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API 510
CH 1,2 Scope
non-code vessels constructed without a construction code/recognized construction code.
nonstandard vessels constructed by code but has Lost Name plate or stamping.
The application of API 510 code is restricted to owner-operators employ authorized inspection agency, repair
organization, engineer, inspector and examiners.
Inspectors are to be certified as stated in this inspection code Appendix B (see Annex B).
Appendix A in API 510 lists the types of vessels that MAY be excluded from the code.
Conflict between the two codes, the requirements of API 510 shall take precedence.
this inspection code does not permit its use in conflict with any prevailing regulatory requirements.
However, if requirements of this code are more stringent than requirements of regulation, the requirements of
this code shall govern.
owner-operators shall respond to any inspection results require corrective actions to assure continued safe O/P.
excluded if, (Appendix A)
- pressures not exceeding 15 psi,
- Cargo or volume tanks on trucks and ships,
- containing water not exceeded design (300 psi) 99 °C (210 °F).
excluded if pressure vessels that do not exceed (Appendix A)
- (5 ft) in volume and (250 psi) design pressure.
- (3 ft) in volume and (350 psi) design pressure.
- (1.5 ft) in volume and (600 psi) design pressure.
API Publication covers welding & hot tap API 2201.
RBI in accordance with the principles in API RP 580
fitness-for-service (FFS) assessment API 579-1/ ASME FFS-1
documents cover NDE examiner qualification and certification CP Standard and ASNT Practice

CH 3 Terms and Definitions

Q pressure vessel engineer person acceptable to the owner-operator who is knowledgeable and experienced in
the engineering disciplines, by through consultation with other is a composite of all entities needed to assess
technical requirements for pressure vessel. Q
Alteration physical change in any component that has design implications that affect the pressure-containing
Q Alteration? Alteration has design implications beyond the scope of the existing data reports
The following should not be considered alterations:
- any comparable or duplicate replacement
- the addition of any reinforced nozzle less than or equal to the size of existing reinforced nozzles
- addition of nozzles not requiring reinforcement.
Authorized inspection agency
- inspection organization of the jurisdiction
- insurance company licensed
- inspection organization of an owner-operator and not for vessels intended for sale or resale
- independent organization or individual under contract to and under the of an owner-operator
Examiner Person who assists an inspector by performing specific NDE on pressure vessels but does not evaluate
exam results per API 510
Q CML: designated area on pressure vessels where periodic examinations are conducted.
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Controlled-deposition welding CDW: Any welding technique used to obtain controlled grain refinement and
tempering of the underlying HAZ in the base metal. Various CDW techniques, such as temper bead and half bead.
- Temper bead (tempering of the layer below the current bead being deposited)
- Half bead (requiring removal of one-half of the first layer)
Q Hold Point: in the repair or alteration process beyond which work may not proceed until the required
inspection or NDE has been performed.
Indication: A response or evidence resulting from the application of an NDE
Defect: imperfection whose type or size exceeds the applicable acceptance criteria (Reject)
MAWP: at the top, this pressure is based on calculations using the minimum thickness for all critical vessel
elements and adjusted for applicable static head pressure and non-pressure loads.
Rerating change, either an increase or a decrease, in either design temperature rating, MDMT or MAWP rating
Q Derating (rerating below original design conditions) is a permissible way to provide additional corrosion
allowance.
Q Temper Embrittlement reduction in toughness due to a metallurgical change that can occur in low-alloy steels
(e.g., 2 1/4Cr-1Mo) of long-term exposure in the temperature range of 345 °C to 575 °C (650 °F to 1070 °F).
Q Transition temperature at which a material fracture mode changes from ductile to brittle.
Q Design temperature, per API 510: temperature used in the code Design calculation of the pressure vessel
QA All planned, systematic, and preventative actions specified to determine if materials, equipment, or services
will meet specified requirements to perform satisfactorily in service
Required thickness: The minimum thickness based on the design code calculation not including corrosion
allowance

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CH 4 Owner-operator Inspections Organization

Owner/User Organization
- responsible to execute the inspection plan including the established schedule
- exercise overall control of activities inspection, repair, alteration & rerating of vessels.
- responsible for developing, documenting, implementing, executing, and assessing pressure vessel
Repair Organization shall be performed repairs and alterations.
Repair organization is responsible to the owner/user and shall provide the materials, equipment, QC and
workmanship
Engineer responsible to the owner-operator to make certain that activities involving design, engineering review
and analysis, or evaluation of pressure vessels and PRDs.
Inspector responsible to the owner-operator to assure the inspection, NDE, repairs, alterations, and pressure-
testing activities meet API 510 code requirements.
Examiners:
- shall perform the NDE in accordance with job requirements.
- does not need API 510 inspector certification.
- does not need to be an employee of the owner-operator
- does need to be trained and competent in the NDE procedures being used
- may be required by the owner-operator to prove competency by holding certifications (ASNT SNT-TC-1A, ASNT
CP-189)

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CH 5 Inspection and Examination

5.1 Inspection Plan
Inspection Plan strategy defining how and when will be inspected,
repaired, and/or maintained.
Inspection plan should be developed by Inspector and/or Engineer
Corrosion Specialist consulted to identify credible damage mechanisms and locations.
Inspection plan is developed from the analysis of several sources of data.
Inspection plan shall be developed using the most appropriate sources of information.
Inspection plans shall be reviewed and amended as needed.
Contents of an Inspection Plan
- a) define type of inspection (e.g., internal, external)
- b) identify the next inspection date;
- c) describe the inspection and NDE techniques;
- d) describe the extent and locations of inspection and NDE;
- e) describe the surface-cleaning requirements;
- f) describe the requirements of any needed pressure test (e.g., type of test, test pressure, and duration);
- g) describe any previously planned repairs;
- h) describe specific considerations due to process or mechanical changes (e.g., MOCs), IOW exceedances
Additional Contents of an Inspection Plan
- describing the types of damage anticipated
- defining the location of the damage
- defining any special access requirements
Generic inspection plans: types of inspection plans are based on industry standards and practices.
The contents of the plan should be readily accessible from inspection data systems.

