API 653: Tank Inspection, Repair, Alteration, and Reconstruction

Question 1

What type of weld joint must be used when reconstructing a tank shell? (API 653-14, Section 8.2.2)

Answer 1

All new shell joints shall be butt-welded joints with complete penetration and complete fusion.

Question 2

What should be the minimum dimension for a replacement shell plate? (API 653-14, Section 9.2.2.1)

Answer 2

The minimum dimension for a replacement shell plate is 12 in. or 12 times the thickness of the replacement plate, whichever is greater.

Question 3

What are acceptable shapes for replacement shell plates? (API 653-14, Section 9.2.2.1)

Answer 3

The replacement plate may be circular, oblong, square with rounded corners, or rectangular with rounded corners except when an entire shell plate is replaced.

Question 4

Prior to welding new vertical joints, what must be done to existing horizontal welds that contact the new vertical joint? (API 653-14, Section 9.2.2.2)

Answer 4

Prior to welding the new vertical joints, the existing horizontal welds shall be cut for a minimum distance of 12 in. beyond the new vertical joints.

Question 5

When installing a replacement shell plate, which joints (vertical or horizontal) should be welded first? (API 653-14, Section 9.2.2.2)

Answer 5

The vertical joints shall be welded prior to welding the horizontal joints.

Question 6

What type of joint should be used to install shell replacement plates? (API 653-14, Section 9.2.3.1)

Answer 6

Shell replacement plates shall be welded with butt joints with complete penetration and complete fusion, except as permitted for lapped patch shell repairs.

Question 7

How far from the edge of a weld joint in the annular plate ring or sketch plate must the edge of any vertical weld attaching a replacement plate be? (API 653-14, Section 9.2.3.3)

Answer 7

For shell plates of unknown toughness not meeting the exemption criteria of Figure 5.2, the edge of any vertical weld joint attaching a replacement plate shall be at 3 in. or 5t from the edge of a weld joint in the bottom annular ring or 18 weld joints in bottom plates under the tank shell.

Question 8

What may be used for the closure of holes caused by the removal of existing shell openings or by the removal of severely corroded areas? (API 653-14, Section 9.3.2)

Answer 8

Lapped patch repair plates may be used for the closure of holes caused by the removal of existing shell openings or the removal of severely corroded or eroded areas.

Question 9

What two items must be entirely removed prior to installation of a repair plate? (API 653-14, Section 9.3.2.2)

Answer 9

Nozzle necks and reinforcing plates shall be entirely removed prior to installation of a repair plate.

Question 10

How can lack of fusion in a weld be repaired? (API 653-14, Section 9.6.1)

Answer 10

Cracks, lack of fusion, and rejectable slag and porosity that need repair shall be removed completely by gouging and/or grinding and the resulting cavity properly prepared for welding and then welded.

Question 11

How should unacceptable surface defects, such as arc strikes, discovered in or adjacent to welded joints be repaired? (API 653-14, Section 9.6.5)

Answer 11

Unacceptable surface defects shall be repaired by grinding and/or welding.

Question 12

In a replacement shell penetration larger than NPS 4, what should be the diameter of the insert plate? (API 653-14, Section 9.8.6)

Answer 12

The minimum diameter shall be at least the greater of:

a) twice the diameter of the opening in the insert plate that accommodates the radial oriented nozzle, or
b) the diameter of the opening in the insert plates plus 12 in.

Question 13

If a new tank bottom is installed above an existing bottom, the spacing between existing welds around penetrations and the new bottom-to-shell weld may not meet API 650 requirements. What are three ways of altering the penetrations to meet API 650? (API 653-14, Sections 9.9.2 through 9.9.2.3)

Answer 13

1) The existing reinforcing plate may be trimmed to increase the spacing between the welds provided that the altered detail complies with the requirements of API 650, Section 5.7.
2) The existing reinforcing plate may be removed and a new reinforcing plate added except that reinforcing plate replacement is not permitted in existing stress relieved assemblies unless the requirements of 11.3 are met.
3) The existing penetration may be moved by cutting the section of the shell containing the fitting and reinforcing plate, and raising the entire assembly to the correct elevation (see Figure 9.9).

