EXH900 inspection and testing

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.

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 mine 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

913 Shop Inspection of Shell and Tube Exchangers

914 Shop Inspection of Air Cooled Heat Exchangers

924 Inspection of State Registered Unfired Steam Generators

941 Inspection Techniques

942 Pressure Testing Techniques

943 Safety

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 ance that the equipment meets specification and order requirements, displays good workmanship, and is free of significant damage or defects

assur-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 fabri-cator to inspect the exchanger and sign the Manufacturer’s Data Report The Autho-

rized 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:

1 Dimensions or orientations (except for diameter and thickness)

2 Presence of all required nozzles, baffles, or impingement plates; ness/squareness of nozzles

plumb-3 Limitations or restrictions in Company specifications on materials or welding processes

4 Special construction details in Company specifications that exceed ASME Code requirements

5 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 them-selves are listed in chronological sequence Degrees of inspection are listed gener-ally in accordance with the importance of the visit

Purchasing QA usually establishes the visits required based on the specifics of an order, but the job engineer can always participate in this decision Figures 900-1 and 900-2 define the basic purpose for each visit but do not list all of the tasks that the Company inspector is required to complete during these visits (see Section 915)

Fig 900-1 Degrees of Inspection for Shell and Tube Heat Exchangers

Visit Notes:

A This visit is required for any parts of exchanger that are required to be PWHT’D This does not apply to stress relief of tube bends.

B This visit is made prior to any hydrostatic test and after PWHT if any For exchangers with fixed tubesheets, internal inspection of the shell prior to attachment of closing tubesheet is required.

C This visit is required for all stacked exchangers with interconnecting nozzles.

D This visit is required for Degree 9, 10, and 11 inspection if finish paint is shop applied.

General Notes:

1 Add supplementary visits A, C, and D as applicable.

2 Visits for purposes other than listed may be warranted and added (for example, to witness penetrant test of sealwelded tubes/tubesheets).

3 This matrix does not include all of the inspection tasks that an inspector completes during the required plant visits shown A list of detailed inspection tasks can be several pages long This list is normally part of the inspection plan for a particular exchanger Inspection plans are usually prepared by Purchasing QA.

4 Each visit is not necessarily a full 8-hour day.

5 Problems with quality, specification compliance, or vendor cooperation/scheduling could increase the number of visits beyond the number shown.

Fig 900-2 Degrees of Inspection for Air Cooled Exchangers

Visit Notes:

A Outside face of tubesheet must be painted prior to tubing bundle if painting outside face is important; not normally done.

B Test erection and shop run are normally required This visit can usually be included with visit for final inspection.

General Notes:

1 Add supplementary visits A and B as applicable.

2 Visits for purposes other than listed may be warranted and added.

3 This matrix does not include all of the inspection tasks that an inspector completes during the required plant visits that are shown A list of detailed inspection tasks can be several pages long This list is normally part of the inspection plan for a particular exchanger Inspection plans are usually prepared by Purchasing QA.

4 Each visit is not necessarily a full 8-hour day.

5 Problems with quality, specification compliance, or vendor cooperation/scheduling could increase the number of visits beyond the number shown.

913 Shop Inspection of Shell and Tube Exchangers

Figure 900-1 identifies the different degrees of inspection for shell and tube exchangers Figure 900-3 summarizes when to use the various degrees Degree 4 is

about the minimum for any shell and tube exchanger in hydrocarbon or critical

service Degree 10 is appropriate where any of the following apply

• The exchanger has a fabrication time over 6 weeks

• The exchanger is very large (over 4 feet diameter)

• The exchanger wall thickness is over 1-1/4 inch

• The exchanger has a high pressure rating (flanges 600 pounds or more)

• The exchanger is fabricated from low alloy or high alloy steels

• The exchanger has substantial cladding or weld overlay

Degree 11 (resident inspection) is rarely applied to heat exchangers but could be considered during fabrication of heavy wall shells or channels (over about 4 inches thick)

Visits for purposes in addition to those listed can be added to cover any special concerns

