Do I Need A Fitting With a CRN?

Updated Oct 13 2015, Sept 8 2016 LRB

Fittings are small pressure containing devices, either stand alone or attached to piping or vessels. In most countries these fittings do not require registration. The Canadian B51 based CRN system is a more restrictive, more inclusive system that requires registration on many of these fittings.

The B51 Charts (Table 1 below) indicate whether a pressurized device is a fitting or a vessel. Do you need to use a registered fitting for your application? Unfortunately this is a difficult topic.

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Fitting Classification

Fittings are broken down into categories for registration. A manufacturer must apply separately with different statutory declarations for each category that their registered product line covers. This unfortunately increases the registration costs but has allowed BC and Saskatchewan to declare categories A, B, C and G as not requiring registration. They no longer provide CRNs in these categories, and they no longer require them on registered vessels or piping systems. Other provinces still require these items to be registered. (BC Safety Authority and Technical Safety Authority of Saskatchewan.) (Also, Quebec has future plans where category A, B and C will not require registration – contact RBQ for more information on your project.)

CSA B51-14 Table 1: Categories of Fittings
Category Type of Fitting
A Pipe fittings, including couplings, tees, elbows, wyes, plugs, unions, pipe caps, and reducers
B All flanges
C All line valves
D All types of expansion joints, flexible connections, and hose assemblies
E Strainers, filters, separators, and steam traps
F Measuring devices, including pressure gauges, level gauges, sight glasses, levels, and pressure transmitters
G Certified capacity-rated pressure relief devices acceptable as primary overpressure protection on boilers, pressure vessels and pressure piping, and fusible plugs
H Pressure-retaining components that do not fall into Categories A to G
(1) These categories do not take into account size, materials, end connections, ratings, schedules, and methods of fabrication.
(2) Category H can include
2(a) small pressure vessels registered and inspected as specified in Figures 1(a), (b), or (c). Such pressure vessels shall be designed and constructed in accordance with Clause 7, except that items that fall under Figures 1(a) and (b) may be designed and constructed to Clause 8, provided that the pressure vessel
2(a)(i) does not require full radiography in accordance with the ASME Code;
2(a)(ii) does not have a quick-actuating closure;
2(a)(iii) is not in cyclic service; and
2(a)(iv) is 4 NPS or smaller;
2(b) an assembly of components (including piping components), provided that the diameter of any component does not exceed 152 mm (6 in) and the total volume of the assembly does not exceed 42.5 L (1.5 ft3). Such an assembly is considered a single Category H fitting for the purposes of fitting registration; and
2(c) condenser coils and evaporator coils as defined in CSA B52 and air heater coils, provided that the diameter of any component does not exceed 152 mm (6 in) and the design pressure does not exceed 4.14 MPa (600 psig).

Notes 1 and 2 bring Canada wide registration closer to the current Alberta practices. Clause 7 is for pressure vessels, clause 8, piping and fittings. The addition of clause 8 to fittings 4″ or less diameter now makes it possible to register category H items like filter housings made of die cast aluminium in Alberta.

Where provinces have legislation requiring items like medical/dental autoclaves of fitting size to be registered, they are now registered as vessels (clause 7) instead of fittings (clause 8). This can be an important change for both the manufacturers and end users. The fittings as vessels require authorized inspector sign-off and National Board registration.

Refer to the CSA B51 Graphs (Fig 1a, 1b, 1c) to determine if you have a vessel or a category H fitting. The above dimension limitations only apply to category H fittings. Category A-E fittings can be any size and remain a fitting.

Do I Have A Vessel or a Category H Fitting?

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 mater 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? See: Do I Need A Fitting With a CRN?


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 – Do I Need a Registration?

Standard Fittings that are Exempt from Registration (Vessels Only)

Every fitting on a registered pressure vessel or a registered piping system needs a CRN unless it is exempted. B51 clause 4.2.1 provides an exemption:

All fittings shall be registered… unless they form a part of a boiler or pressure vessel that is subject to inspection by an authorized inspection agency…

This exemption is universal in its scope – exempting any fitting. In practice provincial jurisdictions will only use this exemption for items found in ASME VIII-1 table UG-44 which covers:

  • B16.5 flanges
  • B16.9 wrought butt weld fittings
  • B16.11 forged fittings
  • B16.15 bronze threaded fittings
  • B16.20 metallic gaskets
  • B16.24 cast copper alloy pipe flanges and fittings
  • B16.42 ductile iron pipe flanges
  • B16.47 large diameter flanges

All other items not found on this list require CRNs for use on pressure vessels. Contrary to the B51 standard, CRNs are also not required for these same fittings when used on a UM vessels which are not subject to inspection by an Authorized Inspector. This exemption does not apply to Assemblies of Components.

Assemblies of Fittings

A fitting can also be a collection of other fittings. Per CSA B51-14 Table 1 Notes(2):

Category H can include (b) an assembly of components (including piping components), provided that the diameter of any component does not exceed 152 mm (6 in) and the total volume of the assembly does not exceed 42.5 L (1.5 ft3). Such an assembly is considered a single Category H fitting for the purposes of fitting registration;

This is like a miniature piping system. A recent requirement is that these assemblies of components must now be made from registered components. Sections of pipe are calculated. Custom components made by the manufacturer require calculations or burst tests or separate CRN registration. All other parts need CRNs.

Fittings in Piping Systems

Manufacturers of UG-44 listed standard components would need CRNs for use in registered piping systems or assemblies of components. This picture shows when the same fittings require registration or not.

Categories of Fittings

The standard flanges, couplings and elbows listed in UG-44 located on the CRN registered UM vessel (not subject to authorized inspection) do not require CRNs. The identical flanges, elbows and couplings located on the registered piping system which will be inspected by an Authorized Inspector do require CRNs. Although it does not make any sense, this is how the rules are currently being applied.

Special Rules on Stand Alone Fittings

Fittings not attached to piping or vessels do not require registration. Most provinces also have special rules requiring and exempting classes or types of fittings in specific services. These requirements are usually outlined in the provincial vessel/piping safety rules. (Provincial Contacts)

Example: air powered shell launchers for avalanche control are stand-alone fittings that have to be registered in some provinces.

Registration Confusion

Primarily due to confusion, customers will request registration on items that cannot be registered, like pipe (which is not a fitting but a calculated part of a pressure vessel or piping system), or items that do not require registration for the service that they are in. It can be easier for a customer to request a CRN than determine if it is required or not. A manufacturer often cannot determine if a fitting needs a CRN without knowing their customer’s intended service.

A CRN is often used as a marketing tool. Competition with a registered competitor can lead to CRN registration even if it will never be required for the service the fitting will see. It is also less confusing to have a CRN even if it is not required.

Flowchart for Fittings

Disclaimer: While every effort is made to make these pages accurate and up to date as the CRN system changes, this information is only the opinion of Laurence Brundrett P. Eng., President of Pressure Vessel Engineering Ltd.