Question 14

What areas constitute the “critical zone” for repairs to tank bottoms? (API 653-14, Section 3.10)

Answer 14

The portion of the tank bottom or annular plate within 3 in. of the inside edge of the shell, measured radially inward.

Question 15

What types of repairs are NOT allowed in the tank bottom critical zone? (API 653-14, Section 9.10.1.2)

Answer 15

No welding or weld overlays are permitted within the critical zone except for the welding of: widely scattered pits (see 4.3.2.2), pinholes, cracks in the bottom plates, the shell-to-bottom weld, welded-on patch plates, or where the bottom plate welded to the shell is being replaced.

Question 16

What types of repairs are allowed in the tank bottom critical zone? (API 653-14, Section 9.10.1.2)

Answer 16

Welded on patch plates.

Question 17

When replacing an entire tank bottom, what type of material should be used as a cushion between the old and new bottoms? (API 653-14, Section 9.10.2.1.1)

Answer 17

Suitable noncorrosive material cushion such as sand, gravel, or concrete shall be used between the old bottom and the new bottom.

Question 18

When replacing an entire tank bottom, what procedures must be followed when installing and attaching the new bottom to the existing shell? (API 653-14, Section 9.10.2.1.2)

Answer 18

The shell shall be slotted with a uniform cut made parallel to the tank bottom. The cut edges in the slot shall be ground to remove all slag and burrs from cutting operations. The new bottom plate shall extend outside the shell as required by API 650, Section 5.4.2. All rules for weld spacing shall be followed.

Question 19

When replacing an entire tank bottom, what should be done with voids in the foundation below the old tank bottom? (API 653-14, Section 9.10.2.1.3)

Answer 19

Voids in the foundation below the old bottom shall be filled with sand, crushed limestone, grout, or concrete.

Question 20

What should be the minimum thickness of new roof plates for a supported cone roof? (API 653-14, Section 9.11.2.1)

Answer 20

The minimum thickness of new roof plates shall be 3/16 in. plus any corrosion allowance as specified in the repair specifications.

Question 21

What should be the nominal thickness of new roof plates for self-supporting roofs? (API 653-14, Section 9.11.3.1)

Answer 21

The nominal thickness of new roof plate shall be 3/16 in. or the required plate thickness given in API 650, Section 5.10.5 or Section 5.10.6, plus any specified corrosion allowance, whichever is greater.

Question 22

What should be the minimum height of tank liquid above a hot tap location? (API 653-14, Section 9.14.1.2)

Answer 22

The minimum height of tank liquid above the hot tap location shall be at least 3 ft during the hot tapping operation.

Question 23

What type of electrode should be used for hot tap welding? (API 653-14, Section 9.14.1.3)

Answer 23

Welding shall be done with low hydrogen electrodes.

Question 24

What defects in shell plate preclude the installation of hot taps? (API 653-14, Section 9.14.1.5)

Answer 24

Hot taps shall not be installed on laminated or severely pitted shell plate

Question 25

Hot taps are not permitted where the heat of welding may cause __________ (API 653-14, Section 9.14.1.6)

Answer 25

Environmental cracking (such as caustic or stress corrosion cracking)

Question 26

When preparing for a hot tap installation, how many shell thickness measurements shall be made? Where should they be made? (API 653-14, Section 9.14.3.2)

Answer 26

Shell plate thickness measurements shall be taken at a minimum of four places along the circumference of the proposed nozzle location.

Question 27

After completing the welding portion of the hot tap procedure, what pressure should be used to test the nozzle prior to mounting the hot tap machine? (API 653-14, Section 9.14.5.3)

Answer 27

After the valve has been installed on the flange, a pressure test at least 1.5 times the hydrostatic head shall be performed on the nozzle prior to mounting the hot tap machine, which shall be bolted to the valve.

