How Should Nonconforming Tower Internals Be Handled Before Shipment?
Custom tower internals are manufactured to project-specific drawings, materials, dimensions, and inspection requirements.
During fabrication, an inspection may occasionally identify a condition that does not fully match the approved requirement.
Examples may include:
a dimension outside the specified tolerance;
an incorrect hole location;
a weld that does not meet the acceptance requirement;
a material identification problem;
local deformation;
an incorrect segment interface;
a missing component;
a fabrication detail that differs from the approved drawing.
The correct response should not be:
“It is close enough—ship it.”
Nor should every deviation automatically mean the entire component must be scrapped.
The appropriate approach is to identify the nonconformance, determine its engineering significance, define an approved disposition, complete the required corrective work, and close the issue before shipment.
For custom tower internals, this quality-control process is particularly important because a small workshop deviation can later become a much larger installation or hydraulic problem inside the tower.
What Is a Nonconformance?
A nonconformance exists when a product, material, dimension, fabrication detail, inspection result, or document does not meet an applicable approved requirement.
The reference requirement may come from:
approved manufacturing drawings;
purchase specifications;
material specifications;
project standards;
inspection and test plans;
agreed tolerances;
approved fabrication procedures.
The first question is therefore not:
“Does this part look acceptable?”
The first question is:
“Does the actual condition conform to the approved project requirement?”
Without a defined reference, quality acceptance becomes subjective.
Identify the Nonconformance Clearly
An NCR should describe the actual condition precisely.
A useful record normally identifies:
component or drawing number;
affected location;
specified requirement;
actual measured or observed condition;
quantity affected;
inspection method;
supporting photographs or measurements.
Avoid vague descriptions such as:
“Dimension slightly incorrect.”
A more useful description is:
Drawing requires 1250 ± 3 mm. Actual measurement: 1256 mm at Segment S3.
That allows engineering personnel to evaluate the real consequence.
Stop the Affected Item From Moving Forward
Once a significant nonconformance is identified, the affected component should not continue through fabrication, packing, or shipment as if nothing happened.
The objective is to prevent:
accidental mixing with accepted components;
additional fabrication that hides the issue;
shipment before disposition;
installation of the wrong component.
Depending on project procedures, the item may be:
tagged;
physically separated;
electronically placed on hold;
identified on an NCR register.
This is particularly important when several nearly identical tower-internal segments are being manufactured together.
Not Every Nonconformance Has the Same Risk
A deviation should be evaluated according to its effect on the finished internal.
Consider a liquid distributor.
A cosmetic scratch and an incorrectly located liquid outlet are not equivalent problems.
One may have little functional consequence.
The other may affect liquid distribution across the packing bed.
Similarly, for a packing support grid:
a minor surface mark;
an incorrect beam position;
inadequate open area;
a distorted segment joint
do not represent the same engineering risk.
The disposition should therefore be based on function, fit, material integrity, and project requirements—not simply on how easy the defect is to repair.
Four Common Disposition Paths
A nonconforming component generally leads to one of several possible decisions.
1. Rework to Full Conformance
Rework means bringing the component back into full compliance with the original approved requirement.
Example:
A bolt hole is drilled at the wrong location, and an approved rework method allows the component to be restored so that the final part fully matches the drawing.
After rework, the relevant dimension or feature should be reinspected.
If full conformity is restored, the item can proceed according to the normal quality process.
2. Repair
Repair differs from rework.
A repair may make the component technically acceptable without restoring it exactly to the original configuration.
For example, a damaged fabricated area might be repaired using an approved method that results in an acceptable final component but introduces a condition not originally shown on the drawing.
Repair therefore normally requires engineering evaluation.
The repair procedure should define:
what material will be removed;
what will be added;
welding or fabrication method;
dimensional requirements;
required reinspection.
A repair should never simply hide the original defect.
3. Accept as-is / Engineering Concession
Sometimes the actual condition differs from the drawing but engineering review determines that it does not affect:
fit;
structural integrity;
hydraulic function;
corrosion requirement;
installation;
maintenance.
In this case, the project may permit acceptance under an approved concession or deviation.
For example:
A noncritical dimension may be several millimeters outside the drawing tolerance while still providing adequate clearance and no functional effect.
However:
The manufacturer should not unilaterally convert an out-of-tolerance condition into an acceptable tolerance.
Where customer or EPC approval is required by the project, the deviation must be submitted before shipment.
4. Reject and Remanufacture
Some conditions should not be repaired or accepted.
A replacement may be the safer choice when the nonconformance affects:
critical geometry;
material identity;
load-bearing integrity;
process function;
installation fit;
repair reliability.
The cost of remanufacturing one segment in the workshop can be much lower than discovering the problem during a plant shutdown.
Fit Problems Need Special Attention
Tower internals are often custom-built to fit a specific vessel.
A dimensional deviation can affect:
shell clearance;
support-ring fit;
neighboring segments;
bolt-hole alignment;
manway assembly;
nozzle connection.
