This is another example of a change to our process that may not require a wrench to complete, but it is my opinion, as well as now the National Board’s, that changing the service of a pressure vessel is indeed a change that should undergo an MOC. The National Board Inspection Code (NBIC) Part 2, SUPPLEMENT 9, REQUIREMENTS FOR CHANGE OF SERVICE offers a very much needed insight into all that should be considered when changing the service of a pressure vessel. AND for those who purchase USED pressure vessels with a KNOWN HISTORY and your usage would be a “change in service”, you too should consider these items/requirements for your change in service.
S9.2 CLASSIFICATION OF SERVICE CHANGES
S9.2.1 SERVICE CONTENTS
A change in service contents is considered to be any modification to the commodity or contents that the pressure-retaining item was originally intended to contain when the pressure-retaining item was constructed. For example, a change:
a) From LP gas service to air receiver service.
b) From lethal to nonlethal service.
S9.2.2 SERVICE TYPE OR CHANGE OF USAGE
A change in service type is considered to be a change of how the pressure-retaining item is being used. For example, a change:
a) From above ground service to underground service for LP gas tanks.
b) From mobile or transport use to stationary use.
S9.3 FACTORS TO CONSIDER
Before a change of service is to be made, the owner or user shall consider and evaluate the effects of the new operating conditions or environment on the existing condition and suitability for service of the pressure- retaining item. Various factors will have an impact on the reliability of the pressure-retaining item in its new service environment. Changes can be successfully adopted providing there is an understanding of the effect on the pressure-retaining item. However, there are some cases where changes are detrimental to the existing pressure-retaining item. The owner or user should seek the technical guidance of experienced personnel in appropriate areas affected by the change of service (e.g. design, metallurgy, or operations of the pressure retaining item). The following is a listing of criteria that should be evaluated as appropriate. The criterion is not limited to that listed herein.
Other factors may be considered as necessary;
a) Design Consideration
1) The thickness of existing vessel material.
2) Vessel or system flow rate or pressure.
3) The weight of vessel with new contents.
4) Existing or additional loads imposed on nozzles and highly stressed areas.
5) Change in pressure or temperature, and cycling.
6) Compliance to product or industry standards, such as ANSI K61, API 579, or NFPA 58.
b) Material Consideration
1) Chemical and mechanical properties of existing material or any new material to be added or replaced to ensure it has the required strength and toughness to withstand the pressure and temperature effects of the new environment.
2) Effects of erosion or corrosion.
3) Time-dependent effects of service life – creep or fatigue, or both effects combined.
c) Environment
1) The physical condition of the pressure-retaining item.
2) Overpressure protection needs.
3) Regulatory environment – Verification of compliance with new or existing jurisdictional rules or regulations.
4) Vessel cleanliness – When changing lading fluids or contents consideration should be given to cleaning or decontaminating the vessel as appropriate.
d) Operational History
1) A review of current and past operational logs or records should be made to ensure that no conditions existed where any further use would render the pressure-retaining item hazardous or otherwise unsafe.
2) Records to be obtained and reviewed would include Manufacturer’s Data Reports, Repair and Alteration Forms, Inspection reports, etc.
e) Repairs and Alterations Made: A review of any repairs, alterations, ratings, or reconfigurations that have been performed on the pressure- retaining the item, so as to ensure that they will not have a detrimental impact on the intended use.
f) Proposed Rework
1) Any physical work to be performed to restore the material to the existing or intended state or to meet any requirements for the new operating conditions.
2) Repairs and alterations shall be performed in accordance with NBIC Part 3, Repair and Alterations.
3) The effects of heat applied as a result of welding or heat treatment on the material or shaped parts.
4) The method and extent of any physical or nondestructive examination should be considered.
5) Any physical testing or pressure testing to be performed to determine or verify leak tightness or structural integrity of the pressure-retaining item.
6) The pressure-retaining item shall meet the code requirements for the new environment at the time of change.
g) Documentation
1) Review existing records that are required to satisfy customer, user, or legal requirements.
2) Review the need for any marking, stamping, or labeling required for the intended service.
3) Review the need for developing or revising an inspection plan to ensure safe operation. Refer to Part 2, Section 1.5.2.1, Inspection Plan.
S9.4 SOME EXAMPLES FOR CHANGE OF SERVICE
Table S9.4 lists examples of what constitutes a change in service and some factors to consider. Note: This list is not all inclusive. There may be other service changes not mentioned. The listing of “Factors to Consider” is also not all inclusive. There may be other elements that can influence the safe and reliable operation of the pressure retaining item. The owner shall check with the Jurisdiction where the pressure retaining item is to operate in the new environment and review local building codes, laws, and regulations for additional requirements or prohibitions against a change of service.
TABLE S9.4 EXAMPLES OF CHANGE OF SERVICE CONDITIONS
| LP Gas to Ammonia |
|
| Ammonia to LP gas |
|
|
LP gas service: from above ground to underground |
|
| LP gas to air receiver |
|
| Boiler Service: steam to hot water |
|
|
Boiler Service: High-Pressure to Low-Pressure |
|
|
Sulfur Dioxide Service Sweet to Sour Gas Service |
|
|
Inert to Oxidizing or Reducing Atmosphere |
|
| Lethal Service to Non-Lethal |
|
| DOT Railcars of ICC Transport Tanks to Stationary Service |
|
S9.5 DOCUMENTATION OF CHANGE OF SERVICE
Any records, forms, or reports required documenting the change of service event that may be required by contract or the jurisdiction where the pressure retaining item operates shall be completed. Such documentation should be retained by the owner or user for future reference or use as needed.