BOILER FAILURES
What causes thick-lip stress rupture of a boiler tube?
What causes thin-lip stress rupture of a boiler tube?
Besides overheating, what other factors can cause plain tubes failure?
Is tube burst is a common failure in fire-tube boilers?
What is water starvation of plain tubes and what are the common causes?
What can cause tube bulging in water-tube boilers? How do you prevent this from happening?
What are the common causes of overheating?
What is flame impingement on tubes, and how does it happen in sold-fuel boiler?
What is creep and at what temperature creep becomes a consideration?
Why prolonged operation with leaking tubes (minor leaks) is not recommended?
What are the causes of superheater tubes failure?
What can cause steam starvation in superheater tube?
How can deposits build up in superheater tubes?
What is porosity and how would you describe it? Is pinhole on weldment dangerous?
What is the difference between a bulge and a blister and explain what each of them is?
Can a tube burst in a fire-tube boiler?
What is the cause of the tube to sag and where it is common to find tube sagging?
What are the normal problems associated with steam drum?
Give examples of typical failures in steam drum.
Cracks may develop on the tube-plates of multi-tubular boilers. What are the possible causes of these cracks?
What is fire crack and should fire cracks be repaired?
What is thermal shock?
What is the difference between thermal fatigue and thermal shock?
Give an example of failure due to thermal shock.
What is the condition conducive to thermal shock in a steam boiler?
Which is more susceptible to thermal shock, thin metal or thick metal plate?
How to prevent thermal shock?
Explain what an implosion on a boiler is, and why this would happen?
What causes furnace explosion?
How to avoid furnace explosion?
What causes thin-lip stress rupture of a boiler tube?
Besides overheating, what other factors can cause plain tubes failure?
Is tube burst is a common failure in fire-tube boilers?
What is water starvation of plain tubes and what are the common causes?
What can cause tube bulging in water-tube boilers? How do you prevent this from happening?
What are the common causes of overheating?
What is flame impingement on tubes, and how does it happen in sold-fuel boiler?
What is creep and at what temperature creep becomes a consideration?
Why prolonged operation with leaking tubes (minor leaks) is not recommended?
What are the causes of superheater tubes failure?
What can cause steam starvation in superheater tube?
How can deposits build up in superheater tubes?
What is porosity and how would you describe it? Is pinhole on weldment dangerous?
What is the difference between a bulge and a blister and explain what each of them is?
Can a tube burst in a fire-tube boiler?
What is the cause of the tube to sag and where it is common to find tube sagging?
What are the normal problems associated with steam drum?
Give examples of typical failures in steam drum.
Cracks may develop on the tube-plates of multi-tubular boilers. What are the possible causes of these cracks?
What is fire crack and should fire cracks be repaired?
What is thermal shock?
What is the difference between thermal fatigue and thermal shock?
Give an example of failure due to thermal shock.
What is the condition conducive to thermal shock in a steam boiler?
Which is more susceptible to thermal shock, thin metal or thick metal plate?
How to prevent thermal shock?
Explain what an implosion on a boiler is, and why this would happen?
What causes furnace explosion?
How to avoid furnace explosion?
How fuel can enter the furnace in unburned state?
How boiler overloads can damage boilers?
What causes vibration, and can vibration cause failure to boilers?
What do you understand by boiler failure due to “external loading”?
Describe the various possible scenarios that may lead to the collapse of a plain furnace in a solid-fuel boiler.
Recommend the methods to prevent furnace walls from failure.
What are the causes of failure in steam headers? How to assess the extent of damage
What is the typical cause of failure in deaerator?
What is the common failure of an economizer?
Are deposits between the tube fins in an economizer dangerous?
How water vapor is formed in the flue gas?
Describe whether the composition of the fuel burnt in the boiler furnace has an influence on the dew point of the flue gas.
In case of oil-fired boilers, can you avoid acid dewpoint in economizer by raising the exit flue gas temperature?
BOILER REPAIRSHow boiler overloads can damage boilers?
What causes vibration, and can vibration cause failure to boilers?
What do you understand by boiler failure due to “external loading”?
Describe the various possible scenarios that may lead to the collapse of a plain furnace in a solid-fuel boiler.
