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
$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
- 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
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:
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).
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).