Heat exchanger failures cause many plant shutdowns and slowdowns. The cost of these failures is high due to lost production and replacement of the exchangers. Inspection’s responsibilities are to: (1) inspect existing exchangers when they are taken out of service to determine extent of repairs and remaining life; (2) verify that repairs are completed to the tolerances specified; and (3) maintain accurate long term records that facilitate accurate forecasting. This section covers inspection and testing requirements for new and existing shell and tube and air cooled heat exchangers. The type of damage found in exchangers is discussed, along with the primary inspection and testing techniques used to determine the condition of an exchanger. Detailed shutdown inspection checklists are included. Acceptable dimensional tolerances are discussed, and guidance on Safety Instruction Sheets (SIS) for shell and tube exchangers and air cooled heat exchangers is provided.
900 Inspection and Testing Abstract This section covers both shop inspection of new equipment and inspection of existing units during maintenance turnarounds The section on shop inspection covers information on shop testing and inspection to verify that new units are built to specification and with good workmanship Heat exchanger failures cause many plant shutdowns and slowdowns The cost of these failures is high due to lost production and replacement of the exchangers Inspection’s responsibilities are to: (1) inspect existing exchangers when they are taken out of service to determine extent of repairs and remaining life; (2) verify that repairs are completed to the tolerances specified; and (3) maintain accurate long term records that facilitate accurate forecasting This section covers inspection and testing requirements for new and existing shell and tube and air cooled heat exchangers The type of damage found in exchangers is discussed, along with the primary inspection and testing techniques used to determine the condition of an exchanger Detailed shutdown inspection checklists are included Acceptable dimensional tolerances are discussed, and guidance on Safety Instruction Sheets (SIS) for shell and tube exchangers and air cooled heat exchangers is provided Chevron Corporation Contents Page 910 Shop Inspection of New Exchangers 900-3 911 General Comments 912 Degree of Inspection 913 Shop Inspection of Shell and Tube Exchangers 914 Shop Inspection of Air Cooled Heat Exchangers 915 Inspection Tasks 920 Inspection of Existing Shell and Tube Exchangers and Air Cooled Exchangers 900-9 921 The Inspection, Engineering, Operation, and Maintenance Team 922 Inspection Sequence 923 Double Pipe Exchangers 900-1 December 1989 900 Inspection and Testing December 1989 Heat Exchanger and Cooling Tower Manual 924 Inspection of State Registered Unfired Steam Generators 930 Types of Damage Found In Exchangers 900-11 940 Inspection and Testing Techniques 900-12 941 Inspection Techniques 942 Pressure Testing Techniques 943 Safety 950 Dimensional Tolerances 900-14 960 Safety Instruction Sheets 900-15 970 Maintenance Inspection Checklists 900-17 900-2 Chevron Corporation Heat Exchanger and Cooling Tower Manual 900 Inspection and Testing 910 Shop Inspection of New Exchangers 911 General Comments Shop inspection is warranted for virtually all heat exchangers except “off-the-shelf” lube oil coolers Inspection at the fabrication plant is normally done by the Quality Assurance (QA) section of Purchasing, or by an inspector contracted by Purchasing QA to inspect the exchanger The purpose of shop inspection is to provide assurance that the equipment meets specification and order requirements, displays good workmanship, and is free of significant damage or defects ASME Code uses the term “Authorized Inspector” to describe the inspector who works for a state, municipality, or insurance company and must be used by the fabricator to inspect the exchanger and sign the Manufacturer’s Data Report The Authorized Inspector is not the same shop inspector that Chevron uses The Authorized Inspector’s responsibility is to verify that the exchanger is designed and fabricated in accordance with ASME Code, but he has no interest in and does not check such things as: Dimensions or orientations (except for diameter and thickness) Presence of all required nozzles, baffles, or impingement plates; plumbness/squareness of nozzles Limitations or restrictions in Company specifications on materials or welding processes Special construction details in Company specifications that exceed ASME Code requirements Inspection or testing requirements in Company specifications that exceed ASME Code minimums 912 Degree of Inspection Figures 