Appendix 3-2 Guidance for non-destructive inspection for construction of offshore structure

1. Applications

Theses requirements apply structure.

to radiographic and ultrasonic inspection for construction of offshore

2. Extent of Inspection of Welds

(1) General

(A) The minimum extent of nondestructive testing to be conducted is indicated in (4) or (5) below. The distribution of inspected welds is to be based on the classification of application of the welds, as mentioned in (3) and the variety of weld sizes used in the structure.

(B) Nondestructive testing is generally to be carried out after all forming and postweld heat treatment, and procedures should be adequate to detect delayed cracking. Welds which are inaccessible or difficult to inspect in service are to be subjected to increased levels of non- destructive inspection.

(C) Nondestructive examination of full penetration butt welds is generally to be carried out by

radiographic or ultrasonic methods. Where a method(such as radiography or ultrasonics) is selected as the primary nondestructive method of inspection, the acceptance standards of such a method govern.

(D) Where inspection by any method indicates the presence of defects that could jeopardize the integrity of the structure, removal and repair of such defects are to be carried out to the satis-faction of the attending Surveyor.

(E) Should the ultrasonic method be used as the primary inspection method, such testing should be supplemented by a reasonable amount of radiographic inspection to determine that ad- equate quality control is being achieved.

(F) To assess the extent of surface imperfections in welds made in Group III steels used in critical structural locations, representative inspection by the magnetic-particle or dye-penetrant method should also be accomplished.

(2) Plans

A plan for nondestructive testing of the structure is

but not be restricted to. visual inspection of all dye- penetrant inspection of tee and fillet welds not

to be submitted. This plan should include,

welds, representative magnetic-particle or subjected to ultrasonic inspection, and the

inspection of all field welds by appropriate means. The extent and method of inspection are to

be indicated on the plan, and the extent of inspection is to be based on the function of the structure and the accessibility of the welds after the structure is in service. For automated welds

for which quality assurance techniques gree of inspection may be permitted.

(3) Classification of Application

Welds are to be designated as being function and severity of service of the

indicate consistent satisfactory performance a lesser de-

either special, primary or secondary depending on the structure in which the welds are located. Special welds

are those occurring in structural locations of critical importance to the integrity of the structure

or its safe operation. Secondary welds are those occurring in locations of least importance to the overall integrity of the structure. Primary welds are those occurring in locations whose im-

portance is intermediate between the special and secondary classifications. Reference can be made to Appendix 3-1 for examples of applications following this classification system.

(4) Extent of Nondestructive inspection - Steel Jacket Type Structures

In general, the number of penetration type welds(i.e., butt, T, K and Y. joints) to be inspection each classification is to be based on the percentages stated below. Alternatively, the extent of radiographic and ultrasonic inspection may be based on other methods, provided the alternative will not result in a lesser degree of inspection. Where the extent of welds to be inspected is stated as a percentage, such as 20% of primary welds, this means that complete inspection of 20% of the total number of welds considered to be primary is required.

(A) All welds considered special are to be inspected l00% by the ultrasonic or radiographic method.

(B) Twenty percent of all welds considered primary are to be inspected by the ultrasonic or ra-

diographic method.

Ch3 Materials and Welding Ch 3

(C) Welds considered to be secondary are to be inspected on a random basis using an appro- priate method.

(D) In locations where ultrasonic test results are not considered reliable, the use of magnetic-par-

ticle or dye-penetrant inspection as a supplement to ultrasonic inspection is to be con-ducted. For T, K, or Y joints, approval may be given to substituting magnetic-particle or dye-pene- trant inspection for ultrasonic inspection when this will achieve a sufficient inspection quality.

(E) Magnetic-particle or dye-penetrant inspection of fillet welds is to be accomplished for

- all permanent fillet we1ed in jacket construction

- all jacket-to-pile shim connections, and

- all fillet welds in special application ares the deck structure.

- The random inspection of other deck fillet welds is to be carried out at the discretion of

the Surveyor.

(5) Extent of Nondestructive Inspection Steel Plate or Shell Type Structures

The minimum extent of the ultrasonic or radiographic inspection of plate or shell type structures

is to be equivalent to, or in general agreement with, the number of check points obtained by the following equations. As practicable, the length of each checkpoint is to be at least 750 mm.

(A) For structures which are rectangular in shape

Ÿ G ÄFA ĞǼFĤĖÈĦÈ

where,

Ÿ = number of check points (2 is minimum number) Ä = length of greatest dimension of structure, in m A = greatest breadth, in m

Ǽ = greatest depth at the center, in m

(B) For structures which are other than rectangular a proportional number of check points should be supplied.

(C) For structures which are circular in shape

Ÿ G ÄẀĤĖÈĦÈ

where,

Ÿ = number of check points(2 is minimum number)

Ä = length of the circular structure, in m

Ẁ = diameter of the circular structure, in m

(6) Additional Inspection - Special Conditions

Additional inspection may be required depending on the type and use of the structure, the mate- rial and welding procedures involved, and the quality control procedures employed.

(7) Additional Inspection - Production Experience

If the proportion of unacceptable welds becomes abnormally high, the frequency of inspection is to be increased.

(8) High Through Thickness(Z-Direction) Stresses

At important intersections welds which impose high stresses perpendicular to the member thick- nesses(Z-direction loading) are to be ultrasonically inspected to assure freedom from lamellar tearing after welding.

Ch3 Materials and Welding Ch 3

3. Acceptance Criteria

As stated in 202. 4 recognized acceptance criteria such as those issued by the AWS are to be employed. When employing Guidances relating to Pt 2, Annex 2-9 of Rules for Classification of Steel Ships "Guidance for Radiographic and Ultrasonic Inspection of Hull Welds", Class 1 and Class 2 criteria are to be applied as follows.

(1) Class 1

Acceptance criteria are to be used for special application structure and critical locations within primary application structure such as circumferential welds of cylindrical and built up columns or legs, weld intersections of external plating in platforms, etc.

(2) Class 2

Acceptance criteria are to be used for primary application structure where Class 1 acceptance does not apply

(3) Class 3

Acceptance criteria are to be used for secondary application structure

(4) When radiographic or ultrasonic inspection is specified for other types of connections, such as partial penetration and groove type tee or corner welds, modified procedures and acceptance cri-

teria are to be specified which adequately reflect the application.

Ch 4 Design of Structures Ch 4