5.2 RBI
RBI used to determine Inspection intervals and type and extent of future inspections and examinations.
RBI assessments determine risk by Combining the probability and the consequence of equipment failure.
After an RBI assessment is conducted, the results used to establish inspection plan.
RBI assessments used to set vessel inspection intervals; assessments shall be Updated after each inspection.
Identifying and evaluating credible damage mechanisms, current equipment condition, and the effectiveness
past inspections are important steps in assessing the probability of failure.
Identifying and evaluating the process fluid(s), potential injuries, environmental damage, equipment damage,
and equipment downtime are important steps in assessing the consequence of failure.
Identifying and implementing IOWs for key process variables is an important adjunct to RBI
Q Probability Assessment: shall be based on all forms of damage that could reasonably be expected to affect a
vessel in any particular service.
Q Equipment failure data will also be important information for this Probability assessment.
Q Consequence Assessment: The consequence of a release is dependent on type and amount of process fluid
contained in the equipment. And shall consider the potential incidents that may occur as a result of fluid release.
After an RBI assessment is conducted, the results can be used to establish the vessel inspection plan and better
define the following:
- a) most appropriate inspection and NDE methods.
- b) extent of NDE.
- c) interval for internal, external, and on-stream inspections;
- d) need for pressure testing after damage has occurred or after repairs/alterations have been completed;
- e) prevention and mitigation steps to reduce the probability and consequence of failure
RBI Documentation: all the factors contributing to both the probability and consequence of a failure
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Frequency of RBI Assessments

assessment shall be updated after each inspection; each time process or hardware changes significantly affect
damage rates or damage mechanisms and anytime an unanticipated failure or inspection discovery occurs due
to a damage mechanism.

5.3 Preparation for Inspection

Confined space entry the vessel shall be positively isolated, drained, purged, cleaned, ventilated, and the
atmosphere inside it gas tested before it is entered.
Before entering a vessel, individuals shall obtain permission from the responsible operating personnel (AA)
Applicable regulations (e.g., those administered by OSHA) govern many aspects of vessel entry and shall be
followed. In addition, the owner- shall be reviewed and followed.
Records Review Before performing API 510 inspections, inspectors shall familiarize themselves with prior
history of the vessels and current inspection plan, as well as any engineering evaluations.

5.4 Different Types of Damage Mechanisms

Q The API inspector shall be directly involved in field inspection activities
Heavy-wall process vessels (over 5 cm [2 in.] thick) should have minimum allowable temperature (MAT) and
operating procedures established to minimize the potential for brittle fracture during heat up and cool downs.

5.5 Types of Inspection and Surveillance

5.5.1 General types of inspection
Different types of inspections, examinations, and surveillance
- a) internal inspection, b) on-stream inspection, c) external inspection, d) thickness examination, e) CUI/CUF
inspection, f) operator surveillance.

5.5.2 Internal Inspection

Internal inspection shall be performed by an inspector in accordance with the inspection plan.
other personnel acceptable to the owner-operator (NDE examiner) may assist (but not replace) the inspector.
Q primary goal of the internal inspection is Find damage that cannot be found by regular monitoring of external.
Inspection through manway or inspection port can be substituted for internal inspections when the vessel is too
small to safely enter or when the use of remote visual inspection techniques (e.g., borescope, drones, and robotic
crawlers) can visually inspect the areas internal vessel surface.
Internals may need to be removed, to the extent necessary, to allow inspection of pressure boundary surfaces.
The internals need not be removed completely as long as reasonable assurance exists that: damage in regions
rendered inaccessible by the internals is not occurring to an extent beyond that found in more accessible parts.
Inspector, in consultation with the corrosion specialist, should determine when it is necessary to remove
deposits or linings to perform adequate inspections
Q If corrosion is suspected underneath refractory linings, the refractory can be removed to allow further
inspection or ultrasonic thickness scanning may be made from external metal surfaces.

5.5.3 On-stream Inspection

on-stream should be conducted by either an inspector or examiner accordance with the inspection plan.
performed by an examiner shall be authorized and approved by the inspector
In situations where on-stream inspection is acceptable, such inspection may be conducted either while the vessel
is depressurized or pressured.

5.5.4 External Inspection

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Visual external inspections are normally performed by an inspector.

other qualified personnel may conduct the external inspection when their qualifications to do so are acceptable
to the owner-operator.
persons performing the external inspection in accordance with API 510 shall be qualified with appropriate
training as specified by the owner-operator.
Q Where should an external inspection of a pressure vessel begin? Ladders, stairways, platforms, or walkways
Q Attention should be given to welds used to attach components (e.g. reinforcement) for cracking or other
defects.
Checklist should be developed by or made available to the responsible inspector or engineer.
Vessels shall be examined for visual indications of bulging, out-of-roundness, sagging, and distortion.

Inspection of Buried Vessels

Inspection interval shall be based on an assessment of the cathodic protection system

and on corrosion rate obtained from one of the following methods
- connecting piping of similar material
- similarly buried corrosion test coupons of like material
- representative portions of the actual vessel
- from a vessel in similar circumstances.
Scanning UT thickness readings and/or other appropriate scanning NDE methods for determining the condition
of the external surface condition could be conducted from internally to monitor for external corrosion.

5.5.5 Thickness Examination

Above which temperature would a correction adjustment typically be applied when measuring the ultrasonically?
65C (150 F)
The owner-operator is responsible to assure all individuals taking thickness readings are trained and qualified as a
UT TM (thickness-monitoring) examiner in accordance with the applicable procedure used during the examination

5.5.6 CUI/CUF

CUI shall be considered for externally insulated vessels and those in intermittent service or operate at
temperatures between:
- a) 12 °C (10 °F) and 177 °C (350 °F) for carbon and low-alloy steels;
- b) 60 °C (140 °F) and 177 °C (350 °F) for austenitic stainless steels;
- c) 138 °C (280 °F) and 177 °C (350 °F) for duplex stainless steels.
Q Carbon and low-alloy steels, CUI usually causes localized corrosion.
Q Austenitic and duplex stainless-steel materials CUI is usually form of external chloride stress corrosion cracking
Q If CUI damage is found, the inspector should inspect other susceptible areas on the vessel.
CUI damage may still be occurring underneath good condition external insulation. CUI inspection may require
removal of some or all insulation (i.e., removing selected windows in the insulation).
If external coverings are in good condition and no reason to suspect damage behind them, not necessary to
remove insulation.
In lieu of insulation removal for a vessel, what alternative Shell thickness measurements taken internally during
internal inspections.

