Rotating Equipment

API 610 Nozzle Loads: Table 5 Allowable Forces & Moments

Why piping loads on a pump's nozzles must be limited, how API 610 (12th ed.) Table 5 is organized by flange size and orientation, the nozzle coordinate system, and how full acceptance is done per Annex F.

Launch Calculator See Table 5

Basis

Table 5

Allowable nozzle forces & moments by flange size and orientation.

NOTE 2

± allowable

Each tabulated value is a range −val to +val; direction does not change the limit.

Full qualification

Annex F

Combined two-nozzle + displacement check; conditional 2× allowance.

Contents

Use this guide when you need to:

  • Understand the failure modes excessive nozzle loads cause.
  • Read API 610 Table 5 allowables by size and orientation.
  • Know when a Table 5 exceedance needs an Annex F check.

1. Why Nozzle Loads Matter

Every length of pipe bolted to a pump pushes and twists on the pump's suction and discharge nozzles. Thermal growth, pipe weight, spring-hanger setting, valve actuation, and fit-up gaps all impose forces and moments on the nozzle flanges. API 610 limits these loads because a pump is not a structural anchor — it is a precision machine with internal running clearances measured in thousandths of an inch.

The failure chain

When piping loads exceed what the casing was qualified for, the consequences cascade:

Effect What happens
Casing distortion The pump case deflects and the wear-ring and impeller clearances close up or go eccentric, causing internal rubbing and lost efficiency.
Shaft misalignment The casing movement springs the bearing housing and pulls the coupling out of alignment with the driver.
Seal damage Misalignment and shaft deflection force the mechanical seal faces open, leading to leakage and short seal life — the single most common pump failure mode.
Bearing failure Off-design loads and vibration shorten bearing life well below the API 610 rated minimum.
Baseplate / soft-foot High nozzle loads transmit through the feet into the baseplate, undoing field alignment.
The design intent: By holding piping loads to API 610 Table 5, the casing distortion and coupling misalignment stay inside the tolerances the pump manufacturer qualified the machine for — preserving seal life, bearing life, alignment, and rated performance.

This is why a competent pipe-stress model of the pump suction and discharge lines is a standard deliverable on any API 610 installation, and why the piping engineer and the rotating-equipment engineer must agree on the allowable nozzle loads early.

2. The Nozzle Coordinate System

API 610 defines a right-handed coordinate system at each nozzle so that the allowable in Table 5 can be tied to a physical direction. The axes are defined relative to the nozzle and the pump shaft:

Force axes (per nozzle): FX = parallel to the pump shaft (axial) FY = vertical (perpendicular to the shaft) FZ = horizontal, perpendicular to the shaft (transverse) Moment axes: MX, MY, MZ act about the corresponding axes. Resultants: FR = √(FX² + FY² + FZ²) MR = √(MX² + MY² + MZ²)

Nozzle orientation

The same flange can sit on the pump in three orientations, and the force allowables differ between them because the casing is stiffer in some directions than others:

Orientation Description
TopNozzle points vertically upward.
SideNozzle points horizontally, transverse to the shaft.
EndNozzle points horizontally, along the shaft axis (typical end-suction).
Moments are orientation-independent. In Table 5 the moment allowables (MX, MY, MZ, MR) are identical for top, side and end nozzles — only the three force components change with orientation.

3. How API 610 Table 5 Is Organized

Table 5 in API 610 (12th ed.) tabulates the maximum allowable force and moment for each nozzle as a function of nominal flange size and nozzle orientation. Allowables increase with flange size, since a larger, heavier-walled nozzle and casing can react more load.

NOTE 2 — each value is ±. Every number in Table 5 is the magnitude of an allowable range, from −value to +value. You compare the absolute value of each applied load to the tabulated number; the direction of the load does not change the limit.

USC allowable forces (lbf) by flange size (NPS)

Component ≤2346810121416
Top FX1602403205608501200150016001900
Top FY1302002604607001000120013001500
Top FZ20030040070011001500180020002300
Top FR290430570101015602200260029003300
Side FX1602403205608501200150016001900
Side FY20030040070011001500180020002300
Side FZ1302002604607001000120013001500
End FX20030040070011001500180020002300
End FY1602403205608501200150016001900
End FZ1302002604607001000120013001500

USC allowable moments (ft·lbf) — same for all orientations

Component ≤2346810121416
MX340700980170026003700450047005400
MY17035050087013001800220023002700
MZ260530740130019002800340035004000
MR4609501330231035005000610063007200

SI values (forces in N by DN ≤50–400, moments in N·m) are tabulated in the same Table 5 and are selectable in the calculator. Source: API 610 (12th ed.) Table 5.

