If The Foundations Be Shaken

Addressing Inspection And Repair Of Recip Foundations

More comprehensive investigations (Stopped compressor) 

More comprehensive investigations can be done if the machine is stopped. In case of a foundation repair or regrout, these investigations can be useful for deciding if anchor bolts need to be replaced or to find out how much of the concrete has to be chipped away.

Core drilling and investigations

Diamond-drilling of core samples is required in order to check the depth of oil penetration into the block. These cores may also be used for a more extensive carbonation investigation [6] and to check the quality of the concrete. Differences in homogeneity of the concrete can be identified and a compressive stress test can be performed. Oil penetration and changes in concrete quality can also be noticed when new anchor pockets are drilled or old anchor bolts are removed (Figure 5).

Figure 5
Figure 5. Cores with oil penetration.
Alignment checks

The alignment of the compressor to the driver and the alignment of the extensions to the frame need to be checked since foundation issues will ultimately lead to alignment issues. Also, the alignment of the rotor to the magnetic center needs to be checked to determine web deflection and rod runout. Depending on the need for further investigation, more values can be measured such as the flatness of soleplates and the linebore (center line measurement).

Inspection of the anchor bolts

Anchor bolt stretch may be measured with an ultrasonic bolt meter, provided the anchor model and data are known. Are there signs of bolt over-stretching? If the grout layer has blocked the anchor to stretch, it will typically stretch just below the nut.

If the compressor is removed, it is also possible to investigate bonding of the anchor into the concrete foundation by using a hollow plunger cylinder and a dial indicator. This can be done by placing the cylinder over the bolt and applying load with a hydraulic cylinder while the dial indicator is attached to the head of the anchor bolt. If the bolt comes up more than the stretch length after applying the design load (be careful not to apply too much load) for 24 hours, then one can be sure that the anchor is debonding from its pocket.

Analysis And Correction Plan

After all the data from the desk and field research has been gathered and combined, it is time to write an analysis and correction plan. The analysis plan is an evaluation of foundation and anchoring and should also contain an indication of the urgency.

For example, a loose anchor bolt, in combination with vibration levels above EFRC reference values, requires high urgency since the machine’s anchoring cannot be guaranteed. The machine should be stopped in order to perform at least an emergency repair. Cracks in a grouting layer in combination with normal vibration levels, in general, require no special urgency. A repair can be planned during the next overhaul or when convenient.

It is hard to provide a list to indicate which problems require immediate attention and which not, since there is always a combination of problems and every situation is different. Hence, in general, one can say that every problem that is an immediate threat for anchoring, and load transfer of the compressor should be a reason for instant repair.

Repair methods

After the urgency of a repair is determined, the repair method is to be selected. If an urgent repair is compulsory, it is also possible to perform a crisis repair on short notice while planning a more durable repair during a maintenance stop.

There are more factors that influence the selection of a suitable repair method. The most important (but surely not the only) factors are:

  • Urgency of the repair.
  • Safety conditions.
  • Timeframe for the repair.
  • Possibility of removing the machine or not.
  • Time of the year (weather conditions).

Table 1 shows a brief summary of some common problems, their typical urgency, and possible repair methods. Please, note that this list is not a complete reference with required urgency indications and repair methods.

table 1
Table 1. * A pull anchor pulls separated parts of a foundation together. See Figure 6.

The correction plan should include a proposal for repair, specifying alignment, usage of soleplates, anchoring method, grouting, injecting, and other activities with a time schedule. It is also important to conduct a safety and risk analysis and to provide a budget price for the repair.

Practical Issues During Repair

When repairing a compressor foundation (regularly incorporating a regrout of the machine), some issues require special attention. New techniques, materials, and insights may require a change of mind for many companies. To avoid unexpected changes in planning and budget, these subjects should be discussed at an early stage.

Figure 6
Figure 6. Pull anchor.
3-D positioning 

Before an installation is removed, the exact position of the complete line should be registered. A 3-D tracking laser is used to measure the exact position of the frame, anchors, cylinders, crosshead supports, centerline of the crankshaft, expansion vessels, and all flanges of the main piping (Figure 7). This 3-D position measurement provides a complete set of data on the position of the installation.

For example, the measurement can tell whether the total installation (compressor-driver) is within tolerances in the water-level plane. This information may indicate possible tilting of the total foundation. Corrections at the time of reinstallation need to be addressed as early as possible. The consequences are to be considered case by case.

Figure 7
Figure 7. Measuring a foundation with a 3-D laser tracker.

