How to Avoid Those Common Site Troubles During Commissioning

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HOW TO AVOID THOSE COMMON SITE TROUBLES

DURING COMMISSIONING 5 JAN 2016

By: Muhammad Imran – Mechanical Rotating Engineer – LUKOIL International Services B.V Dubai

re-commissioning, Commissioning and Startup is the most critical stage in the life cycle of any Oil

& Gas project. This is the project phase when each system component is thoroughly checked and

prepared for readiness to receive the test or actual process fluids (Pre-commissioning), subjected

to operational test run most often as an independent system or equipment (Commissioning) and

henceforth sequentially taken into operational service in an integrated manner (Start-up).

Operational test run during Commissioning is fundamentally different from normal plant operation.

Most often testing fluids are substitutes rather than the actual process fluids. Though system cleanliness

is ensured, there is a high probability of contamination due to left over pipe scales, welding slags or

innate contamination of the testing or process fluids. Some system control functions are inhibited or

bypassed to achieve a selective mode of operation. Despite the fact that most of the equipment is

already tested and approved satisfactorily in the vendor shops, site construction and installation is

always new and yet to be qualified until Commissioning is done. Startup is essentially a first ever

attempt to operate various units in an integrated manner. Therefore most often, the Commissioning and

Startup involves troubles which are commonly not found during the normal plant operation. This is the

stage when surprise events occur due to several contributing factors which include human errors, lack of

availability for proper guidelines and procedures, inadequate adherence to the guidelines and

procedures in place, lapses in the previous stages of construction and pre-commissioning, some

essential aspects not considered at the design stage including FEED and EPC. Most often these site

troubles involve major damage of the equipment causing unforeseen cost and schedule impacts.

This paper highlights some of the common site troubles faced during Commissioning. The main focus is

not to provide few lesson learnt items but to familiarize the reader (mainly Engineers without any site

experience) with nature of site troubles and to create awareness on how certain design aspects from

engineering stage become leading cause for site troubles during Commissioning. To emphasize the

point, a number of typical examples are presented from the actual site experience. Finally,

recommendations are provided on how such common site troubles may be avoided by taking proper

actions at the early stages of the project.

1. COMPRESSOR SUCTION STRAINER

Industry has faced numerous cases of compressor damages by the suction strainer failure. During a

plant startup, one of the 4 MW piston reciprocating compressor was heavily damaged due process gas

contamination. There was no differential pressure monitoring on the compressor suction strainer. Due

to very high differential pressure induced by the dirty process gas, the strainer element was broken and

dirty process gas silently made its way through the compressor system causing irreparable damages to

the compressor internals including valves, cylinder liner and piston rider bands etc.

P

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Figure 1-a: Damaged valve rings Figure 1-b: Damaged valve seat

Compressors are sensitive machines and not tolerant to contamination from the piping system or the

process fluids. It is highly recommended to always provide a suction strainer in the compressor suction

with differential pressure monitoring with alarm and trip functions.

2. INADEQUATE LUBE OIL SUPPLY PRESSURE

During Commissioning of a lube oil system, the oil supply pressure (1.3 barg) was lower than the

required supply pressure (1.5 barg). Several checks and investigations revealed the root cause as wrong

installation of two orifice plates in the system. The orifice plates were found installed in the wrong

orientation (upstream vs downstream side), though correct orientation was marked on each orifice

plate stem. When the system was operated with correct orientation of the orifice plates, the oil supply

pressure was achieved as 1.5 barg as per the design.

Figure 2: Lube oil system showing various system components

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In a similar case, the Auxiliary lube oil pump repeatedly failed to build discharge pressure. After several

checks and investigations, it was found that the check valve at the AOP suction was installed with an

undersized flange gasket (Figure 3-a). The smaller gasket was obstructing the valve disc opening and

hence it was responsible for starving the AOP suction. The lube oil system was successfully operated

when restored with the correct size gasket (Figure 3-b).

Figure 3-a: Check valve with undersize gasket Figure 3-b: Check valve with correct gasket

3. MECHANICAL SEAL FAILURES

Mechanical seals failure is one of the major issues during Pre-commissioning and Commissioning.

