Michael Forsthoffer is President of Forsthoffer Associates (FAI), a Rotating Machinery Consultancy that focuses on optimal machinery reliability in projects and during the life of a plant. FAI conducts site-specific training and condition assessments/ troubleshooting globally for machinery of every type of application. For more information, contact michael@forsthofferassociates.com.

Michael Forsthoffer

Figure: Using a back pressure control valve in the primary vent as part of the monitoring of secondary seal condition in a dry gas seal.

In the last 10+ years there has been a significant increase in the technology and instrumentation used on dry gas seal systems to monitor the condition of the seals. Most notable has been the call to monitor secondary seal condition – there have been significant failures of the secondary seal without any issue with the primary seal. The majority of these failures have been due to oil migration across the separation seals. As the oil is not drained out, it accumulates around the secondary seal, fills the grooves, and causes the secondary seal faces to contact. 

There are various approaches to monitoring secondary seal condition. Probably the most beneficial is utilizing a back pressure control valve in the primary vent (Figure 1). This sets the primary vent at a pressure below the primary seal gas supply pressure, but high enough for the user to be able to set a low-pressure alarm and trip (if required), indicating the secondary seal has failed. This pressure should probably be set somewhere between 15-25 psig, as this will provide a good differential pressure across the secondary seal and improve its lifespan by slightly increasing the gap between the faces (less wear). 

By using a positioner (wireless positioners are available) on the back pressure control valve, a user will be able to be proactive in determining if the secondary or primary seal is going to fail. For example, if the valve is normally set at 60% open and it starts to open more, this could indicate excessive primary seal leakage (assuming if intermediate nitrogen is being supplied, the flow has not increased). Likewise, if the back pressure control valve begins to close more, this could indicate excessive secondary seal leakage. 

By trending the position of this valve, one can predict at what point the valve will no longer be able to control the pressure. If the valve position stays relatively steady throughout a run on a compressor, it is not recommended to change the dry gas seals. However, if it has changed by more than 20% over a run time, it would be recommended to do so

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Dry gas seals

Establish a database of Lessons Learned with cost of unavailability in order for all corporate plants to utilize

Obtain daily revenue value (based on nominal market prices) and calculate the time that specific issues (Lesson Learned) have resulted in a shutdown or reduced rates and what the total loss of revenue was for each Lesson Learned.

This information should be tabulated in a company-wide database along with the Best Practice that would be focused on eliminating the root cause. Then all facilities within the corporate umbrella can utilize these Best Practices to resolve ongoing issues, but most importantly assure that future projects incorporate the appropriate Best Practices.

Of course, this database should be used by the “Project Team” when a new or upgrade project is in the PRE-FEED phase.

Failure to utilize Corporate Wide LL/BP Database has resulted in certain plants within the company that have ongoing issues that other plants have already solved 

Not having specific Lessons Learned in a corporate database segregates the plants from each other and if one plant has solved a machinery issue, the others may not know the solution and continue to lose daily revenue.

Not incorporating this BP will also result in new construction/upgrade projects that end up with the same exact issues that have been present since day 1 of startup in other similar corporate-wide projects.

This Best Practice has been used by Forsthoffer Associates, Inc. since 1990 and has been incorporated into companies with the following types of Plants with the benefits listed earlier:

As someone who has been involved with projects as a rotating equipment vendor, end user, and consultant since 2004 (and with experience of personnel within the company since the 1970s), I have had the opportunity to see custom designed rotating equipment projects from all industry viewpoints. Regardless of your position, you will face the challenges of company profit optimization, depleted workforce experience levels and time constraints.

The Vendor, EPC, and End Users all have different objectives and the more that the End User can provide up front early in the project the better chance the Vendor and EPC will understand their objectives. Vendor lessons learned are detailed in Table 1.1.1.

Table 1.1.2 details the lessons learned by the End User.

Review Tables 1.1.1 and 1.1.2 and observe the similarities all imposed by time and budget constraints. Also, observe how the involved individuals seldom have the opportunity to observe how their client operates and what their objectives are

Time constraints forced the acceptance of what was on the datasheet

The tendency was to think inside the flanges of the compressor only and not consider the process

Questions to the end user/contractor were minimal based upon competitive pressures and time constraints

Copying from past jobs “cut and paste” was a necessity to minimize engineering hours and Today (21st Century) is electronic cut and paste

Contractor/end-user questions diminished valuable engineering time. There was little time or money for visits to client plants unless there were significant design problems

Time constraints forced acceptance of what was on the process data sheet without time to question the basis for the stated conditions

The tendency initially was to think inside the machinery flanges, but eventually it was understood that all equipment is directly influenced by the process

Contact with the client (plant where the equipment will be installed) was minimal based on project team pressures for schedule milestones

Company specification contents were increasing rapidly since all company divisions and plants were required to review specifications and therefore naturally contribute something

There was limited project budget for visits to client plants unless there were equipment design problems.

Since 1990, Forsthoffer Associates, Inc. has engaged in troubleshooting, machinery selection and revamps, as well as site-specific operator, maintenance, and engineering training. There are other challenges but the similarities are striking and the challenges are the same. These facts are noted in Table 1.1.3.

