Tower Internals Spare Parts Planning: What Should Be Stocked and What Should Be Manufactured to Drawing?
Direct Engineering Answer
A reliable tower internals spare-parts strategy should not depend on keeping one complete spare assembly for every installed component.
Instead, maintenance and procurement teams should classify replacement requirements into three categories:
Physical spares: Standardized, interchangeable components that justify holding stock.
Drawing-controlled replacements: Custom components that can be manufactured when required using verified drawings, material specifications and bills of materials.
Engineering-review items: Components whose replacement may change hydraulic performance, mechanical loading, material compatibility or equipment interfaces.
The correct decision depends on failure consequences, replenishment lead time, interchangeability, storage requirements and the cost of an unplanned shutdown.
1. Why Keeping Spare Parts Is Not Always Enough
A common problem occurs when a plant prepares for a scheduled turnaround but discovers that its spare-parts inventory does not match the actual equipment configuration.
Typical situations include:
A spare liquid distributor has different outlet dimensions from the installed assembly.
Replacement support-grid panels do not match the original support beams.
A demister pad is available, but its frame dimensions are incorrect.
The original packing model is discontinued.
Old drawings do not reflect modifications made during previous maintenance.
Custom-fabricated components have longer procurement lead times than the shutdown schedule allows.
Having a spare component does not automatically mean that the equipment can be restored.
The important question is whether the replacement is technically compatible with the installed tower.
2. Three Different Spare-Parts Strategies
Not every tower internal should be managed in the same way.
Category
Recommended strategy
Typical examples
Standardized components
Keep physical stock where justified
Approved fasteners, clips and replaceable standard components
Custom fabricated components
Maintain controlled drawings and manufacture to order
Liquid distributor sections, support-grid panels, demister frames
Performance-critical replacements
Require engineering review
Modified distributors, alternative packing geometry, redesigned supports
The distinction helps avoid two expensive mistakes:
Holding excessive inventory of large, project-specific assemblies.
Discovering during a shutdown that a critical custom component has not been engineered or ordered.
3. Which Tower Internals Should Be Kept as Physical Spares?
Physical stock is most useful when a component is small, standardized, interchangeable and difficult to obtain within the available maintenance window.
Potential candidates include:
Project-approved fasteners and retaining hardware.
Standardized replacement nozzles.
Approved clips and attachment components.
Small replaceable mechanical elements.
Standard mesh or demister components where dimensions and specifications are identical.
However, a physical spare should only be considered interchangeable after confirming its material grade, dimensions, connection details and applicable specification.
A standard-looking component is not necessarily compatible with every tower.
4. Which Components Are Better Manufactured from Approved Drawings?
Large or customized tower internals often make more sense as drawing-controlled replacement items rather than permanent finished inventory.
Liquid Distributors
A liquid distributor may be designed specifically for:
Tower internal diameter.
Liquid operating range.
Outlet arrangement.
Distribution-point density.
Installation elevation.
Support configuration.
Keeping an approved assembly drawing, sectional drawings and a complete bill of materials can make future reproduction easier.
However, an old drawing must be checked against the actual installed configuration before manufacturing.
Packing Support and Hold-Down Grids
These components are often customized according to:
Tower diameter.
Support-ring dimensions.
Beam spacing.
Packing weight.
Required gas open area.
Installation segmentation.
Keeping verified panel drawings and interface dimensions can reduce future engineering clarification.
A replacement grid must still satisfy the required structural loading and hydraulic open-area conditions.
Mist Eliminators
Mesh-pad and vane-type mist eliminators may have project-specific:
Overall dimensions.
Segment arrangements.
Frame structures.
Support details.
Material requirements.
Drainage configurations.
A spare pad without the correct dimensions or supporting arrangement may not be suitable for installation.
Structured Packing
Structured packing modules are often manufactured according to specific tower dimensions and installation arrangements.
Rather than stocking complete assemblies for every tower, maintaining the approved block dimensions, material specifications, corrugation details and segmentation drawings may be more practical.
