Loop Checking Instruments Commissioning of Instrumentation Control System

Loop checking

What is Loop?

Loop checking will ensure wiring is landed on the proper termination points and verifies the overall integrity of the loop from field device, through I/O modules, logic solver, and ending at the HMI operator console displays.

Loop checking will ensure compliance of the following aspects of an instrument loop:

Wiring is landed on the proper terminations and overall wiring loop integrity
Confirmation of proper instrument voltage levels and grounding against design requirements and standard practices
Verification of proper range and operation of the instrument and sensor according to supplier and specifications
Verification that PES input range is in agreement with field instrumentation and specification

Proper documentation shall be performed to track all devices, and all pertinent information shall be stored on a loop-by-loop basis and become a permanent record stored at site. At a minimum, the flow sheet and/or cable schedule shall be highlighted as a record of signals checked out.

Notes: Additional parameters that shall be checked during loop check.

Sensor Check:

To verify proper function of the instrument and sensor, each instrument will need to sense the process and vary its output accordingly. In general, this implies pressure devices will be attached to a pump, level switches/transmitters will have the vessels/legs filled and temperature elements shall be immersed in a temperature bath.

Regulatory Transmitters and Information Transmitters:

A one-point check on the sensor is the minimum requirement. The recommended one point check shall be at 100% of range.

Note: For certain regulatory and information transmitters with extensive operating experience, the use of a Smart communicator to force the output is acceptable instead of pumping the sensing element. Extensive operation means the use of the same model/manufacturer in the same application at more than one Air Products location without problems.

Transmitters associated with Shutdown interlock logic:

A 3-point check (0%, 50%, 100%) of the sensor is required. If this check requires special calibration equipment that is not available, a single point check can be made provided it is driven through the trip setpoint for shutdown transmitters or higher than normal operating pressure for regulatory transmitters.

Note:This does not require the use of calibration quality equipment. The intent is not to check the calibration; the intent is to verify the sensing element functions properly. Adjustments to the calibration shall only be made if the device is outside an agreed upon tolerance.

Smart Transmitter Loop Checks

Smart transmitters loop checking shall be achieved by establishing communication with each instrument by using a compatible HART communicator. The communicator can be placed anywhere in the loop and once communication is established, perform the following checks:

Note: If communication with transmitter cannot be established or is intermittent traditional transmitter loop check shall be performed, see non smart transmitter loop check.

Verify instrument parameters against engineering specification.
Parameters to confirm include: tag name, configuration range, units (including zero suppression for level transmitters).
Verify all diagnostic information to be normal with no abnormalities.
Verify proper transmitter LCD display if applicable.
Verify proper calibration by exercising the final sensing element.
Verify proper jumper/configuration settings to ensure fail direction (important for transmitters associated with critical safety systems).

Non-Smart Transmitter Loop Checks

Non smart transmitter loop checking will assume a more time-honored role. In general the following procedure should be used with exceptions as required based on the instrument and associated loop.

Notes: Non-smart devices typically don’t have an electronic tag name associated with it; the physical tag name label shall be checked during visual inspection checks.

The wiring integrity check can be combined with the calibration check. After the wiring integrity to the PES has been verified, a calibration check of the instrument will be performed. Checks will be made according to paragraph 8.3.1. Adjustments shall be made as required to ensure accurate and linear response from the instrument. Proper voltage levels and grounding shall be performed against standard practices.

Control Valve Functional Grid

Function	Smart	Non-Smart
Verify calibration of the positioner	Smart Communicator	Traditional calibration method
Verify actuator bench set	Smart Communicator	Physical check
Verify positioner fully unloaded at 4 ma (vice versa for FO)	Smart Communicator	Physical check
Verify positioner fully loaded at 20 ma (vice versa for FO)	Smart Communicator	Physical check
Confirm calibration by 3 point check	Smart Communicator	Physical check
Confirm proper stroke length	Smart Communicator	Physical check
Confirm proper stroke speed	Smart Communicator	Physical check
Verify all diagnostic parameters are configured properly	Smart Communicator	Not applicable

Smart Control Valves Loop Checking

Control valves with Smart positioners shall be calibrated or verified with a compatible communicator. The communicator shall perform an automated step response of the control valve by forcing the valve to stroke through 0-100% travel. After completion, the data will be reviewed and a calibration will be performed if outside the specifications.

The PES shall be used to force the control output from 0% to 100% of range. If proper calibration was performed, the valve should stroke accordingly. During valve stroking, the following shall be confirmed:

Actuator bench set.
Positioner fully unloaded at 4 ma (vice versa for FO valves).
Positioner fully loaded at 20 ma (vice versa for FO valves).
Linear travel from 0% to 100%.
Stroke length.
Stroke speed.
Ensure smooth and continuous travel with no binding.
Verify packing gland for proper fit, compression, and torque.
Inspect tubing, fittings, and stem or linkage coupling.
Verify all diagnostic information to be normal with no abnormalities.

