Generic Designs

It is desirable that Manufacturers be able to maximize the use of their registered designs. Hence the desire to register generic designs. However, 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.

  • The design conditions (MAWP, design temperature & MDMT) must be fixed.

  • Vessel diameter and shell and head thicknesses must be fixed. Maximum and minimum
    lengths shall be shown on the drawing.

  • Materials of construction must be fixed. Reasonable substitutions identified on the
    drawing may be permitted. An example of an acceptable substitution would be
    SA-106 Grade B for SA-53 Grade B.

  • Corrosion allowance must be fixed.

  • All optional nozzle sizes must be identified.

  • For each nozzle size in the shell of the vessel, only one configuration of minimum nozzle neck thickness, minimum internal projection, minimum weld size(s) and added reinforcement shall be permitted. Some leeway would be permissible for fittings covered by UW-16(f). See sketches below.

  • For each nozzle size in the heads of the vessel, only one configuration of minimum nozzle neck thickness, minimum internal projection, minimum weld size(s) and added reinforcement shall be permitted. Some leeway would be permissible for fittings covered by UW-16(f). See sketches below.

Note that different types of small fittings may have different spacing requirements for the same NPS connection because of the different size openings in the pressure vessel.

  • Only one dished head form may be used on a design. For small vessel diameters (up to 24″ O.D.), optional flat heads or flanged ends with blind flanges are permissible, if detailed on the drawing.

  • 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. See Note below.

  • Any provisions for openings in nozzle necks shall be detailed as for nozzles themselves.

  • Any provisions for communicating chambers such as sumps, boots or domes must be fully detailed, including the form of the closure. These and any openings in them shall be treated the same as nozzles with respect to separation from any other nozzles or communicating chambers.

  • Nozzle outboard ends may show options of being flanged, threaded, beveled for welding, grooved etc. Care must be taken that the minimum required nozzle neck thickness is maintained in grooved or threaded ends. (Ref. UG-45)

  • The applicable welding procedure specifications must be identified.

  • Where applicable, postweld heat treatment holding temperature and holding time must be specified.

  • It is permissible to identify that, where postweld heat treatment is not a Code requirement, postweld heat treatment may be performed at an identified holding temperature for an identified time, provided that the drawing also stipulates the welding procedures to be used in the event that PWHT is performed as a customer request.

  • Nozzles in heads must be sufficiently reinforced so as to meet Code whether they are in the dish region or the knuckle region; otherwise, the nozzles and the material required for reinforcement shall be confined to the dish area alone. This latter shall
    be done by limiting the nozzle centreline offset from the centre of the head.

  • Nozzles must be defined as being normal to the shell or head surface or otherwise defined such that all nozzles can be shown to be adequately reinforced in any permitted orientation. Finished opening size must be established for each nozzle size, position
    and angle of intersection with the vessel shell or head or with a communicating chamber shell or head.

  • The minimum extent of radiography or other Code-required nondestructive examination shall be specified.

  • Inspection openings must be identified and may not be moved significantly from the locations shown or eliminated from the finished vessel. Such a note must appear on the drawing. This applies equally for Code-required vents and drains.

  • Bills of materials must identify every piece of pressure-boundary material that might be used in any vessel built to the registered generic design.

  • Vessels may be shown as supported optionally horizontally or vertically.

  • All applicable Code requirements must be shown to have been met.


Attention is drawn to the requirements of UG-36(c)(3) which can further limit spacings in clusters of three or more nozzles for which reinforcement calculations would not be necessary if the nozzles were isolated. Note that, where small nozzles have been calculated to show adequate reinforcement, the requirements of UG-36(c)(3) for clusters will not apply. It is suggested that for thin wall designs, demonstrating that as many small nozzles as possible are adequately reinforced will give the greatest flexibility to the design.

ABSA is supportive of the registration of generic designs. It must be appreciated though, that when creating a generic design, the designer will be giving up some design flexibility. It would not be practicable, for example, to include nozzle positionings varying from “on the centre line of head” to “tangential to the shell and parallel to the vessel centreline” (maximum offset on the head) or to include every combination of width and thickness of reinforcing pad to provide a given area of reinforcing material. In our experience, Manufacturers who have a need for generic vessel designs are generally involved in the supply of vessels for very specific services, e.g. air receivers, refrigeration vessels, propane vessels etc. There is typically no real value in trying to include every conceivable nozzle size, position, angularity and proximity to any other opening. There would likely be a typical number of nozzles, in fairly predictable locations, for a given type of vessel. The Manufacturer knows his product line best, so he should keep the generic design aligned with that. Trying to include every variation imaginable, even though a configuration has never been made and probably will never need to be made, is a waste of time.

Remember, the originator of a generic design expects to get more value from the registered design, so it is only reasonable that more work must go into preparing and presenting the design. One can’t get something for nothing.

Last Modified: 2/14/2019 4:25:28 PM