Pump Wisdom. Robert X. Perez

Never waste your time on bidders that take blanket exception to your entire specification.

       If the owner–purchaser of a process plant grants a waiver to a certain specification clause, he should understand the extent to which noncompliance will lead to increased maintenance requirements, downtime, or even catastrophic failure risk.

       In the end you get not what you expect, but you get what you inspect. Inspection is one of the costs of getting reliable process pumps.

References

      1 1 Lubrication Systems Company; “Photo contributed by and used with the permission of Don Ehlert”, Houston, Texas, 2008.

      2 2 Ingram, J.H.; "Pump reliability – Where Do You Start", presented at ASME Petroleum Mechanical Engineering Workshop and Conference, Dallas, TX, September 13–15, 1981.

      3 3 Alfred Conhagen Inc.; Houston, Texas, 2010.

      4 4 Sulzer Pumps, Ltd.; Winterthur, Switzerland. By permission, 2010.

      5 5 Bloch, Heinz P.; “Optimized Equipment Lubrication: Conventional Lubrication, Oil Mist Technology, and full Standby Protection”, DeGruyter Publishing, Berlin/Germany, 2021 (ISBN 978‐3‐11‐074934‐2)

3 Foundations and Baseplates

      Pumps can be found mounted in many different ways; there are times and places to do it at least cost and times and places to do it with uncompromisingly high quality.

Plants that use stilt mounting (Figure 3.1) often fall short of achieving best‐possible equipment reliability. Best practices plants secure their pumps more solidly on more traditional foundations. Stilt‐mounted pump sets lack overall stiffness but have been used for small ANSI pumps where the sideways‐move capability of the entire installation was thought to equalize piping‐induced stresses. Among its few advantages is low initial cost.

      However, there are serious shortcomings since stilt‐mounting will not allow pump vibration to be transmitted through the baseplate to the foundation and down through the subsoil. Proper foundation‐mounting permits transmission of vibration which can result in a significant increase in mean time between failures (MTBFs), longer life of mechanical seals and bearings, and favorably low total life‐cycle cost [1].

Securing Pumps in Place – With One Exception

Again, proper field installation of pumps has a measurable positive impact on pump life. Even a superb design will give poor results if poorly installed. A moderately good pump design, properly installed, will give good results [2]. Proper installation refers to a good foundation design, no pipe strain (see Chapter 4), and good shaft alignment (Chapter 14) to name just a few. No pump manufacturer designs its pumps strong enough to act as a solid anchoring point for incorrectly supported piping, or piping that causes casings and pump nozzles to yield and deflect. Also, pumps have to be properly secured to their respective baseplates, and these baseplates have to be well‐bonded to the underlying foundation. Epoxy grout is used to do this bonding in modern installations.

Figure 3.1 ANSI pump set on a stilt‐mounted baseplate.

      Source: ITT/Goulds, Seneca Falls, NY.

There is one exception, however. Vertical in‐line pumps (Figure 3.2) are not to be bolted to the foundation. They are intended to respond to thermal and other growths of the connected piping and must be allowed to float or slide a fraction of an inch in the x‐ and y‐directions. The foundation mass under vertical in‐line pumps can be much less than that under the more typical horizontal pump.

Making the foundation mass three to five times the mass of the pump and its driver has been the rule of thumb for horizontal pumps. For vertical in‐line pumps, it is acceptable to make the concrete foundation about one‐and‐a‐half to twice the mass of the pump‐and‐driver combination [3].

Figure 3.2 Vertical in‐line pumps are not to be bolted to the foundation. They should be allowed to move with the connected pipes.

Why Not to Install Pump Sets in the As‐Shipped Condition

There are obviously some flaws in the grout surrounding the baseplate in Figure 3.3. (On the other hand, the equipment owner invested in a very modern small oil mist lubrication unit). Note the hollow space under the electric motor. Lack of support under motors often invites resonant vibration. Rigorous written installation procedures are needed and must be adhered to if long equipment life is to be achieved.

Before delving into other installation matters, note the alignment jacking provisions in Figure 3.4, where the purchaser specified an arrangement that allows insertion (and later removal) of alignment‐jacking tabs in the x‐ and y‐directions next to each of the four motor feet. (A fixed jacking tab arrangement can be seen later – Figure 14.3).

Portable jacking tabs, Figure 3.4, (inserted in a welded‐on bracket), allow driver alignment moves to be made. Thereafter, the jacking bolts are backed‐off, and the entire tab is removed. When jack screws are left tightened against the motor feet, motor heat, and thermal growth might force the feet into these bolts even more, sometimes causing the entire motor casing to distort [1]. Note, therefore, that backing‐off jacking bolts should be one of many installation checklist items.

Figure 3.3 A typical, but obviously flawed, “conventional” pump foundation.

      Source: Lubrication Systems Company, Houston, Texas.

Figure 3.4 Removable alignment jacking tabs shown inserted in three of four locations next to the two motor feet shown here.

      Source: Stay‐Tru^®, Houston, Texas.

To ensure level‐mounting throughout, the baseplate is placed on a foundation into which hold‐down bolts or anchor bolts (Figure 3.5) were encased when the reinforced concrete foundation was being poured [2]. For proper stretch and long life, these anchor bolts