You Should Be Registering Generic Vessels!
Two of the most common complaints we hear with respect to the CRN system revolve around the length of time it takes to complete a registration and the costs involved. For some manufacturers it may be possible to combat both of these concerns by using generic registrations.
What is a Generic Design?
A generic registration covers a range of possible vessel configurations in one CRN. Without changing the operating conditions, diameter, wall thickness and material, a wide variety of changes can be made to a vessel. It can be vertical or horizontal. Its length can change within an acceptable specified range. It can have an extensive variety of nozzles on the heads and shell and the location and spacing of these nozzles can change. All these changes can be covered in one drawing and calculation set.
ABSA has written a very useful guideline outlining what can and cannot change in a generic design. Reading the ABSA guide is a good start along with a review of our sample below.
Generic Design Limitations
The designer needs to decide how much to include in the generic design. Not every option can be included; some unusual designs will still have to be registered separately. The number one option for generics is a large range of nozzle designs: configurations, sizes. Note that Alberta restricts the number of variations allowed on each nozzle size. ABSA:
…only one configuration of minimum nozzle neck thickness, minimum internal projection, minimum weld size(s) and added reinforcement shall be permitted [per shell or per head].
The largest problem is normally covering the location and spacing of the nozzles. This is covered in a nozzle spacing table (see our sample job). ABSA again:
Nozzle quantities and positions shall preferably be fixed. If this is not the case, tables specifying the minimum centre-to-centre distance in inches or millimetres between any two nozzles shall be provided.
More time is usually spent on the issue of nozzles than all others combined, but a large number of options are possible.
Also typically covered are options like vertical and horizontal mounting, varying shell lengths and varying mounting locations for external equipment. The generic drawing needs to have all the desired options documented.
What’s Involved with Registration
The calculation set needs to cover all of the build options and will be longer than a typical one-off design. Likewise, the drawing needs to show all of the possible configurations and will be more complicated than a single design. As a result, the submission package is larger and the engineering and reviews take more time. We budget extra time for the registration and about twice the standard amount for registration fees.
Despite the additional time and cost, if you plan to build even one derivative of the initial generic design, it pays for itself immediately. There is no need to submit anything for additional units after the initial registration, so there is zero time spent on the CRN process and no costs incurred for any units beyond the first one.
Production can continue until the code changes or the manufacturer updates their design. Recent B16.5 flange weld size and Appendix 2 flange flexibility updates are examples of code changes that could require updates to the generic design.
Using a Generic Design
The registered generic drawing is often too complicated to build from. Typically the fabricator makes a new drawing for each application, which refers to the registered drawing. The Authorized Inspector can verify that the new drawing falls within the registered scope so that the generic CRN number applies.
The generic calculation set is reviewed by the shop and Authorized Inspector on a yearly basis, the same as for repeat production of unique CRN designs or regular National Board fabrication. For fabricators outside of Canada, National Board registration is also required on each production batch with vessels destined for Canada.
All Vessel Registrations Are Generic
The generic drawing is deliberately set up to allow the AI to review a derived production part without need to review code calculations. The generic drawings with limits on length and nozzle spacing tables are specifically set up to make this process easy. However, all designs are generic to a limited extent, even if derived designs were not considered at the time of original registration. ABSA’s guideline is “an inspector performing his Authorized Inspector duties in the Manufacturer’s shop or looking at a vessel in the field should be able to quickly see that the vessel is covered by the registered design.” AI’s are willing to sign off on some designs as being generic even if they do not meet the guidelines presented here. Following these guidelines makes the process easier and more certain.
What changes can be made to a registered design without having to submit a new CRN application? If you make a change to the design that requires a calculation to be modified, or new calculations run, you need to update the existing CRN or apply for a new one. Making changes that do not change the calculations in any way are all acceptable under the original registration. Manufacturing a vessel for a lower design pressure without changing the design is acceptable. Left and right versions of a vessel only require a single registration, and the drawing does not need to state that a mirror image design will be built. Shortening the length of the shell is typically not a problem. Although this can change nozzle spacing, the AI can see at a glance whether nozzle interference is a problem. Nozzles can be moved and removing them is not an issue, unless they are required for inspection.
Adding new nozzle designs, raising design temperatures, lowering MDMT, changing inspection and changing materials beyond the original scope are all grounds for new or revised CRNs. If an AI will allow the CRN to be used on a derived design, then the original design is generic.
The process is longer and more expensive, but picture the upside – once complete you have a series of vessels that can be built the same as if the CRN system did not exist and Canada was only part of National Board. Future registration costs and delays have been removed. Your designs have been locked down because design review with the potential for changing requirements is not required each time you make a derived design. More companies should seriously consider generic registrations.
These concepts also apply to the registration of fittings. The difference is that fitting registrations can be much more flexible. The restrictions on the diameter, material, wall thickness, pressure and temperature do not apply to fitting registrations. All details must still be covered in the calculations, testing and drawings, but with fewer restrictions.
The important point to take home is that manufacturers with lines of related products can save time and cost by doing more registration work up front. Go for it!