Recommend the methods to prevent furnace walls from failure.
What are the causes of failure in steam headers? How to assess the extent of damage
What is the typical cause of failure in deaerator?
What is the common failure of an economizer?
Are deposits between the tube fins in an economizer dangerous?
How water vapor is formed in the flue gas?
Describe whether the composition of the fuel burnt in the boiler furnace has an influence on the dew point of the flue gas.
In case of oil-fired boilers, can you avoid acid dewpoint in economizer by raising the exit flue gas temperature?
Repairs refer to restoration or replacement of pressure retaining items of the boiler proper and do not include other maintenance activities associated with the operation of the boiler. What is boiler proper?
What is the definition of repair to a boiler and how repairs are classified?
What is the definition of alteration of a boiler?
Give few examples of alterations to boilers?
Who must authorize repairs?
What are the typical types of boiler repairs?
What are several methods of boiler tube repairs? Does any of the method of repair require Authorized Inspector’s approval?
What is the classification of pressure vessels for welding? Steam boiler is classified in which category?
Give three (3) advantages and three (3) disadvantages of Shielded Metal Arc Welding (SMAW).
Describe briefly gas welding, brazing, tungsten-inert gas welding, and plasma arc welding. Give two (2) reasons why post weld heat treatment is required in certain circumstances.
Can an unqualified welder weld on any part of the boiler proper?
If a welder is qualified to repair a tube, does it make him qualified for other welds on the boiler?
What are the advantages and disadvantages of Gas-Tungsten Arc Welding (TIG)? Why TIG is used in root-penetration welding?
What is manual shielded arc welding and why this method of welding suitable for boiler repairs
How do you know if the welding company is qualified to do welding on a boiler?
How do welders become qualified?
What NDE is required for welded repairs?
What are WPS and PQR in qualifying welders?
What are the positions that a welder can qualify?
Give some general guidelines on repair procedure using welding?
At what temperature shall a metal be preheated before welding?
Why PWHT is important after welding?
How PWHT is carried out?
What are some common welding defects? Explain in details and include sketch in your answers.
What should be done prior to welding the second side of a double butt weld?
In boiler construction, what is the maximum permitted undercut in welding?
Sketch and give the definition of the below type of joint: butt joint, T-joint, and lap joint
Give examples of some welding preparation in SMAW for butt joint.
What is 6G-position in welding? What are other positions in groove welding that you are familiar with?
Why weld joints are inspected? Sketch fillet weld and groove weld. Include nomenclature of welds in your answers.
Where welding is to be carried out in both the downhand and overhand position, the larger V or U preparation should be arranged for the downhand position. Why?
Why low-hydrogen electrode must be used in welding boilers?
Give an example of a low-hydrogen electrode, and what do you understand by the code for the electrode?
What is the relationship between ASME Section IX and AWS? Which code should be used to weld pressure vessel and piping?
What is the method of inspection to check failed tubes?
Besides visual examination, what is the quick NDE to assess the condition of tubes?
What are the preferred NDE for steam drums?
How do you remove a damaged tube in a watertube boiler?
How do you install new tubes (after the damaged tubes were removed) in a watertube boiler?
How to operate the expander? Include sketch in your answer.
Does beading the fire tube give holding power to the tube?
Describe in details the procedures to remove the defective tubes and renew the tubes in firetube boilers?
If boiler re-tubing did not involve any welding, is hydrostatic test still required?
How do you plug burst generating tubes (water tube boiler) and what are the precautions?
Why is it necessary to drill a hole on a plugged tube?
Can superheater tubes be plugged?
What are the tubes that cannot be plugged?
If you noticed visually that there is a surface bruise on one of the waterwall tubes, should you replace the tube?
On visual inspection, you found that one of the waterwall tubes is dented, but there in no leak. Should you change the tube?
When expanding a fire tube into a tubesheet how do you know when it is tight?
Can a plain tube in fire-tube boiler be re-expanded if leaking?
Illustrate using suitable diagrams how water tubes are attached to the steam drum, the mud drum, and the headers. State the precautions that need to be taken during tube attachment process.
Why do the rear ends of tubes on a high-temperature boiler leak in case of low water?
