice.

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3.2.1 Method of Inspection and decision for repairs.

Pressure vessels are designed to any recognized code of design and construction. We must under stand that the design thickness can be considerably lower than the actual Fabricated . During design itself corrosion allowance is added in the base metal thickness and the manufacturer fabrication chooses the next available thickness. Thereby we have a excess thickness available for the service which result in a considerably lower operating stress value.

Steps involved in the decision making for repairs.

Operating conditions, Inspection history, Material of construction of pressure vessel . Reasons for failure . Location of the damaged area by visual inspection and evaluation by NDTs. Re-evaluate the need for repairs (Back to design calculations). Repair Methods, (For pressure retaining parts) . Preparation of repair procedures. Replacement of major components.

1:- Operating conditions, Inspection history, Material of construction of Pressure vessel: A careful study of the operating parameters and inspection history and properly maintained internal inspection reports, materials of construction, its behavior with the process fluid, welding techniques used during construction, design consideration etc, also gives an adequate confidence level about the use of pressure vessel. Such information is also useful for making the repair decision. Carefully selected material of construction and the fabrication procedures, welding procedures as well as inspection and certification by the competent inspection authorities during fabrication stage, always intend to give such information.

2:-Reasons for failures: Undesirable premature failures can occur due to any one or more of the following reasons . Faulty design, faulty workmanship, wrongly selected material of construction, wrong welding techniques such premature failures generally occur in an early service period, where as the normal service failures are attributed to corrosion, changes in the

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working parameters, operation of the vessel for which it is not designed, impurities in the operating fluids, metallurgical changes in the base metal etc.Once the damage is identified the pressure vessels must be thoroughly inspected to evaluate the extent of damage, need for repair and the repair method. Thorough visual inspection of the pressure vessel can be supplemented by a suitable NDT examination, to locate the defects and the extent.

3:- Location of the damaged area by visual inspection and evaluation by NDT.On opening the equipment it is necessary to make it safe for entry as the remaining fluid or fumes of gases could be dangerous for human life. The personnel may be required to stay for internal inspection there could be possible repairs where hot work is involved, there fore a safe entry permit from a competent authority i.e from the safety and operation departments. During internal inspection, some responsible operator should always be accessible to the inspector performing internal inspection. Such assistance can always be handy for any critical situation.

The external surface should be checked for any corrosion below the insulation, obvious leakages, structural attachments, connections, foundations, leak proof tightness of pressure relief valves etc.The internal surface should be reasonably cleaned so as to visually verify its condition, condition of threaded connections, Flange connections, closures, internal sand damage due to corrosion. Different corrosion problems anticipated are pitting, line corrosion. General uniform corrosion, grooving, Galvanic corrosion, Fatigue, Creep, temperature, Hydrogen attack / Embitterment, Stress corrosion cracking, Inter-granular corrosion, etc.

4:-Following design considerations are reviewed during re-evaluation

Patch repairs welded by fillet welding can be used on temporary basis. Such repairs shall be checked and verified by the design Engineer. The same should be replaced with permanent measure at the next available maintenance opportunity. A fully encirclement lap joint may be considered as a permanent repair method. Such full encirclement patches shall also be designed to meet the code requirements.

Minimum thickness observed shall be evaluated for MAWP and the corrosion rate, so as to decide the next inspection interval.

Location of localized corrosion, such as on the base metal, away from L seam, Away from C seam, on the weld joints, on crown portion of the head, etc. thereby, comparing the original design requirement. e.g. by carrying out L seam Radiography, the joint efficiency can be revised to 1 and the remaining thickness acceptable can be revised.

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The Inspector should think out all such possibilities and advise the owner user, so as to take a precise judgment on the repair.

5:- Repair methods: (For pressure retaining parts)

The cracks are gouged out or removed and weld repairs can be carried out from both sides, if approach is available,

The deep pits or localized corrosion can be weld built to restore the original thickness. The larger area, which cannot be welded by build up, can be replaced with patch or a

shell course or a head.

So far SMAW or GTAW has been the most widely accepted welding processes in the industry, for its availability of welding equipment and skilled welders. However FCAW or GMAW processes can also be used if sufficient expertise and equipment are available.