900-1 and 900-2 show the degrees of inspection for shell and tube heat exchangers and for air cooled exchangers, respectively The degrees of inspection ranging from one or two inspection visits to resident inspection The visits ver this test allows individual leaking tubes to be plugged off because the tubesheet is accessible Roll leaks also can be individually identified and repaired U-tube bundles are easily tested with the shell enclosed Floating head bundles require the use of a test ring to observe the floating tubesheet during the shell test Figure 900-5 is a schematic of a test ring Chevron Corporation 900-13 December 1989 900 Inspection and Testing Fig 900-5 Heat Exchanger and Cooling Tower Manual Test Ring - Floating Tubesheet (Courtesy of TEMA) Leakage Tests Tests for leakage can be conducted at the operating pressure for repairs not affecting the vessel “strength,” such as plugging tubes Bleeder Tests Shell and tube bleeder tests can be applied quickly; however, they will indicate only that the unit is leaking The type of leak will be unknown When the shell or tubes are pressured, inspect for leaks at the channel or shell drains Testing Medium The testing medium should be oil or water Gas tests are more sensitive, but are extremely dangerous Such tests over 15 psig require the approval of local management 943 Safety The inspector must remember that pressure tests involve certain hazards In addition to gaskets blowing out, previously driven plugs can blow out as well While witnessing pressure tests, the inspector should stand to one side Unauthorized personnel should not be in the vicinity of the exchanger on test The test pump must have a safety valve set at the test pressure, and a gage with a range of roughly double the test pressure (i.e., if test pressure is 150 psi, gage range should be to 300 psi) 950 Dimensional Tolerances Dimensional tolerances for standard shell and tube exchangers are tabulated in Section of the Standards of Tubular Exchanger Manufactures Association (TEMA) December 1989 900-14 Chevron Corporation Heat Exchanger and Cooling Tower Manual 900 Inspection and Testing Copies of TEMA Tables F-1 and F-2 are included for your quick reference (See Figures 900-6 and 900-7.) Dimensional tolerances for air cooled exchangers are covered by API Standard 661, also included in this manual 960 Safety Instruction Sheets Safety Instruction Sheets (SISs) are used by several organizations as a singlesource summary document for important data on operating equipment These data are important to operations, technical groups, inspection and maintenance, and they include: • Safe operating limits (temperatures, pressures, rotational speeds, etc.) • Particular precautions for safe operation • Specified routine tests required for safe operation • References necessary to operate and/or maintain the equipment • Inspection/technical data (minimum thickness, corrosion allowances, test pressures, relief valve settings, minimum pressurizing temperatures, etc.) SI sheets should be completed for (1) new exchangers and (2) existing exchangers that have been altered in any way that affects the SI sheet content This includes: material changes, derating, minimum thickness changes SI sheets are routinely filled out by a project engineer and countersigned by an operating representative They become permanent records in the inspection groups and in the equipment manuals for the plants Many technical groups also maintain compiled copies Some organizations are now shifting this information to a centralized information database, PEIS (Plant Equipment Information System) Regardless of the format, the SI sheet is a good checklist of important information to have readily available A significant problem with SI sheets has been getting them accurately and completely filled in prior to startup One reason for this is that vendors are not always as responsive during the latter stages of a project, after the equipment has been purchased and installed If you are committed to having SI sheets, you should consider methods to motivate vendors to complete them (or provide data) after all design and operating data are confirmed Instructions for completing the following SI sheets are included in the Safety Instruction Sheet Section: • • Chevron Corporation EXH-EF-787 Shell and Tube and Double Pipe Heat Exchangers SI Sheet EXH-EF-788 Air Cooled Heat Exchangers SI Sheet 900-15 December 1989 900 Inspection and Testing Fig 900-6 Heat Exchanger and Cooling Tower Manual Standard Tolerances for External Dimensions, Nozzle and Support Locations of Heat Exchanger (Courtesy of TEMA) December 1989 900-16 Chevron Corporation Heat Exchanger and Cooling Tower Manual Fig 