5.5.7 operator surveillance.

When walking through the facility, operators should report anything unusual associated with vessels and PRDs
to the inspector or engineer
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5.6 Condition-monitoring Locations (CMLs)

CMLs are designated areas on where periodic examinations to monitor the presence and rate of damage.
o Selected and placement of CMLs shall consider potential for localized corrosion and service-specific
damage.
Q Each pressure vessel shall be monitored by conducting a representative number of examinations at CMLs to
satisfy the requirements for an internal and/or on-stream inspection
Q Corrosion rates, the remaining life, and next inspection intervals should be calculated to determine the
limiting component.

5.7 Condition-monitoring Methods

Each pressure vessel shall be monitored by conducting a representative number of examinations at CMLs to
satisfy the requirements for an internal and/or on-stream inspection.
Corrosion rates, remaining life, next inspection intervals should calculate to determine the limiting component
CMLs may be eliminated or reduced when the probability and/or consequence of failure is low (e.g., clean
noncorrosive hydrocarbon service), a corrosion specialist should be consulted.

5.8 Pressure Testing

Inspector responsible for determining if a hydrostatic test must be performed after repairing pressure vessel.
Pressure test is normally required after an alteration or major repair.
After repairs (other than major repairs) are completed, a pressure test shall be applied if the inspector believes
one is necessary and specifies it in the repair plan.
A close visual inspection of pressure vessel components shall not be performed until the vessel pressure is at or
below the MAWP.

hydrostatic Test pressure in psig (MPa) = 1.5 x MAWP × (Stest temp/Sdesign temp), prior to 1999 addendum.
hydrostatic Test pressure in psig (MPa) = 1.3 x MAWP × (Stest temp/Sdesign temp), 1999 addendum and later

Q Before applying a hydrostatic test, the supporting structures and foundation design should be reviewed to
determine they are suitable for the hydrostatic test load

Pneumatic Pressure Tests

Pneumatic Test pressure = 1.1 x MAWP × (Stest temp/Sdesign temp).

Pneumatic test procedure should be developed by the engineer
used when hydrostatic testing is impracticable because of limited supporting structure or foundation, refractory
linings, or process reasons.
Q Potential personnel and property risks of pneumatic testing shall be considered by an engineer before
conducting the test

Test Temperature and Brittle Fracture Considerations

Q To minimize the risk of brittle fracture during a pressure test, the metal temperature should be maintained
- at least 17 °C (30 °F) above the MDMT or MAT for vessels THK > 2" (5 cm)
- at least 6 °C (10 °F) above the MDMT or MAT for vessels THK = 2" (5 cm) or less

The test temperature need not exceed 50 °C (120 °F) unless there is information on the brittle characteristics of
the vessel material indicating a higher test temperature is needed.
When hydrotesting solid weld overlaid or clad austenitic stainless steel, the water temperature should not
exceed 50 °C (120 °F) to avoid possible chloride stress corrosion cracking.
A number of failures have been attributed to brittle fracture of steels that were exposed to temperatures
below their transition temperature and to pressures greater than 20 % of the required hydrostatic test
pressure. Special attention should be taken when testing:
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- low-alloy steels, especially 2 1/4 Cr-1Mo, because they may be prone to temper embrittlement
- Other metal that may be prone to embrittlement per the damage mechanism.

Pressure-testing Alternatives

Substituting NDE procedures for a pressure test after an alteration or major repair may be done only after
approved by engineer and inspector.
For cases where manual UT is used to examine welds in lieu of pressure test, the owner-operator shall specify
industry-qualified angle beam examiners

5.9 Material Verification and Traceability

During repairs or alterations of pressure vessels, the inspector shall verify all new materials (including carbon
steel as well as all alloys) are in compliance with the specifications.
Q discretion of the owner operator or the inspector, this assessment can be made by 100 % verification
checking, 100 % positive material identification (PMI), or by sampling a percentage of the materials0.
Q If vessel component experiences accelerated corrosion or should fail because an incorrect material was
inadvertently substituted for the specified material, the inspector shall consider the need for further
verification of existing materials.
Q During repairs or alterations of pressure vessels verifies new materials 100% verification checking or by
sampling a percentage of the materials in critical situations

5.10 Inspection of In-service Welds

Q welds and weld heat-affected zones are often inspected for corrosion and/or service-induced cracking as part of
the in-service inspections.
Crack-like flaws, environmental cracking and preferential weld corrosion shall be assessed by the inspector and
either an engineer or corrosion specialist.
Dissimilar metal welds (DMW) may be prone to cracking or preferential in-service corrosion

5.11 Inspection and Repair of Flanged Joints

Accessible flange faces should be examined for distortion and to determine condition of gasket-seating surfaces.
surfaces damaged and likely to result in a joint leak should be resurfaced prior to placed back in service.

CH 6 Interval/Frequency
pressure vessels and associated PRDs shall be inspected and tested at the intervals/frequencies provided in section 6.

Appropriate inspection shall provide the information necessary to determine all of the essential sections or
components of the equipment are safe to operate until the next scheduled inspection.
The risks associated shutdown and start-up and increased corrosion due to exposure of vessel to air and
moisture should be evaluated when an internal inspection is being planned.
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6.2 Inspection During Installation and Service Changes
Vessel Installations
Pressure vessels shall be inspected by an inspector at the time of installation.
- Q To verify the equipment is safe for operation and that no damage occurred during transportation
- To initiate plant inspection records for the equipment.
- Opportunity to collect desired baseline information and to obtain the initial thickness readings at designated
CMLs.

