Determining if you have a vessel or fitting only applies to items that look like large or small pressure vessels. Determining if you have a vessel or fitting only applies to Category H, the items that do not fit into other categories. These Category H fittings often look like miniature vessels.


This accumulator (which has a lot in common with a vessel) is either a Vessel, a Category H Fitting, or does not need registration – see the charts below…

These charts are from the Canadian B51-14 standard and include more items as pressure vessels than the definition found in ASME VIII div 1 section U-1.

Service Categories

There is a grey area when it comes to determining if vessel contents are more hazardous than water. For assistance in deciding which chart to use, it is useful to have Material Safety Data Sheets (MSDS). The MSDS sheets will not specifically tell you which chart to use, but a review of the “Toxicity” and “Health Effects and First Aid” on the MSDS can help you decide. The jurisdictions are not responsible for classifying service; it is the responsibility of the owner/user to perform this evaluation. Lethal service is defined in the B51-14 code, what is more hazardous than water is not:

Lethal substances — poisonous gases or liquids of such a nature that a very small amount of the gas or of the liquid’s vapor mixed or unmixed with air is dangerous to life when inhaled. For the purposes of Part 1 of this Standard, this definition includes substances of this nature that are stored under pressure or can generate pressure if stored in a closed vessel.

Vessel or Fitting Charts

Important note: These charts are from the Canadian B51 Standard. Each province also has a pressure vessel regulation which modifies these charts. Be sure to check the regulation for the province that your product will be shipped to!

B51 Figure 1(a)

Figure 1(a): Registration and inspection requirements for pressure vessels (and pressure vessels registered as Category H fittings) for liquid service with liquids not more hazardous than water

B51 Figure 1(b)

Figure 1(b): Registration and inspection requirements for pressure vessels (and pressure vessels registered as Category H fittings) containing a non-lethal gas or vapor or a non-lethal liquid not covered by Figure 1(a)

B51 Figure 1(c)

Figure 1(c): Registration and inspection requirements for pressure vessels (and pressure vessels registered as Category H fittings) containing lethal substances

Each chart references Table 1 (above), Clauses 4.1.1 and 4.8.2 below:

CSA B51-14, 4.1.1: The calculations, drawings, and specifications pertaining to the designs of boilers, pressure vessels, fittings as specified in Clause 4.2, fired-heater pressure coils, and piping shall be submitted to the regulatory authority in the province where the item is intended to be used. The submission shall identify the substance for which the item is intended. It shall be the responsibility of the users or an agent they designate to determine whether the substance is lethal. Figures 1(a), (b), and (c) shall be used to determine whether items are to be registered as pressure vessels or Category H fittings (see Table 1). The name of the authorized inspection agency to be employed when a boiler or pressure vessel is to be manufactured outside Canada shall also be submitted when required by the regulatory authority. Acceptance and registration shall be obtained before construction begins. Manufacturers who commence construction prior to receiving design registration shall rectify any design deficiencies that are identified in the design registration process.

CSA B51-14, 4.8.2: Vessels shall be subject to individual shop inspection except as follows: (a) low-pressure steel boilers with 4.5 m2 (50 ft2) or less of wetted heating surface; (b) cast iron and cast aluminum sectional boilers; (c) miniature pressure vessels, as defined in Section VIII, Division 1, of the ASME Code, when the manufacturer has registered its quality control manual with the regulatory authority where the manufacturing shop is located and has completed a manufacturer’s data report for miniature pressure vessels [see Figure D.1(a)]; (d) hot water tanks, hydropneumatic tanks, and cushion tanks not exceeding 762 mm (30 in) in diameter (with no limit on capacity); (e) propane storage tanks for recreational vehicles not exceeding 0.09 m3 (3.2 ft3) in volume and 2153 kPa (312 psi) in design pressure; (f) electric boilers of a capacity up to 60 kW; and (g) small pressure vessels registered as Category H fittings and inspected in accordance with Figures 1(a), (b), and (c).


Every province has exemptions or modifications to the B51 requirements. As an example, TSSA takes complete exemption to charts 1a, 1b and 1c above. Instead they use:

Fitting Fittings as categorized in [B51] Table 1 including those described in NOTE 2 that are not attached to a boiler, pressure vessel, or piping under the Act, are exempt from CSA B51. Additional notes to CAD amendment: The definition for fitting identifies that it is not a fitting unless the fitting is attached to an item such as a boiler, pressure vessel or piping system that is under the regulation and this is consistent with O. Reg. 220/01. That is stand-alone items that are best categorized as fittings are exempt and this includes category H items e.g. pressure vessels with a volume less than 1.5 cubic feet or a small piping system that has an internal diameter less than 6″ and internal volume less than 1.5 cubic feet. [Code Adoption Document (CAD) BPV-13-01, March 11, 2013, 1.3 ii]


Figures 1 a), b) and c) are revoked and replaced with the following: Figures 1 a), b) and c) Items less than 6″ in internal diameter or less than 1.5 cubic feet in internal volume are classified as Category H fittings not pressure vessels. [Code Adoption Document (CAD) BPV-13-01, March 11, 2013, 1.29]

these two definitions of fittings from the code adoption document are not the same, working with the definition from Code Adoption Document section 1.29 we get this chart:

Vessel or Fitting in Ontario

Items that are Always a Fitting

These charts do not apply to all Category A-G fittings listed above.  For example, a valve no matter how large is always a fitting. Not being in Category H, the above charts do not apply.


Not a Category H fitting – always a fitting no matter what size…

Fabrication of Vessels vs Fittings

A Pressure Vessel must be built in a shop with an accredited quality control program, and the finished vessel inspected by an Authorized Inspector (Except UM vessels which are inspected by the shop). A CRN (Canadian Registration Number) is required, and is written on the manufacturers data form. The CRN is also stamped on the vessel nameplate.

For a pressure vessel built outside of Canada, the shop’s National Board and U-stamp authorization would be proof of the quality control program. The fabricator has to CRN register AND National Board register the vessel.

A Fitting that needs to be registered also has to be built to a quality control program, but the inspection will be by the shop that fabricated it, according to the shop’s quality control program, proof of which is included in the registration package.

Does your fitting need registration?  If it’s part of a piping system, the answer is always yes.  If it’s on a vessel, the answer is a little more complicated, but usually no.  If the fitting you are using is built to a specification listed in Table U-3 of Section VIII-1, you can use it on your vessel without a CRN.  If the standard is not listed in Table U-3, you need to use a registered fitting.


The above charts do not include piping, the definition for which can be found in B31.3:

300.2: “piping: assemblies of piping components used to convey, distribute, mix, separate, discharge, mete, control , or snub fluid, flows.”

CSA B51 2009 – 11.4: “a series of components (including piping components) joined together to form a single fitting, provided that the diameter of any component does not exceed 152 mm (6 in) and the total volume of the fitting does not exceed 42.5 L (1.5 ft3).can be registered as Category H fittings.”

The registration of piping can be more restrictive than vessels or fittings, so registering small piping systems as fittings is a considerable convenience. See more about piping at: Piping Registration