Contamination of the seal system is a leading cause of the seal failures; it results from the already

contaminated system not properly cleaned form the supplier shop, or contaminated by the dirty

test/process fluid during Commissioning or by the contamination migrated from the unclean

buffer/barrier fluids. Quite often, the portable filling units for the buffer/barrier fluids are inadequate in

number and are exchanged for different type of sealing fluids. While transferring the sealing fluids in

between the portable filling unit and temporary holding pots, the sealing fluids get cross contamination

as well as catch contamination from the environment inside and outside the temporary holding pots.

Figure 4: Portable buffer/barrier fluid filling unit ( typical )

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Sometimes seals leakage occurs due to a design fault in the seal or the pump itself. A good example is a

pump seal leakage which occurred due to manufacturing defect in the pump seal chamber, the seal and

seal system itself was perfect. The seal chamber bore (Figure 5-a) was not perfectly round to the extent

that it failed to provide proper seating of the seal O-ring resulting into a leak path (Figure 5-b) for the

barrier fluid to leak out of the seal cavity.

Figure 5-a: End view of pump seal chamber Figure 5-b: Mechanical seal drawing

4. HIGH VIBRATION ON VERTICAL PUMPS

Vertical pumps are critical in terms of installation and operation. Improper installation and lack of

proper considerations during startup are among major causes of the high vibration on vertical pumps.

During commissioning of a vertical pump, levelness of the pump mounting plate was leading cause of

high vibration. In another case, resonance of pump structure was root cause of high vibration for more

than 40 vertical pumps. It was due to manufacturing fault in the pumps; the screening test to detect this

fault was not specified in the Engineering Stage and was not performed in the vendor shop.

Figure 6-a: Vertical pump installation Figure 6-b: Mounting plate levelness check

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5. SPECIAL TOOLS AND ACCESSORIES

There are cases when lack of proper special tools and accessories is the root cause for the site troubles.

During Pre-Commissioning in a project, several pulsation dampeners for dosing pumps were damaged

during the first nitrogen charging. The reason was not bad quality of the bladder material rather it was

the inappropriate nitrogen charging kit. The project had supplied several nitrogen charging kits with a

much larger pressure range scale than actually required. So it was very difficult for the commissioning

staff to minutely control the charging pressure in a narrow range using a wider scale charging kits and

hence several bladders were damaged due to accidental over-pressurization.

Figure 7: Nitrogen charging kit ( typical )

Figure 8: Dosing pump installations with small pulsation dampeners ( typical )

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6. LACK OF PRESERVATION & RUST PREVETION

Several damages occur at the site due to lack of proper preservation after installation and before

commissioning. As a typical example, total eight large air fin cooler fan bearings were badly damaged

due to lack of preservation after installation.

Figure 9-a: Damaged bearing as installed Figure 9-b: Damaged bearing – dismantled

Another example, a multistage pump was found in a bad condition due to ingress of rust and dirty

moisture inside the pump internals. The pump had to be dismantled and reconditioned before the

actual Commissioning.

Figure 10-a: Damaged pump – partially dismantled Figure 10-b: Damaged pump – dismantled cover

Lack of proper preservation also causes damages for the equipment and material placed inside the

warehouse. For example, a reciprocating compressor valves for 2 year operating spares were found

badly damaged within 3 months of plant startup.

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Figure 11-a: Damaged valve – view from top Figure 11-b: Damaged valve – view from bottom

7. BEARING HOUSING OIL LEAKAGE

Bearing housing oil leakage is a common punch list item during commissioning. The most frequent cause

is the overfeeding by the constant level oiler. The constant level oiler control point is not set properly

and most often this setting information (Figure 13) is not provided in the vendor documents. The

improper setting of the control point results into overfeeding of lube oil to the bearing housing which

causes the oil leakage.

Figure 12-a: Pump with constant level oiler Figure 12-b: Sight glass showing excessive oil level

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Figure 13: Constant level oiler setting information by Vendor ( typical )

8. LACK OF SAFETY IN DESIGN

Incorporating safety in design is highly important and should be considered to the utmost level. Lack of

safety in design may result into irreversible damages. During initial operations of a plant, one of the field

operators lost his eyes due to accidental spurting of 50% caustic solution into the eyes. The suction line

for the caustic transfer pump was provided with calibration pot with an open vent/overflow. Standing

beside the suction line, the operator opened isolation valve in order to fill the calibration pot keeping his

face upright looking at the pot level. In a matter of seconds, the pot went into overflow due to fast

opening of the filling valve and the overflowing caustic solution entered into the operator’s eyes causing

damage and ultimate loss to his vision.

