Section 7 — Pressure Vessels

Repairs and Alterations for Flanges

IPE Engineering Practice IPE-EP-7-3-3

Document number: IPE-EP-7-3-3 · Section: 7 — Pressure Vessels

SCOPE

• This Practice covers the requirements for repairs or alterations to existing pressure vessel and piping flanges.
• Any deviation to this Practice must be approved by the procedure given in EP 1-1-3.
• An asterisk (*) indicates that a decision by the Owner or Owner's Engineer is required. or that additional information is furnished by the Purchaser.
• A revision bar indicates all changes made to this Revision.

2.0 REFERENCES

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

DEFINITIONS

• Alteration - Per the NBIC, an Alteration is any change in the item described on the original Manufacturer's Data Report which affects the pressure containing capability of the pressure vessel. Non-physical changes such as an increase in the maximum allowable working pressure (internal or external) or design temperature of a pressure vessel shall be considered an alteration. A reduction in the minimum temperature such that additional mechanical tests are required shall also be considered an alteration. Per API 510, an Alteration is a physical change in any component which has design implications which affect the pressure containing capability of a pressure vessel beyond the scope of the items described in existing data reports. It is not intended that any comparable or duplicate replacement, the addition of any reinforced nozzle equal to or less than the size of existing reinforced nozzles, the addition of nozzles not requiring reinforcement, or rerating be considered an alteration.

• Contractor - Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.
• Inspector - A Inflection Point Engineering, LLC appointed engineer or inspector.
• Manufacturer - The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a manufacturer by a contractor or the Owner. An indirect order is one issued to a manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.
• Owner - Inflection Point Engineering, LLC.
• Owner's Engineer - A Inflection Point Engineering, LLC appointed engineer.
• Purchaser - The party placing a direct purchase order. The purchaser is the Owner's designated representative.
• Repair - The work necessary to restore a vessel to a condition suitable for safe operation at the design conditions. If any restorative changes result in a change of design pressure and temperature, the requirements for Rerating shall also be satisfied.

4.0 GENERAL

A change or repair to an existing flanged joint shall not be made without an evaluation of the design of the joint. Guidelines for this evaluation are given in this Practice.

FLANGE REPAIRS

• Pipe Flanges
• Repairing flange gasket seating surfaces on piping flanges by taking skim cuts is an acceptable practice provided the remaining thickness is above the minimum thickness specified in paragraph 6.3 in ASME/ANSI B16.5.
• Machining below the thickness given in ASME/ANSI B16.5 is strictly prohibited. Building up the seating surface with weld metal prior to machining is acceptable provided proper weld procedures and stress relief procedures are followed.
• Pressure Vessel Flanges
• Repairing flange gasket seating surfaces on pressure vessels by taking skim cuts is an acceptable practice which requires no engineering evaluation provided the remaining thickness is above that which is shown on fabrication drawings or as specified in ASME/ANSI B16.5 or B16.47, as applicable. EP 7-1-1 stipulates an extra 1/4 inch on the thickness for new pressure vessel flanges designed per Code procedures to allow for future machining. Removal of this extra thickness is allowed without further engineering evaluation.
• Machining which removes a nubbin or which reduces the thickness below the thickness shown on fabrication drawings or as specified in ANSI/ASME B16.5 or B16.47 will require additional evaluation per Section 6.2 of this practice.

FLANGE ALTERATIONS

• General

• Any Alteration that is made to a pressure vessel flange must be in accordance with EP 7-3-2.

• Rerating of the pressure vessel in accordance with EP 7-3-1 is required when an Alteration to a pressure vessel flange results in a reduction of the Maximum Allowable Working Pressure (MAWP) of the pressure vessel.
• Examples of Alterations to existing flanges include but are not limited to the following:
• A change in the bolt material or diameter.
• A change in the gasket style or material.
• Field machining that changes the facing details (e.g. removal of tongue or nubbin).
• Flange face machining of gasket seating surface (skim cuts) which reduces the flange thickness below the minimum required thickness as calculated by the procedures given in the ASME Code, Section VIII or as specified in ASME/ANSI B16.5.
• Design Review
• A design review of the flange must be completed prior to performing any Alteration to the flanged joint.
• For pressure vessels and heat exchangers, the MAWP of the flanged joint shall be determined using the procedures given in the ASME Code Section VIII, (Appendix 2 for Division 1, and Appendix 3 for Division 2). If the flange MAWP is reduced below the design pressure of the vessel, the vessel shall be rerated per EP 7-3-1.
• If bolt load requirements change because of a flange alteration, revised bolting procedures shall be developed per EP 5-5-4.

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