How to Close Technical Deviations in Tower Internals Quotations Before Purchase Order
Direct Engineering Answer
Before issuing a purchase order for tower internals, the buyer should identify every difference between the RFQ requirement and the supplier’s final quotation.
These differences should be classified as:
compliant;
clarified;
accepted deviation;
rejected deviation;
supplier assumption;
scope exclusion;
pending information.
The objective is not simply to obtain a lower final price.
The objective is to make sure that:
The purchase order describes the same equipment that the engineering team believes it is buying.
Material, dimensions, hydraulic basis, fabrication scope, interfaces, inspection requirements and documentation should be technically aligned before commercial award.
An unresolved sentence such as:
“Subject to final technical confirmation”
may appear harmless during quotation.
After purchase order placement, the same unresolved point can become:
a design change;
an additional cost;
a schedule delay;
a manufacturing hold;
or a performance dispute.
1. What Is a Technical Deviation?
A technical deviation is a proposed difference from the issued RFQ, specification, datasheet, drawing or other agreed technical requirement.
For example, the RFQ may request:
SS316L liquid distributor, 3 mm plate thickness.
The supplier may quote:
SS316L liquid distributor, 2 mm plate thickness based on supplier standard.
That is a technical deviation.
Another RFQ may specify:
Existing 25 mm random packing to be replaced with equivalent packing.
The supplier may offer:
38 mm packing to reduce pressure drop.
That is not simply a commercial alternative.
It changes the technical basis and requires engineering review.
2. Deviation, Assumption, Clarification and Exclusion Are Not the Same
These terms should not be mixed together.
Technical Deviation
The supplier proposes something different from the stated requirement.
Example:
RFQ: SS316LOffer: SS304
Assumption
Required information is missing, so the supplier uses a temporary design basis.
Example:
Tower internal diameter assumed as 1200 mm pending approved vessel drawing.
Clarification
The requirement is unclear and needs interpretation.
Example:
“Complete distributor” — does this include supports, fasteners and gaskets?
Exclusion
The supplier explicitly does not include part of the requested scope.
Example:
Installation supervision excluded.
Alternative
The supplier proposes a technically different solution for evaluation.
Example:
Vane-type mist eliminator proposed instead of wire-mesh demister due to high liquid loading.
Each category requires a different response.
A buyer should not treat all five as ordinary quotation notes.
3. Why Technical Deviations Must Be Closed Before the PO
After purchase order placement, several activities may begin quickly:
material procurement;
detailed drawing preparation;
production scheduling;
subcontracting;
fabrication;
inspection planning.
If the technical basis is still open, one party may proceed using assumptions that the other party never intended to approve.
This creates a common project problem:
Commercial award occurs before technical alignment is complete.
Later, the customer says:
“This is not what we requested.”
The supplier replies:
“This was stated in our quotation.”
Both statements can be true.
That is precisely why deviations should be closed before award.
4. Start With One Governing RFQ Revision
Technical clarification becomes unreliable when different parties are reviewing different document revisions.
Before comparing the final offer, identify the governing documents.
Typical references include:
RFQ number;
technical specification revision;
process datasheet revision;
vessel GA drawing revision;
tower internals drawing revision;
material specification;
inspection requirements;
documentation requirements.
The quotation should clearly identify which revision was used.
A supplier cannot be expected to comply with a document it never received.
At the same time, a buyer should not approve a quotation based on an outdated technical package.
5. Build a Technical Deviation Register
Do not leave important deviations scattered through:
emails;
quotation footnotes;
WhatsApp messages;
drawing comments;
meeting minutes.
Use one controlled deviation register.
A practical format is:
No.
RFQ Requirement
Supplier Proposal
Type
Technical Impact
Status
TD-01
SS316L
SS304
Deviation
Corrosion resistance
Rejected
TD-02
3 mm plate
2.5 mm plate
Deviation
Mechanical stiffness
Under review
TD-03
1200 mm ID
1196 mm assumed
Assumption
Fit / sealing
Awaiting drawing
TD-04
Hydraulic report required
Preliminary calculation only
Scope deviation
Deliverable
Clarify
TD-05
Installation included
Excluded
Commercial scope
Site execution
Accepted
The exact format can vary.
The important part is that every open point has:
a reference;
a technical consequence;
an owner;
a final disposition.
6. Review Material Deviations First
Material deviations can affect:
corrosion resistance;
temperature capability;
mechanical strength;
contamination risk;
service life;
certification requirements.
Examples include:
SS304 instead of SS316L;
PP instead of PVDF;
alternative ceramic composition;
different gasket material;
different fastener grade.
Do not accept a material deviation only because:
“The alternative is commonly used.”
The review should consider the actual process chemistry and operating conditions.
