chapter 9m prv repair

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PRV Repair

Chapter 9

PRV Repairs

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Repair work is necessary to restore a pressure relief device to a

and satisfactory condition. Pressure relief devices should be care

repaired in accordance with the manufacturers manuals

recommendations. The repair method should conform to a nat

standard, and the work should be done by qualified repairers.

repair is not done properly, the pressure relief device may give m

technical problems in service.

Pressure relief valves may be repaired on the system or ma

repaired in a valve repair shop. Repairs on pressure relief valves sh

be performed by a repairing firm or person, who has necessary

and surface finish data for the valves. As a part of repair proces

dimensions of the nozzle, disk, disk holder, ring, guide, and sp

should be checked and restored to their original standard.

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If all the dimensions and surface finish data is not available for re

the parts should be replaced by the parts from the original valve mufacturer. The valve may not function properly when parts supplied

a company other than original valve manufacturer is used. All part

be used should be free from scoring damage to critical guiding surfac

On completion of all repairs, pressure relief valve should be tested

sealed to ensure that no unauthorized adjustments are made. Genertesting is done in a valve repair shop, where necessary testing facil

are available and the shop has adequate test capacities. If all the v

operating characteristics cannot be tested in the shop, they should

verified when the boiler is on line.

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Generally, jurisdictions permit a VR stamp holder to repair all ty

of pressure relief valves. The VR Certificate of Authorization is issued

the National Board of Boiler & Pressure Vessel Inspectors. A sam

Certificate of Authorization to use the VR stamp is shown in Fig. 9.1

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9.1 Repairers

A repair organization must have experience in handling, maintena

and repair of all types of pressure relief devices. Most jurisdictions hqualification requirements for a repair organization in the laws and ru


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Figure 9.1 A VR Certificate of

Authorization. (Courtesy

National Board.)

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Each repair organization should have a fully documented quality c

system. As a minimum, the following requirements and sets o

umentation should be included in the quality control system:

Title page - Revision log - Contents page - Statement of author

responsibility - Organization chart - Scope of work - Drawin

specification controls - Material and part control - Repair and insp

program - Welding, nondestructive examination, and heat trea

procedures - Valve testing, setting, leak testing, and sealing - General ex

of the valve repair nameplate - Procedures for calibrating measureme

test gauges - Controlled copies of the quality system manuals - S

forms - Repair personnel training or qualifications.

Each repair organization should also have a fully documented t

program that will ensure repair personnel are qualified within theof the repair work.

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9.2 Repair of Pressure Relief Valves

The repair organization should establish procedures for repairing spr

loaded pressure relief valves. The procedures should cover step-by-repair methods to ensure proper repairs.

Generally, repair of pressure relief valves is done in a shop, wher

the machines, equipment, and tools for repair are readily available

9.2.1 Visual inspection as receivedWhen pressure relief valves are received in the shop, each v

should be visually inspected to detect problems. Generally,

inspection is made by repair mechanic as a routine procedure

authorized inspector (AI) or pressure vessel inspector should be ca

for inspection if unusual corrosion, deposits or conditions are noted

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Check body wall thickness

Check pilots and associated parts (for pilot operated relief valve

9.2.2 Preliminary test as receivedA preliminary performance test is conducted prior to actual repair

valve to identify any problems the valve faced in service. Genera

pressure relief valve is mounted on the test block, and the inle

sure is slowly increased. The pressure at which the valve reli

recorded as theas

received

pop pressure or set pressure. The pinary test should record: Set pressure or cold differential test pressure (CDTP) as per the mafacturers recommendations and the ASME Code.

The test pressure should not exceed 116% of the set pressure.

Conduct at least three tests to obtain consistent results.

If results do not correlate with field performance, then make necesary correction to obtain fluid and temperature conditions.

Record preliminary test results and test bench identification data.9


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9.2.4 Cleaning parts

Each part should be cleaned after disassembly of a safety relief va

Parts may be cleaned with solvents, emery paper, wire brush, sblasting, or carefully scraped. The valve parts should be properly mar

and segregated so that they are not mixed with parts of other valve

Proper parts cleaning and condition is a vital part in pressure r

valve performance and valve life. Parts which show signs of wear,

ting, corrosion or any other damage should be replaced.

Follow the procedures below to clean all parts of pressure relief val Wire all small parts together and clean by means of an abrasive.

Do not clean using a chemical solution.

Protect seating surfaces, guiding surfaces, and threads prior to cleani

Protect valve nameplate when sandblasting body.

Avoid sandblasting stems, nozzles, disks, and guides whenever possible.

Never use steel shot to clean any parts.


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9.2.5 Inspection

After cleaning, all the components should be inspected for wear, co

sion, and other deterioration. Each part should be checked for dimsions with reference to the original valve manufacturers drawings

specifications.

Perform the following inspection on pressure relief valve componen

Check spring for damage such as erosion, corrosion, cracking, br

age or compression below free height. Check nozzle for cracks using a suitable nondestructive examinat

(NDE) method. Look for any unusual wear.