900-7 900 Inspection and Testing Standard Clearances and Tolerances for Tubesheets, Partitions, Covers, and Flanges (Courtesy of TEMA) 970 Maintenance Inspection Checklists Attached are inspection checklists for the following: • • Shell and Tube Exchangers (Figure 900-8) Air Cooled Exchangers (Figure 900-9) This information was excerpted from the CUSA Manufacturing Inspection Manual Chevron Corporation 900-17 December 1989 900 Inspection and Testing Fig 900-8 Heat Exchanger and Cooling Tower Manual Inspection Checklist—Shell and Tube Exchangers (1 of 3) Date: Exchanger: Service: Tube side Shell side Initial: _ Preshutdown Inspection: Discuss and agree on the “shutdown objectives with Operations, Engineering, and Maintenance.” _ Records Check: Review records and become familiar with corrosion history Prepare a sketch indicating type and location of previous corrosion _ External Visual Inspection: Inspect exchanger supports for proper bearing and anchoring _ Look for corrosion on the shell where it is in contact with the concrete fireproofing _ Check slide plates or slotted bolt holes for freedom of movement at the exchanger supports _ Inspect support leg fireproofing for cracks and spalling and corrosion underneath _ Inspect the anchor bolts for necking down at the baseplate _ Where exchangers are saddled into a concrete support, inspect the shell for external corrosion _ Inspect the insulation and retainers Corrosion often occurs where moisture penetrates the insulation and the shell is not hot enough to dry it out Insulated exchangers which operate below ambient temperature are susceptible to this type of corrosion Representative sections, or even all of the insulation, should be removed to permit a complete external inspection and ultrasonic gaging _ Inspect all small piping for leaks and external corrosion, including vents, drains, relief valves, plugs, and other small screwed fittings _ Look for gasket leaks on the inlet and outlet piping flanges and at the channel or shell cover flanges Evidence of leaks can be seen as deposits on the ground or platform under the unit _ Check the packing gland on the bottom leg of the reboilers for leaks _ Check gaskets and gasket surfaces for evidence of leakage _ If the unit is a water cooler or condenser, note the water outlet temperature either by dial thermometer or by feel Excessively high water temperature (above 120°F for salt water) indicates possible fouling and probable high corrosion rates in the tubes _ Ultrasonic Inspection: Take ultrasonic gage measurements at locations where internal corrosion is suspected A sufficient number of measurements should be taken to provide reasonable assurance of the exchanger’s integrity It is important to recognize that external gage points can reflect general corrosion rates, but that actual remaining wall thickness is probably lower December 1989 900-18 _ Chevron Corporation Heat Exchanger and Cooling Tower Manual Fig 900-8 900 Inspection and Testing Inspection Checklist—Shell and Tube Exchangers (2 of 3) Shutdown Inspection: Shell and Covers: Verify exchanger is properly cleaned for inspection Cleaning can be done by water-washing, chemical cleaning, or by sandblasting The amount of cleaning required depends on the severity of the corrosion and fouling in the unit _ Internally inspect shells 20 inches or greater in diameter Look for evidence of corrosion, noting particularly the nozzle, flange and shell welds, and the locations where the transverse baffles contact the shell _ Take ultrasonic (UT) gage measurements in corroded areas and at representative locations on the shell cover and channel section to establish an accurate picture of the corrosion patterns UT the shell at the inlet and outlet nozzles _ Prior to cleaning, check gasket surfaces for evidence of leakage _ After buffing, inspect gasket surfaces and flanges for evidence of corrosion or mechanical damage Severely corroded gasket surfaces can require weld buildup and machining Lightly damaged gasket surfaces can be repaired by machining or drawfiling _ Inspect the baffles in channel sections for warpage, distortion, corrosion, or evidence of bypassing _ Ensure that baffle stay rods are not cracked or broken _ Inspect lifting lugs on channel sections and covers for mechanical damage or corrosion to ensure they are safe for continued use _ Hammer-test or UT gage all small piping on the channel, shell, or shell cover and inspect all threaded fittings as necessary On high pressure, or stainless steel piping, radiography should be used instead of hammer-testing _ For services other than water, verify that all piping connections, including small piping, are welded up to the first root value