For corrosion-sensitive service, confirm relevant information such as:
process medium;
concentration;
operating temperature;
upset conditions;
cleaning chemicals;
contaminants.
Where SS316L is specified, the agreed material requirement should also be reflected consistently in the PO and material documentation.
7. Check Geometry Deviations — Not Just Product Names
Two suppliers may use the same equipment name while quoting different geometry.
For random packing, compare relevant parameters such as:
nominal size;
wall thickness;
geometry;
surface area;
void fraction;
bulk density.
For liquid distributors:
number of outlets;
outlet diameter;
trough dimensions;
distribution-point arrangement;
overflow arrangement;
support geometry.
For mist eliminators:
mesh or vane geometry;
thickness;
section arrangement;
frame design;
drainage arrangement.
For support grids:
opening size;
open area;
beam arrangement;
panel thickness;
load path.
The words:
“Equivalent tower internals”
do not prove technical equivalence.
8. Identify Hydraulic Deviations
Some deviations are mechanical in appearance but hydraulic in consequence.
For example:
Changing Packing Size
May affect:
pressure drop;
capacity;
flooding tendency;
effective contacting area;
support-grid compatibility.
Changing Distributor Outlet Size
May affect:
outlet flow;
liquid head;
distribution uniformity;
turndown behavior.
Changing Support-Grid Open Area
May affect:
gas resistance;
local velocity;
pressure drop.
Changing Mist Eliminator Geometry
May affect:
face velocity;
separation behavior;
pressure drop;
liquid drainage.
These deviations should not be approved only through dimensional inspection.
If geometry affecting flow has changed, the hydraulic basis may need to be reviewed.
9. What Hydraulic Information Should Be Checked?
Depending on the equipment and agreed project scope, relevant information can include:
gas flow rate;
liquid flow rate;
operating pressure;
operating temperature;
gas density;
liquid density;
viscosity;
tower diameter;
allowable pressure drop;
required turndown;
packing geometry;
distributor geometry.
Possible evaluations may include:
vapor and liquid loading;
pressure drop;
capacity;
flooding margin;
liquid distribution;
equipment sizing.
The important principle is:
A hydraulic result is valid only for the geometry and operating basis used in the calculation.
If that geometry changes during quotation clarification, the calculation basis must remain aligned with the final equipment.
10. Check Mechanical Interfaces
Many tower internals fail to fit not because the component itself was manufactured incorrectly, but because the interface was never fully defined.
Review:
tower internal diameter;
support-ring elevation;
beam position;
nozzle projection;
manway dimensions;
lining thickness;
neighboring internal elevations;
segment size;
bolt locations;
field welding restrictions.
A supplier may quote equipment based on:
nominal tower ID = 2000 mm
while the actual available installation diameter is affected by:
shell ovality;
lining;
weld seams;
internal clips.
That difference should be identified before fabrication.
11. Do Not Ignore Plate Thickness Deviations
Plate thickness frequently affects quotation price.
A lower quotation may use less material.
But thicker is not automatically better either.
The correct question is:
Does the proposed thickness satisfy the required mechanical function and approved design basis?
Depending on the component, thickness can influence:
stiffness;
deflection;
vibration resistance;
transport stability;
support loading;
total equipment weight.
For a distributor, excessive deformation can also change outlet levelness.
Therefore thickness should not be treated as only a commercial number.
12. Check Whether the Engineering Scope Has Changed
“Design included” is too vague.
Clarify what the supplier will actually provide.
Possible deliverables include:
preliminary selection;
hydraulic calculation;
GA drawing;
assembly drawing;
fabrication drawing;
installation drawing;
calculation note;
material list;
inspection records.
A quotation including:
Tower Internals Design
does not automatically mean the supplier is accepting responsibility for complete process-column design.
The engineering boundary should be stated clearly.
For DAIER projects, technical support may include product selection, customized internals engineering and basic hydraulic evaluation within the agreed supply scope and available process data.
Final process responsibility and project acceptance remain subject to the agreed technical package.
13. Review Inspection and QA Deviations
The RFQ may require:
material certificates;
dimensional inspection;
PMI;
weld inspection;
trial assembly;
leak testing;
inspection reports;
third-party inspection.
The supplier may have priced only standard factory inspection.
That difference must be identified before PO placement.
Inspection requirements added later can affect:
manufacturing sequence;
production schedule;
documentation;
third-party cost;
hold points.
Therefore QA requirements belong in the technical clarification stage, not only after production begins.
14. Review Documentation Requirements
Industrial projects often require much more than a commercial invoice and packing list.
Depending on the project, requested documents may include:
material certificates;
COA;
inspection reports;
approved drawings;
dimensional reports;
test records;
installation instructions;
final data book.
