Pressure Vessel FAQs

What information is needed to design custom pressure vessels?

When designing custom pressure vessels, we require the following details:

  • Size (diameter and length or capacity)
  • Vessel orientation (horizontal or vertical)
  • Type of supports (saddles, legs, skirt or support lugs)
  • Design pressure (internal and external)
  • Design temperature (min and max)
  • Corrosion allowance (if applicable)
  • Material of construction
  • Product including design specific gravity
  • Openings: Quantity, size, type and location
  • Type of external paint or internal lining if applicable.
  • Appurtenances: internals, insulation supports, ladders or platforms
  • Location of installation for wind/ seismic design and freight estimate
  • Specifications beyond ASME requirements

Please use our Request For Quote form to submit your requirements.

What is the minimum design pressure requiring an ASME label?

Design pressures exceeding 15 psig are generally ASME labeled and considered ASME pressure vessels. However, vessels that meet all ASME code requirements may be labeled at a lower pressure when requested by the customer.

What is the maximum design pressure covered by ASME Section VIII, Division 1?

The maximum design pressure for ASME pressure vessels covered by ASME Section VIII, Division 1 is 3,000 psig. Higher design pressures require special evaluation and consideration before they can be labeled to Division 1.

Why are two saddles preferred over multiple saddles for larger pressure vessels?

Two saddles are preferred due to the potential for unequal loading with multiple saddle support points.

What is the typical minimum design temperature that does not require additional design considerations?

Pressure vessels with a minimum design temperature of -20 Degrees F generally do not require additional design considerations.

What are some common types of heating or cooling jackets or coils for jacketed pressure vessels?

  • Conventional Jacketed Pressure Vessels: A secondary shell and/or head typically fabricated with a 2-3” space from the primary vessel.  Advantages: These jacketed pressure vessels can accommodate heavier corrosion allowances. Cut-outs can be located to accommodate nozzles passing through the jacket. Disadvantages: The external pressure on the inner vessel due to jacket pressure can require a heavy internal vessel wall.
  • Half Pipe Jacketed Pressure Vessels: Split pipe or extruded half pipe shapes welded to shell or head. Advantages: Suitable for high pressures on jacket side and for improved heat transfer.  Disadvantages: Can be difficult to route around supports and openings that pass through the jacket area into the primary vessel.
  • Internal Pipe Coils: Typically 2” or 3” NPS internal pipe coils. Advantages: Cost effective and more efficient heat transfer.
  • Bayonet or Bundle Type Insert Heaters: Pipe or tube bundle type heater inserted through a flanged opening. Advantages: Easy to replace.
  • Clamp-On Jacketed Pressure Vessels: Various types. Double inflated type from gauge material is common. Jacket is bolted onto the vessel with clips. Heat transfer mastic is typically used between the vessel and jacket. Advantages: Easily replaced. Disadvantages: Can be a high cost long lead item. Nozzles passing through the jacket must be finalized early in the design process to allow prefabrication of cut-outs into the jacket.
  • Dimple Jacketed Pressure Vessels: Sheet type material welded directly to the vessel on 1.5” to 2” centers. Advantages: Cut-outs for nozzles can be easily located to allow nozzles passing through jacket to inner vessel. Better heat transfer than clamp on style. Does not require an increase in shell thickness due to jacket pressure. Disadvantages: Thin wall material is not acceptable for heavier corrosion allowances. Fabrication is labor intensive. Difficult to repair.

How are external nozzle loads incorporated into pressure vessel design?

Nozzles are not designed for external loads unless specifically requested by the purchaser. When nozzle loads are required for pressure vessels, common approaches include:

  1. Purchaser provides loads for a few specific nozzles, (example agitator).
  2. Purchaser provides a predefined table of nozzle loads by nozzle size to be incorporated into the initial estimating design.
  3. Purchaser requests allowable nozzle loads. The nozzle is designed for pressure and temperature, and then back calculated to determine allowable external loads. This is the most expensive, least desirable method and may provide allowable loads too low to be practical.

External loads are not normally considered in reducing the flange pressure ratings unless specifically requested by the purchaser.

The loads are generally applied to the intersection of the pipe and vessel wall vs. the end of the nozzle flange.

The cumulative effects of the nozzle loads are not considered in the design of the vessel supports.

Typical methods of calculating nozzle loads include Welding Research Council bulletin 107 (WRC 107) or Finite Element Analysis (FEA).