The installation inspection shall verify

- The nameplate information is correct per the .
- Installed correctly, supports are adequate and secured, exterior equipment ladders and platforms are secured.
- PRDs satisfy design and installation requirements.
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If noncompliance is found or the requirements for the PRD are not met. Repairs or engineering assessment that
may be necessary to confirm the vessel is fit for service and properly protected from over-pressure.
Internal field inspection of new vessels is not required when provided appropriate documentation assures the
vessels comply with the specified design and specification requirements.
Q If missing t should? Perform an internal inspection
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Vessel Service Change
If the service conditions are changed (e.g., process contents, maximum operating pressure, and the
maximum and minimum operating temperature) the inspection intervals shall be established for the
new service conditions.
If both the ownership and the location of a vessel are changed, the vessel shall be internally and externally
inspected before it is reused.
Inspection should include baseline examinations for any anticipated future examinations (for anticipated
Damage) planned as a result of the new service.
In some cases (e.g., movement to a new location of) reanalysis or review/revalidation of the user design
specification may be required

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6.3 RBI Interval
RBI may allow established inspection intervals for internal or on-stream to be exceeded from limits specified in
6.4 and 6.5, RBI intervals on external inspections shall not exceed 10 years.
When an RBI interval for the internal or on-stream inspection exceeds the 10-year limit, RBI assessment shall be
reviewed and approved by the engineer and inspector at intervals not to exceed 10 years.
When RBI is used to extend the internal or on-stream inspection interval, the assessment should include a review
of the inspection history and potential fouling of the PRD(s).
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6.4 External Inspection Interval
Q aboveground vessel shall visual external inspection at an interval that does not exceed the lesser of five years or
required internal/on-stream inspection.
The interval is established by the inspector or engineer in accordance with the owner-
External inspection intervals for vessels in noncontinuous service are the same as for vessels in continuous service.
Equipment Abandoned-in-place, may need to conduct appropriate external inspections to make sure do not
deteriorate and not become a hazard to personnel or other equipment.
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6.5 Internal, On-stream, and Thickness Measurement Inspections
Internal or on-stream inspections shall not exceed one-half remaining life of the vessel or 10 years, whichever is
less.
When the remaining life is less than four years, the inspection interval may be the full remaining life up to
maximum of two years.
Inspector or engineer in accordance with the owner- establishes the interval.
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The period between thickness measurement inspections shall not exceed the lesser of one-half remaining life or 10
years. When the remaining life is less than four years, the inspection interval may be the full remaining life up to a
maximum of two years.
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Vessels in noncontinuous service, the interval is based on the number of years of actual service provided that when
idled, the vessel is
- a) isolated from the process fluids,
- b) not exposed to corrosive internal environments (inert gas purged or filled with noncorrosive hydrocarbons.
Vessels in noncontinuous service and not adequately protected from corrosive environments may experience
increased internal corrosion while idle, the corrosion rates should be carefully reviewed
Q For vessels in non-continuous service, the maximum internal or on-stream inspection interval shall be the 10
years of actual service.

Q (projected MAWP) Alternative method to establish inspection interval is by calculating the projected MAWP
vessel. The maximum inspection interval using this method is also 10 years.
next inspection interval for vessels in corrosive service should be determined by calculating the remaining life of
the limiting component.
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6.5.2 On-stream Inspection in Lieu (substituted) of Internal Inspections
When internal inspection physically impossible.
Or RBI assessment determines risk associated is low, NDE is adequate for the expected damage mechanism.
Or physically possible and all of the following conditions are met:
- CR < 0.125 mm (0.005 in.),
- RL>10 years,
- temperature does not exceed the lower temperature limits for the creep rupture range
- not subject to environmental cracking or hydrogen damage,
- corrosive character established at least five years of the same or similar service,
- Vessel does not have non-integrally bonded liner such as strip lining or plate lining.
- No questionable condition is discovered during the external inspection.
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6.5.3 Same and Similar Service
On-stream inspection can be substituted for an internal inspection. The vessel has been internally inspected,
inspection of one vessel (preferably the worst case) may be taken as representative of the whole train, When the
following conditions are observed:
- a) Two or more pressure vessels are installed in series and no potentially corrosive contaminants.
- b) the operating conditions in any part of the train are the same
- c) Sufficient corrosion history has been accumulated.

Vessel is subject to environmental cracking or hydrogen damage, the results of an internal inspection on a similar
service pressure vessel cannot be used to substitute an on-stream inspection for an internal inspection.
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6.5.4 Multizone Vessels
Q Large vessel with two or more zones of differing corrosion rates, each zone may be treated independently when
determining the inspection intervals. Each zone shall be inspected based on the interval for that zone.
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6.6 Pressure-relieving Devices
PRDs shall be tested and repaired by a repair organization
PRDs shall be inspected, tested, and maintained in accordance with API RP 576 and API 510.
Each PRV repair organization shall have a fully documented QA system. shall be included in the QA manual
Each repair organization shall have a documented training program that shall verify that repair personnel are
qualified the scope of the repairs.
PRDs shall be tested and inspected at intervals frequent enough to verify the devices perform reliably in the
particular service conditions
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The inspector, engineer, or other qualified individual per the owner-operators QA system determines
inspection interval for all PRDs.
Test and inspection intervals for PRDs should not exceed:
a) five years for typical process services, and
b) 10 years for clean (no fouling) and noncorrosive services.

Q What is the maximum interval of visual on-stream inspection of PRDs: 10 Years

As-received pop testing conducted prior to cleaning yield accurate as-received pop testing results that will
help establish the appropriate inspection and servicing interval.
When a PRD is found to be heavily fouled or stuck shut (not opened) or PRD fails an as received pop test, the
inspection and testing interval shall be reevaluated and interval should be shortened or corrective action taken
After maintenance of the valve(s) is completed and the valve(s) is reinstalled, a full visual on-stream
inspection shall be performed by the inspector or designee before startup.
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6.7 Deferral (Simplified Deferral and Deferral)
Q Deferral an approved and documented postponement of an inspection, test, or examination
Simplified Deferral A short-term deferral may be approved by owner-operator if all following are met:
- The current due date for the inspection, test, or examination has not been previously deferred.
- The proposed new due date not increase due date by 10 % of interval or six months, whichever less.
- Deferral approval of personnel including the inspector representing or employed by the owner-operator.

Deferral requests not meeting conditions simplified deferral above shall follow a documented deferral.
Q Perform a documented risk-assessment or update an existing RBI assessment to determine if the proposed
deferral date would increase risk.
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6.8 Deferral of Repair Recommendation
Equipment shall remain within the limits of the minimum required thickness as determined in this code or by
other engineering evaluation during the period of deferral.
Recommendations are changed or deleted; inspection records shall record the reasoning, date of
change/deletion, and name of person who did the review.