Valves in inaccessible locations shall be checked as thoroughly as possible. Proper installation and checkout shall have been performed before being made inaccessible (that is, coldbox valves and instruments).

If a solenoid valve(s) is part of the control valve configuration, the solenoid shall be forced through the PES or via a hardwired electrical jumper to verify all loop wiring and ensure proper wire terminations in the field. In addition, this will verify proper solenoid tubing and electrical configuration.

Non-Smart Control Valves

The first step to loop testing a control valve is to perform a calibration on the control valve positioner. The calibration will verify proper loading and unloading of the positioner and actuator. The PES shall be used to force the control valve output from 0%–100% of range. The following parameters shall be confirmed:

Actuator bench set.
I/P test.
Positioner fully unloaded at 4 ma (vice versa for FO valves).
Positioner fully loaded at 20 ma (vice versa for FO valves).
Linear travel from 0% to 100%.
Stroke length.
Stroke speed.
Ensure smooth and continuous travel with no binding.
Verify packing gland for proper fit, compression and torque.
Inspect tubing, fittings, and stem or linkage coupling.

Valve Ancillary Equipment

The following shall be tested and verified to work according to design requirements:

Solenoids
Boosters
Regulators
Quick exhaust
Filters
Hand wheels
Position transmitters
Position switches

Electrical Interfaces

Functional checkout of the electrical system is outside the scope of this standard. This standard addresses the interfaces between the PES and the electrical system.

The engineer performing electrical interface loop checking must work with the responsible electrical personnel to ensure proper interface operations between the PES and electrical equipment include:

Hardwired panels
MCC
Switchgear
Variable frequency drives
Heaters
Soft-starts

The interfaces between the PES and the electrical systems must be functionally checked to the greatest extent possible. Functionality tests shall be initiated at the electrical system while observing proper operation of electrical system outputs and the PES inputs and responses. It is not acceptable to lift interfaces wires to test functionality. The goal is to test the system as a whole to the greatest extent possible.

Perform testing to ensure design intent of the failure modes of the interface signals to the PES. Normally these systems and interfaces are designed fail safe. Testing for fail-safe functionality may include loss of power, loss of communications, loss of interface wiring, loss of sensor input, etc.

Analyzer Interfaces

Functional checkout of the analyzer system is outside the scope of this standard. This standard addresses the interface between the PES and the analyzer system.

The engineer performing loop checking must work with the responsible analyzer personnel to ensure proper interface of signals between the PES system and any analyzer or analyzer system.

The interfaces between the PES and the analyzer systems must be functionally checked to the greatest extent possible. Functionality tests shall be initiated at the analyzer while observing proper operation of the analyzer outputs and the PES inputs and responses. It is not acceptable to lift interfaces wires. The goal is to test the system as a whole to the greatest extent possible.

Perform testing to ensure design intent of the analyzer system failure modes and the failure modes of the interface signals to the PES. Normally these systems and interfaces are designed fail safe. Testing for fail-safe functionality may include loss of power, loss of instrument air, loss of communications, loss of interface wiring, malfunction of sampling system, range switches, automatic calibration, etc.

Functional Checkout of Control/Shutdown/Auxiliary Systems

The control systems engineer will verify all the control functionality on the flow sheet and shutdown table has been programmed as planned and is functioning as a whole and is not operating in a degraded state.

The minimum requirements of a functional checkout include confirmation of:

Process pre-alarm and alarm setpoints displayed on alarm summary screens of the HMI
Transmitter bad quality alarms
Maintenance bypass switch and alarm for each shutdown transmitter
Proper operation and display of all graphics with associated input and outputs
Test and confirm all hardwired “shared signals” are configured and displayed properly on all graphics. (Shared signals are hardwired signals between logic solvers. The typical application is a 2 out of 3 analog transmitter 4–20 ma power from the safety system shared as a voltage signal to the regulatory logic solver.)

– Verification of all logic not associated with simple I/O loops covered during loop check. An example would be a 3 transmitter 2 out of 3 voting circuit. The three transmitters would be inspected and loop checked but would not be completely function tested during loop check. A thorough verification would include a functional checkout of any maintenance bypass switches, key lock of bypass handswitch and setpoint changes. Proper diagnostic alarms (that is, bad quality, deviation, bypass switch functionality, etc.).Compressor Surge and loading logic.

3 element control, etc.
Validation of sequence programs for various plant equipment (PSA, TSA, reversing heat exchangers, membrane systems).
Verification of automatic start up sequences.
Verification of external billing system computers.
Verification of foreign device interfaces to other control systems.
Verification of management of change controls.

Control/Safety System Visual Inspection

The visual inspection shall include but not be limited to:

All hardware properly installed according to manufacturer’s requirements.
Routing of cables and wires for proper AC/DC segregation.
Ensure all cables and wires are properly supported.
Ensure all cable connectors are secure and relieved of stress.
Make sure wire connections are mechanically strong.
Verify HMI system network topology is installed according to design drawings.
Verify security setting for field devices and PES devices.
Safety systems segregated and secured properly identified, reference 2S113.