A component may still look professionally fabricated while being impossible to install.
For fit-related NCRs, engineering review should consider the complete assembly rather than the individual part alone.
A 5 mm deviation may be insignificant in one location and critical in another.
Hydraulic Deviations Are Not Only Dimensional Problems
For components such as liquid distributors, collectors, redistributors, or trays, fabrication deviations may affect hydraulic behavior.
Examples include:
wrong outlet diameter;
missing outlet;
incorrect hole elevation;
incorrect weir height;
blocked flow opening;
wrong trough spacing.
These conditions should not be evaluated only by asking whether the component can physically fit inside the tower.
The engineering question is also:
Will it still perform the intended hydraulic function?
A mechanically acceptable deviation may still be hydraulically unacceptable.
Material Nonconformances Require Traceability Review
If inspection finds a material problem, the review should not stop at one component.
Questions may include:
Which material batch was used?
Which other components were made from the same batch?
Was the material identification transferred correctly?
Are welding consumables or plastic welding rods also affected?
Does additional sampling need to be expanded?
This is particularly important for visually similar materials such as:
SS304 vs SS316L;
different polymer grades;
different PVDF resin grades.
A material NCR can potentially affect multiple components rather than one isolated dimension.
Repair Must Be Followed by Reinspection
A repaired component is not automatically an accepted component.
The affected feature should be inspected again according to the applicable requirement.
Examples include:
dimensional remeasurement;
visual weld inspection;
leak testing;
material verification;
assembly fit check.
The inspection method should correspond to the original problem.
If the NCR involved a leak-tight collector weld, checking only the surface appearance after repair may not be enough if the project requires leak verification.
Update Drawings When the Accepted Condition Changes the Final Configuration
If an approved deviation changes the final physical configuration, project documentation may need to reflect the actual supplied condition.
This may include:
redline drawing;
revised manufacturing drawing;
as-built record;
NCR reference.
The purpose is to ensure that future maintenance personnel do not compare the installed equipment with an obsolete drawing and assume the field condition is wrong.
Documentation should represent what was actually accepted and supplied.
Do Not Ship With Open Critical NCRs
A shipment deadline should not automatically override unresolved engineering issues.
Before release for shipment, confirm that applicable NCRs are:
dispositioned;
repaired or reworked where required;
reinspected;
approved where customer approval is necessary;
formally closed.
If an NCR remains open by agreement, its status should be explicitly communicated and controlled.
The customer should not discover an unresolved deviation only after opening the crate.
NCR Records Also Help Suppliers Improve Manufacturing
The purpose of an NCR is not only to document a mistake.
Repeated NCRs can reveal process weaknesses.
For example:
Repeated segment misalignment may indicate a problem with:
fabrication jigs;
drawing interpretation;
dimensional control.
Repeated weld repairs may point to:
poor joint preparation;
unsuitable procedure;
operator training issues.
Repeated material identification problems may indicate:
warehouse segregation weakness;
traceability breakdown.
Reviewing NCR trends helps reduce recurrence.
What Should a Buyer Expect From a Tower Internals Supplier?
For custom engineered internals, a professional supplier should be able to distinguish between:
conforming product
and
nonconforming product that has been evaluated and formally dispositioned.
The supplier should not quietly modify drawings after fabrication simply to make the manufactured component appear compliant.
Where a significant deviation exists, the proper sequence is:
Identify → Record → Evaluate → Disposition → Correct → Reinspect → Approve → Close
That process provides a much stronger quality basis than informal workshop decisions.
A Practical NCR Workflow
Step 1 — Identify
Inspection finds a condition outside the approved requirement.
Step 2 — Record
Document the requirement and actual condition.
Step 3 — Hold
Prevent uncontrolled further processing or shipment.
Step 4 — Evaluate
Determine effect on:
function;
fit;
strength;
hydraulics;
material;
installation.
Step 5 — Select Disposition
Choose:
rework;
repair;
accept by concession;
reject/remake.
Step 6 — Obtain Required Approval
Follow the project approval requirement.
Step 7 — Perform Corrective Work
Complete the approved action.
Step 8 — Reinspect
Verify the final condition.
Step 9 — Update Documentation
Record final configuration where necessary.
Step 10 — Close the NCR
Release the item only after required actions are complete.
Final Engineering Perspective
Custom tower internals are often one-off engineered components.
That means quality cannot be controlled only by comparing the final product with a standard catalog sample.
The approved drawing and project specification define what the component is supposed to be.
When actual fabrication differs from that requirement, the correct response is not to hide the deviation and not automatically to scrap the product.
The correct response is to make an engineering decision based on the real consequence.
A good NCR system answers four questions clearly:
What is different?
Does it affect function or fit?
What corrective action is required?
Who must approve the final condition?
Managing these questions before shipment helps prevent a small manufacturing deviation from becoming a major tower-installation problem at site.