Check Stresses Before Testing

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Check ASME Vessel & Exchanger Stresses Before Testing

The ASME Code requires that all vessels undergo hydro (or pneumatic) testing following fabrication and before Code stamping. As this test provides mechanical stress relief it may be thought of as the final step in the fabrication process. The hydro test is an effective way to screen for design, material and fabrication deficiencies as well as to prove the structural integrity of the equipment.

However, this raises the question – what constitutes a hydro test “design deficiency”? Although ASME Section VIII-1 does not prescribe a test stress limit, vessels that undergo “objectionable distortion” during testing may be rejected by your AI. The COMPRESS Hydro Test Feature assists you by:

  • Calculating component test stresses and warning if they are excessive (objectionable distortion check)

  • Checking for formed head buckling (see details)

  • Checking that the vessel supports can carry the weight of the test water

  • Warning if the test water temperature is too cold (brittle fracture check)

  • Determining the test pressure to apply (as read on the gauge at the top of the vessel)

Is the Hydro Test Report a standard COMPRESS feature?
How do I view it?

Yes, the Hydro Test Report is available to all COMPRESS users. To prepare your report:

  1. Design your vessel or exchanger.

  2. Select your test basis in Set Mode Options > Defaults > Testing.

  3. Press F3 to generate the Code calculations. Click "Hydrostatic Test" on the left to view the report.

  4. Check for overstressed components and revise your design as necessary. To speed your review, COMPRESS also includes any overstressed components in the Deficiency Report.

Criteria for Limiting Hydro Test Stress in COMPRESS

Because ASME VIII-1 does not provide guidelines for determining allowable stress values for the test condition, COMPRESS uses the following method by default. It is taken from the 2004 Edition of ASME VIII-2, paragraph AD-151.1. If needed, you can define a different percentage of yield allowed at test in the Set Mode Options > Defaults > Testing area.

(a) Pm ≤ 0.9 * Sy
(b) Pm + Pb ≤ 1.35 * Sy for Pm ≤ 2 / 3 * Sy
(c) Pm + Pb ≤ 2.2 * Sy − 1.5 * Pm for 2 / 3 * Sy < Pm ≤ 0.8 * Sy

 

In the equations above,  Pm is the primary membrane stress and Pb is the primary bending stress. The yield stress Sy is taken as the smallest of the shell, reinforcing pad or nozzle neck Sy values.

The discontinuity stress state at a nozzle includes both primary membrane and bending components. As equation (a) governs for shells and either equation (b) or (c) governs for nozzles, the test allowable may be different for nozzles and shells even when they are made from the same material.

For further information, please see the Hydro Test section in our Support Center.

If you don’t have software that performs hydro test calculations, it’s time to explore the benefits of COMPRESS. Find out more by emailing sales@codeware.com or calling (941) 927-2670.

2017-03-16T15:43:51+00:00July 28th, 2010|Categories: COMPRESS, Power Users|Tags: , |

About the Author:

Codeware was founded in 1983 in Ontario, Canada. We opened our first U.S. office in 1993. We currently have offices in Sarasota, Florida and Austin, Texas. Codeware's founder, Les M. Bildy, P. Eng., has served as President since 1983.