COMMISSIONING OF BOILER ( PART-IV) ,VALVES

It is expected that after completion of Full Hydro ( except re heater) completion of

stage1B next step is conducting Boiler Hydro test within 21 days . But there may be

some problem to achieve that then one should proceed for wet preservation of the Boiler.

The Boiler is pressurized to 5-10 Kg/cm² with hydrazine and Ammonia treated DM

water containing not less than 200 ppm of Hydrazine and sufficient quantity of

Ammonia to have pH value of 9.5-10.0 and retained at this value for preservation.

Boiler water samples can be collected periodically say once a week or fortnight,

depending on the pressure holding worthiness of the system, and tested for

pH and hydrazine content. Sampling point will be low point drain.

In case the sample water does not meet the criteria for preservation of Boiler

the same is to be boosted up using Boiler fill pump and dozing arrangement and

at the same time venting sufficiently through the air vents in the top level of the boiler.

Alternatively, preservation can also be done under nitrogen capping at

0.35 Kg/cm² at vents of separator and Super-heaters.

Next system commissioning will be Pre- boiler flushing with temporary pumps

and piping . Same facility will be used for acid cleaning/ alkali boil out operation.

However we will first discuss about the individual items like valves ( manual,

electrical ,Hydraulic ) , Pipe installation ( oil ,air ,steam ) hanger supports ,misc.

accessories of the system.

A commissioning engineer should look for the technical deficiency in the

erection and get it rectified before commissioning the system. If it is not possible

then same is to be recorded in the register so that early action can be taken to

resolve the issue.

Manual Valve ( only big valves are considered)

Following common aspect to be looked after by commissioning engineer

before he starts any activity. Deviation from that may lead to unsafe condition

for commissioning.

Access to the plant item is adequate

Illumination in the plant area is adequate.

Any other requisite safety provision is adequate for the    immediate commissioning activity.

Plant item is in a clear condition.

All necessary locks and keys for padlocks, interlocks etc. are available.

Hot  surfaces lagged or screened or screened sufficiently to provide protection for personnel.

Ensure that manual valves installed correctly as per latest PID.

Heavy valves are supported properly and independent of the pipe line. Valve should

not carry the load of the pipe line.

Direction of flow marked and correct.

Also see that valve position is such that it is easy for repair, replacement and maintenance.

Ensure that if limit switches are available then they are set by physically moving the valve

open or close.

No fouling with near by structure or equipment noticed. After commissioning, valve

should be kept in closed condition and protocol to be made and kept as future reference.

Motor operated valve.

Ensure that motorised valves installed correctly as per latest PID. Check the Tag No.

and name plate.

Heavy valves are supported properly and independent of the pipe line. Valve should

not carry the load of the pipe line.

Direction of flow marked and correct.

Also see that valve position is such that it is easy for repair, replacement and maintenance.

Adequate space is available for setting of limit switches of the valve.

Ensure that limit switches are set and position transmitters are also set. Indication

on the valve is available. For small bore valve the valves can be set manually but same

can also be set electrically by keeping the valve in middle position. Before checking

with electrical please ensure that direction of rotation of motor is checked.

It is a thumb rule that set the valve open position with position limit switch and

set close position with torque switch.

Each motorised valve has minimum two position limit switches and two torque

limit switches. Torque limit switches are factory set should not to be disturbed.

Before commissioning of motorised valve please talk to senior about the valve

position. I remember in my early days I was commissioning a motorised valve and

about to break the wet preservation of the Boiler.

Commissioning protocol to be made that is current take by motor, limit switch

setting , manual operation, clutch – gear operation, indication, local /remote operation etc.

You  need good communication set up as  manpower required to assist you in MCC ,

control desk , logic panel /DCS simultaneously all the place.

After commissioning keep the valve in closed condition.

 

continued to part-v


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