Glossary

Connection loads

Connection loads are the forces and moments a piping system transmits to connected equipment, machinery, valves or supporting structures.

Also: Interface loads · Equipment loads · Terminal point loads

Also known as

Interface loads
Equipment loads
Terminal point loads

What a pipe transmits to its connection

Every pipe ends at something: a pump, a vessel, a heat exchanger, a turbine or the steel structure. At that point it hands over three forces and three moments. They result from weight including contents and insulation, but above all from restrained thermal expansion – the pipe wants to grow and the connection resists. Pressure thrust from unrestrained expansion joints, wind, earthquake and pressure surges add to this.

The pipe itself may be perfectly acceptable. Stresses in the pipe and loads on the connection are two separate checks – and the second is often the harder one.

Where the allowable values come from

Allowable connection loads are stated by the manufacturer of the connected equipment. For centrifugal pumps the figures are often based on API 610 or ISO 13709, for steam turbines on NEMA SM 23, where the limits are particularly low. For vessels and heat exchangers the fabricator either specifies allowable loads or verifies the loads reported by the piping designer.

Every value comes with a reference point and a coordinate system. Without these two pieces of information a table of allowable loads cannot be applied.

How connection loads are calculated

A pipe stress analysis delivers the forces and moments at the connection node for each load case. What matters is how the connection is modelled. Equipment is not an immovable anchor: it expands itself and its nozzle moves with it, and this movement is imposed on the pipe as a displacement. The flexibility of a vessel shell can reduce the loads noticeably if it is included in the model.

The comparison covers not only the hot operating condition but also the cold condition and – where required – occasional loads.

Reducing excessive connection loads

The same order nearly always works: routing first, supports second, special components last.

Add flexibility: longer legs perpendicular to the direction of expansion, or an expansion loop.
Take the weight: a support close to the nozzle, a spring hanger where the pipe moves vertically.
Direct the expansion: place guides so that movement runs away from the connection.
Reduce friction: low-friction sliding supports near sensitive machinery.
Expansion joints only once the routing options are exhausted – they bring forces and maintenance of their own.

Common mistakes

Most exceedances arise not in the calculation but in its assumptions.

The equipment is modelled as rigid and immovable; its own thermal growth is missing.
The manufacturer’s coordinate system and that of the analysis model are mixed up.
Only the operating condition is checked, not the cold condition after installation.
Friction at sliding supports is neglected.
Allowable values are requested only after the pipe has been routed.

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Overview

Connections and their allowable loads

Connection	Source of allowable values	What matters
Centrifugal pump	Manufacturer, often based on API 610 / ISO 13709	Alignment of shaft and coupling
Steam turbine	Manufacturer, often based on NEMA SM 23	Very low allowable values
Vessel, heat exchanger	Fabricator or nozzle verification	Stress in the vessel shell
Flanged joint, valve	Flange check, valve manufacturer’s data	Tightness under bending moment
Steel structure, building	Structural engineer	Loads per support and load case

Frequently asked questions

Frequently asked questions about Connection loads

What is the difference between connection loads and nozzle loads?

Nozzle loads are the connection loads at the nozzle of a vessel or other equipment. Connection loads is the broader term: it also covers loads on machinery, valves and supporting structures.

Why are the allowable loads on pumps and turbines so low?

Because the limit is not the strength of the casing but its deformation. Even small distortions disturb the alignment of shaft and coupling and load the bearings and shaft seals.

Who is responsible for compliance?

The piping designer determines the loads; the equipment manufacturer states the allowable values. Both need to be coordinated early – while the routing can still be changed.

Does an anchor directly in front of the nozzle help?

Rarely. A short, stiff piece of pipe remains between anchor and nozzle, and the thermal growth of the equipment itself generates high loads in it. A support with a deliberately chosen function is usually the better solution.

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