914 Shop Inspection of Air Cooled Heat Exchangers

Figure 900-2 identifies the degree of inspection for air cooled heat exchangers

Degree 5 is about the minimum for any air cooled exchanger in hydrocarbon or

critical service Factors similar to those listed in Section 913 above are used to decide when more inspection visits are warranted; consult Purchasing QA for addi-tional guidance

915 Inspection Tasks

Figures 900-1 and 900-2 do not list all of the tasks the Company inspector is required to complete during the plant visits These tasks are normally listed in an inspection plan prepared by Purchasing QA The tasks listed in the inspection plan can be several pages long Some of the principal tasks are:

1 Verification that welding procedures and welders are qualified per ASME Code

2 Review of material test reports for principal exchanger parts and verification that exchanger parts are traceable to material test reports

3 Verification that welding procedures and preheat requirements are being followed

4 Visual inspection of all welds for flaws, contour, size, and reinforcement

5 Reading all radiographs (“x-rays”) and witnessing other nondestructive nation, if required

exami-6 Complete dimensional and orientation check against Company reviewed vendor drawings

Fig 900-3 Application of the Degrees of Inspection for Shell and Tube Exchangers (1 of 2)

GUIDELINES FOR CHOOSING THE APPROPRIATE DEGREE OF INSPECTION

FOR SHELL AND TUBE HEAT EXCHANGERS

(NOTE THAT THESE ARE GUIDELINES ONLY)

Degree 1 when:

1 No Company specification applies, and

2 Exchanger:

a is small and simple (under 18 inch diameter), and

b is carbon steel (tubes can be another material), and

c has low pressure rating (under 250 psig), and

d is not in flammable or hazardous services.

Degree 2 when:

1 No Company specification applies, and

2 Exchanger:

a is of moderate size (18 inch to 30 inch diameter), and

b is carbon steel (tubes can be another material), and

c has low pressure rating (under 250 psig).

OR

3 Only one low dollar value hair-pin type exchanger is on a purchase order (an attempt is made to accomplish Degree 2 inspection in one visit to include inspecting parts, witnessing assembly, and witnessing hydrostatic tests).

Degree 3 when:

1 Company specifications and/or standard drawings apply, and

2 Exchanger:

a is small and simple (under 18 inch diameter), and

b is carbon steel (tubes can be another material), and

c has low pressure rating (under 250 psig), and

d is in relatively noncritical service (choose at least Degree 4 for critical services).

Note “Critical Service” is difficult to define; judgment is required; factors to consider are type of service (contents of exchanger), consequences of failure with regard to the process, consequences of failure with regard to personnel and surrounding facilities.

Degree 4 (this is the normal minimum for exchangers in hydrocarbon service) when:

1 Company specifications and/or standard drawings apply, and

2 Exchanger:

a is of moderate size (18 inch to 30 inch diameter), and

b is carbon steel (tubes can be another material), and

c has moderate pressure rating (150 pound or 300 pound flanges), and

d is in relatively critical service.

Degree 5 when:

1 Company specifications and/or standard drawings apply, and

2 Exchanger:

a is of large size (over 30 inch diameter), and

b is carbon steel (tubes can be another material), and

c has moderate pressure rating (150 pound or 300 pound flanges), and

d is in relatively critical service

Degree 6 when:

1 Company specifications and/or standard drawings apply, and

2 Exchanger:

a is of large size (over 30 inch diameter), and

b is carbon steel (tubes can be another material), and

c has shell thickness 3/4 inch or more, and

d has moderate pressure rating (150 pound or 300 pound flanges), and

e is in relatively critical service.

Degree 7 (same as Degree 6 but when diameter, thickness of tubesheet, or tubesheet material warrants a visit for

tubesheet/baffle inspection before installing tubes; this visit should always be made for tubesheets that are clad,

weld overlayed, or will have tube/tubesheet welds, and can be considered for all moderate size and large size process exchangers.)

Degree 8 (same as Degree 7 but when surface preparation required for painting is “near-white” or “White

Metal.”)

