# How to Avoid Zero Anchor Loads?

Read
about START-PROF pipe stress analysis software

### Why Software may show Zero Anchor Loads?

While stress analysis and supporting considerations it is always a better
engineering practice to provide line stops or axial stops or anchors at
the neutral point of the straight portion of the piping. It is believed
that at the neutral point, thermal movement is zero and frictional resistance
equalizes from both sides of the piping system. In such a scenario, the
frictional forces cancel out as forces are positive at one side and negative
at the other. Also as there is no thermal movement, there will be zero
axial loads due to temperature effect. So, the software will show zero
anchor loads in such locations.

### Example of Zero Anchor Loads

For example, In the following symmetric system with two U-shape loops
as shown in Fig. 1, The leg length on both sides of the intermediate anchor
is equal. Thus the intermediate anchor node 11 becomes a neutral point.

Fig. 1: Symmetrical piping system with Intermediate
Anchor

As can be seen in Fig. 2, The load along the pipe in an intermediate
anchor (node 11) will be zero.

Fig. 2: Zero Anchor Load for the System
shown in Fig. 1

In reality, the piping heating up can be uneven, the friction forces
can be different on the left and right part of piping, piping design can’t
be ideal. Therefore, the real load on the anchor will not be zero.

### How to Avoid Zero Anchor Loads?

To avoid such a situation the Anchor Factor “k” is used in piping stress
engineering practice. In PASS/START-PROF piping stress analysis software
this is a built-in function in Loads on supports
and restraints table.

- If loads from pipes to the left and right of the support (N1
and N2) are in the same direction, they are combined as N1+N2
- If loads N1 and N2 are in different directions, the lower
values are multiplied by k and then combined as N1+N2*k (|N2|<|N1|)
- If the support is on an end node, factor k is not used

Factor k applied only for loads in the horizontal plane: axial force,
lateral force, horizontal moment.

The common value, that is recommended by some piping stress analysis
codes is k=0.8. If we use 0.8 value the result will be as shown in Fig.
3. and Fig. 4.

Fig. 3: Actual Anchor Load in Axial Direction

Fig. 4: Intermediate Anchor with Actual
Anchor Load in Start-Prof

The following training video shows how to
create this model. It takes 2 minutes: https://youtu.be/BaFlJa57UXA