Need less to state that any code requirements, contractual requirements or any statutory / regulatory requirement must be complied during weld repairs. Original construction drawing, calculation data and inspection records are important for repairs. If the original construction data is not accessible, then an analysis of the base material, including previous weld deposits, becomes mandatory. If dimensions require close tolerances or if flatness is critical, then benchmarks that will aid the repair without causing excessive and expensive damage to the work piece must be established.The crack in weld joint or a defect in the base metal can be repaired by preparing a "U" or a "V" groove to the full depth and length of crack and then fill up by weld metal deposit as described here. If the crack exists in the stress concentration region then consult a competent pressure vessel design Engineer. Corroded area may be restored by weld metal deposition as described here.

6:-Preparation of a repair procedure:

The repair procedure should take care of the requirements of the base metal, welding consumables, sequential weld deposits, requirements of preheat, Interpass temperature, post weld heating, PWHT, impact test and the NDT requirements. The repair procedure shall be qualified as per the recognized code such as ASME sec IX, using an experienced welder. Maintain the records of procedure qualification as well as performance qualification. If PWHT is required in original construction and it is not practicable or advisable during

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repairs, then the Inspector and the Pressure Vessel Design Engineer shall review the reason for original PWHT of the equipment. If the Original reason why PWHT was done is due to the service requirements, then the alternative methods given below may be avoided, Details of Repair Procedures and consideration are given in 3.0 of this article. It is allowed by the Repair & Inspection code to avoid the PWHT as well as Pressure test after repairs.

3.3 Considerations for repair Procedures:

3.3.1 Repair procedure alternative to PWHT, Pre heating method, where impact testing is not done on the original equipment.

Impact testing is not required when this welding method is used. This procedure is limited to P1-Gr. 1 & 2; P3 -Gr. 1 & 2 (Excluding Mn-Mo steels) The weld area is pre heated and maintained at a minimum 150 deg C, during welding.

The temperature is measured to ensure 4" material or 4 times thickness (whichever is greater) from the each edge of weld is maintained during welding.

The maximum Interpass temperature does not exceed 315 deg C Carry out welding as per the qualified procedure.

3.3.2 Repair procedure alternative to PWHT, where impact testing is performed on the original equipment. When the original construction required impact test, Notch toughness testing as required by the code of construction is required. A procedure need to be qualified separately by using a groove welding on the plate Some additional requirements that can be considered over and above the supplementary essential variable are:

This procedure is limited to P1; P3 and P4 steels. All supplementary essential elements of ASME Section IX para QW-250 are applied. The weld area is pre heated and maintained at a minimum 150 deg C, during welding.

The temperature is measured to ensure 4" material or 4 times thickness (whichever is greater) from the each edge of weld is maintained during welding.

The maximum Interpass temperature does not exceed 315 deg C . Maximum heat input shall be calculated and implemented during repairs. The

maximum heat inputs as per qualified procedure must not exceed during welding. Qualification thickness for the plate material and the grooves are as per the table 1. If the welding is to be done under NACE standard, MR 0175, then additional test for

hardness measure to be applied. For SMAW welding process, electrodes with additional supplemental diffusible

hydrogen designator H8 or lower shall be used. The gas used in GTAW or GMAW or FCAW shall exhibit a dew point no higher than minus 50 deg C.

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Welding shall be carried out as per controlled deposition, temper bead or Half bead technique.

After completion of welding, without allowing to reduce the preheat, the temperature is raised to 230 to 280 Deg C. and held for minimum period of about 2 Hrs to assist as Hydrogen bake out treatment.

The Hydrogen bake out treatment can be omitted if electrodes having supplemental diffusible hydrogen designator H4 are used.

After cooling the weld metal, the excess layer of reinforcement is ground off to match the surface contour of base metal.

3.3.3 Non-Destructive Examination and testing of repaired location.

The prepared surface can be checked by using MPI or LPT before welding. After completion of welding, NDE acceptable to the Authorized Inspector or the owner

user are selected and applied to ensure soundness of the weld. After repairs the need for pressure test is to be decided by the Inspector. The test

temperature and the minimum design metal temperature of Pressure vessel shall be carefully evaluated.

If Hydrostatic test is impracticable, then pneumatic test should be considered with appropriate safety consideration.

3.3.4 Repair to Stainless steel overlays and clad.

In event any overlay or cladding area is removed, then the base metal gets exposed to the service environment.

