CRN Essentials

As the year progresses and new codes are published, there are a few things to keep a lookout for, particularly with respect to material property requirements.

Two materials are of particular interest, and are reportedly likely to change with the 2019 edition of ASME Section VIII-1. The potential ramifications of these changes on pressure equipment designs and CRNs are quite significant and interesting.

SA-105, Specification for Carbon Steel Forgings

As many Canadians can attest, particularly this year, Canada is not a stranger to cold weather. The thermometer drops below -29C (-20F) with uncomfortable regularity here. As such, impact toughness characteristics and impact test requirements are of primary concern when designing pressure equipment for Canadian use. Nobody wants a pressure boundary to crack and lose containment.

With respect to the SA-105 material specification, somewhat recent brittle fracture incidents at relatively moderate temperatures have been reported, despite adherence to current code rules. As is, ASME Section VIII-1 2017 lists the SA-105 specification as a curve B material per ASME Section VIII-1 Figure UCS-66. We understand that the 2019 Edition of ASME Section VIII-1 will likely change this and instead list SA-105 as a curve A material, thereby requiring impact testing for SA-105 when it wasn’t required before.

We are relatively unsure about whether reclassification of A105 will immediately be reflected by the newest anticipated edition of ASME B31.3 or ASME B31T.

Regardless, the reclassification of SA-105 will be of interest to industry. SA-105 is a common choice for flanges and other forgings for all sorts of pressure piping, and would likely be one of the most, if not the most, prevalent type of carbon steel forging currently used in pressure equipment design.

Since this code change will be more stringent than recent requirements, the onus will be upon end users and manufacturers to ensure that pressure equipment being made, sold and used meets current code requirements. Over the recent past, code changes have instead relaxed requirements in general and so designs with pre-existing CRN were automatically grandfathered by subsequent code changes.

It will also be interesting to see how regulators administer this code change given it makes the code more stringent than what was originally required for pre-existing registered CRNs. Regulators maintain an archive of all registered designs and can compel manufacturers and end users to adapt to more stringent code requirements as needed.

Grade P91 Alloy Steel

This material seems to be a preferred choice for some thermal power plant station designs, given its reported relatively high strength at high temperatures.

However, concerns about P91 material failures and measurements of reduced strength in some circumstances have reportedly led the 2019 Edition of ASME Section I to consider substantial reductions in allowable strength! Minutes from a recent Pressure Equipment Sub-Council meeting report that expected allowable strength reductions are to be in the order of up to 19%!!

As you probably know, permitted pressure is directly proportional to the strength of the material containing that pressure. If code requires that the allowable strength of P91 pressure boundaries to be reduced by 19% then, excluding corrosion allowance if any, the maximum permitted pressure will also be reduced by a proportional amount.

The effect on the existing power plant operation and future designs could be substantial. For reliable and efficient operation, design conditions of power plants are carefully controlled and specified. Needless to say, a prescribed pressure reduction in maximum operating pressure could be, at best, very problematic for the power industry and the public that depends on electricity.

Similar to code changes relating to the SA105 material specifications, it will be interesting to see how regulators administer code changes relating to P91 grade material, given these changes make the code more stringent than what was originally required for pre-existing boiler CRNs. On behalf of the public, regulators must be satisfied that pressure equipment designs are as safe as, or safer than, what current code requires. Regulators maintain an archive of all registered designs and can compel manufacturers and end users to adapt to more stringent code requirements as needed.

Well, hopefully this won’t sound repetitive, but CRN registration is required unless an exemption or Variance applies!  Requirements vary by province/territory – some regions have specific exemptions and others have more general ones.  Alberta has an entire regulation devoted to some exemptions.  See this article for more .

And, of course, CRN registration is required before the pressure equipment is operated in Canada.  To follow the legislation and CSA B51 even more carefully, CRN registration is required before the pressure equipment is even built, while still at the finalized design stage.  So as to avoid a whole host of complications, a good rule of thumb to follow is that CRN registration is required before the assembled equipment leaves the manufacturer.

But sometimes, this is not possible.  For example, boilers assembled in the field obviously need to be put together after leaving the manufacturer but nevertheless, the design should have a CRN well before assembly.  As another example, unregistered code stamped vessels can potentially be registered after they leave the manufacturer, but the rule of thumb stated above is the best way to avoid issues.

For those unfamiliar with CRN requirements, the obvious question is why are CRN numbers required?  No other nation beside Canada has them.  One reader recently wrote to ask these questions: Do CRN numbers improve safety, or help Canada to be competitive?  Our answer was that given their indirect reference in public safety legislation, governments in Canada recognize the importance of CRN numbers.  They help to ensure that pressure equipment is designed, built and tested to codes and standards that have, through careful collective deliberation, been written to help ensure public safety by using adequate safety margins and other considerations.  In Canada, designs that meet code and legislated requirements are competitive.

Canadian Registration Numbers (CRN numbers) are used by provincial governments to record,  document, and ascribe responsibility for pressure equipment designs in Canada that are non-exempt from registration.  The exemptions associated with each province should be considered carefully for each type of design to ascertain the differences between each jurisdiction.  If a Canada wide CRN number is required then the jurisdiction that has, on balance, the most stringent requirements with the fewest exemptions should be identified and applied to first  – pursuant to harmonization and efficiency.

Similarly, revisions or additions to a CRN number must be registered in related regions following a particular sequence to avoid issues. Permission from the province that first issued the CRN is needed before the revisions in another region can be registered.  And this can cause problems and delays if this requirement is not known.

For example, suppose a category H fitting or a vessel design was registered in Ontario first and then registration was subsequently sought in Alberta.  Further suppose that Alberta (ABSA) requirements exceed those in Ontario for the design in question.  In that case Ontario will need to consider the revised design before ABSA will consider registering it with the same CRN number.

CRNs follow a format as specified in CSA B51 and are first issued by the region identified by the digit following the decimal point.  Other registration numbers for alternative or special designs are issued numbers with a different format, but they are relatively rare. CRN numbers are unique for each design.  Referencing specific CRN numbers cannot be done without linking the design owner.  Without owners’ written permission, publication of CRN numbers could cause confidentiality issues.