Boiler Survey, Inspection and Tests

Boiler Regulations by SOLAS

When installing and operating a marine boiler, it is important all the regulations laid under SOLAS Chapter II are followed. Some of the important regulations for safe operation of marine boilers are listed below:

  • Every steam boiler and every unfired steam generator shall be provided with not less than two safety valves of adequate capacity. However, having regard to the output or any other features of any boiler or unfired steam generator, the administration may permit only one safety valve to be fitted if it is satisfied that adequate protection against overpressure is thereby provided
  • Each oil-fired boiler which is intended to operate without manual supervision shall have safety arrangements which shut off the fuel supply and give an alarm in the case of low water level, air supply failure or flame failure
  • Water tube boilers serving turbine propulsion machinery shall be fitted with a high-water-level alarm
  • Every steam generating system which provides services essential for the safety of the ship, or which could be rendered dangerous by the failure of its feed water supply, shall be provided with not less than two separate feed water systems from and including the feed pumps, noting that a single penetration of the steam drum is acceptable. Unless overpressure is prevented by the pump characteristics means shall be provided which will prevent overpressure in any part of the systems
  • Boilers shall be provided with means to supervise and control the quality of the feed water. Suitable arrangements shall be provided to preclude, as far as practicable, the entry of oil or other contaminants, which may adversely affect the boiler
  • Every boiler essential for the safety of the ship and designed to contain water at a specified level shall be provided with at least two means for indicating its water level, at least one of which shall be a direct reading gauge glass
  • For pilot burners of auxiliary boilers if provided, an additional Marine Diesel Oil (MDO) tank for eight hours may be necessary
  • Ventilating fans for engine and boiler rooms should be installed
  • Similar arrangements should be made at boiler furnace fronts to intercept any oil, which may escape from the burners. In the case of top fired boilers, special care should be taken in arranging the save-alls and coamings to prevent the spread of any oil spillage
  • Master oil valves at boiler furnace fronts should be of the quick closing type, and fitted in conspicuous and readily accessible positions. It is recommended that they are painted bright red to aid identification in an emergency. Provision should be made to:
    • I. prevent the supply of oil to any burner unless it has been correctly coupled to the oil supply line; and
    • II. prevent the removal of the burner before the oil supply is shut off

Regulations for roof-fired boilers

As roof-fired boilers present particular fire hazards, the surveyor conducting the first and subsequent surveys should be satisfied that:

  • there are adequate coamings and, where necessary, screens around the oil burners to prevent the spread of oil
  • the space surrounded by the coamings is adequately drained
  • the oil burner platform and surrounds are painted in light color
  • the oil burner platform is adequately lit
  • there are sufficient fire appliances ready at hand to tackle a fire on the burner platform
  • there is a means of quickly shutting off the supply of fuel to the oil burners from a position not likely to be cut off by a fire near the burners

Boiler Survey Schedule

Auxiliary water tube boiler which is 8 years old to be surveyed every year and the survey interval can be extended to 2 ½ years if the surveyor is satisfactory of correct feed water treatment with proper boiler water analysis.

  • Two boiler surveys are required during each 5 year period of the classification certificate
  • The interval between any two successive boiler surveys is not to exceed 36 months
  • The survey shall be carried out on or before the due date. Time window is not applicable
  • One survey shall be carried out in conjunction with the renewal survey, i.e. during the 15 months prior to expiry date of the classification certificate

At main class annual survey, the following requirements to be followed:

  • External examination of the boiler
  • Verification of boiler water management
  • Verification of integrity of oil burning equipment on boilers
  • Testing of safety and protective devices, including operational test of safety valves by use of relieving gear
  • Function test of exhaust gas economizer safety valves may be carried out by the chief engineer at sea and recorded in the engine room logbook prior to the survey

For the complete boiler survey, i.e. the survey including the internal examination, the following requirements to be followed:

  • Verification of boiler water management
  • Verification of procedures to protect boilers taken temporarily out of use (normally part of the instruction manual)
  • For Shell type exhaust heated economizers, all welded joints to be examined for cracks

Boiler Safety Valve

Regulation:

Boiler safety valve is set to lift at any pressure, but not more than 3% above working pressure. Also the safety Valve re-sits at 5% below working pressure.

