How to Retrofit Tower Internals Without Triggering ASME Recertification
Welding to code-certified vessels drives up cost, extends turnaround windows, and adds recertification risk. No-weld solutions eliminate the entire sequence
Retrofitting or revamping a process column typically requires welding new support rings, beams, and clips to the vessel wall. However, welding to an ASME code-certified vessel typically triggers a costly sequence of post-weld requirements — heat treatment, recertification, and third-party inspection — that often costs more in time and labor than the internals themselves.
For many column projects, this welding and recertification sequence can be avoided entirely. No-weld retrofit solutions use engineered mechanical attachments — expansion rings, proprietary structural designs, and other weld-less methods — to secure new internals to the vessel without welding to the pressure boundary. This approach eliminates the need for heat treatment and recertification, shortens turnaround windows, and reduces installed cost.
This post covers when no-weld retrofits make engineering sense, what the approach involves, and how to evaluate whether your next column project is a candidate.
Why Welding Is the Most Expensive Part of a Tower Internals Retrofit
Most process columns in refining, petrochemical, chemical, and gas processing service are ASME code-certified pressure vessels. This certification allows the vessel to operate safely under pressure, but it also means that welding to the vessel wall typically triggers a defined sequence of post-weld requirements.
After welding new support rings, beams, clips, or other attachment structures to the vessel shell, the welded area typically requires heat treatment and the vessel must be recertified. The specific requirements depend on factors like material type and thickness, but for the carbon steel vessels common in refining and petrochemical service, post-weld heat treatment is frequently required. This adds significant time, labor, and cost to what might otherwise be a straightforward internals replacement or upgrade. (For more on the regulatory framework governing in-service repairs and alterations to pressure vessels, see the National Board Inspection Code.)
The internals themselves — whether trays, structured packing, liquid distributors, mist eliminators, or packing supports — are often less expensive than the welding, heat treatment, and recertification work required to install them. No-weld solutions address this cost inversion by eliminating the welding and its associated post-weld requirements from the project scope.
For turnaround planners working against tight shutdown windows, the additional days required for post-weld heat treatment and inspection can extend an outage beyond its scheduled completion, adding lost production, delayed startups, and cascading impacts on downstream units.
How No-Weld Retrofit Solutions Eliminate the Recertification Sequence
No-weld retrofits use engineered mechanical attachment methods — expansion rings and proprietary structural designs — to secure new internals to the vessel without welding to the shell wall. These solutions use existing vessel geometry and attachment points to provide the structural support that welded rings and clips would otherwise provide.
This approach requires more engineering upfront than a conventional welded installation. The design team needs to evaluate the existing vessel — its diameter, wall thickness, nozzle locations, existing support rings or clips, and the loads that the new internals will impose — to determine whether a weld-less solution is structurally viable.
At AMACS, that evaluation includes mechanical analysis of existing attachments using finite element analysis (FEA) to verify that the proposed no-weld structural supports can handle the required loads. AMACS performs static analysis, vibrational analysis, thermal expansion analysis, buckling analysis, and frictional resistance analysis — all critical for ensuring that a weld-less support performs reliably under actual operating conditions. For complex cases, AMACS also partners with industry CFD and FEA specialists for third-party evaluation.
The result is a support structure that meets the mechanical requirements of the application without welding to the vessel wall, eliminating the need for heat treatment and recertification and typically allowing for faster installation during the turnaround window.
Is Your Column a Candidate for a No-Weld Retrofit?
Not every column modification is a candidate for a weld-less approach. The decision depends on several engineering and operational factors.
Strong candidates for no-weld retrofits include:
- Vessels where existing support rings or clips are still structurally sound but the internals they support need to be replaced or upgraded. In these cases, the new internals can often be designed to interface with the existing attachment infrastructure — avoiding the need for new welds entirely.
- Columns being retrofitted with internals for the first time, or vessels that previously had no internal supports. These situations require creative use of the vessel’s existing geometry — shell contours, nozzle reinforcement pads, manway frames — to anchor new support structures without welding.
- Projects where the turnaround window is tight and the additional days for post-weld heat treatment and recertification would push the outage past its scheduled completion. In these cases, a no-weld approach may be the only path to completing the upgrade within the planned shutdown.
- Older vessels where the metallurgical condition of the shell makes welding risky or requires extensive pre-weld evaluation. Weld-less solutions avoid introducing heat-affected zones in aging vessel walls.
Situations where welding may still be required:
Extremely high-load applications where the mechanical analysis shows that weld-less supports cannot provide adequate structural margins. Some heavy tray installations or large-diameter distributor systems may still require welded ring supports.
Vessels with no usable existing geometry — smooth-wall columns with no nozzles, manways, or existing clips to anchor against. While proprietary designs can address many of these situations, some configurations simply don’t have enough existing structure to work with.
Applications where the operating company’s internal engineering standards specifically require welded attachments regardless of the mechanical adequacy of alternatives.
Integrating No-Weld Retrofits Into Your Turnaround Plan
No-weld retrofits offer both an engineering and an operational advantage. Eliminating the welding, heat treatment, and recertification sequence removes one of the longest and least predictable segments of a column turnaround.