Question 28

When bottom plates are to be reused, how should they be cut? (API 653-14, Section 10.3.2.1)

Answer 28

Bottom plates that will be reused shall be cut by deseaming of lap welds; or by cutting alongside of the remaining welds at a minimum of 2 in. away from existing welds, except where cuts cross existing weld seams.

Question 29

When roof plates are to be reused, how should they be cut? (API 653-14, Section 10.3.4)

Answer 29

Roof plates shall be cut by deseaming of lap welds, or by cutting alongside of the remaining welds at a minimum of 2 in. away from existing welds, except where cuts cross existing welds.

Question 30

If an entire tank bottom is to be reused in a reconstructed tank, how should the bottom be separated from the existing shell if there is no existing butt welded annular ring? (API 653-14, Section 10.3.2.2)

Answer 30

The bottom may be cut 12 inches from the shell, leaving the shell with part of the bottom (annular region) attached

Question 31

When shell plates are to be dismantled and reused, what are three ways in which they can be cut? (API 653-14, Section 10.3.3.1)

Answer 31

1) Any shell ring may be dismantled by cutting out existing weld seams and the heat affected zone (HAZ) of the weld. For the purpose of this method, the minimum HAZ to be removed will be 1/2 of the weld metal width or 1/4 in., whichever is less, on both sides of the weld seam.
2) Any shell ring 1/2-in. thick or thinner may be dismantled by cutting through the weld without removing the HAZ.
3) Shell rings may be dismantled by cutting vertical and/or horizontal cuts through the shell a minimum of 6 in. away from existing welds, except where cuts cross existing welds.

Question 32

If shell stiffening rings are removed, what must be done to the temporary attachment points? (API 653-14, Section 10.3.3.2)

Answer 32

The area where temporary attachments are removed shall be ground flush with the shell plate.

Question 33

If a tank shell is to be dismantled for reuse with a new bottom, where should the shell be cut from the existing bottom? (API 653-14, Section 10.3.3.3)

Answer 33

The shell shall be cut a minimum of 1/2” above the bottom plate.

Question 34

When can the existing shell-to-bottom weld connection be reused in a reconstructed tank? (API 653-14, Section 10.3.3.3)

Answer 34

The existing shell-to bottom weld connection shall not be reused unless the entire bottom is to be reused intact.

Question 35

What provisions should be made with regard to joint alignment during the reconstruction of a tank? (API 653-14, Section 10.4.2.1)

Answer 35

Provisions shall be made during the reconstruction of a tank to ensure that weld spacing requirements of Figure 9.1 are maintained. New vertical joints in adjacent shell courses, made in accordance with 10.3.3.1, shall not be aligned but shall be offset from each other a minimum distance of 5t, where t is the plate thickness of the thicker course at the point of the offset.

Question 36

What should be done with tack welds used in the assembly of vertical joints on the tank shell when the joints are welded manually? (API 653-14, Section 10.4.2.7)

Answer 36

Tack welds used in the assembly of vertical joints of tank shells shall be removed and shall not remain in the finished joint when the joints are welded manually.

Question 37

What should be done with primer coatings on surfaces to be welded? (API 653-14, Section 10.4.2.8)

Answer 37

If weldable primer coatings have been applied on surfaces to be welded, they shall be included in welding procedure qualification tests for the brand, formulation, and maximum thickness of primer applied. All other coatings shall be completely removed from the weld area prior to welding.

Question 38

Which should be welded first: bottom plate joints or shell-to-bottom joints? (API 653-14, Section 10.4.3.2)

Answer 38

The welding of the shell to the bottom (except for door sheets) shall be completed prior to the welding of bottom joints.

Question 39

What is the maximum allowable vertical butt joint misalignment when the plate thickness is 5/8 inch thick or less? (API 653-14, Section 10.4.4.1)

Answer 39

Misalignment in joints 5/8-in. thick or less shall not exceed 1/16 in.

