One Day Seminar on

Safety Examination, Operation & Maintenance of Gates

For Dams, Canals, Drains, and Other structures.

July 3rd. 2015

Subject: Safety Inspection of Gates and its documentation.

By M.V.S.Murthy C.E. (Retired) WRD GOG

Need for Safety Inspection of Gates:

Safety Inspection of Gates is a part of Dam Safety Activity

While routine maintenance of Gate components is the responsibility of the Field Staff,

Safety Inspection of Gates on a project and its documentation by an Independent group of

senior personnel and specialists, is useful in assessing overall performance capability and

reliability of these Equipment, and identify areas of deficiency. This activity can be called

‘Safety Audit of gates’. It also assesses the adequacy of Gate maintenance procedures and

records, and Field Officers‘ preparedness to handle problems which may arise, before they

develop into distress.

Further, as Dam Spillway and canal outlets are built to meet the maximum anticipated

demand, there could be some redundancy during off-season or normal working. If some

equipment becomes inoperative, its absence may remain unnoticed or overlooked by the field

staff. Such lapses are not uncommon, and may prove disastrous during emergency. Safety

Inspection avoids such a situation.

A review of Safety Inspection of Gates on different projects in a state may bring out

existence of outdated and defective gates and construction practices and initiate review and

modification. This would improve the overall reliability and safety of Dams.

Safety Inspection and its Documentation:

The safety inspection activity can be broken down into three steps:

1. Preparation for the task.

2. Inspection technique

3. Documentation of report

Preparation for the task

1. Pre- planning of Inspection.

This may be necessary as Reservoir water level should be acceptable for testing of equipment and

inspection of components. Minimum wastage of storage and interruption to water demand, should be

attempted. Necessary precautions are to be taken for this un-timely operating of gates, such as, prior

notification, and warnings to downstream areas of likely increase in flow .etc

2. Reviewing Documents

Following records may be collected and studied.

(a) Final Construction and Installation Drawings for Gates and related equipment including

Supplier’s Operation Manual

(b) Details of any major alterations, modification, carried out and when why and by

whom.

(c) Review of Pre-monsoon and Post-monsoon inspection and servicing Records for their

adequacy.

(d) Standard Operating Procedures for gates, displayed in control room.

(e) Security arrangements to prevent unauthorized person, operating gates.

(f) Check sources of Power supply for Gates operation, its dependability during heavy

floods, Stand-by power supply, its exclusiveness, adequacy for number of gates to be

operated simultaneously at a time to handle maximum flood, effective communication

between standby power source and gates control area.

(g) Contingency plan to restore power if one of the Power cables to gates, fails.

(h) Fire Hazard prevention: As the environment is windy humid and wet, and power

cables are abundant, possibility of short-circuit and fire hazard are high. A valid Inspection

and Testing certificate for Electrical Installation for Gates operation, from a competent

authority is desirable. Also, availability of Fire-fighting Equipment and their working may

be checked and noted.

3. Preparation on the field.

Tools Tackle and manpower to be mobilized (Many of these are not likely to be available

at site)

A list is indicated: Steel Tape. Steel Rule with graduation. Machinist’s Spirit Level. Heavy

Plumb. Steel Right Angle. Inside-Outside Calipers. Micrometers, Filler Gauges, Heavy Duty

Tool Kit with Wrenches Spanners, Stud removers Impact wrenches, Torque Wrenches

Chisels Hammers hand drills etc.

Mirror, Magnifying Glass. Depth-gauge Steel shim plates of assorted thickness.

Wire brush Blow torch, Camera with flash. Torchlight, Electrical Testing meters, tester for

testing insulation and earthing. Ammeters Volt meters Tong testers for measuring current

in a cable. Degreasing fluid, cotton waste, Dye for Dye-penetration test etc

The list is indicative only.

Personal Safety arrangement: As Inspection involves movement on wet and slippery

surface, approach by boat, climbing on temporary ladders ,working in heights and above

flowing water, the officer who is to inspect should be healthy agile and alert.