Degree 9 (same as Degree 7 but when surface preparation required for painting is “near-white” or “White Metal”

and inspection of dry primer is judged to be warranted.)

Degree 10 when:

1 Exchanger:

a fabrication time is over 6 weeks, or

b is very large (over 4 feet diameter), or

c has wall thickness over 1-1/4 inch, or

d has a high pressure rating (flanges 600 pound or more), or

e is fabricated from low alloy or high alloy steels.

f is fabricated from clad or weld overlayed material.

Degree 11 (Resident inspection is rarely applied to heat exchangers but could be considered during fabrication of

heavy wall shells or channels; heavy wall means over 4 inches thick.)

Fig 900-3 Application of the Degrees of Inspection for Shell and Tube Exchangers (2 of 2)

7 Verification that all nozzles are present, and that they are correct size, rating, and material.

8 Verification that bundle has all required baffles and support plates, and that baffle and tubesheet holes have been deburred; verification that tubes have been properly expanded into tubesheet holes

9 Review of Manufacturer’s Data Report to verify all entries are correct

920 Inspection of Existing Shell and Tube Exchangers and Air Cooled

Exchangers

921 The Inspection, Engineering, Operation, and Maintenance Team

While much of the standard maintenance work on exchangers is initiated by tion, the major decisions must be made with input from inspection, engineering, operations and maintenance These decisions include:

inspec-• Retubing or rebundling

• Plugging tubes

• Nozzle replacement

• Major shell repairs or replacement

• Gasket surface repairsThe above organizations also must work together to establish the objectives of exchanger repairs well in advance of the shutdown These objectives include:

• Exchanger or bundle design life

• Time between internal inspections (for some cases, this is determined by state regulations; i.e., waste heat boilers)

• Degree of internal or external leakage which is acceptable over the life of the bundle

• Degree of cleaning required (often dictated by process economics)Section 1000 contains a Heat Exchanger Bundle Repair Worksheet for helping the engineer coordinate the decision making process

922 Inspection Sequence

Inspection of existing exchangers and air coolers involves the following steps:

1 Set objectives as discussed above

2 Examine inspection and maintenance records to note any trends and make initial recommendations

3 Perform preshutdown inspection to note leaks and any areas which must be inspected in more detail when the unit is shut down.

4 Determine need for bleeder tests prior to opening

5 Inspect and photograph shell and bundle after exchanger has been opened but before cleaning to look for patterns and types of fouling and evidence of plugged tubes

6 Inspect shell and bundle after cleaning and make recommendations for repairs

7 Inspect repairs and witness testing

8 Record gagings and repairs in the inspection file to anticipate what to expect in the future

9 Process paperwork for any code repairs or operating permits for state tered equipment

regis-Section 970 contains a detailed inspection checklist for exchangers and air coolers

923 Double Pipe Exchangers

Double pipe or “hairpin” exchangers can be one pipe or several pipes inside another pipe In either type of exchanger the corrosion is usually found in the area of the inlet nozzle and at the return bend

All these units are usually small enough in diameter to radiograph Radiography can reveal the inner and outer pipe wall thickness, tube-wall thickness, and any fouling problem, without taking the unit out of service Most repair work can there-fore be planned before the plant is actually shut down

In one double pipe exchanger, called a “chiller,” the stock in the inner pipe is scraped using a scroll, and corrosion is usually found externally because of low temperature conditions The scrolls may also break or become disconnected

924 Inspection of State Registered Unfired Steam Generators

Like fired boilers, unfired steam generators require periodic inspection and state certification by qualified boiler inspectors Generally, unfired steam generators are

of tubular heat exchanger design Consequently, inspection and repair follow the same general pattern as that used for process heat exchangers

1 The tube bundles are removed, cleaned, and inspected externally and internally

2 The shells and flash drums are internally inspected and ultrasonically gaged

3 The gage glasses, pressure gages and alarms are cleaned and serviced The safety valves are removed, cleaned, tested and reset

4 Hydrostatic tests, when applied, should include the flash drum, if any, and all interconnected piping and appurtenances