Based on my experience, I have learned, most of the time the hard way, that all three of these groups (vendors, contractors, and end users) have the same objective but different means of obtaining that objective. Table 1.1.4 presents these facts.

It is important to remember these facts at all times during the entire project. The information contained in the following figure should be the basis for convincing the Project Team that all decisions regarding equipment purchase should be made on the basis of Process Unit life cycle cost and not capital cost and/or schedule considerations. The specific objectives of the end user are presented in Table 1.1.5.

TABLE 1.1.3 Contractor/Consultant Lessons Learned 

Both vendors and clients have limited experience bases

Decisions are made quickly, often without benefit of all the pertinent facts

Most projects are run on the basis of minimum capital investment and not life cycle cost

Vendor and end user’s interface infrequently—usually only during field failures

TABLE 1.1.4 The Objective—Maximum Profits 

Everyone has the objective of maximum profits but the means to accomplish this end is different:

Contractor—engineers and installs for minimum cost

End user—must operate the custom-designed equipment 24/7 for 30 years or more. Therefore, the end users objectives can be directly opposed to the vendor’s and contractors!!!

TABLE 1.1.5 End user—Specific Objectives for Maximum Profit 

These objectives result in.............................................. maximum up time

which will yield .............................................................. maximum revenue

and .................................................................................maximum profits

For the entire life cycle of the process unit!!

Is the amount of revenue obtained in 24 h of operation

Trip of an un-spared item = exposure to revenue loss

Daily revenue values can range from 1MM$ to 5 MM$+

Always justify Project Scope requirements on the basis of daily revenue loss

Assign an Actual Daily Revenue Loss amount to each proposed Best Practice if it is not implemented

The most important factor in lifecycle cost considerations is daily revenue and obtaining this figure should be the number one priority in the early stages of the project. It will be a key fact in obtaining management support for your project action plans. Table 1.1.6 presents these facts.

Therefore, the company lifecycle revenue and profit potential will be a result of incorporating all of your project best practice requirements into the project action plan at the first opportunity before the first project budget estimate is prepared. Fig. 1.1.1 shows the advantages of incorporating this philosophy as early as possible into the project.

This action should be taken when the project is first announced and the project team is assembled, before the Project Budget Estimate is calculated. The approach taken during the first 3–6 months after the initial project kick-off will determine the level of reliability and lifecycle cost savings for the entire life of the process unit (over 30 years). Most important is the necessity of establishing immediate creditability with the project team so that your ideas are implemented.

Hopefully, the previously mentioned information will be of use in your project involvement in terms of lessons learned. The resulting best practices should be developed into a project philosophy that will eliminate all the issues noted

 FIGURE 1.1.1 The lifespan of rotating equipment[/caption]

earlier and will obtain and maintain your management’s support throughout the entire project from the pre-feed phase to field operation.

Note that while this book is concerned with rotating equipment Best Practices, many of the principles in this Book are equally applicable to all assets included in a project.

Note: The above is Best Practice 1.1 located in Forsthoffer’s More Best Practices For Rotating Equipment by Michael Forsthoffer, which can be purchased 

Project best practices

Given the present entirely justified Cost Containment Environment of the industry, machinery safety and reliability is now in most cases the sole responsibility of plant machinery specialists.  The 46

 TPS affords all attendee’s a terrific opportunity to increase their machinery knowledge base.

Therefore, we have a question for all attendee’s that can significantly affect the way you treat your driven machinery (pumps, compressors, fans etc.).  

What are the design objectives of driven machinery?  

Closely examine figure 1 below  and do not continue reading until you answer our question utilizing this figure and your present machinery knowledge base.

What are the design objectives of Pump and Compressor OEMs?  To provide _____________________________ while  _______________________.    This objective is true for both dynamic (centrifugal and axial) pumps and compressors and positive displacement types.  Figure 1 was drawn for dynamic types since approximately 95% of the pumps and compressors in your facilities are dynamic types.   If your answer is the correct one, what should be your action plan when you go back to your facility?    Another way of stating this question is who should you discuss the knowledge gained during the 46

 TPS other than your immediate supervisor and associates?

Movement of what and equilibrium with what?   What happens if equilibrium requirements are not as anticipated?  Are there performance and mechanical protection systems for the machinery?

Look at the figure again and ask yourself. What does dynamic machinery provide, energy or flow?  From the beginning of STEM education, we naturally read curves from the horizontal axis (“X”) up to the curve and then cross horizontally to the vertical (“Y”) axis!   Is this the case for dynamic machinery?  The machinery is designed for a certain flow and energy but are these values always the same in the field?

 TPS and remember our question.  Prioritize the Discussion Groups, Case Histories and the Exhibition Floor.  Papers, Tutorials and Short Courses (If you were fortunate to attend a Short Course) are important of course but leaving the TPS with facts to be a proactive machinery specialist is what your management wants and needs from you.  IE; start a “RCA” (Root Cause Analysis) when machinery performance and mechanical parameters change!  Let’s try to eliminate RCFA’s!!!  One last message: Always remember the Y axis in figure 1 and associate with the people who relate to the Y axis.

(Answer: Plant Flow requirements while staying in equilibrium with the process requirements )

(Answer: Plant Flow requirements while staying in equilibrium with the process requirements)