The Inspector should give consideration to remove the possible entrapped hydrogen if the service and the base metal is prone to hydrogen entrapment, hydrogen embrittlement, Temper embrittlement etc. A heating treatment such as Hydrogen bake out at 230 to 280Deg C, for about 2 Hrs. shall be given.

3.4 Execution of welding repairs:

The repairer, under close supervision and surveillance of the Inspector, executes actual repairs. The written and qualified procedures are strictly followed. In case the Impact testing is specified, the welding parameters are also monitored and ensured to be within the range at which the procedure is qualified.

Specified NDE before welding repairs and after welding repairs are carried out and shall be approved by the Inspector.

After repairs the inspection record and the history of equipment, giving details of repairs, is

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updated and next inspection schedule shall be recommended to the owner user.

3.5 Welding techniques:

3.5.1 Temper bead welding technique:The heat affected zone of the bottom bead due to the top bead applied with lower size electrode, leaves less than 20 to 30 % of the weld metal cross sectional area as a " typical columnar grains" and the balance is a normalized structure. The top layer of the reinforcement mainly consisting of columnar grains, is required to be ground out, to match the surface contour.

3.5.2 Half bead welding technique:After every pass, the top half of the weld bead is ground off before applying the next layer.Such half bead technique also achievs the similar effect of temper bead technique, but then the consumption of welding electrodes can shoot up.

3.6 Conclusion: I wish to draw the following conclusions:

Repairs of pressure vessels are not always warranted, the decision of welding repairs must be taken with due consideration to the location of defect, carefully evaluated and interpreted NDE results, Design Calculations, Construction condition such as PWHT and Impact test.

Once the decision of welding repairs is taken then it is necessary to document the repair procedure giving details of NDT test necessary, Per heat and PWHT, welding sequence, monitoring the welding parameters, pressure test requirements etc.

Prepare the inspection reports and follow up inspection at a predefined inspection

3.7 References:

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API 510 - Pressure vessel inspection code. ANSI NB 23 - National Board Inspection code.

Table 3.1: Qualification thicknesses for test coupon and test repair groove.

Depth ofTest Groove

Repair groove DepthThickness ofTest Coupon

Plate Thickness of Base

t < t < 2" Up to 2"t < t > 2" Above 2"

Site of Reference:

Refernce-1: Matrixcsi.com

Reference-2: www.arcraftplasma.com

CHAPTER-4QUALITY ASSURANCE PLAN

4.1 DESIGN FEATURES

DESIGN CODE : ASME SEC VIII DIV 1 ED 2001

RADIOGRAPHY : SHELL: FULL, DISHENDS: FULL, LIMPET: NIL

HYDRO TEST PRESSURE : AS PER ORDER

TABLE 4.1:

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Sr. * Components & Operation

Characteristics

Reference Document Acceptance Norms

Format of Record

HOLD POINTS

SKF Client

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B. DOCMUMENT CONTROL1. Drg. Approval As per Clients

requirements.P.O. and Specification.

Drg P

2. Review of wps As per Clients requirements.

ASME sec vill Div 1 & Sec IX

Records P

C. INPROCESS CONTROL3. Pressure part a)

Material

Identification

for

shell. Dished

ends, shaft

b) Nozle pipe &

Nozzles

flanges

Dimension, Physical and Chemical properties

Chemical

As per respective material Specn & Mfgr's Test Certificates and approved Drgs.

Inspection Report

W

4. Non – Pressure parts,

materials identification for Lugs, lifting lug, name plate bracket, gussets etc.

Dimensions, Surface Defects

As per respective Materials spend. & Approved Drags.

Internal Inspection Report

W

5. PQR Weld soundness, physical test.

ASME sec IX Test Reports P

6. Material stamp transfer for shell, dished end, etc

Dimensions, Material grade Molly test

As per respective Materials specn. & Approved Drg

Inspection Report

W

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7. Set up of long seams of main shell courses, dish ends and fabricated pipes etc.

Weld geometry offset, Profile W.R.T Template ID, ovality, Etc.

ASME Sec VIII Div I

Internal Inspection Report

W

8. D,P. test of back chip of long seam welding

Welding defects.

ASME Sec V Internal Inspection Report W

9. Dished ends forming

Profile as per the template and Dimensions Including thinning at KR, SF, DP test

ASME Sec VIII Div I & Approved Drg.

Internal Inspection Report

W

10. Circ Seams set up of shell courses.

Weld geometry Offset Alignment Dimensions.

