ASSIGNMENT SHEET

 

BOILER HYDROS

Assignment Sheet Number 62B-233

 

 

INTRODUCTION

 

            Hydrostatic boiler testing is the same for all naval propulsion boilers.  Each hydrostatic test serves a definite purpose to ensure the boiler is safe to operate.  Testing must be accomplished everytime the pressure vessel has been opened for any reason.

 

LESSON TOPIC LEARNING OBJECTIVES

 

Terminal Objective:

 

8.0       DESCRIBE the principles, construction, function, components, control and monitoring systems, and operation of a conventional steam propulsion plant and associated auxiliary support systems.  (JTI:A)

 

Enabling Objectives:

 

8.178   DESCRIBE and explain the purpose, preparation and requirements for boiler hydrostatic testing.

 

8.179   DESCRIBE and explain the requirements for the boiler hydrostatic pump,  set up and hoses.

 

8.180   DESCRIBE and explain the requirements for blank flanges.

 

8.181   UNASSIGNED; reserved for future use.

 

8.182   UNASSIGNED; reserved for future use.

 

8.183   UNASSIGNED; reserved for future use.

 

STUDY ASSIGNMENT

 

1.  Read Information Sheet 62B-233.

 

2.  Outline Information Sheet 62B-233 using the enabling objectives for lesson 62B-233 as a guide.

 

3.  Answer study questions.and scenarios.

STUDY QUESTIONS

 

1.         What is the purpose of any boiler hydrostatic test?

 

2.         What are the requirements for the hydrostatic test pump?

 

3.         State the order in which multiple boiler hydrostatic tests should be applied.

 

STUDY SCERINOS

 

While standing EDO inport cold iron you are informed that the engineers will be doing a 135% hydrostatic test on 1A boiler.

 

1.         What work would have been done in order for the engineers to do a 135% hydrostatic test?

 

INFORMATION SHEET

 

BOILER HYDROS

Information Sheet Number 62B-233

 

 

INTRODUCTION

 

Hydrostatic boiler testing is the same for all naval propulsion boilers.  Each hydrostatic test serves a definite purpose; to ensure the boiler is safe to operate.  Testing must be accomplished everytime the pressure vessel has been opened for any reason.

 

REFERENCES

 

            (a)  Boilers  NSTM Chapter 221

            (b)  Boilerwater/Feedwater Chemistry  NSTM Chapter 220 V2

            (c)  Repair and Overhaul Main Propulsion Boilers  S-9221-C1-GTP-010

 

INFORMATION

 

A.                 Purpose

 

1.         The object of boiler hydrostatic tests is to demonstrate either tightness or strength of the boiler and its parts.  The tests apply to, and include, the entire boiler pressure vessel.  This includes the first or most proximate valve on each connecting line to the boiler.  This valve may be any one of the following:  safety valve, bottom blow valve, surface blow valve, main steam stop, auxiliary steam stop, superheater protection steam inlet and outlet valve, chemical feed valve, vent valve, direct and remote water gauge cut out valves, pressure and temperature gauge connections, drain or feed valves.  Piping on opposite sides of these valves is discussed in Piping Systems NSTM Chapter 505.

 

2.         Hydrostatic test pressures for a particular boiler can be determined by reference to the design and operating data listed in reference (c).  Each boiler hydrostatic test pressure has a definite purpose.  Testing too often or at pressures higher than required to prove the test objective increases the risk of damage to the boiler and injury to personnel

 

B.                 Desuperheater

 

1.         Prior to conducting boiler hydrostatic testing, the desuperheater shall be hydrostatically tested to 150 psig or the maximum operating differential pressure for the assembly, whichever is higher.  This test is for tightness at the joint or tube seats when the assembly is installed in the boiler.  If repairs were conducted on the assembly it shall be tested to 150 percent of the desuperheater design pressure or 350 psig if data is unavailable.  This is to verify tightness of the repairs.   This test is usually conducted with the unit removed from the boiler.

 

C.                 Preparation

 

1.         To prepare a boiler for hydrostatic test, flush it out with feedwater or potable water using a hose at a pressure of approximately 50 psig.  Flush the steam and water drums, the gage glass through drum penetrations, and all tubes and headers to remove all loose deposits.

 

2.         A careful examination of the boiler shall be made to ensure no tools are left in the boiler.

 

3.         Ensure that all gasket, handhole, and manhole surfaces are clean and remake all joints.

 

4.         Blank or gag all safety valves when the boiler is subjected to hydrostatic test pressures above operating pressure.  To minimize bent valve stems, it is recommended that the valves be blanked off rather than gagged for hydrostatic tests above 100 percent operating pressure.  Blanking is required for 150 percent of design tests.

 

5.         Before applying a hydrostatic test, close all connections on the boiler except the air vent, direct reading water gauge, test pressure gauge, and valves in the line through which pressure is to be applied.  When applying a 150 percent hydrostatic test, the direct reading water gauge connections shall be shut.

 

6.         The safety valves and boiler blow valves shall be removed and blanked.  All blank flanges used to blank off any opening in the boiler, including temporarily cut large tubes or piping, must be in accordance with NAVSEA drawings.

 

7.         Feedwater used for hydrostatic testing should be between 20°C and 50°C (70°F and 120°F).  The danger in using hot feedwater for hydrostatic tests is that water spraying from leaks can flash into steam and injure personnel.  Warm the feedwater in the deaerating feed tank (DFT) with steam or use an independent mixing tank to heat the water before filling the boiler.

