Nozzle Loads : Types & Considerations

One of the challenges for any piping stress engineer is to ensure that the loads on the equipment nozzle are within allowable limits. Nozzle loads are the thrust loads and moments exerted on mechanical equipment from the thermal expansion and weight of the connected piping and equipment.

All the mechanical equipment connected to piping systems can be categorized into two main groups, namely Static Equipment and Rotating Equipment.

Static Equipment

EPC companies generally follow project-specific, defined allowable values for static equipment made of steel and ferrous materials. Some of the standard static equipment used in Oil & Gas industry are pressure valves, columns, shell & tube heat exchangers reactors, separators, filters, tanks, drums, and other similar types of equipment. The table is prepared considering two essential parameters – nozzle diameter and flange rating. It is crucial to understand how the used equipment interacts with the other aspects of the plant, especially piping.

The mechanical engineer’s team is responsible for sending the defined load tables to the equipment manufacturers. It indicates a minimum table value to design the noddle connections. Hence, it avoids any confusion at a later phase.

Typically, for most of the mechanical equipment, nozzle loads are to be obtained from the manufacturers, vendors, or some ASME B31.3 code specified standards depending on the type of material. In the unavailability of vendor data, relevant codes like API 661, API 662, API 650, API 560, API 621, or any other proven international practices/codes can be used.

Rotating Equipment

Different types of rotating equipment are designed based on some fixed codes and standards. And, according to the selected code, the limiting loads are taken from respective standards.

Let’s have a look at some commonly used types of equipment mentioned below:

Centrifugal Pumps (Radial flow, Semi-axial, and Axial flow pumps): The centrifugal pumps used in EPC industries are designed based on the defined API standards, suitable loads have to be taken from API 610. For nozzle sizes above 16 inches, the ANSI standard is considered for allowable loads. And, for non-API pump, loads are generally obtained from the vendor.

Positive Displacement Pump (piston, gear, screw): It is recommended to use API 676 for allowable nozzle loads. Or else, loads can be taken from the vendor.

Reciprocating Pumps: Loads are obtained from the vendor.

Centrifugal Compressors: It is recommended to use API 617 for defining limiting loads.

Steam Turbine: Use API 612 or refer NEMA SM 23 for equipment nozzle loads.

Gas Turbine: Loads are to be obtained directly from the manufacturer.

Now, what’s the reason behind the increase in the nozzle loads on equipment than the allowable values? Let’s read on to find ways to minimize the nozzle loads.

In case of lesser flexibility, try reducing the nozzle load by accumulating some additional flexibility in the piping system.

If you experience more load due to the weight of the piping system, then provide additional support.

Provide proper restraints to direct the thermal expansion away from the equipment

In extreme conditions, you can consider applying an expansion joint or cold spring.

Also, hot modules of elasticity can be used to calculate equipment nozzle loads.

To conclude, nozzle loads are one of the most essential and sensitive components of piping stress analysis. It is mandatory to keep nozzle loading as per company standards. We hope that the considerations and parameters mentioned above for the nozzle loading of various equipment will help you evaluate it for your next project. If you seek help for static and rotating equipment engineering, consider hiring an expert engineering team for optimal design and great value.

Judith Morrison is an expert in the field of industrial engineering and writes articles related to piping, civil, equipment engineering related articles.