Safety precautions should be taken, hard hats, Gum boots etc. used. Boats with lifejackets,

rescue and First aid facilities to be at hand where necessary. As worksites are likely to be

windy, loose clothing should be avoided by persons involved.

Inspection technique.

Physical inspection of Equipment, and Components, and recording findings, is the main purpose of this

exercise. This should give an overall assessment of their reliability for safety of Dam. The Inspector has

to decide what gates are to be tested, and which critical components to be checked, based on his

experience, and literature available.

The booklet “Guidelines for Operation and Maintenance of Spillway Gates on Dams” by M.V.S.Murthy, is

one such literature available for free download from link given below:

http://pothi.com/pothi/book/ebook-m-v-s-murthy-guidelines-operation-and-maintenance-spillway-

gates-dams

1. Preparation for inspection at site:

Study and make notes of Drawings and sketches of parts to be inspected, Decide gate/s to be

selected for detailed inspection and trial, sketches of components to be drawn, to identify

them in the report. Sequence of components to be checked to be decided. Problem areas,

and limitation in checking to be noted down. Restoring the equipment to normal operation

after inspection to be planned.

2. Inspection of Gates:

Though there are different types and sizes, such as spillway gates, radial type and vertical lift

type, dam outlet gates fixed wheel type and slide gates, Canal gates etc., some inspection

aspects are common while others are specific to the type. We may discuss the common

aspects first.

Common Aspects:

Corrosion, pitting, Cavitation and Electro-chemical reaction on metals, crack in weld, are some

of the defects common to all types of gates. Causes and remedies are discussed in the booklet

“Guidelines on O&M of Spillway Gates on Dams” by M.V.S.Murthy)

(a) During visual inspection of gates, we may look for signs of Rusting, Corrosion and pitting

of components and record their location possible cause and suggest remedy. Cavitation

occurs where flow is not streamlined and turbulent flow occurs. The area will have to be

dewatered to check the extent and seriousness of problem of cavitation.

(b) Where Stainless steel plates are used as seal seat and are fixed to MS base plate in

Embedment by intermittent welding, cracking of weld and peeling off of seal seat, may

cause leakage, damage to seal, and rough movement of gate. Above points need be

verified and recorded. These defects are difficult to rectify and may need detailed

planning.

(c) Some of the old design and fabrication practices adopted, particularly in the case of

Vertical Lift Type Gates for Spillways and Dam outlets, are prone to cause major problems

over years of use. A few are indicated below which may be checked during Safety

Inspection.

(d) Fixing of Seal travel seat with Base plate in the embedment.:- Brass plates were used

as Seal Seats and fixed to embedded steel Base plate by brass countersunk screws

.Frequent travel of seal during gate operation, unevenness of surface, leakage at seals,

pressure buildup behind the seal seat, and vibration, could cause loosening of screws,

falling off of seal plate, seal damage, vibration and even gate failure, particularly in case

of dam outlet gates.

(e) Seal Quality: Quality check of seals used or stored as spare, may be verified as molded

type seals of correct specification are much costly compared to look-alike seals available

in the market.

(f) Fixing of MS Track Plate (for wheel travel) to base plate with countersunk bolts. Over a

period of use Track Plate wear, waviness, loosening of bolts, heavy vibration, etc. may

pose a source of potential danger.

(g) In the case of fabricated steel outlet gates and canal gates, the shape of Gate lip could be

source of turbulence and vibration of gate. This may be observed during trial operation

and commented

(h) During Safety Inspection of gates on a project, it may not be feasible to operate and test

all gates. There are a number of dams where there are 30 to 35 spillway gates. In such

cases, while superficial visual inspection of all such gates may be carried out and recorded,

detailed, component-wise trial and inspection and operating the gate for full travel, may

have to be judiciously restricted. For example, one gate in the middle of the spillway

which is frequently used may be chosen for detailed inspection, to observe smooth

operation and wear and tear of components, another on additional spillway or a gate

towards the end of spillway, may be chosen to test its reliability during emergency. Same

principal could be adopted in the case of outlet gates.

