PetroStreet

In refinery , practically under what conditions do we require each O-lets ( Weldolets , threadolets, Elbolets, sockolets, latrolets)...?

Any idea?

Scockolets - are used for taking branch connection in smaller sizes up to 1-1/2" for piping upto 600# rating (see note 1)
Weldolets - are used for taking branch connection in sizes from 1/2" to like 6" or 8" for piping above 600# pressure rating (see note 1)
Note 1: The difference between sockolet and weldolet is towards branch end connection which is socket welded in sockolet and butt welded in weldolet. Later having more strength.
Threadolets - are used in screwed / threaded piping having branch side end connection of threaded joint. They are only used when all the piping is having threaded connections having low pressure conditions
Elbolets - are used to take tapping from elbows for inserting thermowells, pressure gauges, venturi or taking a branch connection. These are used only under some specific requirements.
Laterolets - are used where an odd entry into the running pipe is required to be given in order to have smooth flow into the running pipe with minimum flow interruptions.

Thank you very much Sir for your valuable response.

In case of latrolets , Is there any specific chemicals which require minimum flow interruptions.???

Latrolets are used where minimum resistance to flow is required.

Is there any specific chemicals which require minimum flow interruptions.???

You are welcome novice.
Chemicals not particularly. It depends on the flow conditions, in order to induce lesser turbulence, lesser delta P. Need for latrolet is always a call by process engineer.

Thanks you boss

1) What is the criteria for using reinforcing Pad for stub-ins . when we will use reinforcing pad for stub-in and when we will not?

Regards

There is no short cut to assess the requirement of reinforcing pad else performing calculations as described in relevant design code.