What is the "PMCap Repair Method", and how does it differ from other repair methods?
  • The PMCap repair method restores pressure retaining components to Code compliance by encapsulating the degraded area to form a new pressure boundary.
  • The PMCap forms a new pressure chamber and is installed as an Alteration to the vessel. 
  • PMCaps are supplied as ASME Section VIII or Section III stamped component PARTS.  PMCap repairs satisfy NBIC and API 510 criteria.
  • The PMCap is welded to the outside surface of a component using a full penetration weld and replaces the encapsulated pressure boundary. 
  • Code compliance is restored without requiring degraded area removal.  Cutting of pressure boundary, foreign matter intrusion, and exposure of vessel internals to the environment, is eliminated.
  • The PMCap includes a corrosion allowance, or can be constructed of corrosion resistant material or with a corrosion resistant liner.
  • PMCaps are designed and constructed to ASME Code rules and are supplied as ASME code-stamped components.  The complete package includes hardware, partial data reports, shop fabrication drawings, material test reports, and certified calculations.
  • The "PMCap Repair Methodology" is Patent Protected under U.S. Patent 6,860,297 and is the exclusive property of PMC Engineering Solutions,
To what Codes are PMCaps constructed?

PMCaps can be constructed to numerous Codes and Standards including but not limited to ASME Section III, Class 1, 2, 3, or MC, ASME Section VIII, Div. 1 or Div. 2, ASME B31.1, ASME  B31.3, API 620, and API 650

How are PMCaps different from lap plates?

PMCaps have an undercut and hub that allows for full penetration to the component wall.  Lap plates on the other hand are fillet welded to the component wall.  The fillet welds or lap plates are inherently subject to failure due to fatigue due to cyclic thermal and pressure loading.  The National Board Inspection Code does not permit repairs using lap plates.

Can't I just perform a weld overlay on the external side of degraded pressure retaining component wall?

Non - the National Board Inspection Code requires that weld overlay to restore degraded wall be performed on the internal surface of the degraded component wall.

What are the advantages of a PMCap repair vs. the traditional "flush patch" or "weld overlay" methods of repair?

The PMCap repair alleviates many negative aspects of traditional repairs.  Advantages of the PMCap repair method include but are not limited to:  The PMCap:

  • does not require cutting out local degraded material areas
  • requires minimal preparation of pressure retaining material.  In contrast, "flush patch repair" or "weld build-up repair" methods may require significant weld preparation.
  • generally smaller than flush patch.  Flush patch must match surrounding material thickness.  PMCaps may be attached to sound material of any thickness that meets code requirements.
  • eliminates exposure of personnel to lethal or hazardous fluid contents such as chemical, gas, or radioactive fluid contents of a pressure retaining item.
  • eliminates potential damage to internal parts of pressure retaining items such as damage to tubes of heat exchangers
  • eliminates potential intrusion of foreign materials into the internals
  • simplifies any required hydrostatic or pneumatic testing of pressure retaining item since pressure boundary is not breeched
  • is not limited to a specific geometrical shape and may be constructed to most any regular or irregular shape including but not limited to round, obround, square, or any combination of the these shapes.
  • May be split to encapsulate nozzles.
  • generally only requires surface examination of attachment welds, however, full volumetric examination of welds is possible
  • satisfies all ASME Code criteria, National Boiler Inspection Code, API-510 Pressure Vessel Inspection Code, and has been accepted by State Jurisdictional Authorities and major insurance carriers
Do you perforate the shell prior to installing the cap to make it a true pressure boundary?

The degraded component wall may have a small hole drilled in or may be completely removed with no affect on the PMCap or vessel Code compliance.  However, we do not recommend it as remaining wall acts as a corrosion/erosion barrier.  Over time the component wall that is degrading may waste away sufficiently so that it opens itself up to the internal chamber of the cap.  At that time the PMCap becomes pressurized.

Can you measure/monitor the thinning on the shell once the cap is installed, in the degraded area?
No, unless access port are provided within the PMCap.  Monitoring metal loss in the encapsulated wall is not required.  All encapsulated material is considered as sacrificial and for analytical purposes to have completely wasted away.  Design calculations take no consideration of either encapsulated wall material or the margin in the wall of the pressure component surrounding the PMCap.  All code wall reinforcement for the encapsulated area is 100% built into the cap.
Is the PMCap machined from plate or forging?

Both.  Actually, the PMCap may be constructed using any type Code approved material (bar, casting, pipe, etc.).  It depends on both the Code, economics, and schedule needs for the PMCap.  Typically, plate and forging are used for ASME Section VIII, PMCaps and the material selection is based on final configuration and economics.  For ASME Section III, forgings would primarily be used, although we do have designs where plate can be used.