Figure 14: Pump installation showing calibration pot with open vent/overflow

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9. DEVIATING THE COMMISSIONING PROCEDURES

All pumps and compressors look similar in appearance; however internal design and hence operational

requirements may be different. Plant operation becomes streamlined during normal operation with

relevant procedures in place, well understood and implemented after requisite trainings. However,

people trained in the normal plant operation are usually not aware of specific checks and prerequisites

which should be considered and ensured during the Commissioning stage.

There are several cases when the equipment not yet commissioned is damaged by the owner’s

operation team while attempting to operate it without involving Contractor’s Commissioning team. For

example, a between bearings pump was damaged by the owner’s operation team, the root cause was

failure of lubrication to the bearings during pump start attempt. The pump was provided with non-

pressure fed ring oil lubrication. The pump was long time standby after installation waiting for the

Commissioning activity to take place when actual hydrocarbon fluid was available. The owner’s

operation team did not perform the specific prestart checks and actions, no hand turning was done, the

pump shaft was probably not free and the oil ring in the bearing housing did not assist the lubrication

function.

Figure 15-a: Damaged pump partially dismantled Figure 15-b: Pump shaft showing bearing inner race

10. SYSTEM DESIGN FAULTS

A number of site troubles arise due to the system design faults where lack of experience is the leading

cause. In such cases, the equipment design is perfect; however a bad system design deprives of all the

credit. A good example is a pair of diaphragm type reciprocating pumps provided with suction and

discharge pulsation dampeners. The pumps suffered from high pulsation and vibration issues on the

discharge piping with heavy knocking sounds capable of being heard even from half a kilometer

distance. The root cause was the wrong installation of the discharge pulsation dampener. The discharge

pulsation dampener was installed far away from the pump discharge nozzle. This was against the

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fundamental design rule that the discharge pulsation dampener must be installed as close as possible to

the pump discharge nozzle.

Figure 16: Pump installation showing location for discharge pulsation dampeners

11. MAINTENANCE ACCESSIBILITY

Each equipment has specific maintenance accessibility requirements which should be considered during

plant design and construction. Such requirements are specified in relevant engineering drawings.

However, several cases are seen when lack of information exchange among various disciplines results

into a design where the recommendations from core discipline are not incorporated into the actual

construction. One example is for a 2 stage BB2 type pump; the GA drawing (Fig. 17) clearly indicated

required maintenance space, however actual plant construction did not consider this recommendation.

While removing pump rotor, it was revealed that the available maintenance space is far less (Fig. 18)

than what was specified on vendor drawings and this situation made the rotor removal activity a very

difficult task.

Figure 17: Vendor GA drawing showing required maintenance space for rotor removal

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Figure 18: The actual maintenance (rotor removal) space available in front of the pump

12. EQUIPMENT SELECTION / APPLICATION

There are cases when misapplication of certain type of equipment is the root cause of site troubles. A

good example is for the off spec condensate transfer pumps in a project which were badly failed during

initial operations due to wrong selection of the pump type. The service was dirty and magnetically

coupled Sealless pumps were not suitable for this dirty service, the pumps repeatedly failed during

initial plant operations and finally pump type was changed as the ultimate solution.

Figure 19-a: Damaged pump in workshop Figure 19-b: Containment shell badly worn & cracked

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CONCLUDING REMARKS:

Commissioning and Startup activities are always replete with troubles involving equipment damage and

subsequent cost and schedule impacts. However, most of these site troubles can be avoided with proper

considerations at the FEED and EPC stage.

A suction strainer is a vital piece of component in the compressor system during Commissioning, Startup

and initial operations. However, a suction strainer without differential pressure monitoring and without

alarm/trip functions is not a real protection. Cost saving ideas should not compromise equipment safety;

therefore a suction strainer with differential pressure transmitter with alarm/trip function should always

be specified for the compressor inlet.