CH 7 Inspection Data Evaluation, Analysis and Recording

7.1 Corrosion Rate for Existing Vessels
LT & ST CR These different rates help identify recent corrosion issues from those acting over the long term.
Corrosion rate (LT) = (t initial-t actual)/ time between.
Corrosion rate (ST) = (t previous-t actual)/ time between.
When evaluating corrosion rates Inspector, in consultation with a corrosion specialist, shall select CR that
best reflects current conditions.
Evaluating corrosion rate Estimated time of initiation of the corrosion problem (if not from initial
operation) as a basis for measuring wall loss and appropriate time interval for determining corrosion rate.
Evaluating corrosion rate consider areas subject to fluid impingement, stagnant areas, process change.

Corrosion Rate for Newly Install Vessels or Changes in Service

One of the following methods shall be used to determine probable corrosion rate:

Data collected by owner-operator in the same or similar service, appropriately placed ultrasonic sensors on
equipment, by a corrosion specialist, published data on vessels in same or similar service.
In a case items listed cannot be applied inspection plan shall include determine wall loss change rate on-stream by
direct measurement after six months of service. This may not actual corrosion rate.
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Subsequent shall be made at appropriate intervals until a credible corrosion rate established. If it is later inaccurate
corrosion rate was assumed, corrosion rate in remaining life calculations shall change to actual corrosion rate.
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7.2 Remaining Life Calculations

Remaining Life (RL) = (tactual - treq)/ CR
Remaining Corrosion allowance = (tactual - treq) from BOK.
Remaining life calculations have a significant impact on the efficiency and effectiveness of the inspection
corrosion rate and thickness data used in remaining life calculations should be validated
Bad data can lead to increased likelihood of unanticipated equipment failure or premature retirement.
Statistical analysis may be applied for assessment of substituting an internal inspection or for determining the internal
inspection interval.

Statistical analysis may be used in the corrosion rate and remaining life calculations for vessel.
Statistical analysis may not applicable to vessels with random but significant localized corrosion.
Statistical approach may be applied for assessment of substituting an internal inspection or for determining the internal
inspection interval
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7.3 MAWP
MAWP for the continued use of pressure vessel shall be based on computations determined using
applicable construction code. Q
Resulting MAWP from these computations shall not be greater than the original MAWP, unless a rerating is
performed in accordance with 8.8.
Wall thickness used in MAWP computations shall be the actual thickness as determined by inspection minus twice
the estimated corrosion loss before the date of the next inspection, as defined by (corrosive service)
t = tactual -2(CR x Interval), Use this calculated t in the MAWP calculation form according appl. construction code.
Multiple thickness measurements shall be taken when the actual thickness determined by inspection is greater or
lesser than the thickness reported in the material test report or the , especially if the
component made by forming process.
Thickness measurement procedure shall be approved by the inspector.

7.4 Analysis of Corroded Regions / FFS Level 1

Previous edition: Evaluation for local thinning area corroded area of consider the wall thickness may be
averaged over a length not exceeding:
- For ID < or = 60" - then the length L=1/2 ID or 20" whichever is less
- For ID > 60" - then the length L=1/3 ID or 40" whichever is less

7.4.3 Evaluation of Pitting:

Widely scattered pits may be ignored as long as all of the following are true.
- Remaining thickness below the pit is greater than one-half required thickness (½ trequired) and greater than 1.6 mm.
- within any 20 cm (8 in.) diameter circle the total area of the pitting deeper than the corrosion allowance does not
exceed 45 cm2 (7 in.2). --- ( r2 )
- Along any straight 20 cm (8 in.) line, the sum of the pit diameters whose depths exceed the corrosion allowance
does not exceed 5 cm (2 in.).
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7.4.6 Corroded Areas in Vessel Heads

Hemispherical Heads
- Use the appropriate hemispherical head formula in the construction code.
Ellipsoidal Heads
- knuckle region of the head, use the appropriate Ellipsoidal head formula in the construction code.
- Central portion head defined as center of head equal to 80 % of the shell diameter. Use the hemispherical
head formula in the construction code.
To get L for Ellipsoidal: L=K1D ---- K1 = from table by D/2h get the K1 value.
ToriSpherical Heads
- knuckle region of the head, use the appropriate Tori-Spherical head formula in the construction code.
- Central portion head defined as center of head equal to 80 % of the shell diameter. Use the hemispherical
head formula in the construction code.
To get L for Tori-Spherical: L equal to the outside diameter of the shell.
7.4.4 Alternative Evaluation Methods for Thinning
If allowable stress S < or = 2/3 Yield strength use the S value.
If allowable stress S > 2/3 Yield strength use the 2/3 of Yield strength.

7.4.5 Joint Efficiency Adjustments

Area at a weld from toe 1" or (2*treq) whichever is greater for each side.
- If corrosion in this area the E < 1.
- If corrosion away from this area may be E = 1.
Blend ground areas where defects have been removed. It is important to verify there are no sharp corners
in blend ground areas to minimize stress concentration effects.

7.6 Required Thickness Determination

shall be based on pressure, mechanical, and structural considerations
For services with high potential consequences if failure were occurred, engineer should consider increasing the
required thickness above the calculated minimum thickness to provide for unanticipated or unknown loadings,
undiscovered metal loss, or resistance to normal abuse.

7.7 Evaluation of Existing Equipment with Minimal Documentation

Vessels that have no nameplate and minimal or no design and construction documentation
1) Perform inspection to determine condition of the vessel, including a complete dimensional checking of all
components necessary to determine the minimum required thickness.
2) Define design parameters and prepare drawings.
3) Perform design calculations based on applicable construction codes and standards.
- a) Material UG-10(c) for evaluation of unidentified materials ()
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- OR If UG-10(c) is not followed for carbon steels, use allowable stresses for SA-283 Grade C and for alloy and
nonferrous materials, use X-ray fluorescence analysis.
- b) Do not use allowable stress values of the current ASME BPVC for vessels designed due to the change in design
factor used Design Margin (table) to establish allowable stress values
- c) Q Use joint efficiency of
0.7 For Type No. (1)
0.65 For Type No. (2) Butt welds and
0.85 For seamless shells, heads, and nozzles
Or consider performing radiography if a higher joint efficiency is needed.
Attach a nameplate or stamping showing the MAWP and temperature, MAT, and date
Perform pressure test as soon as practical, as required by code of construction used for design calculations.