In firetube boiler, what are the usual causes of crack, and where are the locations?
The rear tube plate of a firetube boiler leaked after the fuel is changed from MFO to natural gas. What could be the cause?
What are the guidelines for tube repairs for water-cooled tubes (generating tubes, economizer tubes, furnace wall) or furnace and shell walls?
What are the guidelines for tube repairs for steam-cooled tubes (superheaters, re-heaters)?
How would you repair a “burst” tube in a HRT boiler if there were not enough time to change to a new tube?
How would know if you had a broken stay bolt?
How should stay bolts be examined and tested?
Can broken stay be welded and reused?
What are the three (3) methods of detecting the cracks?
Can you repair a ligament crack on a firetube boiler? Outline the repair procedures
What cracks may not be repaired?
Recommend the measures required to be taken in order to prevent recurrence (cracking of ligament).
What causes cracked tube plates? How is this defect repaired?
Where are the areas where cracks are most likely to appear?
What is 6G position in welding and why 6G-position is used in qualifying welder for boilermaker?
Where are the potential crack locations in a firetube boiler? Discuss the causes of the cracks in details.
Where flame cutting or overheating has occurred, why it is important to do hardness plots (destructive test)?
May a bulge on a plate be driven back?
Describe in detail the proposal that you will make to repair the bulge on shell of a HRT boiler. Reference should be made to statutory requirement in the proposal.
A tube has a small bulge at one portion and the rest of the tube is still in good condition. In addition, the circumference of the tube is hard to access. Can flush patch be done on the tube? If yes, outline the repair procedure.
A portion of a tubesheet is wasted due to corrosion. After the judgment by the Inspector, the wasted area can be repaired. Outline the procedures for repair.
Outline the procedures to repair blister.
In the mud drum, there is a metal chip-off (dented) about 3 mm in depth and the mud drum shell thickness is 31.75 mm due to manufacturing defect. Outline the steps to repair the dent.
From ultrasonic thickness test, you have found that a portion of boilerplate of outer shell has worn thin due to corrosion. The plate thickness is now 0.5 inch while the original thickness is 0.8 inch. How would you assess the extent of damage and decide whether to continue or discontinue the boiler operation? The inside diameter of the shell is 84 inches. The MAWP of the boiler is 155 psig and the boilerplate for the shell is SA-192.
List typical refractory firebricks used in boilers.
What is monolithic refractory and give the examples of the most frequently used monolithic refractories in boiler furnaces.
Describe how to replace castable lining in a boiler. State all the precautions.
Upon inspection, you notice some hairline and minor cracks on the castable refractory. Do you need to patch the cracks?
How do you patch cracks on castable refractory with high-temperature bonding mortar? Is there any other method to repair the cracks?
Describe the various possible scenarios that may lead to the collapse of a plain furnace in a fire-tube boiler.
Describe how to replace refractory brick in a boiler.
For solid fuel boilers, is it necessary to remove slag from the surface of refractory?
What is castable and where is castable used in boiler furnace?
Suppose that one of a set of boilers does not get the proper amount of feed, although the check valve is sufficiently open; what might cause this trouble?
What should be done prior to welding the second side of a double butt weld?
In boiler construction, what is the maximum permitted undercut in welding?
Sketch and give the definition of the below type of joint: butt joint, T-joint, and lap joint
Give examples of some welding preparation in SMAW for butt joint.
What is 6G-position in welding? What are other positions in groove welding that you are familiar with?
Why weld joints are inspected? Sketch fillet weld and groove weld. Include nomenclature of welds in your answers.
Where welding is to be carried out in both the downhand and overhand position, the larger V or U preparation should be arranged for the downhand position. Why?
Why low-hydrogen electrode must be used in welding boilers?
Give an example of a low-hydrogen electrode, and what do you understand by the code for the electrode?
What is the relationship between ASME Section IX and AWS? Which code should be used to weld pressure vessel and piping?
What is the method of inspection to check failed tubes?
Besides visual examination, what is the quick NDE to assess the condition of tubes?
What are the preferred NDE for steam drums?
How do you remove a damaged tube in a watertube boiler?
How do you install new tubes (after the damaged tubes were removed) in a watertube boiler?