If the buyer requires these documents, they should be included in the agreed supply scope.
Do not assume:
“The supplier will provide them later.”
Some records can only be generated correctly if the requirement is known before manufacturing.
15. Check Scope Exclusions Carefully
A low price may reflect excluded scope.
Common exclusions can include:
support beams;
hold-down grids;
fasteners;
gaskets;
installation;
supervision;
hydraulic calculations;
third-party inspection;
spare parts;
export packaging;
documentation.
The question is not whether an exclusion is acceptable.
Many exclusions are completely reasonable.
The question is whether the buyer understands them before comparing the total price.
16. Check Quantity Basis
For tower packing, quantity may be quoted by:
m³;
kg;
pieces.
These are not automatically interchangeable.
For random packing, required quantity usually begins with the packed volume.
Weight is then estimated using bulk density.
For example:
Required packing volume
=
Tower cross-sectional area × packed height
Then:
Estimated packing weight
=
Packing volume × bulk density
If two suppliers quote different bulk densities, a USD/kg comparison may not represent the same installed volume.
Always normalize the quotation basis.
17. Check Whether “Equivalent” Really Means Equivalent
Words frequently used in industrial quotations include:
equivalent;
alternative;
similar;
standard;
optimized;
upgraded.
None of these words defines technical equivalence.
If an alternative is offered, ask:
Equivalent in what respect?
dimension?
material?
hydraulic capacity?
pressure drop?
mass-transfer area?
mechanical strength?
installation interface?
An alternative can be technically better in one parameter and worse in another.
That is why equivalence must be defined against the project requirement.
18. Separate Mandatory Requirements From Preferences
Not every RFQ requirement deserves the same approval level.
A useful classification is:
Mandatory
Cannot change without formal engineering approval.
Examples:
material grade;
tower interface;
required process capacity;
applicable code.
Performance-Critical
Can change only after calculation or engineering review.
Examples:
distributor outlet geometry;
packing type;
mist eliminator geometry;
support open area.
Project Preference
Can potentially change without affecting technical performance.
Examples may include certain packaging or document-format preferences, depending on the contract.
This classification prevents engineering teams from spending equal effort on critical and noncritical deviations.
19. Use Three Final Dispositions
Every technical deviation should eventually reach one of three clear outcomes.
ACCEPTED
The proposed change is approved.
It should then become part of the final technical basis.
REJECTED
The supplier must comply with the original requirement.
The quotation should be revised accordingly.
ACCEPTED WITH CONDITION
The deviation is acceptable only subject to a defined condition.
Example:
2.5 mm distributor plate accepted subject to approved structural and dimensional verification.
Avoid leaving items marked only:
“Noted.”
“Noted” does not tell production what to manufacture.
20. Revise the Quotation After Clarification
Do not rely on a long email chain to modify the quotation.
After technical clarification, the supplier should issue a revised quotation or final technical offer incorporating the agreed basis.
The revised document should reflect:
final material;
final geometry;
final quantity;
agreed engineering scope;
inspection requirements;
documentation;
exclusions;
delivery basis.
The commercial price should correspond to that final technical scope.
21. Freeze the Technical Basis in the Purchase Order
Once deviations are closed, the PO should reference the controlling technical documents.
Typical references can include:
final quotation revision;
approved technical datasheet;
final deviation register;
approved drawing;
material specification;
inspection requirement.
The PO does not need to reproduce every engineering detail.
But it should clearly identify which documents define the purchased equipment.
This creates traceability.
22. Do Not Let Unresolved Assumptions Become Silent Design Inputs
One of the most dangerous quotation phrases is:
“Assumed.”
Assumptions are useful during preliminary quotation.
They are not automatically acceptable for fabrication.
Typical assumptions include:
tower diameter;
process flow;
operating pressure;
material;
installation clearance;
support geometry.
Before affected manufacturing begins, critical assumptions should be replaced with confirmed project data.
If information remains unavailable, its status and design consequence should remain visible.
23. When Should a Deviation Trigger Recalculation?
A recalculation should be considered when the proposed change affects a parameter used in the original engineering evaluation.
Examples include changes to:
packing type;
packing size;
packing bed height;
distributor geometry;
tray open area;
support-grid open area;
mist eliminator face area;
tower diameter;
operating flow.
Not every dimensional change requires a full hydraulic redesign.
But hydraulically significant changes should not be accepted only because fabrication is easier or cheaper.
24. A Practical Pre-PO Technical Clarification Checklist
Before issuing the purchase order, confirm:
Design Basis
RFQ revision confirmed.
Process datasheet revision confirmed.
Tower drawing revision confirmed.
Operating cases defined.
Product
Equipment type confirmed.
Product model confirmed.