There are 2 safety valves. Both the safety valves are to be set at a pressure not exceeding 3% of the normal working pressure (stamped on name plate). Let us say the working pressure of the boiler is 7 bar. 3% of 8 bar is (7+0.21) = 7.21 bar.

This means, both the safety valves have to be set at a pressure not exceeding 7.21 bar.

Apart from that, let us say one of the valves have been set at a pressure 7.13 bar (assuming two digit decimal even though the practice is not referring to 2 digits), then the other valve must be set at a pressure range of 10% within this i.e the other valve setting must be 7.16 bar.

The second safety valve must be set within 10 % of the setting of the first safety valve.

Safety Valve Setting Procedure:

The boiler comprises of 2 safety valves set at different lifting pressures. The valve, which is to be set at lower pressure, is locked in position by the “gagging tool”. The valve not to be set is gagged when the boiler pressure reaches 80%. Raise the steam pressure and simultaneously tighten the gagging tool. Care must be taken not to over-tighten the gagging tool as it may lead to bending of valve spindle or other problem.

If due to insufficient tightening leakage of steam occurs, decrease the pressure until the leakage stops and then retighten the gag.

Operated hand-easing gear at about 90% of the set pressure of the valve. If the valve lifts before or after the set pressure, decrease the boiler steam pressure to 90% of the safety valve setting and then adjust the setting screw accordingly. If setting of safety valve pressure is required to be increased, tighten the setting screw and vice versa. Ensure to tighten the locking screw each time the setting procedure of safety valve pressure is performed.

locking

Boiler Tests

Hydraulic Pressure Test:

The Regulation requires a hydrostatic test to 1 ½ times the maximum allowable working pressure. In preparing for a hydrostatic test, the boiler will be filled with water of not less than 70°F and not more than 160°F. The safety valves shall be secured by means of gags or clamps.

In addition to the hydrostatic testing, auxiliary boilers must be subjected to operating tests, which must be completed after final installation.

Hydraulic testing is to be performed in the presence of a surveyor, unless otherwise agreed. The test pressure should be applied and maintained for at least 30 minutes to permit visual examination of all surfaces and joints. The vessel should exhibit no sign of general plastic yielding or leakage.

The pressure test should be such that it does not result in general membrane stress in any part of the vessel during the test exceeding 90% of the lower yield stress at room temperature. Before boiler insulation, accessible parts shall be emptied, opened up, and all interior faces shall be examined for defects from hydrostatic testing.

After installation on board, operations and checks of all safety, controls, alarms, and relief valves are to be performed in the presence of a marine inspector. Boiler operations are observed at Sea Trials for safety deficiencies.

The following piping systems shall be tested to 1.5 times the maximum allowable working pressure of the system:

  • Class I steam, feed, and blow-off piping, including attachment to boilers with no practical means of blanking off
  • All boiler mountings to be tested to twice the approved design pressure, except for feed check valves and other main feed system components which are to be tested to 2.5 the approved boiler design, or twice the normal pressure developed in the feed line in service, whichever is greater

Accumulation of Pressure Test:

The accumulation of pressure test is done to test the capacity of the safety valve and attached easing piping system.

The boiler pressure is not to rise more then 10% above the maximum allowable working pressure when the steam stop valve is closed under the full firing condition for a duration of 15 min for fire tube boiler and 7 minutes for water tube boiler. During this test, no more feed water is to be supplied than that necessary to maintain a safe working water level in the boiler drum.

References

A Guide to Boiler Operation and Maintenance. Anish Wankhede [2015]

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Метки: Marine boiler

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