Question 40

At what interval must the welder’s identification mark be stamped along completed weld joints? (API 653-14, Section 11.2.2)

Answer 40

The welder or welding operator’s identification mark shall be hand- or machine-stamped adjacent to and at intervals not exceeding 3 ft along the completed welds.

Question 41

What method of nondestructive examination should be used to detect shell plate laminations when adding a hot tap connection? (API 653-14, Section 12.1.2.1)

Answer 41

Ultrasonic examination

Question 42

What type of nondestructive examination should be used to examine completed welds attaching a nozzle neck to the tank shell? (API 653-14, Section 12.1.2.3)

Answer 42

Completed welds attaching nozzle neck to shell, and reinforcing plate to shell and to nozzle neck, shall be examined by the magnetic particle or liquid penetrant methods.

Question 43

What type of nondestructive examination should be used to examine completed repairs of butt welds? How much of the weld should be examined? (API 653-14, Section 12.1.3.2)

Answer 43

Completed weld repairs of butt welds shall be examined over their full length by radiographic or ultrasonic methods.

Question 44

How should the first pass of the shell-to-bottom weld be inspected? How long should this procedure take? (API 653-14, Section 12.1.6.1)

Answer 44

The first weld pass shall be examined by applying light diesel oil to the side opposite the first weld pass made. The oil shall be allowed to stand at least 4 hours (preferably overnight) and then the weld examined for wicking action.

Question 45

What should be the minimum diagnostic length of a radiograph of a weld? (API 653-14, Section 12.2.1.7)

Answer 45

The minimum diagnostic length of each radiograph shall be 6 in.

Question 46

What is the minimum duration of a hydrostatic test for a reconstructed tank? (API 653-14, Section 12.3.2)

Answer 46

That liquid level shall be held for a minimum of 24 hours.

Question 47

What is a requirement for new vertical and horizontal shell butt-welds? (API 653-14, Section 12.2.1.6)

Answer 47

New and replaced shell plate and door sheet welds shall be radiographed. All junctions between repair and existing welds shall be radiographed. If defects are found, 100 % radiography shall be performed on the repaired weld.

Question 48

Major repairs and major alterations to a tank may require a full hydrostatic test. What are six examples of the type of work that is considered a major repair or major alteration? (API 653-14, Section 3.21)

Answer 48

1) installing a shell penetration larger than NPS 12 beneath the design liquid level;
2) installing a bottom penetration within 12 in. of the shell;
3) removing and replacing or adding a shell plate beneath the design liquid level where the longest dimension of the replacement plate exceeds 12 in.;
4) removing or replacing annular plate ring material where the longest dimension of the replacement plate exceeds 12 in.;
5) complete or partial (more than one-half of the weld thickness) removal and replacement of more than 12 in. of vertical weld joining shell plates or radial weld joining the annular plate ring;
6) installing a new bottom;
7) removing and replacing part of the weld attaching the shell to the bottom, or to the annular plate ring, in excess of the amounts listed in 12.3.2.5.1 a);
8) jacking a tank shell.

Question 49

Where on the tank must an air leak test be conducted? (API 653-14, Section 12.4)

Answer 49

New or altered reinforcing plates of shell penetrations shall be given an air leak test in accordance with API 650, Section 7.3.5.

Question 50

When surveying for tank settlement during a hydrostatic test, what is the minimum number of measurement points? (API 653-14, Section 12.5.2)

Answer 50

The minimum required number of settlement measurement points is D/10, but no less than eight.

Question 51

How should roof supporting structures be dismantled? (API 653-14, Section 10.3.4)

Answer 51

Roof supporting structures shall be dismantled by removing bolts (if bolted) or deseaming the structural attachment welds.