If the old anchor bolts are to be removed, the 3-D measurement data is used to install the machine on the exact same (or improved) coordinates. In urgent cases, it is even possible to install the anchor bolts in place before the compressor is back on-site.

Soleplates

Not all reciprocating compressors are installed with soleplates (Figure 8). Some compressor configurations require a little free horizontal movement of the crosshead due to thermal expansion. If this is the case, it will be indicated by the compressor manufacturer. Soleplates (in these configurations called sliding plates) or bending plates allow these movements, while grouts will crack.

Another big advantage of installing soleplates is the ease of removal of the crosshead support without having the grout jacked away. Especially, since nowadays high-performance epoxy grouts are advised, it will save a lot of time and money if one does not have to jack away and replace the grouting. Furthermore, precision alignments are easier to perform at any later time.

Figure 8
Figure 8. A soleplate installed between a compressor and grout layer.

When designing soleplates, it is important to avoid sharp corners (otherwise, the grout will crack) and include a good jacking solution (leveling bolts). Also, the design should be stiff and there must be a possibility to apply a corrosion-resistant coating to the soleplate on-site, depending on location and local coating specifications. In many cases, it is not possible to apply a coating beforehand because the epoxy grout needs to bond with the steel and not with the coating. Therefore, during the design phase, a plan should be made as to how such a coating can be applied on-site.

In some cases, adapting a special anchoring system with coupling is also required so it becomes possible to loosen the extension and slide it away. This is required for many reciprocating compressor models, otherwise, removing the extension will not be possible.

Method of alignment

Unfortunately, the use of adjustable jacks, steel shim blocks or wedges is still frequently advised for alignment of pumps, skids, base frames, or even compressors.

These steel jacks make the equipment stand on “high heels,” forming a direct steel contact between machine frame and concrete foundation. Instead of having the necessary constant compression on the grout, the machinery stands on noncompressive steel blocks, which allows oil and water to penetrate. Neither the anchors nor the grout can function according to their design as pre-tension is lost on the steel jacks and grout is merely an aesthetic cover. Furthermore, these parts are subjected to corrosion, which jeopardizes the alignment. Leaving adjustable alignment tools in place is strongly discouraged. (API RP 686) [9].

The only correct solution is to use jack bolts. They are easy to apply in soleplates, skids or frames. The bolts are removed after full cure of the grout, followed by proper torquing of the anchors. Jack bolts should be engineered to carry the full weight of the machine skid under all conditions expected during skid leveling.

Figure 9
Figure 9. Improper use of adjustable jacks and proper use of jack bolts.

On the concrete foundation, a round metal landing pad should be placed to carry the jacking screw. The design of the pad is stainless steel with rounded edges and can be found it the API RP 686 (Figure 9).

Anchoring 

Anchor pockets are to be drilled according to the calculated anchor data. Besides the fact that the adhesive surface of the pocket is determinative, the diameter to be drilled should be chosen based on the existing situation of the old anchor. One must consider: Is it only the anchor that is to be removed, or is there also a metal sleeve or a hammerhead construction that must be removed?

The best practice for anchor bolt installation requires having the anchors hanging free, and centered, from the machine feet into the pockets before grouting them (Figure 10). This method guarantees correct height and position, without touching the concrete. An equal space between anchor and machine foothole is obtained, which makes the necessary alignment possible.

A group of anchors, such as those installed in the frame, should perform as equally as possible. Having one or two anchors apply excessively more or less load than the others should be avoided; a deviation of less than 10% is best practice. For this reason, avoid replacing one or two anchors only and leaving the others in place.

Grouting

According to API RP 686 and other recommendations, epoxy grouts are always best for reciprocating compressor systems.

Epoxy grout has many advantages over cement grout; however, there are also some issues. If the application is done by a certified and experienced company, these difficulties will have no negative influence. Inexperienced applicators will face some unexpected situations that will lead to problems. Some examples of essential concerns are:

• Creep calculation.
• Temperature limitations.
• Mixing techniques.
• Usage of expansion joints.
• Edge lifting.
• Temperature during application.

There are many different epoxy grouts available. Compare the quality, ease of application and technical properties. The best option is to choose a proven product such as Chockfast Red epoxy grout and a reliable applicator such as EMHA.

Figure 10
Figure 10. Installation of compressor with anchors hanging free.
Injection of cracks

As explained earlier, there is a big difference in cracks in grouting and cracks in cold joints in the concrete foundation.