Trip Analysis

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GAS PLANT RELIABILITY – TRIP

ANALYSIS: A QUICK TOOL FOR

PLANT MANAGEMENT

Stefan Winter and Keith Worrell Winter completed his chemical engineering education in

Germany and Austria. He has an MS from the Technical

University Aachen and a PhD from the Technical

University Vienna. He joined Saudi Aramco in 1998 at

‘Uthmaniyah Gas Plant after working for engineering

and operating companies in Germany and Canada. He is

now with the Marjan Offshore Producing Department in

Capital Projects.

Worrell is a 1974 graduate of North Carolina StateUniversity in Raleigh. He is the supervisor of mainte-

nance quality assurance at Saudi Aramco’s ‘Uthmaniyah

Gas Plant. Worrell has 27 years of experience in mainte-

nance engineering, with the past 10 years concentrated on

reliability and condition-based maintenance.

ABSTRACT

Newcomers to any production facility need to quickly learn where problems occur,

frequency of repair trips, which equipment requires repairs, the urgency of repairs

and what repair expenses are justifiable. Reviewing trip data identifies problems and

helps employees allocate resources for solutions. A trip analysis, using data from

approximately 250 trip reports from 1996 to 2001, was undertaken to make this

job easier. These reports yielded a significant amount of useful data. Detailed infor-

mation about the cost of each trip and the cost of each repair is not easily or

quickly accessible even when trips are correctly recorded in the distributed controlsystem (DCS), therefore indices for the cost of each outage and its repair will be

applied at ‘Uthmaniyah Gas Plant (UGP). The relationship between outage costs

and cost of repairs will reflect the urgency or priority of the problem. The hypothet-

ical example below easily shows the procedure.

62 SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2002

Stefan Winter

Keith Worrel



LIST OF OUTAGES – OUTAGE MATRIX

All available reports about outages and equipment failures

were collected. These outages were listed with date, equip-

ment with frequent failures and reasons for failure. In this

list it became obvious that some equipment and certain rea-

sons were frequently repeated. Therefore, fig. 1 includes the

section “equipment with frequent failures.” For example:

On the line with #28, the boiler is the “equipment” prob-

lem and the fuse is the “reason.” A hypothetical outage

matrix (fig. 1) offers an overview of the trips. The con-

cerned equipment and the reason are marked with an x.

OUTAGE AND REPAIR INDEX

An outage index will be used to evaluate the importance of

equipment failures. Another index will be used for the repair.

The repair index indicates if a “cheap quick fix” can elimi-

nate the problem or if a million dollar repair is required.

SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2002 63

# DATE TIME Equipment with Frequent Failures Reason

B o i l e r

1

P u m p

1

P u m p

2

P u m p

3

C o m p

r e s s o r 1

C o m p

r e s s o r 2

S u b s t

a t i o n 1

M a i n S u b s t a t i o n

B u r n e

r i n S R U

E l s e

L o s s o f P o w e r

F u s e

R e l a y

L o o s e

W i r i n g

E l e c t r

i c a l - G e n e r a l

I n s t r u

m e n t A i r

O i l I n s t r u

m e n t a t i o n -

G e n e r

a l

V a l v e / S o l e n o i d

S c a n n

e r F a i l u r e

V i b r a t

i o n

B e a r i n

g s

E l s e

30 16-Dec-00 3:16 x x

29 12-Dec-00 3:16 x

28 3-Dec-00 5:45 x x

27 29-Nov-00 5:45 x x

26 21-Nov-00 16:54 x x

25 21-Nov-00 9:05 x x

24 10-Nov-00 2:10 x x

23 12-Sep-00 8:30 x x

22 23-Aug-00 6:25 x x

21 7-Aug-00 7:58 x x

20 5-Aug-00 13:10 x x

19 29-Jul-00 23:30 x x

18 23-Jul-00 14:50 x x

17 30-May-00 11:37 x x

16 15-May-00 8:36 x x

15 14-May-00 3:46 x x

14 9-May-00 14:30 x x

13 3-May-00 12:45 x x

12 21-Apr-00 13:53 x x

11 20-Apr-00 14:32 x x

10 16-Apr-00 2:52 x x

9 15-Apr-00 8:45 x x8 12-Apr-00 17:40 x x

7 28-Mar-00 16:34 x x

6 22-Mar-00 3:30 x x

5 19-Mar-00 12:05 x x

4 15-Mar-00 20:08 x x

3 12-Mar-00 9:17 x x

2 5-Mar-00 12:45 x x

1 6-Feb-00 2:52 x x

Fig. 1. Outage Matrix



Outage Index

The cost magnitude of plant trips will be reflected in the

outage index. The outages can be differentiated in total

plant shut down, partial plant shut down, cascading partial

plant shut down or no plant shut down. For a more

detailed analysis, a further detailed separation with more

indices might be required.

