Troubleshooting Calculation Warnings

This article works through the situations that produce a warning on a support datasheet: what the software is telling you, why it happened, and what your options are.

A note before starting. Pihasa Assistant proposes a model even when checks fail. It returns the closest available option rather than nothing. So a completed datasheet with warnings is not a failed calculation — it is a calculation asking for a decision.

No valid model found

The load and movement combination has no candidate in the catalogue.

Why: usually one of three things. The load is outside the catalogue range for that support type. The movement exceeds what any model of that type can absorb. Or the installation length available is too short for any part that would otherwise fit.

What to check first: the units. A load entered in newtons on a project configured for kilograms is out by a factor of about ten — far enough to fall off the end of the catalogue, and the most common cause of this message.

Then:

• Confirm the Load Calculations setting on a double support. Reading a per-support load as per-spring doubles the design load.
• Check whether the support type is right. Large vertical movement points to a constant rather than a variable spring.
• Check whether the project is set to add accessory weights to the load, which can push a borderline case out of range.

In some extreme cases, a practical solution for supports that are out of range due to excessive loads is to double the support quantities and split the load into two halves, or even into three or four.

Variability exceeds the allowed limit

The load change between cold and hot conditions is larger than the limit set for this support or project.

In order of effectiveness:

1. Select a softer spring series. CVL or CVLL for the same size have lower spring rates and therefore lower variability for the same movement. This is the intended fix and usually resolves it.
2. Reconsider the support type. If even the softest series exceeds the limit, the movement is too large for a variable spring. A constant spring has zero variability by definition.
3. Review the limit itself. The default is a general-purpose value. A project specification may permit more on non-critical lines — but changing the limit to make a warning disappear is only legitimate if the specification supports it.

See Hot load, cold load and variability.

Position outside the recommended travel range

The operating or installed position falls in the outer band of the spring’s stroke — still inside the physical limits, but with little margin.

Why it matters: the margin exists to absorb the difference between calculated and actual movement. A spring that reaches its stop stops acting as a spring and becomes a rigid restraint.

Options:

• Select a model with a longer travel
• Define explicit travel reserves so the software sizes with more margin
• Verify the movement from the stress analysis — an overstated movement produces an oversized travel requirement
• Accept the selection, being aware of the fact that it is close to the limit

See Travel and travel reserves.

Position outside the admissible travel range

More serious than the previous one: the position falls outside the physical stroke. The model cannot work.

Treat this as no valid model found for that particular model and select another.

Hydrostatic test load exceeded

The test load is above the capacity of the load-bearing parts.

First, verify the value. The hydrotest load is the weight of the water-filled line at this support — not the test pressure, and not the operating load times a factor.

Then:

1. Add an additional temporary support for use during the test. Standard practice on large vapour lines where the test load is disproportionate.
2. Accept with documented justification, if your specification permits a reduced factor for a controlled one-off test.

See Hydrostatic test check.

Material quality not valid at this temperature

The selected Pipe Attachment Quality is outside its permitted service range.

This is not a capacity problem and cannot be resolved by reducing load. Change the quality to one rated for the temperature.

If the temperature looks wrong, check whether you left Operational Temperature blank — the software then assigns a default based on the material quality, which may be higher than your actual service condition.

See Temperature and material quality.

Vertical deviation angle warning

The hanger swings more than 4° out of plumb when the pipe displaces horizontally.

Options:

• Lengthen the hanger. The angle falls as the hanging height rises.
• Offset the installed position: hang it deliberately out of plumb in the opposite direction to the movement, so it passes through vertical at mid-travel. This halves the maximum deviation and belongs as a note on the drawing.
• Below 8°, accept and document — frequently the right answer where the absolute movement is small.

See Vertical deviation angle.

Lateral load exceeds the allowable

On a clamp base, guide or U-bolt, the lateral load is above the permitted fraction of the vertical load.

Note that the calculation continues. The software applies a reinforcement rather than rejecting the design, and the reported weight rises above the catalogue value. An unexplained weight on a clamp base is usually this.

Options:

• Add an anti-rotation trunnion, which removes the lateral check
• Provide a separate lateral restraint and reduce the load on this support

Axial load exceeds the allowable

Same family of problems.

Minimum distance between axes not met

On a double support, the two load-bearing elements do not have physical clearance for the pipe, its insulation and the components.

Increase the distance between axes, or select smaller components if the loads permit.

Rod length returned as zero

Not a warning about the design — a signal that the geometry is impossible. The structure elevation has come out below the pipe elevation.

Check that the elevations are the right way round and that both are correct.

Still stuck?

If a warning does not match anything above, or the behaviour looks wrong rather than merely restrictive, contact Pihasa with the project file and the support tag.