Inspection and test plans should be rigorously defined with prime emphasis on inspection for even

minor items such as verifying correct orientation of the orifice plates, installation of correct gaskets etc.

The shop inspection and testing should be witnessed by the core discipline engineer with deep

understanding and knowledge about each and every aspect of the equipment. The shop inspection and

testing for the auxiliaries is usually taken as lightly and mostly remains unwitnessed. The auxiliaries are

very critical part of the main equipment and should be witnessed for inspection and testing in the

vendor shops.

Requirements for the special tools and accessories should be carefully defined with due consideration

on intended use and application. Where cross contamination is probable, multiple accessories should be

purchased for each type of fluid instead of buying shared accessories. For example, where a number of

different type of buffer/barrier fluids are used in a plant (e.g. kerosene, light oil, demin. water etc), a

dedicated buffer/barrier fluid unit should be purchased for each type of buffer/barrier fluid.

Preservation is a highly neglected area which is often poorly defined in the engineering stage. Special

emphasis should be paid in defining specific requirements for the preservation and rust prevention for

each type of equipment and material with due consideration on required storage period and the

prevailing environmental conditions in the storage place. The preservation procedure should also

provide details on how to inspect and maintain the preservation condition during each stage including

transportation, site storage before installation, post installation, post commissioning etc. A core

discipline engineer should be assigned to oversee the condition and maintenance of preservation and

rust prevention during site storage, pre and post installation as well as pre and post Commissioning.

Preservation and rust prevention should also be applied to the spare parts intended for long term

storage such as 2 years operational spares and capital/insurance spares.

Vendor documents should be reviewed with close attention to ensure that all the required information

and details for each phase of the project including installation, pre-commissioning, commissioning and

startup is provided to the full extent. This should include even minor details such as constant level oiler

setting, base plate levelling procedure with acceptable tolerance etc.

Engineering inter-discipline coordination should be structured in such a manner that the final output

document prepared with multidiscipline inputs is reviewed by all the contributing disciplines. For

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example, plant 3D model should be thoroughly checked by each core discipline engineer in the light of

all vendor recommendations specific to the project rather than checking in a general manner.

Inherent experience in normal plant operation should not be relied upon to run any equipment during

Commissioning, dedicated Commissioning team should be allowed for this task with strict adherence to

the defined and approved Commissioning check sheets, guidelines and procedures.

A detailed HAZOP should be done for each piece of equipment in safety critical service. Safety in design

should be implemented right from the FEED stage since people in the EPC stage start focusing on cost

reductions and most often ignore the safety aspects unless picked up and enforced in the HAZOP study.

Each discipline Engineer should focus on the system design approach rather than thinking himself

responsible for the flange-to-flange performance of the equipment. Design aspects for each component

in the system should be considered, such as defining proper location for a pulsation dampener on the

P&ID’s.

Technical specifications should be provided in every project specific to each type of equipment, material

and package. The international codes and standards should not be taken as a standalone governing

document; a dedicated project specification should be prepared on top of the applicable international

codes and standards. There are several clauses in the internal codes and standards which require the

purchaser to provide some additional/specific information or to make a decision for selecting an

optional requirement in line with project/service needs. A project Technical Specification is always

required to cover such requirements. Lack of such technical specification often results into equipment

design falling short of mandatory design features finally resulting into site troubles.

Proper equipment type should be defined from the FEED stage; all aspects for the intended service

should be considered. For example, a Sealless pump may be attractive to get rid of sealing issues,

however due consideration should be paid to the fact that Sealless pumps are not suitable for the dirty

service. Usually equipment type is defined by the Process discipline and it is taken as the ultimate

solution. However, as a Good Engineering Practice, equipment type selection should involve all the

relevant core discipline engineers.

About the author

Muhammad Imran is Mechanical Rotating Equipment Engineer presently working with LUKOIL International Services B.V based in Dubai. He has 15 years of professional experience in Oil & Gas and Petrochemical projects including EPC detail engineering, PRE-FEED, FEED and hands-on experience in the Pre-commissioning, Commissioning, Startup and initial operations. Before joining LUKOIL, he worked for WorleyParsons Qatar as Lead Mechanical Design Engineer for Rotating Equipment and Packages. He can be reached at “muhundis@gmail.com”.