• Outage Index 4: A total plant shut down.

• Outage Index 3: A partial plant shut down. A partial

plant shutdown causes reduced production. An exam-

ple is that a reduction of steam boilers reduces plant

production, except during wintertime when less gas

production is required.

• Outage Index 2: A cascading partial plant shut down

occurs when equipment failure can easily cause a par-

tial plant shut down. An example is when a sulfur

recovery unit (SRU) is overhauled, another SRU fails

and aid gas has to be sent to the acid gas flair.

• Outage Index 1: There will be no plant shut down. Noplant shut down will occur in the hypothetical example

if pump 1 trips and if pump 1 quickly comes back on

line there will be no direct impact on plant production.

Repair Index

The magnitude of the repair cost will be reflected in the

repair index with the question being the cost of the repair.

For a more detailed analysis a further detailed separation

with more indices might be required.

• Repair Index 1: Some repairs are small, quick and easy.

Some outages can be fixed during the night shift with-out involving engineering. For the “cheap quick fix”

Repair Index 1 will be used for estimated costs of

lower than $10,000.

• Repair Index 2: Other outages involve more engineering

or operators who require some training. Estimated

costs of between $10,000 to $50,000 can be expected.

• Repair Index 3: If repairs require a change of design that

includes an engineering package or heavy equipment,

like cranes, costs of over $50,000 can be expected.

Index Ratio

The Index Ratio divides the outage index with the

repair index. Two extremes document the purpose of the

index ratio:

Extreme 1: High Index Ratio

A high index ratio reflects high priority. A high

index ratio results from a high outage index and a low

repair index.

Example: a cheap fuse used in repair index 1 can cause

an expensive total plant outage with the outage index 4.

The ratio will be 4/1 and it will be seen in the index matrix

shown below. It is obvious that this fuse will be given a

high priority.

Extreme 2: Low Index Ratio

A low index ratio reflects low priority. A low index ratio

results from a low outage index and a high repair index.Example: pump 1 (hypothetical example), with a repair

index 3, does not cause any immediate partial plant outage

with an outage index 1. The ratio here would be 1/3. It is

self explanatory that this pump is lower on the priority list

than the above-mentioned fuse.

INDEX RATIO MATRIX

The index ratio matrix covers all possible index ratios.

APPLYING THE INDICES AND INDEX RATIO IN THE OUT-

AGE MATRIX

The index ratio has to be applied in the outage matrix. This

will be completed with the following steps. These steps are

shown in fig. 3.

• Step 1: One additional column is inserted for the

estimated outage index.


estimated repair index.


index ratio.

• Step 4: The index ratio is calculated.

• Step 5: The calculated ratio is transferred into the field

with the “equipment with frequent failures.”

• Step 6: The calculated ratio is transferred into the field

with “reasons.”

• Step 7: Insert row for average index ratios.

• Step 8: In this row the average index ratios are calculat-

ed. (Averages can be calculated for different time

periods: yearly, quarterly, etc.)


1 1 0.5 0.33

2 2 1 0.67

3 3 1.5 1.00

4 4 2 1.33

1 2 3

Index Matrix

Repair Index

Outage

Index

Fig. 2. Index ratio matrix



SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2002 65

# DATE TIME CostsEquipment with

Frequent FailuresReason

O u t a g e

I n d e x

R e p a i r

I n d e x

I n d e x R

a t i o

B o i l e r 1

P u m p 1

P u m p 2

P u m p 3

C o m p r e s s o r 1

C o m p r e s s o r 2

S u b s t a t i o n 1

M a i n S u b s t a t i o n

B u r n e r i n S R U

E l s e

L o s s o f P o w e r

F u s e

R e l a y

L o o s e W

i r e r i n g

E l e c t r i c a

l - G e n e r a l

I n s t r u m e

n t A i r

O i l

I n s t r u m e

n t a t i o n - G e n e r a l

V a l v e / S o

l e n o i d

S c a n n e r

F a i l u r e

V i b r a t i o n

B e a r i n g s

E l s e

Average Index Ratio 2.0 0. 8 1.0 0. 8 0.7 0. 7 1.5 2. 0 2.0 0.5 1. 5 2. 7 3. 0 1.5 0.5 0.9 1.0 0. 8 0. 6 1.0