The Author suggests that, where the number of gates is large, the field officers may plan

such that operating all gates to full travel get covered during a five year cycle, even by

lowering stop log or emergency gates where needed.

In the case of Stop logs during safety inspection, it may be prudent to try-out lowering one

or two stop log elements into each of the vents of spillway to ensure that lowering of stop

logs in any vent during emergency would not be a problem.

Inspection of Radial Gates:

In Up-stream suspension type gates, gate lifting parts and wire-ropes and pulleys are

submerged for most part of the year and accessible for inspection, only if water level in

the dam falls below sill. In case this condition is not achievable, Stop logs are to be

lowered and area between stop log and the gates dewatered. Condition of Clevis, Turn-

buckles, pulleys, wire ropes equalizer bar etc. should be examined and recorded. Wear

on wear-plate on skin plate to be checked. Full opening of gate may be checked for

smooth travel. Rough and jerky movement of gate, leakage in closed position and

excessive leakage during seal travel, Vibration, Drag or excessive rubbing of seal

,abnormal noise, gate sway, increase in hoist load, Trunnion binding, and such

abnormalities are to be observed and the gate position at which these occur are to be

noted. These indicate the defects in gate groove, gate and trunnion alignment, loose

fitting of parts etc.

The condition of sill, any cavitation and erosion of sill groove could be examined in the

raised position of gate

In case of gates with D/S suspension, similar inspection of gate suspension parts could be

carried out if access from downstream is available. Testing under Full gate opening is

desirable as it brings out potential weaknesses and help taking timely corrective action.

Access to trunnion, walk-way and railing Trunion pin lock, bushing wear, lubrication of

trunnion Thrust-pads Trunion anchorage , Hub weld, Horizontal girders, Splice joints,

Field joints in skin plates are some important points to be checked and condition

recorded.

Winch type or hydraulic hoists provided for operating gates, may be inspected and

observations recorded. Gate position Indicators Limit Switches, and their settings may

be checked, Functioning of Limit Switches may be checked

While servicing of Gate components are generally attended to by the field staff, Stoplogs

and Hoist gantry crane and Rail track are likely to be neglected as they are needed during

Emergency only. So, during Safety inspection, special attention may be given to these

Emergency Equipment

Inspection of Vertical lift Gates

Vertical lift type gates are used as spillway gates, in a few old dams and in barrages. Stop

logs on spillways are also of this type. Hoist winches or Gantry Cranes are used for lifting

and handling these gates.

Dam outlet Gates and Canal gates are generally of Vertical lift type. These are of two

types: (a) upstream skin plate type and Downstream skin plate type. The service gate used

for frequent operation for discharge-regulation is a D/S skin plate type. The Emergency

Gate is Upstream skin plate Type.

As service gates are operated frequently, they are generally attended to, by the Field staff.

But Emergency gates which are rarely used tend to be neglected. During Safety

Inspection, condition of Emergency Gates, Storage facility, condition of gate groove,

Lifting and hoist mechanism, need special attention.

Functioning of the gate over full travel may be checked to see if it is smooth and without

binding, vibration or excessive leakage. Cavitation due to inadequate air vent or clogged

air passage needs to be checked.

Use of Hydraulic Hoists is becoming popular due to its being compact with fewer moving

parts, ease of operation, both opening and closing being positive and accurate,. The

system demands clean dust-free environment, moisture-free oil of specified grade,

avoiding leakage in hoses piping, and seals. Meticulous calibrating and servicing of

Hydraulic components such as Hydraulic pumps, pressure regulating valves, Filters,

cylinders etc. is called for. Performance of Hydraulic Hoists may be checked for smooth

movement of piston rod, absence of valve flutter, leakage at seals and connectors,

unsteady pressure gauge, gate creep, etc.

Before closing the Inspection job and leaving the site,, it is necessary to take a review of

data collected and make sure that no data is incomplete and no item is overlooked.