5. Random Packing Requires a Different Inventory Approach
Random packing is generally purchased as a bulk replacement material rather than as an individual mechanical spare part.
Before a planned shutdown, procurement teams should confirm:
Packing type.
Nominal size.
Material.
Required bed volume.
Bulk density.
Estimated total weight.
Packaging and transportation requirements.
Expected procurement lead time.
Do not use an arbitrary 5% or 10% spare allowance as a universal rule.
The required quantity should reflect the actual replacement scope, expected handling losses and project requirements.
For ceramic packing, additional consideration should be given to breakage during transportation, unloading and installation.
6. How to Determine Whether a Component Is Critical
A practical spare-parts assessment should consider five factors.
Assessment factor
Key question
Failure consequence
Could the missing component delay restart or prevent operation?
Procurement lead time
How long will replacement take from approval to site delivery?
Interchangeability
Can an existing standard component be used without modification?
Failure history
Has this component experienced repeated damage or failure?
Storage requirements
Can the component be stored without deterioration or damage?
A component with a high failure consequence and a long replenishment lead time deserves more attention than an inexpensive component that can be sourced quickly.
Importantly, criticality should not be determined by purchase price alone.
7. Why Old Drawings Must Be Verified Before Reordering
One of the most common replacement risks is manufacturing directly from an outdated drawing.
Existing towers may have experienced:
Previous internal modifications.
Field welding.
Support-ring changes.
Replacement of adjacent components.
Different installation arrangements.
Corrosion or mechanical deformation.
Before releasing a replacement order, verify the drawing revision against available as-built information.
At minimum, confirm:
Equipment tag and tower identification.
Current drawing revision.
Overall dimensions.
Material specification.
Connection and support interfaces.
Segment dimensions.
Installation access.
Relevant operating conditions.
If the original drawing cannot be verified, photographs and field measurements may be needed before manufacturing.
8. When Does a Replacement Require Hydraulic Reassessment?
This is particularly important when the proposed replacement is not geometrically identical to the original component.
For example:
Liquid distributor replacement
Changes to outlet diameter, outlet quantity, elevation or distribution layout can alter liquid flow distribution.
Packing replacement
Different packing geometry, size or material may change pressure drop, capacity and flooding behavior.
Support-grid replacement
Changes in open area and structural arrangement can affect gas flow resistance and mechanical support.
Mist eliminator replacement
Changes in vane geometry, mesh density or flow area may affect separation performance and pressure drop.
Therefore, a dimensional match alone does not prove hydraulic equivalence.
For projects involving changed geometry or operating conditions, DAIER can support hydraulic assessment within an agreed engineering scope, using confirmed process data and equipment information.
Depending on the equipment, the review may include:
Vapor and liquid loading.
Pressure-drop assessment.
Hydraulic capacity and flooding evaluation.
Liquid distribution assessment.
Relevant equipment interface conditions.
Final engineering acceptance must follow the project design basis and applicable approval requirements.
9. Calculate the Complete Replacement Lead Time
Procurement teams should not use manufacturing lead time as the only planning reference.
The actual replacement process may involve:
Collecting existing drawings and equipment information.
Technical clarification.
Dimensional and material verification.
Engineering review, where required.
Drawing approval.
Raw material procurement.
Fabrication.
Inspection and documentation.
Export packaging.
Transportation and site receiving.
The total procurement schedule should account for all these stages.
For custom distributors, support grids and demisters, drawing clarification and approval can be just as important as fabrication time.
Work backward from the required site-arrival date rather than waiting until the shutdown is approaching.
10. Storage Conditions Also Affect Spare-Part Decisions
Physical inventory is only useful if the stored component remains suitable for installation.
Different materials require different storage considerations.
Metal internals
Protect against contamination, corrosion and mechanical deformation. Stainless-steel components should be handled and stored in a manner that preserves their surface condition.
Plastic internals
Avoid excessive heat, prolonged direct sunlight where relevant and deformation caused by improper stacking.
