Hi,

As per cl. 5.3.2 of ASME sect. VIII Div.2 the sum of the local primary membrane plus bending principal
stresses shall be ≤ 4S. Can someone tell me whether these bending principal stresses are primary or secondary.

Regards

sachinpawar,

These are primary stresses not secondary, it is my opinion.

_________________
Thanks & Regards,
Nasir
Welding Engineer
DESCON Engineering Limited.
Lahore, Pakistan.
Mobile # 0092-336-4145402

In my opinion not necessarily. It depends from the location and origin of the stress. Table 5.6 gives you some advice if it´s primary or secondary.

Michael

Yes ; at a given location stresses may be primary or secondary or both.

But the limit of 4S (for the sum of principal stresses of membrane plus bending) is to be applied only for primary.

For example for a location away from discontinuity, we shall not consider the through thickness thermal gradient which will introduce secondary bending.

In the nozzle near the junction, the stress coming from FEA will include discontinuty effect; One should separately calculate the primary stresses separately; say hoop and longitudinal stresses under pressure loading. In case of nozzle loading, within limits of reinforcement, FEA will include gross structural discontinuity where as M/z plus axial force /area plus pressure longitudinal stress calculated manually will not include any secondary (discontinuty effect).
In short any secondary stress shall be identified and omitted while checking for 4S

With regards

_________________
R.SRINIVASAN
Sr. VICE PRESIDENT
Head, Design and Engineering
PED,ISGEC,
YAMUNANAGAR
HARYANA -135001
INDIA

Thanks a lot for the reply. Now I want to analyse nozzle to shell junction for piping loads. Please advise whether piping loads due to thermal expansion shall be excluded while carrying out elastic analysis as stresses due to thermal loads will be secondary stresses.

Regards,

Sachin Pawar

Aker Solutions

Already suggested by Mr Frohnert, please refer to Table:5.6. If you incldue loads that are attributable to free end displacement (nozzle loads coming ut of thermal analysis of piping), the bending load is Q and you have to consider for computing PL+Pb+Q

whereas nozzle loads arrived at excluding those arrived at due to restrained free end displacement of attached piping then bending is primary and is required for 4S limit.

Hence as per my understanding and interpretation, both are required. In some projects, where piping routing is not completed but vessel is to be designed and manufactured, some standard nozzle loads are provided. It may not be specified whether these nozzle loads include free end restrained effect or not and moreover only one set of values are provided and in such cases you may have to exercise a conservative judgement.

_________________
R.SRINIVASAN
Sr. VICE PRESIDENT
Head, Design and Engineering
PED,ISGEC,
YAMUNANAGAR
HARYANA -135001
INDIA