How to Retrofit an Old Packed Tower When Original Drawings Are Missing
Brownfield tower retrofit becomes much more difficult when original engineering drawings cannot be found.
This is common in older plants.
The tower may have changed ownership, undergone multiple maintenance modifications, or simply have incomplete documentation.
Yet replacement packing or internals still must fit the equipment that physically exists.
In this situation, field verification becomes part of the engineering design basis.
Never Assume Nominal Dimensions Are Enough
Plant records may state that a tower has a certain nominal diameter.
That does not provide enough information to manufacture replacement internals.
Actual construction may include:
- corrosion allowance;
- lining;
- shell distortion;
- weld projections;
- support rings;
- internal clips.
The true installation dimensions must be measured.
Build a Retrofit Data Package
When original drawings are unavailable, create a new field-data record.
Useful information includes:
- tower inside diameter;
- manway size;
- internal elevations;
- nozzle positions;
- support-ring dimensions;
- beam arrangement;
- existing bed height;
- distributor geometry;
- demister position.
Photographs should accompany dimensions where possible.
Identify Existing Materials
Do not assume all internal materials are original.
Previous maintenance may have replaced individual parts.
Confirm the material of:
- packing;
- supports;
- distributors;
- fasteners;
- demister;
- beams.
Where material identification is critical, plant engineering may need to use suitable verification methods.
Measure at Multiple Locations
Older towers may not be perfectly round.
Internal diameter should therefore be checked at multiple orientations when manufacturing close-fitting components such as structured packing or distributor sections.
A single diameter measurement can hide ovality.
Record Vertical Elevations
Retrofit equipment must fit not only radially but vertically.
Measure distances between:
- support plate;
- packed bed;
- distributor;
- collector;
- manways;
- upper demister.
This identifies the real space available for modification.
Document Existing Support Interfaces
Replacement internals often rely on existing:
- support rings;
- clips;
- beams;
- brackets.
Record their:
- dimensions;
- spacing;
- elevation;
- condition.
An internal designed around an assumed support ring may be impossible to install if the actual structure differs.
Check Access
The absence of drawings makes installation access particularly important.
Measure the real usable manway opening and photograph the internal path.
Manufacturing drawings should be based on what can actually enter and turn inside the tower.
Do Not Copy Unknown Old Designs Blindly
A plant may request “same as existing.”
But if the old component has no drawing and poor performance, reproducing it blindly can preserve the original weakness.
The retrofit should separate two questions:
- What dimensions must remain compatible?
- What performance features should be improved?
This allows dimensional fit without copying outdated hydraulic design unnecessarily.
Use Existing Components as References Carefully
Removed components can be measured.
However, corrosion, distortion, and previous field modification may mean they no longer represent the original design accurately.
Use them as one source of information, not the only source.
Create New As-Built Documentation
One important benefit of the retrofit is the opportunity to rebuild the missing technical record.
After final installation, retain:
- approved drawings;
- final dimensions;
- materials;
- packing quantities;
- internal elevations.
This will make future maintenance far easier.
More Field Data Reduces Fabrication Risk
Manufacturing replacement internals from incomplete information creates expensive risk.
Incorrect dimensions can cause:
- site rework;
- welding;
- cutting;
- delayed startup.
For brownfield projects, a careful measurement stage is therefore often more valuable than rushing directly to fabrication.