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 Manitoba to declare categories A, B, C exempt from registration provided they are designed to standards listed in Table 126.1 (B31.1), Table 326.1 (B31.3), Table 526.1 (B31.5) or Table 926.1 (B31.9). Category G is also exempt from registration if designed to ASME or National Board. Saskatchewan has an outright registration exemption for fittings in category A, B, C, and G. 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.  (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
Notes
(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).

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.