7.8 Reports and Records

Pressure vessel owners-operators shall maintain permanent and progressive records
Permanent records will be maintained throughout the service life of each equipment item.
Progressive records will be regularly updated to include new information pertinent to the inspection and
maintenance history of the vessel and pressure relief devices. as well as operating information
Shall contain four types of information.
- Construction and Design Information.
- Inspection History
- Repair, alteration, and rerating information
- FFS assessment documentation requirements
Site operating and maintenance records, such as operating conditions, should also be available to the inspector
Inspection data management system within 90 days of the completion of the inspection and/or startup.
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CH 8 Repairs, Alterations, and Rerating
8.1 Repairs and Alterations
All repairs and alterations to pressure vessels shall be performed by a repair organization.
the equipment specific repair plan prepared by the inspector or engineer.
repair organization Any one of the following
- a) The holder of a valid ASME Certificate of Authorization that authorizes the use of an appropriate
ASME Code symbol stamp;
- b) The holder of another recognized code of construction certificate that authorizes the use of an
appropriate construction code symbol stamp;
- c) The holder of a valid R-stamp issued by the National Board for repair of pressure vessels;
- d) The holder of a valid VR-stamp issued by the National Board for repair and servicing of relief
valves;
- e) An owner or user of pressure vessels and/or relief valves who repairs his or her own equipment
in accordance with this code;
- f) A repair contractor whose qualifications are acceptable to the pressure vessel owner or user;
- g) An individual or organization that is authorized by the legal jurisdiction to repair pressure vessels
or service relief devices.
8.1.2 Authorization of Repair and Alteration

All repair and alteration work shall be authorized by the inspector before the work is started
The inspector will designate the hold points required for repairs and alterations.
The inspector may give prior general authorization for limited or routine repairs (not req. pressure test
or PWHT).
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Authorization for alterations to any pressure vessels and for repairs to vessels that comply with ASME
BPVC VIII Div. 2 may not be initiated until an engineer has also authorized. (Inspector and Engineer)
Before any repairs are performed, all proposed methods of design, execution, materials, welding
procedures, NDE, and testing shall be approved by the inspector or engineer.
For alterations, major repairs, and temporary repairs, approval by both the inspector and engineer.
The inspector shall approve all specified repair and alteration work at designated hold points and after
completion of the work in accordance with the repair plan.
8.1.3 Design

New nozzles, or replacement parts shall meet the design requirements of the applicable construction
code. and shall employ the same allowable stress criteria as used.
Design, location, and method of attachment shall comply with requirements of the applicable code.
When damage to parts of a vessel is so great that repairs cannot restore them to design requirements,
the parts shall be replaced.
An engineer shall approve all nozzle installations.

8.1.4 Material
Material used in repairs or alterations shall conform to the applicable construction code
Materials used for welded repairs and alterations shall be of known weldable quality and be compatible with the
original material.
The design of replacement parts and new nozzles shall employ the same allowable stress criteria as used for the
vessel design
Carbon or alloy steel with carbon content
- over 0.35 % shall not be welded,
- over 0.30 % (less than 0.35 %) may need special attention and preheating to avoid weld cracking.
If the inspector believes there is any question about material verification documents, PMI should be specified.

8.2 Temporary Repairs

Inspector and engineer are satisfied the repair will render the vessel fit for continued service until
permanent repairs can be conducted.
Q Temporary repairs should be removed and replaced with suitable permanent repairs at next available
maintenance opportunity.
Q Temporary repairs may remain in place for a longer period of time only if evaluated, approved, and
documented by the engineer and inspector.
The inspection plans shall include monitoring the integrity of the temporary repair until permanent
repairs are complete.
8.2.2 Fillet-welded Patches

Temporary repairs using fillet-welded patches shall be approved by an inspector and engineer.
used to make temporary repairs to damaged, corroded, or eroded areas.
Cracks shall not be repaired in this manner unless the engineer determines the cracks will not propagate
from under patch.

Fillet-welded patches require special design consideration, especially related to welded joint efficiency
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- May applied to the internal or external, would preferably be applied on the external surface to
facilitate on-stream examination.
- designed to absorb the membrane strain of the parts s
- ASME PCC-2, Article 212 may be used for designing a fillet-welded patch

Q A fillet-welded patch shall not be installed on top of an existing fillet-welded patch.

Distance between the toes of the fillet-welded patch shall not be less than: d =
Patch plates shall have rounded corners with a minimum radius of 25 mm (1 in.) minimum radius.

8.2.3 Lap Band Repairs

The design is approved and documented by the inspector and engineer.

Cracks shall not be repaired in this manner unless the engineer determines the cracks will not propagate
from under repair
The band is designed to contain the full vessel design pressure.
All longitudinal weld are full-penetration butt welds with the design joint efficiency
Circumferential fillet welds to the vessel shell are designed to transfer the full longitudinal load, using a
joint efficiency of 0.45
Q Band material and weld metal suitable for contact with the contained fluid, provide appropriate CA.
Damage mechanism leading to the need for repair shall be considered in determining the need for any
additional monitoring and future inspection of the repair.

8.2.4 Nonpenetrating Nozzles

May including pipe caps attached as nozzles
Band material and weld metal suitable for contact with the contained fluid, provide appropriate CA.
Damage mechanism leading to the need for repair shall be considered in determining the need for any
additional monitoring and future inspection of the repair.
Nonpenetrating nozzles may be used as permanent repairs of damage other than cracks

8.2.5 Nonmetallic Composite Wrap

nonmetallic composite wrap if the repair is approved by the engineer

Composite repairs shall be reviewed by the engineer in preparation for the next turnaround to
determine if they need to be removed and the pressure vessel needs to be refurbished.

8.3 Permanent Repair

8.3.1 Permanent Repair Techniques

a) excavating the defect and blend-grinding to contour.

b) excavating a defect and repair welding of the excavation.
c) replacing a section or the component containing the defect.
d) weld overlay of corroded area.
e) adding strip or plate lining to the interior surface.

Q Repairing a crack at a discontinuity, where stress concentrations are high should not be attempted without
prior consultation with an engineer.