AMACS supports this through a pre-turnaround planning process that identifies retrofit opportunities well before shutdown. The Hardware Needs Assessment program reviews equipment drawings for each tower, evaluates the work scope and previous inspection history, and provides an itemized price list of required hardware — all during the planning phase, not after the column is opened. This advance review is specifically designed to avoid the emergency parts delays and “hot shot” freight charges that drive turnaround cost overruns.
For retrofit projects, this pre-planning phase is where the no-weld evaluation happens. The engineering team can assess whether the existing vessel geometry supports a weld-less approach, run the FEA, and have the replacement internals and support structures fabricated and ready before the turnaround begins.
AMACS’s Turnaround Services Team provides field service advisors (FSAs) to oversee installation of both conventional and no-weld retrofit internals. With manufacturing facilities in Houston, TX and Monterrey, MX, and an inventory of random packing and hardware maintained in Houston, AMACS can support retrofit projects from engineering through installation — including 24/7 emergency support when turnaround scope changes unexpectedly.
The turnaround services team replaces internals regardless of the original equipment manufacturer, covering everything from conventional sieve, float valve, caged valve, and fixed valve trays to high-capacity trays with complex downcomer arrangements, structured packing, mist eliminators, Plate-Pak™ vane separators, liquid distributors, chimney trays, and packing supports.
The Upfront Engineering That Replaces the Back-End Welding Cost
A no-weld retrofit requires more upfront engineering than a conventional welded installation, but that front-loaded engineering cost is typically a fraction of the welding and recertification expense it eliminates. The mechanical integrity of the solution depends on accurate load calculations, material compatibility assessment, and validation through FEA.
Key engineering considerations include:
Load distribution. Weld-less supports must transfer loads — both static (weight of internals, liquid holdup) and dynamic (pressure surges, thermal cycling, flow-induced vibration) — through mechanical contact rather than metallurgical bonds. The support geometry must distribute these loads across a sufficient contact area to stay within allowable stress limits for both the support structure and the vessel wall.
Thermal expansion. Process columns operate across wide temperature ranges. A no-weld support designed for ambient installation conditions must accommodate thermal growth during operation without losing contact or creating excessive point loads. AMACS’s FEA capabilities include thermal expansion analysis specifically for this purpose.
Corrosion and material compatibility. The contact surfaces between weld-less supports and the vessel wall must be compatible to avoid galvanic corrosion or crevice corrosion over time. Material selection for the support structure needs to account for the process environment, not just the mechanical loads.
Seismic and upset conditions. In facilities located in seismic zones or subject to process upsets (pressure excursions, liquid slugging, thermal shock), the no-weld support design must account for transient loads that exceed normal operating conditions.
Getting Started with AMACS
If you’re planning a column retrofit or revamp and want to evaluate whether a no-weld approach is viable, the first step is an engineering review of the vessel — its geometry, existing attachments, operating conditions, and the internals you’re looking to install or replace.
AMACS has been engineering and fabricating weld-less solutions for retrofits and upgrades for decades, from simple expansion rings to complex support structures for vessels ranging from small to large diameter and covering all types of tower internals.
Considering a retrofit or revamp but want to avoid the cost and downtime of welding? Contact AMACS to discuss your vessel conditions and get a no-weld solution engineered for your application.
Frequently Asked Questions
A no-weld retrofit uses engineered mechanical attachment methods — such as expansion rings and proprietary structural designs — to install new tower internals without welding to the vessel wall. This eliminates the need for post-weld heat treatment and recertification, reducing both turnaround time and project cost.
Most process columns are ASME code-certified pressure vessels. Welding to the vessel wall typically requires post-weld heat treatment of the affected area and recertification of the vessel to confirm it still meets code requirements. The specific requirements depend on material type and thickness, but for the carbon steel vessels common in refining and petrochemical service, this sequence is frequently triggered. It adds significant time, labor, and cost to a turnaround.
No-weld retrofit solutions can support a wide range of tower internals, including trays (sieve, valve, bubble cap, and high-capacity designs), structured packing, random packing, liquid distributors, mist eliminators, packing supports, chimney trays, and collector-redistributors. The feasibility depends on the specific vessel geometry, loads, and operating conditions.
AMACS uses finite element analysis (FEA) to validate weld-less support structures. This includes static analysis, vibrational analysis, thermal expansion analysis, buckling analysis, and frictional resistance analysis. For complex cases, AMACS partners with third-party CFD and FEA specialists for independent evaluation.
No-weld retrofits are a strong fit when the turnaround window is tight, when existing support structures are still sound but the internals need replacing, when the vessel has usable geometry for mechanical attachment, or when the metallurgical condition of an older vessel makes welding risky. They may not be appropriate for extremely high-load applications or smooth-wall vessels with no existing attachment points.
Ideally, the engineering review and feasibility assessment should begin 60 to 90 days before the planned turnaround. This allows time for vessel geometry evaluation, FEA validation, fabrication of custom support structures and replacement internals, and delivery to site — avoiding emergency parts sourcing during the shutdown.
Yes. AMACS provides replacement equipment regardless of the original equipment manufacturer. With manufacturing facilities in Houston, TX and Monterrey, MX, AMACS fabricates replacement trays, packing, mist eliminators, distributors, and other internals for columns originally built by any OEM.