How to operate the expander? Include sketch in your answer.
Does beading the fire tube give holding power to the tube?
Describe in details the procedures to remove the defective tubes and renew the tubes in firetube boilers?
If boiler re-tubing did not involve any welding, is hydrostatic test still required?
How do you plug burst generating tubes (water tube boiler) and what are the precautions?
Why is it necessary to drill a hole on a plugged tube?
Can superheater tubes be plugged?
What are the tubes that cannot be plugged?
If you noticed visually that there is a surface bruise on one of the waterwall tubes, should you replace the tube?
On visual inspection, you found that one of the waterwall tubes is dented, but there in no leak. Should you change the tube?
When expanding a fire tube into a tubesheet how do you know when it is tight?
Can a plain tube in fire-tube boiler be re-expanded if leaking?
Illustrate using suitable diagrams how water tubes are attached to the steam drum, the mud drum, and the headers. State the precautions that need to be taken during tube attachment process.
Why do the rear ends of tubes on a high-temperature boiler leak in case of low water?
In firetube boiler, what are the usual causes of crack, and where are the locations?
The rear tube plate of a firetube boiler leaked after the fuel is changed from MFO to natural gas. What could be the cause?
What are the guidelines for tube repairs for water-cooled tubes (generating tubes, economizer tubes, furnace wall) or furnace and shell walls?
What are the guidelines for tube repairs for steam-cooled tubes (superheaters, re-heaters)?
How would you repair a “burst” tube in a HRT boiler if there were not enough time to change to a new tube?
How would know if you had a broken stay bolt?
How should stay bolts be examined and tested?
Can broken stay be welded and reused?
What are the three (3) methods of detecting the cracks?
Can you repair a ligament crack on a firetube boiler? Outline the repair procedures
What cracks may not be repaired?
Recommend the measures required to be taken in order to prevent recurrence (cracking of ligament).
What causes cracked tube plates? How is this defect repaired?
Where are the areas where cracks are most likely to appear?
What is 6G position in welding and why 6G-position is used in qualifying welder for boilermaker?
Where are the potential crack locations in a firetube boiler? Discuss the causes of the cracks in details.
Where flame cutting or overheating has occurred, why it is important to do hardness plots (destructive test)?
May a bulge on a plate be driven back?
Describe in detail the proposal that you will make to repair the bulge on shell of a HRT boiler. Reference should be made to statutory requirement in the proposal.
A tube has a small bulge at one portion and the rest of the tube is still in good condition. In addition, the circumference of the tube is hard to access. Can flush patch be done on the tube? If yes, outline the repair procedure.
A portion of a tubesheet is wasted due to corrosion. After the judgment by the Inspector, the wasted area can be repaired. Outline the procedures for repair.
Outline the procedures to repair blister.
In the mud drum, there is a metal chip-off (dented) about 3 mm in depth and the mud drum shell thickness is 31.75 mm due to manufacturing defect. Outline the steps to repair the dent.
From ultrasonic thickness test, you have found that a portion of boilerplate of outer shell has worn thin due to corrosion. The plate thickness is now 0.5 inch while the original thickness is 0.8 inch. How would you assess the extent of damage and decide whether to continue or discontinue the boiler operation? The inside diameter of the shell is 84 inches. The MAWP of the boiler is 155 psig and the boilerplate for the shell is SA-192.
List typical refractory firebricks used in boilers.
What is monolithic refractory and give the examples of the most frequently used monolithic refractories in boiler furnaces.
Describe how to replace castable lining in a boiler. State all the precautions.
Upon inspection, you notice some hairline and minor cracks on the castable refractory. Do you need to patch the cracks?
How do you patch cracks on castable refractory with high-temperature bonding mortar? Is there any other method to repair the cracks?
Describe the various possible scenarios that may lead to the collapse of a plain furnace in a fire-tube boiler.
Describe how to replace refractory brick in a boiler.
For solid fuel boilers, is it necessary to remove slag from the surface of refractory?
What is castable and where is castable used in boiler furnace?
Suppose that one of a set of boilers does not get the proper amount of feed, although the check valve is sufficiently open; what might cause this trouble?
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