4. Single-Nozzle Screen vs Annex F

Comparing each nozzle's loads to Table 5 is a per-nozzle screen. It is conservative and fast, and it is the right first check during piping layout and the kickoff of a pipe-stress analysis. But Table 5 alone is not the full acceptance criterion.

What Annex F adds

API 610 Annex F gives the complete qualification method, which considers the pump as an assembly rather than two independent nozzles:

  • Evaluates the combined loads on the suction and discharge nozzles together.
  • Accounts for the resulting pump and baseplate displacements and shaft/coupling alignment shift.
  • Conditionally permits loads up to twice (2×) the Table 5 values when those displacements are evaluated and shown to keep the pump within acceptable limits.
The practical workflow: screen each nozzle against Table 5 first. If everything passes, the installation is comfortably acceptable. If a load exceeds Table 5, the pump is not automatically disqualified — it triggers the full Annex F assessment, which may still pass under the conditional doubled allowable.

⚠️ Scope of this tool: this calculator performs only the single-nozzle Table 5 screen. The conditional 2× allowance and the two-nozzle / displacement checks of Annex F are not implemented here — complete those with the full Annex F procedure and the pump vendor's data.

5. Worked Example

Check the loads on a 6 NPS top nozzle (USC units) against API 610 Table 5.

Step 1 — Look up the Table 5 allowables (6 NPS, top):

FX = ±560 lbf   FY = ±460 lbf   FZ = ±700 lbf   FR = 1010 lbf
MX = ±1700 ft·lbf   MY = ±870 ft·lbf   MZ = ±1300 ft·lbf   MR = 2310 ft·lbf

Step 2 — Applied loads:

  • FX = 300, FY = 200, FZ = 400 lbf
  • MX = 1000, MY = 500, MZ = 800 ft·lbf

Step 3 — Per-axis check (|applied| ≤ allowable):

|300| ≤ 560 ✓   |200| ≤ 460 ✓   |400| ≤ 700 ✓
|1000| ≤ 1700 ✓   |500| ≤ 870 ✓   |800| ≤ 1300 ✓

Step 4 — Resultant check:

FR = √(300² + 200² + 400²) = 538.5 lbf ≤ 1010 ✓
MR = √(1000² + 500² + 800²) = 1374.8 ft·lbf ≤ 2310 ✓

Result: PASS — all six components and both resultants are within the Table 5 single-nozzle allowable.

Now raise FX to 900 lbf. Because |900| > 560, the FX check fails and the overall screen returns FAIL. The pump is not yet disqualified — this is the trigger to run the full API 610 Annex F assessment.

Key Standards & References

  • API 610 (12th ed.) Table 5 – Nozzle Loadings (allowable forces and moments by flange size and orientation; NOTE 2 = ± values).
  • API 610 Annex F – Criteria for piping design / full nozzle-load qualification, including the conditional doubled allowable.
  • API 610 §6.2 – Pump nozzle and casing construction requirements.
  • API 686 – Machinery installation and installation design (alignment, baseplate, grouting).

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Frequently Asked Questions

What are API 610 nozzle loads?

API 610 nozzle loads are the external forces and moments connected piping imposes on a pump's suction and discharge nozzles. API 610 (12th ed.) Table 5 lists the allowable force and moment for each flange size and nozzle orientation, and per NOTE 2 each value is a ± allowable.

Why do pump nozzle loads matter?

Excessive piping loads distort the pump casing, springing the shaft out of alignment and overloading the mechanical seal and bearings, which causes short seal life, premature bearing failure, internal rubbing, and lost efficiency.

What is API 610 Annex F and the 2× rule?

Annex F is the full multi-nozzle qualification: it evaluates the combined loads on both nozzles plus pump and baseplate displacements, and can conditionally permit loads up to twice the Table 5 values when those displacements are checked and shown acceptable.