SITE ACCEPTANCE TEST (SAT)

If a PES is being used as part of the facility control system, it shall have passed a “site acceptance test” before validation. A site acceptance test verifies:

The PES is not operating in a degraded state, any degradation shall alert the operator.
The PES is designed with the appropriate segregation of integrity levels.
The PES is configured and installed according to supplier-specific manuals and Air Products standards.

The site acceptance shall include but not be limited to:

Check of all installed hardware according to system drawings.
Power and grounding checks.
Proper installation of computers/workstations.
Check of all communications networks including visual inspection of wiring for proper supports.
Check of all diagnostic systems statistics.

Redundancy and I/O segregation

Redundancy testing should include I/O modules, logic solvers, communication, and HMI systems. All redundancy aspects of the PES shall be thoroughly tested by causing a failure in one redundant component to determine how well its partner can continue to provide the appropriate functionality. Typically failures are caused by removing power from one of the redundant partners. Each redundant partner must be tested as the failed component to complete the testing of the redundancy operation.

Additional redundancy tests must be completed in order to ensure:

Any specific HAZOP recommendations.
Any specific reliability essential features.
Any specific importance level architecture requirements.

Typical tests include:

Redundant pumps/motors/compressors.
Redundant Valves.
I/O redundancy.
I/O segregation effectiveness as determined by HAZOP.
Test to prove other reliability essential features as needed by the project.
Proper alarming on loss of redundancy/reliability essential features.

CHECKOUT OF AUXILIARY SYSTEMS

All auxiliary systems associated with the control system shall be checked with the appropriate rigor and thoroughness as the core control system. The thoroughness of checkout of auxiliary systems shall be determined by the consequence of failure. Examples of auxiliary systems are:

Controls or control systems external to the main PES.
Foreign Device Interfaces between the control system and an external party.
Stand-alone historian data collecting devices.
Billing systems either internal to the logic solver or external systems.
Callout systems for unmanned plants.
Remote access.
Remote control.

The interfaces between the PES and the auxiliary systems must be functionality checked to the greatest extent possible. Functionality tests shall be initiated at the auxiliary system while observing proper operation of auxiliary system and the PES inputs and responses. It is not acceptable to lift interfaces wires. The goal is to test the system as a whole to the greatest extent possible.

Perform testing to ensure design intent of the auxiliary system failure modes and the failure modes of the interface signals to the PES. Normally these auxiliary systems and interfaces are designed fail safe. Testing for fail safe functionality may include loss of power, loss of instrument air, loss of communications, loss of interface wiring, etc.

NORMAL POWER CHECKOUT

All power distribution equipment must be checked to ensure correct system power sourcing. System grounding must be checked to ensure proper reference levels, isolation from power sources, and proper shielding from electrical noise.

Proper power and grounding is a multidiscipline design effort between the PES supplier, instrument supplier, construction, grounding

electrode system, and individual loop design.

Power and grounding should be checked multiple times during the commissioning process.

Before initial power up of system.
During individual loop installation (that is, buzzer system to ensure lack of continuity between shield and plant power ground. Buzzer system will alert contractor as soon as ground is compromised).
As part of the SAT after the entire system is fully integrated.

Power and grounding must be checked during the SAT according to recommended supplier procedures and any appropriate Air Products electrical design procedures.

Power and grounding checks shall not be waived. They shall be assisted by the electrical technician. The preferred method is to purchase assistance from the system supplier especially if the system is new to the user or first time with local codes/practices. If the proper Air Products expertise exists and system warrantee is of no concern, the Air Products instrument technician may perform the checkout without the system supplier’s assistance.

INSTRUMENT AIR Checkout

The instrument air system as a utility system shall have been commissioned before loop checking. Functional checkout of the instrument air system and/or backup instrument air system is outside the scope of this standard.

Checkout of instrument air during commissioning shall consist of checking from the root valve to the instrument.

Branch air lines to individual instruments shall be disconnected immediately upstream of and adjacent to the instrument air filter regulator, and blown through with clean air until clear of all foreign materials. The tubing downstream of the filter regulator shall be blown through before connection to the instrument.

Check setup of regulator (set for proper pressure) and any other ancillary equipment (boosters, volume tank, quick exhaust).

Backup/Redundant Power Checkout

UPS systems for the control system shall be fully tested to provide:

Adequate bumpless power to all appropriate devices.
Prevent loss of critical data parameter.
Retain PES logic.
Provide adequate time for the operating personnel to place the facility in a safe mode in case of extended power interruptions.

UPS circuits shall be labeled properly as to not place any undue load from noncritical devices being plugged into UPS outlets.

Backup generator systems shall be tested to work in conjunction with the UPS system to provide adequate power coverage.

All backup power systems shall provide appropriate alarms and diagnostics. The interfaces between the PES and the backup power systems must be functionality checked to the greatest extent possible. Functionality tests shall be initiated at the backup power system while observing proper operation of the PES system. It is not acceptable to lift interfaces wires. The goal is to test the system as a whole to the greatest extent possible.