Check disk assembly for cracks using a suitable NDE method. L

for any unusual wear.

Check spindle for trueness, bearing areas, and threaded conditio


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Check guide for wear and galling.

Check adjusting rings for worn threads and wear.

Check ring pins for bent or broken pin and thread condition.

Check bellows, if applicable, for pin holes and corrosion.

Check flange gasket facings for wear and cuts.

Damaged springs, bellows and soft goods should be rejected.

Parts that are worn beyond tolerance or damaged should

rejected.


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9.2.6 Machining

The valve body, flanges, and bonnet may be reconditioned by macing or suitable means. Machine the nozzle and disk as necessary

maintain the manufacturers critical dimension charts.

9.2.7 Lapping

Lapping is required to restore the smooth seating surface of pres

relief valves. If evidence of wear or damage is noticed on the disknozzle, their seating surfaces may be lapped. Lapping can be done

hand or by a machine as shown in Fig. 9.2.

Lapping of the disk or nozzle by hand to remove minor seat damag

accomplished using a ring lap. The following is the lapping process:

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When using a ring lap, ensure that the lap covers the entire se

surface.

Apply a thin even amount of compound to the ring lap and plonto the disk.

Begin lapping in a oscillating motion (back and forth), applying

even pressure.

Lap part for 1-2 minutes.

Remove ring lap and clean both parts thoroughly.

Continue lapping sequence until disk/nozzle seat surface sho

gray shadow across the entire surface.

Polishing is accomplished in the same way with a few exceptions. A

different ring lap should be used for polishing. This allows the seapolished quicker.

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Lapping compounds vary from coarse to very fine. Generally a med

compound is used first, then a very fine compound to finish the pie

The plate and the part should be thoroughly cleaned after edifferent compound is used. Coarse compounds should be used

removing deep scratches and must always followed by finer grades.

following lapping compounds are recommended:

Figure 9.2 Lapping machine. (C

Electron Microscopy Sciences.)16

320 grit for removing small cuts

600 grit for removing scratches 1000 grit for finishing work

1200 grit for polishing


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9.2.8 Adjusting rings

Install the lower ring and guide ring to the same position they w

when removed, or to the manufacturers specifications.9.2.9 Bearing points

Grind all bearing areas with grinding compound to make sure they ar

round and true.

9.2.10 Assembly

After all the parts have been inspected, reconditioned or replaced,valve should be assembled in accordance with the manufacturers dr

ings and instructions. In fact assembly is the opposite process of d

sembly. Each part should be clean, free from burrs and not dama

prior to assembly. Attention should be paid to the seats on the no

and disk. Seats must be free from nicks and scratches.The following operation is included in assembly of the pressure reli

valve:17


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The following operation is included in assembly of the pressure reli

Secure the valve nozzle wrenching surface in a soft jaw vise

the nozzle seat vertical

Check clearance between assembled parts

Assemble all the parts according to the instructions

Do not oil and seating surfaces

Adjust spring to pop as close to the desired set pressure as poss Set blowdown carefully and accurately

9.2.11 Testing

All valves should be tested on the service medium for which they

intended. The following steps should be taken prior to mountingvalve to the text fixture:

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Clean the text fixture and purge the system for any lo

contaminates.

Ensure that test gauges are calibrated.

Secure the valve inlet to the test fixture. Ensure to use the wre

surface of the nozzle when tightening.

Testing should be done in accordance with manufacturers recom-mendations and the appropriate ASME Code. All test data should

recorded. Testing includes: Setting valve to set pressure

Setting valve to blowdown

Checking seat tightness

Changes to valve set pressure and or service medium (air to steam

etc.) may require changing of spring and/or other components. Conthe original valve manufacturer when making such changes.


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9.2.12 Sealing

A pressure relief valve should be sealed to prevent unauthor

alteration or tampering. After final adjustment and acceptance b

quality control inspector, all external adjustments should be sealed w

a safety seal.

The most common method is to use sealing wire to secure the

to the spring housing and housing to the body. It may also be use

lock any blowdown adjuster pins into position. The wire

subsequently sealed with a lead seal, which may bear identificatio

the repair organization or setters trademark. A sealed cap showin

lead seal is indicated in Fig. 9.4.

Fig.9.4 Sealed cap

shows a lead seal.20


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9.3 Repair Nameplates

The repairer is required to install a repair nameplate on each repa

pressure relief valve. A repair nameplate identifying the repairer date of repair should be attached to the valve. If set pressure has b

changed, the new set pressure and new capacity should be indica

on the original nameplate or stamping. The new capacity determine

calculations based on which the valve was originally certified.

original nameplate should never be removed from the pressure r

valve. A repair nameplate is shown in Fig. 9.5.

9.4 Documentation

Repair of pressure relief valves should be properly documented.

document should include condition, repair, and setting record for e

pressure relief valve.

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Fig. 9.5 Pressure relief valve repair nameplate. (Courtesy National Boar

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chapter 9m prv repair

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