You Should Be Registering Generic Vessels!

Back in the pre-history* of the CRN system it was recognized that the cost and delay of registering vessels was an unacceptable obstacle to business in Canada. These were the 2 week / $100 days, not our current era. A solution was worked out: jurisdictions could register generic designs.

*The pre-history of the CRN system as used here is defined as the time before PVEng started up in 1999, but in this case it predates the spinning off of the safety organizations like ABSA and TSSA from their parent government departments in the mid-1990s.

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 huge 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 a huge variety of nozzles on the heads and shell. The location and spacing of the nozzles can change. All these changes can be covered in one drawing and calculation set.

ABSA has written a guideline outlining what can and cannot change in a generic design. Reading the ABSA guide is a good start. Also please refer to our sample below.

The Balance

The designer needs to choose how much to include in the generic design. Not every option can be included; some unusual designs will still have to be registered one off. 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. Even with these restrictions a huge 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.

Getting Registered

The calculation set covering all of the options tends to be long and the matching drawing dense. The weight of paper of a generic registration is about 2.5x more than a comparable one-off. We estimate that there is about 2.5x as much work for designer and the reviewer. The jurisdiction reviews often take twice as long. We budget 2x the registration fees.

Using the Registered Generic Design

Once registered, the work is not done. The registered generic drawing is usually too complicated to build from. Usually 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 scope previously registered and therefore it is acceptable to use the generic CRN number. No new registration is required!

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.

The cost

Generic_Vessels_Image1

The photo here is from a generic registration for seven related vessels differing in diameter. The weight of paper shown is 38.5lbs, representing the mail out after the first province signed off. The total weight of submitted paper is 45 lbs (6.5 lbs per vessel). For reference, a full box of paper with 10 reams weighs 49 lbs. The registration process Canada wide took about one year. Registration fees totalled $16,800 (or $2400 per vessel), higher than would be expected for a series of related one-off designs. If these were not generics, the total weight would be around 15 pounds and the expected total review time about half a year.

Fabricators located outside of Canada still have to pay the National Board registration fees on each batch produced. This batch of 7 vessels can be National Board registered for $128 (cheaper if you file electronically). There is no registration delay with National Board.

The Benefit

Once the cost and delay of the first registration process is covered, the remaining production costs and times are the same as for vessels sent to countries other than Canada. 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 lead to design changes ultimately leading to the need to update the generic design.

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 is accepted as generic even if it is not registered as generic? When manufacturers build left/right pairs of vessels, we only register one hand – the drawing does not have to state that a mirror image part will be built. This has worked every time. Also, producing a vessel with a lower pressure rating without changing the design is acceptable. Shortening the length of a shell is usually accepted. Although this changes nozzle spacings, often the AI can see at a glance that nozzle interferences are not a problem. Lengthening the shell is less likely to be accepted. Removing nozzles is not a problem unless they are required for inspection. Adding nozzles that are identical to existing nozzles is usually acceptable.

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 Big Idea – A Return to Sanity

Yes the process is long and 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 – an unknowable variable – have been removed. Your designs have been locked down because different reviewers with differing requirements will not be looking at each job you are building. 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 balance of this article only considers generic vessels.

The important point to take home is that manufacturers with lines of related products can save cost, time and pain by doing more registration work up front. Go for it!