ASME Sec VIII Div I & Approved Drg.

Internal Inspection Report

W

11. Back chip & D.P.test of Circ Seam welding of Shells.

Welding defects

ASME Sec V Internal Inspection Report

W

12

RT of long seam, Circseam and T- Joints

100% Radiography ASME Sec V R.T. Report P

13

Set up of nozzle pipes to Nozzle Flanges.

Weld Geometry, Gasket Seat facing tell/tale hole

Approved Drg. Internal Inspection Report W

14 Set up of Nozzles on Topdished end.

Weld geometry,orientations, height,

ASME sec VIII Div I& Approved Drg.

InspectionReport

W

Page 30: mp sem-8

bolt hole Straddling

15

Back chip & D.P. test of bottom dished end to main shell.

Welding Defects ASME Sec V Inspection

Report W

16

Circ seam set up of bottom dished end to main shell

Weld geometry, orientation etc.

ASME Sec VIII Div I & Approved Drg.

InspectionReport W

17

Bottom dished end toshell welding.Limpet coil fit up on

Welding Defects ASME Sec V Inspection

Report W

18

Limpet coil fit up on bottom dish and on shell

Weld geometry,No. of turns on shelland bottom dish

ASME Sec VIII DivI & Approved Drg.

InternalInspectionReport

W

19

Limpet coil root runpneumatic test

Press: 1.25 Kg/cm2

(g) to be tested withsoap solution

ASME Sec VIII Div – I

InternalInspectionReport

W

20Set up of topDished end to main shell.

Weld geometry,orientation etc.

ASME Sec VIII DivI & Approved Drg.

InternalInspectionReport

W

21

Back chip & D.P.test of Top dished end to shellWelding.

Welding Defects ASME Sec V

InternalInspectionReport

W

22RT of Top dished end to shell welding.

100% Radiography ASME sec V R.T.Report P

23

Flush grinding of all nozzles from inside androunding off of corners

Corners to be rounded off to a minimum of 3-mm radius.

ASME sec VIII Div I

InternalInspectionReport

P

24 Pneumatic test of

Press: 1.25 Kg/cm2 (g)

ASME Sec VIII Div I

InternalInspection

W

Page 31: mp sem-8

Nozzle RF padsto be tested with soap solution

Report

25

Fabrication andmachining of Lanternstool, bearing housing,jacketed stuffing box,Agitator shaft and Anchorblades etc.

Dimensions as perthe approved drg.

ApprovedDrawing

- W

26

Set up of Lugs support, Lifting Lugs pads & support to Shell

Tightness of Wear Plates, elevation orientation, overall Dimensions etc.

ASME sec VIIIDiv 1 Approved Drgs.

InternalInspectionReport

P

27

Bottom pad fit up on Bottom Dish end

Dimensions, weld geometry.

ASME sec VIII Div – I & Approved Drg.

InternalInspectionReport

W

28

Assembly of Drive system& air running trial outsidethe vessel without Stuffing box Note : Agitator staticbalancing to be donebefore assembly

Run out of shaft attop, bottom, and at stuffing box, concentricity and perpendicularity,Sweep diameter ofanchor blade

Approved Drg

InternalInspectionReport

W

29 Final Inspection & dimensional check of vessel prior to Hydrostatic test

All dimensions to be checked, Internal & External Surface to be

ASME sec VIII Div – I & Approved Drg.

InspectionReport

W

Page 32: mp sem-8

checked for undercut weld defects & arc strikes etc.

30

Hydrostatic Testing of Limpet and shell side

Test pressure as per Approval drg. Medium : water Duration : 30 min.

ASME sec VIII Div – I & Approved Drg.

InspectionReport H

31Load running trial of the vessel

RPM, current drawn at different water level, run out at top

Approved Drg.

InspectionReport H

32 Polishingsurface finish ASME sec

VIII Div – I

InternalInspectionReport

P

33 Stamping & Marking

Design details

ASME sec VIII Div – I

Rub off W

34Painting of external CS parts.

- - - W

35Pre – dispatch & Issue of Release note.

Review of documents like Material Heart Chart, Test Certificates inspection Reports for previous stages etc.

- InspectionReport R

LEGEND: R - REVIEW, H - HOLD, P - PERFORM, W -WITNESS

Reference: www. pressurevessels india.com

Page 33: mp sem-8