The CRN should be applied for before construction begins. To quote B51 –

Acceptance and registration shall be obtained before construction is commenced.

For a foreign manufacturer who has a finished vessel, and has been told on the shipping date that the vessel is bound for Canada, this can be a problem. In reality, this requirement varies by jurisdiction.

The Ontario vessel act offers this alternative:

4.(2) A person who submits a design submission for registration may commence construction of the boiler, pressure vessel, fitting or piping before the submission is registered if the person assumes all risks related to the construction, whether for an installation or alteration.

The CRN can usually be applied for at any point in the construction, the risk is that if any changes are required from the review, the vessel will need to be reworked or scrapped. The earlier the CRN can be applied for, the better. See the Provincial Review Times page. Many Canadian manufacturers really do not wait for their CRN before starting production – it takes too long.

Key Point: Register as early as possible! Allow for unusually long review times.  Do not accept liquidate damages clauses on contracts bound for Canada if you are responsible for the registration!