Stoomwezen design case

Some companies supply only "the Stoomwezen design case" to Stoomwezen. There seems to be a misunderstanding. It is true that the assessments according to the "Rules for Pressure Vessels" are based on design pressure and design temperature. However, this does not mean that only the case with an overall hot (or cold) design temperature should be provided. Loadcases, which lead to higher stresses should be considered and the results at least be reported to Stoomwezen. Different texts in D1101 of "The Rules for Pressure Vessels" are clear about that.

$3.1 of sheet D1101 states:
"Piping systems shall be analysed for the effect of thermal expansion, pressure, weight and wind loading for all applicable sets of operating conditions".

$2.3 of sheet D1101 states:
"If the piping system is intended for use in more than one set of operating conditions, these shall be stated separately".
Examples of cases to be considered are:

  • Cases for which the interaction between hot parts and cold parts of a piping system cause stresses, which are higher than when all parts are hot.
  • Cases when temperature alternates between temperatures above and below assembly temperature, causing a higher stress range then between assembly temperature and design temperature.


Just like any other load (see line 25 p.7 of D1101), friction shall be included in the analysis if relevant. Line 8 of p.10 of D1101 says:

"Approximate and simplified methods of analysis may be applied only within the range for which it has been demonstrated to the satisfaction of the competent body that they are sufficiently accurate".; friction is mentioned in the small symbols.

For Stoomwezen it is important to assess the highest load case. It is understood that friction is included in most analyses. The most severe load case of the two (with or without friction) should be send to Stoomwezen and report that the other one leads to lower stresses (with the exceptions, if any).

Nozzle loadings

Stoomwezen has a sheet for this specific subject (D1141). Moreover $3,2 of D1101 states:

"The load on attachments and structural parts (constructiedelen) attached to the piping system and also the internal forces and moments at the location of piping components (flange connections, valves and the like) in the hot or cold condition shall be determined...."

In the past Stoomwezen did not always ask for allowable nozzle loads. Anyhow engineering companies will agree that nozzle loads are important for the integrity of a system, which makes it a Stoomwezen related matter. The fact if the Rules do or do not give solutions for calculating stresses is not relevant then.

So it should be shown that on in-line flanges and flanges on strain sensitive equipment in particular, the most severe combined loadings, resulting from computer runs with and without friction are acceptable and also to the manufacturers specifications of the connecting parts (including vessels).