Frequency 8 7 1 2 4 1 2 1 3 1 6 3 2 0 1 1 6 0 1 1 3 6 1

30 16-Dec-00 3:16 1 3 0.3 0.3 0.3

29 12-Dec-00 3:16 3 2 1.5 1.5

28 3-Dec-00 5:45 3 1 3.0 3.0 3.0

27 29-Nov-00 5:45 4 2 2.0 2.0 2.0

26 21-Nov-00 16:54 2 3 0.7 0.7 0.7

25 21-Nov-00 9:05 2 3 0.7 0.7 0.7

24 10-Nov-00 2:10 1 1 1.0 1.0 1.0

23 12-Sep-00 8:30 3 2 1.5 1.5 1.5

22 23-Aug-00 6:25 3 2 1.5 1.5 1.5

21 7-Aug-00 7:58 1 1 1.0 1.0 1.0

20 5-Aug-00 13:10 3 1 3.0 3.0 3.0

19 29-Jul-00 23:30 3 1 3.0 3.0 3.0

18 23-Jul-00 14:50 1 1 1.0 1.0 1.0

17 30-May-00 11:37 1 1 1.0 1.0 1.0

16 15-May-00 8:36 3 2 1.5 1.5 1.5

15 14-May-00 3:46 2 3 0.7 0.7 0.7

14 9-May-00 14:30 2 3 0.7 0.7 0.7

13 3-May-00 12:45 2 3 0.7 0.7 0.7

12 21-Apr-00 13:53 1 2 0.5 0.5 0.511 20-Apr-00 14:32 3 2 1.5 1.5 1.5

10 16-Apr-00 2:52 3 2 1.5 1.5 1.5

9 15-Apr-00 8:45 1 2 0.5 0.5 0.5

8 12-Apr-00 17:40 3 1 3.0 3.0 3.0

7 28-Mar-00 16:34 1 1 1.0 1.0 1.0

6 22-Mar-00 3:30 1 2 0.5 0.5 0.5

5 19-Mar-00 12:05 3 2 1.5 1.5 1.5

4 15-Mar-00 20:08 1 1 1.0 1.0 1.0

3 12-Mar-00 9:17 3 3 1.0 1.0 1.0

2 5-Mar-00 12:45 3 2 1.5 1.5 1.5

1 6-Feb-00 2:52 1 1 1.0 1.0 1.0

Step 1

Step 2

Step 3

Step 4 Step 5 Step 6

Step 7

Step 9

Step 10Step 11 Step 8

Fig. 3. Outage matrix with index ratio



• Step 9: From here the priorities for the repair are

obvious: the equipment or reasons with the high

index ratio.

• Step 10: Insert row for frequency.

• Step 11: In this row frequencies are calculated. The

frequency shows how often an outage happens. (They

can be calculated for different time periods: yearly,

quarterly, etc.)

OPERATING PLAN

The operating plan documents the future investments and

intentions of a production facility. Applying the hypotheti-

cal example in fig. 3: fuses, relays, boiler 1, main

substation, burner in SRU should be part of the operation

plan for the following years. Besides the operating plans,

funding for the electrical capital projects and single-point

failure study have to be considered at UGP.

SUMMARY

Learning where problems occur, frequency of repair trips,

which equipment requires repairs, the urgency of the

repairs and what repair expenses are justifiable are impor-

tant details in running a production facility. When

reviewing trip data using indices, employees can quickly

identify problems and allocate resources for solutions. In

trip analyses, using only 30 hypothetical repair trips,

detailed information about the cost of each trip and the

cost of each repair is not available, therefore indices for the

cost of each outage and its repair are used. Index ratios, the

relationship between outage costs and repair costs arefound by dividing the outage index by the repair index cal-

culated in a spreadsheet format. The averages of the index

ratios, the calculated frequency of the equipment failures

and the trip reason document this urgency and priority. The

method of using indices is applied at UGP resulting in

trends that are readily visible, thus justifying use of trip

analyses in parts of future budgets and operating plans.

LITERATURE

The following literature is part of the background of this trip

analysis: “Risk-Based Management, A Reliability-CenteredApproach” (Richard B. Jones, Gulf Publishing Company,

ISBN 0-88415-785-7). It is available in Saudi Aramco

libraries and includes literature references. An Engineering

Standard regarding trip analysis can be developed.

REFERENCES

A version of this article appeared in the May 2002 issue of

Hydrocarbon Procesing.


Trip Analysis

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