How have you validated all aspects of design on the cap in compliance ASME III Division 1?

Yes.  PMCaps have undergone detailed analytical evaluations and are supplied with P.E. certified design calculations.  Our calculations have been review by numerous customer engineers and their A/E's.  There have been no concerns or issues regarding Code compliance.

You mention in your literature that the NRC has "accepted" the component, how have they "accepted" this?

Entergy's James A. Fitzpatrick Nuclear Power Plant encapsulated a degraded area of their Torus.  This "Code Repair" was reviewed and accepted by the NRC.

What is the purpose of the PMCap being "undercut"?

An undercut is machined in the PMCap to form a skirt (hub) on the PMCap.  The PMCap is then formed to fit the curvature of the component to which it is being attached.  The skirt (hub) of the PMCap allows for full penetration welding of the cap to sound wall of the component being repaired

What ASME III Division 1 or ASME VIII Div. 1 or Div. 2 applications can the PMCap Repair Method be applied to?

This repair method can be applied to repair of any Code pressure retaining component - vessel, heat exchanger, piping, metal containment component, etc.

Is the intent of the cap to be a permanent or temporary fix?

All PMCaps are constructed for Permanent Restoration of the degraded component.

Is there any concern of the degrading area spreading outside the location of the cap?

No - jurisdictional authorities and insurance companies mandate the required time period wherein all pressure retaining components must be inspected.  PMC Engineering will perform a Fitness for Service of the equipment using as found component wall values, time in service, and conditions of operation to size the PMCap so that it encapsulates any and all shell area that would, over its required design life, degrade to below the Code minimum value.  Design life for PMCap designs have ranged from 1 1/2 years to 30 years.  In all cases we would expect that the PMCap would last longer than the equipment that it is being used to repair.  PMCaps can be supplied with adequate corrosion allowance - lined with corrosion resistant material or weld overlay - made of corrosion/erosion resistant materials. Also the chamber can be completely filled with a corrosion/erosion barrier material or various types of refractory material. 

Does PMC Engineering perform installation?

Installation of PMCaps is quick and simple.  Typically installation is performed by the owner's maintenance department or maintenance contractor.  PMC can assist the owners in selection of qualified and experienced PMCap installers.

Are PMCaps stock items?  What is the general lead time to obtain them?

Each PMCap is custom designed for a specific need and application.  Typical lead time is 10 weeks standard delivery and 4 weeks expedited delivery.

Emergency delivery is available.  PMCaps maintains an inventory of pre-tested and Code certified material and can construct and deliver PMCaps in emergencies in as short a time as 1-3 days.

What information does PMC Engineering need to design an PMCap?

The following information is required depending on the extent of PMC Engineering's Work Scope

I. ASME Code- Section III and Class, or Section VIII and Division 
II. ASME Manufacturer's Data Report - this document will provide original design information.  If not available then the following information is required:

a. Original Code of Construction including Edition and applicable Addenda. (i.e. 1998 ASME Section VIII, Div. 1, 1965 ASME III, thru Summer 66 Addendum)
b. Design Pressure and Temperature - Internal Pressure
c. Design Pressure and Temperature - External Pressure
d. Material - shell, head, nozzles, nozzle reinforcement pads
e. Original design corrosion allowance
f. Original radiography / joint efficiency factor (E)
g. Vessel Drawing showing dimensional data and material thickness values

III. If Fitness for Service Evaluation and design of PMCap encapsulation component is in the vicinity of a nozzle, or for a nozzle encapsulation, then provide Nozzle Loadings

IV. NDE measured thickness data. [Data in Excel (.xls) format, where available, is preferred]

V. Hours of Service to date (or as of a specific date) for the Vessel

a. Service hours at original operating conditions to date (or as of a specific date) for the Vessel
b. Service hours at power uprate operating conditions to date (or as of a specific date) for the Vessel
c. Power uprate percentage
[Note: above information is not required if size and configuration of PMCap or vessel area to be encapsulated is specified by client]

VI. Number of years of continued Code compliant future service desired without need for inspection after evaluation/repair.

a. At original operating conditions
b. At power uprate conditions
[Note:  above information is not required if size and configuration of PMCap or vessel area to be encapsulated is specified by client]

VII. PMCap material of construction desired if other than Standard.

a. Standard Material of construction is carbon steel (Weld Number P1).  A stainless steel (weld Number P8) impingement barrier liner is generally used but most all other materials such as low alloy steel (CrMo) are available.
b. Additional material requirements such as impact testing

VIII. Size, thickness, and attachment fillet weld size where temporary lap plates are to be encapsulated.