 

D.                 When using deaerated feed water for hydrostatic testing, omit the addition of sodium nitrite to avoid excess concentration of this chemical in the boiler.  Also omit the addition of sodium nitrite if the hydrostatic test is to be applied within 36 hours of securing from ethylene-diamine-tetraacetate (EDTA) cleaning or the test is to be applied during sodium nitrite wet layup. The boiler shall be completely filled with heated water and entirely free of air before pressure is applied.  Air is removed by keeping vent valves open on the steam drum until a steady stream of water flows from them.  The boiler metal temperature should not fall below 70°F during the hydrostatic test.  Hydrostatic tests performed by depot level activities shall be conducted using feed quality water.  Hydrostatic tests performed by ship's force should be conducted using feedwater treated or untreated with sodium nitrite that meets the requirements of NSTM chapter 220 V2.  However, if sufficient feedwater is not available, ship's force may use fresh water.

 

E.                  Applying pressure

 

1.         The test pressure shall be applied by a special high pressure, low capacity hand operated, or pneumatic‑operated hydrostatic pump.  The main feed pump should not be used for hydrostatic testing except in emergencies when an operable test pump is not available.  If the main feed pump is used it shall be limited to the 100 percent maximum steady state operating pressure test.

 

2.         The test pressure should be increased slowly to prevent over pressurization.  The test pressure should be maintained at least 15 minutes before conducting the inspection of pressure parts.  Pressure should be increased slowly and applied carefully to avoid exceeding the test pressure.  A boiler shall not be tested to a higher pressure than required by the test objective.  The pressure to be applied shall not exceed 1‑1/2 times the boiler design pressure under any circumstances.

 

3.         An operator shall be stationed at the test pump regulating valve and pressure gauge during the entire test to monitor and regulate hydrostatic test pressure to prevent over pressurization.  A drain should be used to regulate the boiler pressure by bleeding excess supply to the bilge.  The test pressure should be maintained at least 15 minutes before beginning the inspection of the boiler to minimize personnel exposure to boiler component failure or sudden leakage.  The test should last just long enough to accomplish the inspection.

 

4.         If the boiler is to be tested at pressures higher than the 100 percent maximum steady state operating pressure, the highest pressure shall be applied first and then the next test pressure applied in descending order.  The last test shall be a tightness test at 100 percent maximum steady state operating pressure.  Inspection of all boiler joints and fittings shall be conducted during this tightness test.  Following a 135 percent hydrostatic test, replace individual gaskets that leak however, it is recommended to replace all boiler gaskets.  Upon completion of a 150 percent hydrostatic test, all boiler handhole and manhole gaskets shall be replaced.  The gaskets have to be replaced because the high pressures have over compressed the gaskets and this contributes to failure during operation.

 

F.                  Safety Precautions

 

1.         Ensure that there is no leakage past the main or auxiliary steam stop valves.

 

2.         Compression of trapped air within the boiler during hydrostatic test pressure buildup can lead to an extremely dangerous situation and may prevent achieving the required pressure.  Compression of trapped air could result in extensive damage and possible personnel injury in the event of a pressure part failure.

 

3.         During the hydrostatic test of the boiler, the desuperheater shall be filled with water and pressurized along with the boiler to prevent exceeding the design pressure of the assembly.  This requires that the desuperheater inlet valve be open during the test.

 

4.         While under 150 percent hydrostatic test pressure, the boiler should be subjected to an external visual examination to detect structural defects such as gross leakage, bulges, or distortions or cracks in welds, nozzle connections, and renewed or repaired pressure parts.  Sufficient casing panels shall be removed to permit the visual examination.  Inspection of all boiler joints and fittings shall not be conducted during this test.  Upon completion of the 150 percent hydrostatic test, a close visual examination of the boiler from the outside and inside shall be made of welds, nozzles, connections, and reworked or repaired pressure parts. Do not enter the boiler when under pressure for 150% hydrostatic test.

 

G.                 Hydrostatic test acceptance criteria is as follows:

 

1.         Newly installed rolled tubes are required to be dry.

 

2.         Old tube joints (that is, other than newly installed) need only satisfy the 100 percent hydrostatic test for leakage.  Dampness (that is, a slight ring around a rolled tube joint) with no weep, spray or trickle is not considered to be a leaking joint.

 

3.         If pressure loss is high and only slight leakage exists through the tube joints and gaskets, the loss is due to leaky valve(s) or fitting(s) and these should be overhauled as necessary.

 

4.         Continued gasket leakage can cause damage to the seating surfaces, making follow‑on repairs more expensive.  The leakage criteria for boiler handholes and manholes at the 100 percent maximum steady state operating hydrostatic test pressure are as follows:

 

a)         For operating ships, the leakage rate is preferably zero, but shall not exceed three to five drops per minute.

 

b)        For ships in an availability that includes a boiler overhaul, the leakage rate for repaired or resurfaced handhole and manhole seats shall be zero (bone dry).

 

 

H.                 Economizer

 

1.         The economizer is usually tested along with the boiler unless the test is for specific repairs on the economizer.  Some repairs require the economizer to be tested at 150% of design pressure.  If testing the economizer at 150 percent of design pressure is to be conducted, the economizer shall be isolated to prevent application of an unnecessary pressure on the boiler. 

 

2.         The hydrostatic test pump and fittings shall comply with minimum requirements as follows:

 

3.         All hoses and fittings shall meet either military specifications or the Society of Automotive Engineers (SAE) specification if purchased from an outside vendor.

 

4.         A minimum of one method of manual over pressure protection shall be provided for every hydrostatic test and at least one means of backup over pressure protection is required (manual or by relief valve).  Boiler maintenance manuals specify that a safety relief valve should be installed downstream of the shutoff valve.

 

5.         All flexible hoses should be identified and labeled according to Piping Systems NSTM chapter 505, and tagged with a warning sign stating "for use with hydrostatic test pump only".

 

6.         The hydrostatic test pump and related accessories should be covered and stored in a cool dry area.