Questions regarding the interpretation of the contents of this standard or comments and questions regarding the procedures by which this standard was developed should be addressed in writing to the Director of the Standards Division, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. Proposed revisions are invited and should be submitted to the Director, Standards Division, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C.
Types of Heaters
The choice of materials for heating pipes is based on the intended temperature and pressure of the pipe and the corrosivity of the process. Austenitic stainless steels are often used for piping where temperatures exceed about 1300°F (704°C) or process corrosiveness requires its use.
Types of Boilers
Flue gas flows on the outside of the pipes and air flows on the inside of the pipes. Again, the choice depends on the temperature of the metal and the operating stress of the pipe.
Reliability Programs
Flue gas stacks vent the flue gas produced as part of the burners' combustion process to the atmosphere. Inspection plan and monitoring/assessment of other hardware and equipment that affect the deterioration of the pipes, such as burners, hangers and supports and thermocouples.
Safety
Purpose of Inspection
Inspection of Fired Boilers
Inspector Qualifications
Deterioration of Heater Tubes
Excessive sag is usually caused by a reduction in the structural strength of the pipe due to overheating. Failures are usually caused by a stress fracture in the hottest, most stressed part of the pipe.
Deterioration of Boiler Tubes
Steam binding can cause the insulating effect of slag deposits on the outside of the bottom of the pipe. Overheating results in deformed tubes and oxidation of the tube metal, causing early tube failure.
Deterioration Mechanisms of Other Components
The damage will be somewhat similar to that caused by foundation settlement and may be particularly severe on refractory linings. Air and flue ducts can become damaged, causing cracks at corners or connections.
General
The severity of the deterioration will vary with the temperature of the heater, which in turn is determined by the operating conditions of the process. Subsidence in the foundation can be a serious cause of boiler deterioration because of the severe stresses that can occur in the complicated interconnection of parts, in the external piping, and especially in the refractory linings and bulkheads.
Boiler Inspection Frequency
Fluxing can occur when fuel ash and refractory material are in contact at a moderately high temperature, producing a slag that can be fluid. Settlement of foundations can also be due to heat transfer from the combustion chamber and subsequent drying of the soil.
Heater Inspection Frequency
The general effects of this slag are to reduce the thickness and reduce the insulating effect of the refractory material, thereby allowing a high metal temperature on the supporting steel parts. Visual inspection of the firebox and especially burner flame patterns by operational staff on a routine basis.
Safety
General Preparatory Work
Precautions to Avoid Polythionic Acid Stress Corrosion Cracking
When using a soda washing solution to protect pipes from the outside, care must be taken to protect any ceramic fiber insulation from getting wet as the fiber can sag under the weight of the absorbed liquid.
Cleaning
Precautions must be taken to ensure that water does not come into contact with the bricks of the combustion chamber. During dry cleaning, all stages of the process must be carefully supervised by experienced and responsible individuals.
General
The blowdown line must be disconnected before the washing process to prevent mud and scale from the blowdown drum. If contact cannot be avoided, the brick wall must be carefully dried when the boiler is turned on.
Visual Inspection of Heater Coils
The outer surfaces of the fitting body and the holders must be visually inspected. The surfaces of the tube, especially bends, should be examined for cracks.
Wall Thickness Measurements
The threaded portion of the retaining screw and the dog or cap should be examined for excessive wear. In this type of deterioration, the greatest thinning usually occurs on the fire side of the pipe.
Tube Diameter/Circumference/Sag/Bow Measurements
In some cases, the outside diameter of the pipe can be increased and will have the same general appearance as a pipe with a small bulge. This type of corrosion is generally accelerated on the fire side due to the high metal temperature there.
Pit Depth Measurements
In reality, the tube is flexible and will have some natural sag, so the measurement will not be accurate. Considerable sag can be tolerated before breakage occurs, so this condition is not considered serious unless it prevents cleaning or causes the heads to jam and jam against other heads or against the sides of the headroom.
Intelligent Pigs/In-line Devices
Soft measurements can be used similarly to cross-sectional measurements to estimate the extent of creep. In convection sections, sagging of the tubes in upper rows to a point between those in lower rows can prevent the free passage of flue gas around the tubes.
Radiographic Examination
Borescope/Videoprobe
Visual inspection can be hindered if the inner surfaces of the tubes are not free of coke and other foreign matter. If this type of corrosion is apparent or suspected, the inner surfaces of the pipe at the ends of the pipe can be cleaned using an acetylene torch to burn coke or grinding material from the pits.
Hardness Measurements
Grit blasting is preferred and will damage the tubes the least, as could happen with an acetylene torch.