Size confirmed.
Quantity confirmed.
Material
Material grade confirmed.
Plate or wire thickness confirmed where required.
Gasket and fastener materials confirmed where relevant.
Hydraulics
Relevant gas/liquid conditions confirmed.
Packing geometry confirmed.
Distributor geometry confirmed.
Pressure-drop or capacity requirements identified.
Significant deviations reviewed.
Interfaces
Tower ID confirmed.
Support geometry confirmed.
Nozzle and manway interfaces checked.
Installation segmentation agreed.
Quality
Inspection scope agreed.
Material documentation agreed.
Test requirements agreed.
Third-party requirements confirmed.
Documentation
Drawing scope defined.
Calculation deliverables defined.
Inspection reports defined.
Final documentation scope agreed.
Commercial Scope
Exclusions identified.
Spare scope identified.
Packaging responsibility identified.
Delivery basis confirmed.
Final Release
Technical deviations closed.
Assumptions identified.
Revised quotation issued.
PO technical references frozen.
25. Example: Liquid Distributor Quotation
Consider an RFQ requesting:
SS316L trough liquid distributorTower ID: 1800 mmLiquid rate: defined by project datasheetHydraulic review required
Supplier quotation states:
SS316L trough distributorStandard outlet configurationFabrication drawing included
This quotation is not yet technically complete.
Questions remain:
Is the outlet quantity based on the actual liquid load?
Is the outlet diameter calculated?
What turndown is being considered?
Does the geometry fit the actual tower?
Are supports included?
Is hydraulic calculation included or only fabrication drawing?
The product name matches.
The engineering scope may not.
26. Example: Random Packing Quotation
RFQ:
25 mm SS316L Metal Pall Ring
Supplier offers:
25 mm SS316L Metal Pall Ring
At first glance the offer appears compliant.
But further review may show:
Supplier A:
0.4 mm wall thickness.
Supplier B:
0.3 mm wall thickness.
Supplier C:
different geometry and bulk density.
The quotations should not be compared only on USD/m³.
The technical differences should first be understood and either accepted or rejected.
27. Example: Mist Eliminator Replacement
Existing equipment:
Wire mesh demister.
Supplier proposes:
Vane-type mist eliminator.
This may be a valid engineering alternative.
But it is not a direct replacement merely because both products remove entrained droplets.
The review should consider:
available installation space;
gas velocity;
expected droplet loading;
pressure drop;
drainage;
fouling tendency;
supporting structure.
Only after that review can the alternative be technically accepted.
28. How DAIER Supports Technical Clarification
DAIER supplies:
random packing;
structured packing;
mist eliminators;
liquid distributors;
support and hold-down grids;
customized tower internals.
For project inquiries, customers can provide:
RFQ;
drawings;
process data;
material requirements;
existing equipment information.
Within the agreed engineering scope, DAIER can support review of product selection and relevant hydraulic conditions such as:
vapor and liquid loading;
pressure drop;
flooding risk;
distribution conditions;
equipment sizing.
The objective is to establish a clear technical supply basis before manufacturing.
Preliminary evaluation should not be confused with full process-column design or EPC process responsibility.
Frequently Asked Questions
What is a technical deviation in a tower internals quotation?
It is any proposed difference from the RFQ, specification, datasheet or drawing requirement.
Is a supplier assumption the same as a deviation?
No. An assumption fills missing information temporarily. A deviation proposes a different requirement.
Should technical deviations be closed before the purchase order?
For significant technical requirements, yes. Otherwise the supplier and buyer may proceed using different interpretations of the equipment scope.
Can a lower-cost alternative be accepted?
Yes, if engineering review confirms that it satisfies the required technical function and the deviation is formally accepted.
Does the lowest quotation mean the lowest project cost?
Not necessarily. A lower quotation may exclude engineering, inspection, documentation or required hardware.
Should every deviation require hydraulic calculation?
No. Only deviations affecting hydraulically relevant geometry, operating conditions or performance normally require hydraulic review.
What should happen after all deviations are closed?
The final quotation and purchase order should reference the agreed technical basis and approved revisions.
Engineering Takeaway
A purchase order should not be used to discover what the supplier actually intended to supply.
That work should already have been completed during technical clarification.
A disciplined sequence is:
RFQ
↓
Supplier Quotation
↓
Technical Deviation Register
↓
Engineering Clarification
↓
Accept / Reject / Condition
↓
Final Revised Offer
↓
Purchase Order
The purpose is not additional paperwork.
It is to prevent three common project failures:
Different technical assumptions
Different supply boundaries
Different expectations after award
For tower packing and tower internals, even apparently small changes in material, geometry or hydraulic basis can affect installation, performance, cost and schedule.
Close those differences before the order is released.