Question 52

What should be done with tack welds when vertical joints on the tank shell are welded with a submerged-arc process? (API 653-14, Section 10.4.2.7)

Answer 52

When such joints are welded by the submerged-arc process, the tack welds shall be thoroughly cleaned of all welding slag but need not be removed provided that they are sound and are thoroughly fused into the subsequently applied weld beads.

Question 53

What is the minimum duration of a hydrostatic test for a tank that has undergone major repairs? (API 653-14, Section 12.3.2)

Answer 53

A full hydrostatic test of the tank is not required for major repairs and major alterations.

Question 54

To what types of tanks does this standard apply? (API 653-14, Section 1.1.1)

Answer 54

This standard covers steel storage tanks built to API 650 and its predecessor API 12C. It provides minimum requirements for maintaining the integrity of such tanks after they have been placed in service and addresses inspection, repair, alteration, relocation, and reconstruction.

Question 55

In case of apparent conflicts between the requirements of API 650 and API 653, which standard shall govern? (API 653-14, Section 1.1.2)

Answer 55

In the case of apparent conflicts between the requirements of this standard and API 650 or its predecessor API 12C, this standard shall govern for tanks that have been placed in service.

Question 56

Do temperature cracks in concrete seriously affect the strength of the concrete foundation? What can temperature cracks in concrete eventually result in? (API 653-14, Section 4.5.1.2)

Answer 56

Temperature cracks (hairline cracks of uniform width) do not seriously affect the strength of the concrete foundation structure; however, these cracks can be potential access points for moisture or water seepage that could eventually result in corrosion of the reinforcing steel.

Question 57

What are the 12 historical causes of tank bottom leakage listed in this document? (API 653-14, Section 4.4.2)

Answer 57

1) internal pitting and pitting rates in the anticipated service;
2) corrosion of weld joints (weld and heat affected zone);
3) weld joint cracking history;
4) stresses placed on the bottom plates by roof support loads and shell settlement;
5) underside corrosion (normally in the form of pitting);
6) inadequate drainage resulting in surface water flowing under the tank bottom;
7) the lack of an annular plate ring when required;
8) uneven settlement that results in high localized stresses in the bottom plates;
9) roof support columns or other supports welded to the tank bottom where adequate allowance for movement was not made;
10) rock or gravel foundation pads with inadequately filled-in surface voids;
11) nonhomogeneous fill under the tank bottom (e.g. a lump of clay in a sand foundation pad);
12) inadequately supported sumps.

Question 58

During hydrostatic testing, when should the final settlement measurement be taken? (API 653-14, Section 12.5.3)

Answer 58

When a settlement survey is required in accordance with 12.5.1, tank settlement shall be measured during filling and when the test water reaches 100 % of the test level.

Question 59

What are three approaches that can be used to correct tank shell and bottom settlement? (API 653-14, Section B.1.3)

Answer 59

1) localized repairs of the bottom plates,
2) partial re-leveling of the tank periphery, and
3) major re-leveling of the entire tank bottom.

Question 60

Internal measurements of tank bottom settlement can be made in an out-of-service tank by measuring along the tank diameter. What should be the maximum spacing of these measurements? (API 653-14, Figure B.2)

Answer 60

Maximum spacing of 10 ft across diameter.

Question 61

Uniform tank settlement does not induce stresses in the tank structure. However, where can problems arise when a tank undergoes uniform settlement? (API 653-14, Section B.2.2.1)

Answer 61

Uniform settlement of a tank does not induce stresses in the tank structure. However, piping, tank nozzles, and attachments must be given adequate consideration to prevent problems caused by such settlement.

Question 62

Which type of settlement poses the most severe threat to the structural integrity of a tank shell and bottom? (API 653-14, Section B.2.2.4)

Answer 62

Out-of-plane settlement is the important component to determine and evaluate in order to ensure the structural integrity of the shell and bottom.

Question 63

What is edge settlement? (API 653-14, Section B.2.3.1)

Answer 63

Edge settlement occurs when the tank shell settles sharply around the periphery, resulting in deformation of the bottom plate near the shell-to-bottom corner junction.