Documentation

Large amount of data collected during Inspection, in the form of sketches, notes, pictures, and

measurements, will have to be analyzed categorized, and inference drawn, and presented. The time-

limit for submission of report would be in the letter of authority. This could generally be within 3

months of inspection.

The Report may be in 3 parts:

1. Summary of findings and recommendations (condensed in 3-4 pages.)

2. Detailed Report

3. Annexures containing copies of records, Tables of measurements, Sketches, Photographs

etc.to support the Report.

It is desirable that the report comments on the system and not on an individual.

Detailed Report:

Format for Detailed Report is suggested below:

Introduction:

1. Give reference of Authority letter initiating Safety Inspection. Copy of this letter will be in the

Annexure

2. Mention whether the Inspection is the first of this type for the project. If it is a periodic

Inspection, when previous one was done. Keep copy of Report of previous Inspection in

Annexure.

3. Scope of Inspection: whether overall assessment related to Dam Safety or restricted to a specific

area or group of equipment like Gates of outdated design practice.

4. Personnel in the team, their qualification, Expertise, whether within the organization or hired

for examining specific aspect.

5. Date of commencement of Inspection and reasons for delay if any.

Main Report:

Review the records made available and give comment.

1. Review records of Field Maintenance, Pre-monsoon and post-monsoon inspection by field

staff. Give your view about, format used, whether equipment-vise, component-vise

inspection is maintained, adequacy of details given, defects noticed, quantified, and their

location noted, how and when rectified, whether scrutinized by higher officer and

commented. Suggestion for improving quality of inspecting and reporting may be given. This

may again be brought out in ‘Recommendations’

2. Comment on new equipment and techniques introduced on the project, (e,g. Hydraulic

Hoists, Pre-stressed anchorage remote control operation) and Field staff’s adaptability. Need

for training

3. Comment on security and safety aspects

4. State details of Visual Inspection and findings.

5. Testing of gates in operating condition, and observation

6. Observation and comments on gates of old design and fabrication practices,

7. Suggestion to field officers regarding program for covering all gates for testing for full travel.

8. Overall assessment of Safety aspect of Gates on the dam/project, based on findings in this

exercise

Conclusion:

Based on observations made in the Report above, .specific conclusions are drawn about safety

aspect of gates on the project and their contribution to overall safety of dam. Mention areas of

lacuna noticed and improvements suggested, any lessons learnt which could be adopted on other

projects,

Each conclusion should be specific and linked to the main Report. Adequacy of data and depth of

study should be verified, before drawing conclusions.

Conclusions could be supported by other case studies, Reports and literature available.

Unwarranted alarm or unsupported inferences should be avoided

Vague and unconfirmed conclusions should be avoided.

Recommendations:

Recommendations should be for specific line of action, and based on observations in the Report

and Conclusions drawn

Urgency of implementation of any specific recommendation may be indicated, giving reason;,

financial viability, and such implications .

Do not conclude the Report, without thanking the project authorities, for the courtesy and

facilities extended.

The Report should be signed by all the members of the Team, sealed and submitted to the

’Authority’.

Annexures- Attachments:

Copies of important and relevant communications. Pictures, Sketches, referred in the report

should be numbered, and tagged. Supporting technical literature with source should be

separately attached.

Executive Summary:

A brief Summary of Report of 3-4 pages may be drawn up and signed and sealed and submitted to

the concerned ‘Authority’ and discussed in person by the members of the team.

The Summary report should be brief, precise, and unambiguous. Conclusions should be with Links

to main Report. Recommendations should be numbered and their order of listing to reflect their

importance or urgency.

A well written inspection report is an asset which may be a guide to subsequent inspections.

References

1 Guidelines for Operation and Maintenance of Spillway Gates on Dams.

(Revised-2012) By M.V.S.Murthy B.E.(Mech) C.E. (Retd) GOG

(Free Download link http://pothi.com/pothi/book/ebook-m-v-s-murthy-guidelines-operation-

and-maintenance-spillway-gates-dams}

2 TADS Module- Inspection and testing of Gates Valves, and other Mechanical Systems

3 Indian Standards Spec. IS 10096 part 3 (2002)