Welded Steel Base Frame for Pump, Compressor or Generator Equipment

Rotating equipment does not tolerate a base that is merely square. A pump skid, compressor frame or generator base has to deliver two mounting faces at the right height relative to each other, hold hole patterns that accept the equipment without reaming in the field, and stay stable under torque reaction and vibration. Tianhua Yihe fabricates these bases to customer drawings with post-weld machining of the equipment interfaces.

A skid base with pump and driver on machined pads: the pad pair defines the shaft centreline, so both are cut after welding.

Component profile
Component type Pump skid base, compressor base frame, generator base, engine-driven set base
Typical materials Q235B, Q345B / Q355B; stainless on request for washdown or chemical service
Structure Channel or fabricated box beams, cross members, stiffener plates, mounting pads
Features Machined pads, drip tray or containment, lifting points, anchor and grout holes, cable and pipe brackets
Welding MIG and TIG; continuous welds on containment, intermittent or continuous on structure as specified
Machining Pad facing, pad height control, hole pattern drilling, bore alignment
Finish Primer and topcoat, powder coating, or hot-dip galvanizing through partners
The alignment problem
On a typical pump set, the pump and the driver sit on separate pads, connected by a coupling. The pads therefore define the shaft centreline. If one pad is 0.5 mm high and the other is correct, the coupling faces are no longer parallel, and the alignment work in the field either becomes a shimming exercise or fails acceptance.

The same logic applies to compressor skids, where the driver, gearbox and compressor may each have their own pad group, and to generator sets, where the engine and alternator must sit on a common plane that also has to absorb vibration without loosening anchor bolts.

Three tolerances carry most of the risk:

Pad height relationship between pad groups that share a shaft axis
Pad flatness on each individual pad, which determines contact area and thus bolt preload retention
Hole position relative to the pad, which determines whether the equipment drops on or has to be pulled into place
All three are machining outputs, not welding outputs. That single fact drives the whole process route.

Manufacturing route

Design details that decide whether the base works
Pad machining allowance
Pads are modelled with an allowance that is machined away after welding. The allowance has to cover expected distortion plus straightening error, but not so much that the pad becomes a thin upstand with poor stiffness. On a typical skid this is resolved at drawing review by checking the pad thickness in the model against the welding plan, not by applying a fixed rule to every project.

Drip tray and containment
Where a containment pan is required, it is normally formed into the base rather than added as a separate tray, so that the base and pan share structure. The functional requirements are simple and unforgiving: a floor sloped toward a drain boss, continuously welded corners, no low spots that trap liquid, and a leak test before coating. Weld access to the inside corners is the usual constraint, and it is much cheaper to raise the pan depth or change the beam layout on the drawing than to fight it in fabrication.

Integrated containment: sloped floor, continuous corner welds and a drain boss, leak-tested before coating.

Grout holes and anchor access

Bases that are grouted to a foundation need holes large enough to place and work the grout, positioned where the grout can flow rather than where they happen to land between stiffeners. Anchor bolt access has to survive the stiffener layout as well; a bolt that cannot be reached with a wrench is a field modification waiting to happen.

Lifting and jacking

Lifting points are placed on members that can carry the assembled weight with a sensible centre of gravity, and they are marked on the finished base. Jacking points are kept clear of coating damage zones and of the machined pads.

Vibration and stiffness

Structural stiffness and dynamic behaviour belong to the equipment designer. The fabrication contribution is to build the specified sections and weld sizes consistently, keep pad contact full, and avoid unintended flexibility such as an interrupted weld where the drawing calls for continuous. If a drawing is ambiguous on weld continuity at a load path, that question is raised before production rather than resolved by the welder.

Materials and standards

Q235B, Q345B and Q355B cover the majority of skid bases. Stainless grades are used for washdown, food-contact-adjacent or chemical environments, with the corresponding change in welding procedure and post-weld cleaning. Material certificates to EN 10204 2.2 or 3.1 can be supplied when called for.

Where a project references a recognised baseplate standard, the applicable clauses are reviewed at quotation stage. Requirements such as drain slope, pad flatness limits, grout hole size and stiffness verification change both the fabrication plan and the inspection plan, so they cannot be treated as a drawing note that is absorbed silently.

Inspection and documentation

Inspection points can be defined for:

Overall base dimensions and squareness

Equipment mounting-hole position and diameter

Machined pad dimensions, flatness and height relationship between pad groups

Weld appearance, leg length, and specified weld requirements

Containment leak test record

Material documentation and traceability

Coating thickness and appearance through the finishing partner

The applicable tolerance, welding standard and inspection plan are confirmed for each project rather than assumed. Where a customer requires first-article inspection with recorded values, that report is prepared from measured data on the actual part.

Checking pad height relationship with a straight edge and feeler gauge on the finished skid.

Coating and finish coordination

Skid bases are usually coated after all welding and machining, which means the finish has to protect machined-adjacent areas without contaminating the pads. Standard practice is to mask or plug machined features, blast and coat the structure, then remove masking and apply rust preventive to the exposed machined surfaces. Hot-dip galvanizing imposes additional requirements - vent and drain holes, no sealed cavities, and a steel chemistry suitable for the process - which is why galvanized bases are reviewed for venting at drawing stage.

Send a skid base drawing for review

Include the base drawing or model, equipment layout, material grade, mounting interface requirements, critical tolerances, containment requirement, quantity, finish and destination. We reply with a process route and a quotation.

Email: andywang@qdthyhmetalfab.com

Qingdao Tianhua Yihe Metal Fabrication - welded fabrication and machining for equipment builders and system integrators.