Eliminate connections less than 3/4 inch in size _ Inspect longitudinal grooves or guides in the shell for the horizontal baffle in the bundle _ Inspect alloy lining for cracked attachment welds and pinhole leaks Have leaking or bulged lining removed for inspection under the lining _ If channel cover staybolts are used, observe the bolt holes behind the lining Graphitization frequently enlarges the holes and results in leaks Repairs can be made by using oversize gaskets under the nuts _ Inspect floating head bolts for evidence of corrosion, breakage or overstressing _ Inspect split rings for warpage which can cause leaks at the floating head gasket _ Bundles: A summary of the various types of bundle wear is included in Section 930 of the Heat Exchanger and Cooling Tower Manual _ Before Cleaning: Record plugging and fouling conditions _ Record clean washed areas indicative of high velocity and subsequent corrosion _ Chevron Corporation 900-19 December 1989 900 Inspection and Testing Fig 900-8 Heat Exchanger and Cooling Tower Manual Inspection Checklist—Shell and Tube Exchangers (3 of 3) Walk around the unclean bundle, take pictures, gather samples of fouling products and scale for analysis if necessary Look for distortion, leaks, and any unusual condition Much of this evidence is washed away when the bundle is cleaned _ After Cleaning: Gage O.D of accessible tubes with calipers _ Use a mirror to visually inspect the full length of the outside of as many tubes as possible Have the bundle rotated if necessary _ Look for localized corrosion near the shell inlet nozzle in areas of impingement _ Use a boroscope or a mirror and reflected light to visually inspect tube I.D _ Look at tube ends for corrosion and thinning using a tube I.D gage _ Consider eddy current inspection for tube wall thickness _ Pull specimen tubes in strategic areas if necessary Split the tube and check the entire length for remaining wall thickness The eddy current inspection may give you an idea of where to pull specimen tubes _ Inspect the front and backsides of tubesheets for corrosion _ Verify that all gasket surfaces are clean and free of defects and corrosion that could affect the tightness of the gasketed joint _ Check the tubesheet baffle gasket surfaces for bypassing Bypassing can corrode both the tubesheet gasket surface and the baffles _ Check tubesheets with seal welded tubes for warpage which can cause excessive baffle bypassing _ Inspect the tubesheet which is to be reused as a bundle to ensure that it is retubed Look for the tube hole enlargement using a “go/no-go” gage Look for pieces of thimbles left in the tubesheet serrations Check for cracked ligaments Note the history of the bundle If roll leaks have been a problem, the ligaments are probably spongy, unable to hold a tight roll, and the tubesheet should be replaced _ Inspect the segmental cross baffles for hole enlargement by moving the tubes and observing excess movement _ Look for general thinning of all carcass components _ Inspect the carcass for possible reuse when the bundle is retubed Ensure that the frame will last the life of the bundle, especially when the tube material is being upgraded _ December 1989 900-20 Chevron Corporation Heat Exchanger and Cooling Tower Manual Fig 900-9 Date: 900 Inspection and Testing Inspection Checklist—Air Cooled Exchangers _ Equipment #: _ Service: _ Initial _ Tubes: Inspect fin condition and fouling _ Have header plugs removed and measure tube I.D with an I.D gage _ Consider eddy current inspection to determine tube wall thickness _ Pull specimen tubes if the eddy current inspection indicates it is warranted _ Header boxes and tubesheet: Inspect the header box and tubesheet for wall thickness _ Check the plugs for impingement on the outlet sides _ Check the plug and header hole threads for corrosion and galling _ Fan, driver, and housing: Inspect the fan for cracking or distress _ Check the guards to ensure they are intact, for personnel protection _ Check the light gage steel housing for general condition _ Chevron Corporation 900-21 December 1989 ... Exchanger and Cooling Tower Manual Fig 900-7 900 Inspection and Testing Standard Clearances and Tolerances for Tubesheets, Partitions, Covers, and Flanges (Courtesy of TEMA) 970 Maintenance Inspection. .. Corporation Heat Exchanger and Cooling Tower Manual Fig 900-8 900 Inspection and Testing Inspection Checklist—Shell and Tube Exchangers (2 of 3) Shutdown Inspection: Shell and Covers: Verify exchanger... requirements Inspection or testing requirements in Company specifications that exceed ASME Code minimums 912 Degree of Inspection Figures 900-1 and 900-2 show the degrees of inspection for shell and tube