Dye Penetrant and Magnetic Particle Testing
In-situ Metallography/Replication
Detailed Examination and Destructive Testing of Tube Samples
Testing of Tubeskin Thermocouples
Magnetic Test for Carburization
Hammer Testing
While combustion deposits can vary in texture depending on the fuel used, the deposits resulting from oxidation are generally harder, require a stronger blow to be knocked out of the tube, and have a more flaky texture than deposits from the products of combustion . A magnetic check of the material provides the most conclusive test; oxide shell is magnetic and combustion products shell is non-magnetic.
Inspection of Reformer Tubes
Heater tubes that have been in service may become brittle and have low ductility at ambient temperature. Pigtail clipper designs are available, but must be checked to ensure that the hydraulic system pressure is sufficient to cut off all flow (typically over 5,000 lbf/in.2 [34,474 mPa] meter), that stop points are on the anvils to prevent the pigtail from being sheared off (the design must be based on wall thickness), and that some locking device is available to keep the crimp closed when the pigtail shear pressure is released for removal of the hydraulic cylinders.
General
In such cases, pigtail cutting was used to shrink the intake and exhaust pigtails to cut off the intake and exhaust gases.
Piping
Drums
The interior of the drum and connections to the drum must be inspected when the drum is inspected. The holes in dry pipes should be free of deposits that can restrict flow.
Water Headers
The upper outer surface of drums shall be cleaned of all deposits and the surface shall be examined for corrosion. Welds or rivets attaching internal parts or connections to the drums shall be inspected in the same manner as welds or rivets in the drum itself.
Superheater Header
If external inspection of headers reveals pitting, thickness measurements should be performed using ultrasonic techniques.
Tubes
The tubes should be inspected for signs of leakage that may arise from the cracks. All gas passages should be inspected for slagging or bridging of fly ash or slag buildup.
General
Some types of weirs have widely spaced tubes and the area between the tubes is covered by steel fins attached to the tubes.
Typical Inspection Activities
The use of detector holes serves as an early detection and protection for accelerated or unpredictable thinning of tubes. The location of observation holes is based on the type of corrosion and the configuration of the heater tubes.
External Tube Cleaning
Control drilling practices are considered a loss prevention safeguard and should not be considered a substitute for or a relaxation of good inspection and quality control practices. Heat pipe drilling depths will be calculated according to the withdrawal thickness in API Std 530.
Pre-shutdown Inspection
General
Minimum Thickness and Stress Rupture
As with tubing, it may be advisable to add some thickness, based on judgment and experience, when setting the minimum thickness at which a heat arm fitting must be replaced. However, it may be very possible to prepare one for the boilers of a given refinery.
Creep Rupture Life
Because of stresses that can be set up by closing and clamping members and by thermal expansion, the calculated allowable thickness may be too small to be practical. A width large enough to prevent leakage generally provides adequate strength against blowout, but a smaller width should never be used.
Foundations
Structural Supports
If the excess stress is serious, the design should be investigated and corrective measures should be taken. If the stress is significantly higher than the allowable stress, the weakest part must be reinforced or replaced.
Setting, Exterior, and Casing
The amount of deflection should be checked against that calculated for the load on the beam or beam. Inspection of all connections is not guaranteed, but inspection should be done where corrosion is severe.
Refractory Linings and Insulation
The depth of erosion or flow and the remaining thickness of the refractory material must be measured. Use of smoke for the inspection must be done with due consideration of the hazards associated with the material and the appropriate personnel safety equipment.
Tube Supports
In areas around surf throats, the degree of erosion or flow can be difficult to determine due to the circular or conical shape. Bulging or failure in water dams may be due to the failure of the tubes to transfer the severe heat.
Visual Inspection of Auxiliary Equipment
When the fuel contains corrosive products, all items should be examined for evidence of corrosion. Regardless, deposits should be analyzed to determine if the source of the blockage can be identified and eliminated.
Stacks
The pile painters trolley and cable should be visually inspected for corrosion or mechanical damage prior to use and prior to return to storage. Stack lightning rods and their grounding cables should be visually inspected to see if they are tight and not broken.
Heaters
The condition of the connections at the top of the pulley and the carriage ring and its connections to the stack must be accurately determined. Ladders on steel, concrete and brick piles should be visually inspected for corrosion and physically tested using test weights in excess of those that can be loaded by the personnel using them.
Boilers
This is not comprehensive as other factors may need to be considered for specific situations. Welding procedures qualified in accordance with ASME Section IX for the material and technique appropriate for the welding to be performed.
Materials Verification
Repairs and/or modifications are designed to meet the requirements of the service, including material selection.
General
A copy of this chart must be submitted with the pipe inspection report after each periodic inspection and test. A copy of this diagram should only be submitted with the pipe renewal report when the pipe location in the heater has been changed.
