How to Control Supplier Design Changes After Tower Internals Drawings Are Approved
Approved drawings do not guarantee that nothing will change.
During fabrication, a supplier may discover:
- material shortage;
- tooling limitation;
- difficult weld access;
- structural concern;
- fabrication improvement.
The supplier may then want to modify the approved design.
Some changes are harmless.
Others can affect tower performance or installation.
The important issue is controlling them.
Define What Counts as a Design Change
A controlled change may include:
- material grade;
- sheet thickness;
- component dimensions;
- support arrangement;
- orifice size;
- vane spacing;
- demister density;
- segmentation;
- connection detail.
The project does not need purchaser approval for every tiny shop adjustment.
But changes affecting approved technical characteristics should be disclosed.
Supplier Should Raise the Change Before Implementation
A supplier should not make the change first and ask for forgiveness later.
The change request should state:
- current approved design;
- proposed revision;
- reason;
- technical impact;
- cost impact;
- schedule impact.
This lets the purchaser evaluate the real consequence.
“Equivalent” Must Be Demonstrated
A supplier may say:
“No impact; equivalent design.”
That statement should be supported where the change matters.
For example, changing distributor orifice size may require hydraulic confirmation.
Changing support-beam thickness may require structural confirmation.
Changing packing sheet gauge may require review of the approved product design.
Material Availability Is Not Automatic Approval
A common reason for change is:
specified material unavailable.
The supplier may propose another grade.
Commercial urgency does not remove the need for technical approval.
Material changes should be reviewed against:
- corrosion;
- temperature;
- mechanical requirements;
- welding;
- project specification.
Update the Drawing
If the change is accepted, the approved drawing should be revised.
Otherwise, the project ends with:
one drawing showing the original design and physical equipment showing another.
This creates future maintenance confusion.
Update the BOM and Documentation
Material or component changes may also require updates to:
- BOM;
- material certificates;
- inspection plan;
- calculation;
- installation instructions.
Change control should propagate through the affected documentation.
Evaluate Existing Fabrication
If manufacturing has already started, the purchaser needs to know:
what material has already been cut or assembled.
The decision may involve:
- rework;
- concession;
- partial acceptance;
- replacement.
This should be transparent.
Distinguish Supplier Change from Purchaser Change
Not every change originates with the supplier.
The buyer may change:
- nozzle position;
- bed height;
- material;
- operating condition.
The project should identify who initiated the change because this can affect:
schedule and commercial responsibility.
Use a Change Register
For large packages, a controlled change register can track:
- change number;
- originator;
- affected document;
- reason;
- technical disposition;
- cost/schedule impact;
- approval date.
This prevents important changes from disappearing inside email chains.
Engineering Takeaway
Approved drawings establish a baseline, not a guarantee that manufacturing will never encounter change.
The correct control is to require important changes to be disclosed, justified, approved, and incorporated into revised as-built documentation before shipment.