Ceramic packing
Use suitable packaging and handling procedures to prevent impact damage and breakage.
Demister pads
Protect the mesh or vane geometry from compression, distortion and contamination.
Storage conditions should be included in the spare-parts management procedure.
11. A Practical Pre-Shutdown Spare-Parts Checklist
Before confirming the spare-parts list, review the following information.
Equipment Identification
Tower or vessel tag.
Equipment location.
Internal component name.
Installed quantity.
Replacement quantity.
Technical Information
Approved drawing revision.
Material specification.
Main dimensions.
Connection details.
Component weight where relevant.
Approved replacement specification.
Procurement Information
Supplier.
Manufacturing lead time.
Raw material availability.
Inspection requirements.
Required certificates.
Delivery destination.
Required site-arrival date.
Engineering Review
Is this a direct replacement?
Has the equipment geometry changed?
Has the process duty changed?
Does the replacement affect pressure drop or capacity?
Are support loads still acceptable?
Are installation and access conditions confirmed?
A completed checklist helps distinguish a simple spare-parts purchase from a replacement project requiring engineering work.
12. How DAIER Can Support Tower Internals Replacement Planning
For existing packed towers, replacement planning may involve several components rather than packing alone.
DAIER's product range covers:
Random Packing.
Structured Packing.
Mist Eliminators.
Liquid Distributors.
Packing Support Grids.
Hold-Down Grids.
Related Tower Internals.
For replacement and maintenance projects, the available information can be used to establish whether the requirement is:
A standard product replacement.
A custom component manufactured to approved drawings.
A dimensional adaptation for an existing tower.
A replacement requiring additional hydraulic or engineering assessment.
Useful information to provide includes existing drawings, equipment dimensions, photographs, material requirements, process conditions and the planned shutdown date.
This allows the replacement scope and required engineering work to be identified before procurement begins.
Frequently Asked Questions
Should every packed tower have a complete spare set of tower internals?
No. Complete spare assemblies can create unnecessary inventory and storage costs. The spare strategy should reflect equipment criticality, lead time, interchangeability and replacement complexity.
Should custom liquid distributors be kept in stock?
Usually, maintaining verified drawings, material specifications and manufacturing records is more practical than keeping complete custom distributors in stock. Critical small replacement components may be stocked separately where justified.
Can old tower internals drawings be used for replacement manufacturing?
They can provide a starting point, but the revision, actual installed dimensions, material and interfaces should be verified before manufacturing.
Can a different packing model replace the original packing?
Possibly, but similar nominal dimensions do not establish hydraulic equivalence. Geometry, material, operating conditions, pressure drop and capacity must be considered.
When should spare parts be ordered before a turnaround?
The order should be released early enough to cover engineering clarification, drawing approval, material procurement, fabrication, inspection and transportation, with a project-specific contingency.
Does a spare-parts list replace engineering review?
No. A spare-parts list identifies what may be required. It does not prove that an alternative component is suitable for the original tower.
Engineering Takeaway
A reliable tower internals spare-parts strategy is not about stocking everything.
It is about making the correct distinction between:
Physical inventory → Drawing-controlled replacement → Engineering-reviewed replacement.
Standardized components may justify physical stock.
Customized assemblies are often better managed through verified drawings and manufacturing records.
Components that affect hydraulic performance, structural loading or process conditions require appropriate engineering review before substitution.
The objective is to avoid discovering a missing, incompatible or incorrectly specified component during a planned shutdown.
Need support with tower internals replacement planning?
Provide your existing tower drawings, component list, material specifications, photographs and required delivery date.
DAIER can help review the replacement scope and identify the information required for quotation, dimensional verification and agreed engineering assessment.
Pingxiang Daier Separation Tech
Random Packing | Structured Packing | Mist Eliminators | Liquid Distributors | Tower Internals
Website: https://www.pxdaier.com/
Related Technical Reading
How to Prepare a Tower Packing RFQ with the DAIER Engineering Assistant
How to Use the DAIER Tower Packing Engineering Assistant for an Existing Tower Replacement