8.3.2 Insert Plates (flush patch).

Repaired by removing a section and replacing it with an insert patch (flush patch).
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Insert patches may be used if the following requirements:

- a) Full-penetration groove welds are provided
- b) welds are RT in accordance with the applicable construction code, UT examination may be
substituted for RT, if the NDE procedures are approved by the inspector.
All insert plate corners that do not extend to an existing longitudinal or horizontal weld. Weld proximity
to existing welds shall be reviewed by the engineer.
Q shall be rounded Corner minimum radius 25 mm (1 in.)
8.3.3 Filler Metal Strength for Overlay and Repairs to Existing Welds

filler metal used for weld repairs should have minimum specified tensile strength equal to or greater
than the minimum specified tensile strength of the base metal.
If filler metal is used has a minimum specified tensile strength lower tensile strength of the base metal
compatibility of the filler metal chemistry shall be considered regarding weldability and service damage:
- a) Repair thickness shall not more than 50 % of the required thickness of the base metal (this
excludes corrosion allowance) (Corroded depth d < 0.5 treq)
- b) thickness of repair weld shall be increased by a ratio of minimum specified tensile strength of
base metal and minimum specified tensile of filler metal used for repair. Tfill= d(depth) × Sbase/Sfill
- c) Increased thickness of repair shall have rounded corners and shall be blended into the base
metal using a 3-to-1 taper.
- d) Repair shall be made with a minimum of two passes.
8.3.4 Repairs to Stainless Steel Weld Overlay and Cladding
shall be reviewed and approved by the inspector and engineer before implementation.
For equipment exposed to atomic hydrogen migration in the base meta (operates in hydrogen service at an
elevated temperature or has exposed base metal areas open to corrosion), additional factors shall be considered
by the engineer when developing the repair plan:
- a) outgassing base metal. Q
- b) hardening of base metal due to welding, grinding, or arc gouging.
- c) preheat and interpass temperature control
- d) PWHT to reduce hardness and restore mechanical properties.
Repairs shall be monitored by an inspector to assure compliance to repair requirements.
After cooling to ambient temperatures, the repair shall be inspected by the PT method.
Q Vessels constructed with P-3, P-4, or P-5 base materials; Area of repair should also be examined for cracking by
the UT. This inspection is most appropriately accomplished following a delay of at least 24 hours after completed
repairs for alloys that could be affected by delayed cracking.

8.4 Welding and Hot Tapping

All repair and alteration welding shall be in accordance with the applicable requirements of the ASME BPVC or the
applicable construction or repair code
Refer to API RP 2201 for safety aspects when making on-stream welds (e.g., during hot tapping).
Oil & Gas Industry welding guidelines may be found in API 582

Procedures, Qualifications and Records:

Q The repair organization shall use welders and welding procedures qualified.
Inspectors shall verify
qualifications (WPQ) and within the ranges on the WPS.
Repair organization shall maintain and shall make available to the inspector before the start of welding:
- a) qualified WPS with their supporting PQR.
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- b) records.
- c) welder continuity logs.
- d) weld maps or other means to identify who made specific welds.
API RP 577 provides guidance on how to review
- weld procedures WPS
- procedure qualification records PQR,
- welder performance qualifications WPQ
- how to respond welding nonconformances.

Q Preheat making welding repairs shall be in accordance with the applicable code and qualified WPS.
Preheat Exceptions shall be approved by engineer and will require a new WPS
Inspector should assure the minimum preheat temperature is measured and maintained.

8.5 PWHT
PWHT of vessel repairs or alterations should be made using the relevant requirements of the ASME BPVC, the
applicable construction code, or an approved alternative PWHT procedure, Alternatives to PWHT:
- Local PWHT
- Preheat and Controlled-deposition Welding (CDW) Methods as Alternatives to PWHT

5.5.2 Local PWHT

Local PWHT may be substituted for 360° banding on local repairs on all materials,
provided the following precautions are taken and requirements are met.
Q The application is reviewed, and a procedure is developed by an engineer.
procedure shall be evaluated considering the following factors:
- 1) base metal thickness
- 2) decay thermal gradients
- 3) material properties (e.g., hardness, constituents, and strength);
- 4) changes due to local PWHT
- 5) the need for full-penetration welds
- 6) surface and volumetric examinations after local PWHT;
- 7) overall and local strains and distortions resulting from the heating of a local restrained area of the
pressure vessel shell.

A preheat of 150 °C (300 °F) or higher, as specified by specific WPS, is maintained during welding.
local PWHT temperature shall be maintained for a distance of not less than two times the base metal
thickness(2*THK) measured from the toe of the weld of each side.
Local PWHT temperature shall be monitored by a suitable number of thermocouples (at least two)
Controlled heat shall be applied to any nozzle or any attachment within the local PWHT area.
When PWHT is performed for environmental-assisted cracking resistance, a metallurgical review shall be
conducted to assess whether the procedure is acceptable.

8.6 Preheat or Controlled-deposition Welding (CDW) Methods as Alternatives to PWHT

may be used in lieu of PWHT where PWHT is inadvisable or mechanically unnecessary.
Q Prior to using any alternative method, a metallurgical review conducted by an engineer shall be performed to
assure the proposed alternative is suitable for the application.
- reason for the original PWHT
- susceptibility to stress
- corrosion cracking
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- stresses in the location of the weld

- susceptibility to high-temperature hydrogen attack
- susceptibility to creep
inspector is responsible for verifying the methods used in accordance with owner-operator specification and the
requirements of this section.

8.6.2 Preheating Method (Notch Toughness Testing Not Required)

NOTE: Notch toughness testing is not required when using this preheat method in lieu of PWHT.

preheating method, when performed in lieu of PWHT, is limited to the following

- Materials shall limit to P-No. 1, Groups 1, 2, and 3 and to P-No. 3, Groups 1 and 2 (excluding Mn-Mo steels
in Group 2).
- The welding shall be limited to SMAW, GMAW and GTAW processes.

The preheat method shall be performed as follows:

- a) shall be preheated and maintained at a minimum temperature of 150 °C (300 °F) during welding.
- b) The 150 °C (300 °F) temperature should be checked to assure that 100 mm (4 in.) of the material or four
times the material thickness(4*THK) (whichever is greater) on each side of the groove is maintained at the
minimum temperature during welding.
- c) When the weld does not penetrate through the full thickness of the material, the minimum preheats and
maximum interpass temperatures need only be maintained at a distance of 100 mm (4 in.) or four times the
depth of the repair weld(4*d), whichever is greater on each side of the joint.
- maximum interpass temperature shall not exceed 315 °C (600 °F).

8.6.3 CDW Method (Notch Toughness Testing Required)

CDW method may be used in lieu of PWHT in accordance;

a) Notch toughness testing, necessary when impact tests are required by the applicable construction code.
b) The materials shall be limited to P-No. 1, P-No. 3, and P-No. 4 steels.
c) The welding shall be limited to the SMAW, GMAW, and GTAW processes.
WPS shall be developed and qualified for each application. The WPS shall define and include:
- Preheat temperature
- Interpass temperature
- post heating temperature requirement, qualification THK and etc.
- no case shall the material be lower in strength or have a carbon content of more than 0.35 %.
When impact tests required the PQR shall include sufficient tests to determine if the toughness of the weld metal
and the HAZ is adequate at the MDMT.
If hardness limits necessary for stress corrosion cracking resistance, the PQR shall include hardness tests.
The WPS shall include the following additional requirements:
- 1) The supplementary essential variables
- 2) The maximum weld heat input for each layer
- 3) The minimum preheat temperature for welding
- 4) The maximum interpass temperature for welding.
- 5) The preheat temperature shall be checked to assure that 100 mm (4 in.) or four times the material
thickness (whichever is greater) on each side.
- When weld does not penetrate through the full thickness of the material, the minimum preheat
temperature need only be maintained at a distance of 100 mm (4 in.) or four times the depth of the repair
weld, whichever is greater on each side.

- 6) Use only electrodes & filler metal with optional supplemental diffusible-hydrogen designator H8 or lower.
- shielding gases are use shall exhibit a dew point no higher than 50 °C ( 60 °F)
- Surfaces on welding shall be maintained in dry condition during welding and shall be free of rust, mill scale,
and hydrogen-producing contaminants such as oil, grease, and other organic materials.
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- 7) The welding technique shall be a CDW, temper bead, or half bead technique. The specific technique shall
be used in the procedure qualification test.
- 8) welds made by SMAW, after completion of welding and without allowing the weldment to cool below the
minimum preheat temperature.
- Temperature of the weldment shall be raised to a temperature of 260 °C ± 30 °C (500 °F ± 50 °F) for a
minimum period of two hours to assist outgassing diffusion of any weld metal hydrogen picked up during
welding.
- In lieu of outgassing used filler metal with optional supplemental diffusible-hydrogen H4 (such as E7018-
H4).
- 9) After the finished repair weld has cooled, the final temper bead reinforcement layer shall be removed.

Qualification Limits for Base Metal and Weld Deposit Thicknesses for the CDW Method (Notch Toughness Testing
Required)

Thickness T of Test Coupon Welded Thickness of Base Metal Qualified

T < 2" (50 mm) All thickness < T
T > 2" (50 mm) THK 2" (50mm) to unlimited

8.7 NDE of Welds

Prior to welding, area prepared for welding is examined using a surface NDE technique, e.g., the MT or PT to
determine if defects are present. This examination is especially important after removing cracks and other critical
defects.
After the weld is completed, it shall be examined again by the appropriate NDE technique as required in the repair
specification.
New welds (as part of repair or alteration) that were originally required by the construction code to be
radiographed (e.g., circumferential and longitudinal welds) shall be radiographically.
- where not practical to perform radiography, new weld shall be fully examined using UT in lieu of RT
- used rather than the UT in lieu of RT, the joint efficiency should be reduced to the value corresponding to no
radiography
- Where use of NDE techniques specified by the construction code is not possible or practical. alternative
NDE techniques may be used provided they are approved by the engineer and inspector
- Acceptance criteria for welded repairs or alterations should be in accordance with the applicable sections
- of the ASME BPVC or another applicable vessel design code.

8.8 Weld Inspection for Vessels Subject to Brittle Fracture

Vessels constructed of materials that may be subject to brittle fracture from either normal or abnormal service
(including start-up, shutdown, and pressure testing), appropriate inspection should be considered after welded
repairs or alterations.
Flaws, notches, or other stress risers could initiate a brittle fracture in subsequent pressure testing or service.
MT and other effective surface NDE methods should be considered.
Inspection techniques should be selected to detect critical flaws as determined by an FFS assessment.
All vessels subject to brittle fracture from low-temperature excursions or low ambient temperatures that may need
weld repairs and that do not have an established MDMT or MAT shall be evaluated for these limits prior to being
returned to service
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8.9 Rerating
Rerating a pressure vessel by changing its design temperature, minimum metal design temperature, or MAWP
may be done only after all of the following requirements have been met.
- a) Q Calculations performed by either the manufacturer or an owner-operator engineer (or his/her
designated representative) experienced in pressure vessel design, fabrication, or inspection shall justify
rerating.
- b) Q Rerating shall be performed in accordance with applicable construction code.
Alternately, calculations can be made using the appropriate formulas in the latest edition of the construction
code.
- c) Current inspection records verify the pressure vessel is satisfactory for the proposed service conditions
and the corrosion allowance provided is appropriate.
- An increase in allowable working pressure or design temperature shall be based on thickness data obtained
from a recent internal or on-stream inspection.
- d) The vessel shall be pressure tested using the applicable testing formula from the code used to perform
the rerating calculations unless the following is true
- pressure vessel has at some time been pressure tested to a test pressure equal to or higher than the test
pressure required by the construction code
- vessel integrity is confirmed by special nondestructive evaluation inspection techniques in lieu of testing.
- e) The rerating is acceptable to the engineer.

The pressure vessel rerating will be considered complete when the appropriate engineering records are updated
followed by the attachment of an additional nameplate or additional stamping that carries the information
(Inspector witness)

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38. Pressure tests must be performed on pressure vessels that have been in service when: d) The vessel is rerated
to a higher pressure

48. Equipment not designed for entrance by personnel: d) Inspection ports shall be opened

51. According to API-510, a pressure relief device repair concern must have which of the following? a) A quality
control system

59. Which of the following should be done when a vessel hydrostatic pressure test is being conducted and the test
pressure exceeds the set pressure of the safety relief valve? The safety relief valve should be removed, or test
clamp can be used to hold down the safety relief valve disk

78. Pressure vessel repairs must be in accordance with the original code of construction. What additional inspection
requirements must be considered? a) Jurisdictional requirements, if any, exceeding those of the construction code

93. Q Which of the following is not an acceptable API-510 repair organization? a)

50- Q The API inspector shall? be directly involved in field inspection activities