WELDING PARAMETER CHECKING

Welding parameter check may be applied after to have verified the first production coupon weld soundness.

Before starting fabrication Contractor shall submit to Client's approval the procedure and checking methods that he intends to use to this purpose. Welding parameters checks shall be continuous all over the production. Client anyway may require a production test coupon whenever he considers necessary.

Acceptability of welding parameter checking procedure is solely to Client.

6 FABRICATION

6.1 GENERAL

All fabrication and erection shall be in accordance with these specification requirements.

Work shall not be performed when weather does not permit satisfactory workmanship or when particular conditions prevent adequate inspection.

Fabrication shall proceed on a flat and level surface and frequent checks shall be made on the supports and blocking, and any movement out of the level shall be immediately rectified by appropriate shimming to re establish a level plane.

The Contractor shall survey and control dimensions before fit-up for welding of additional components and sections. Dimensions shall be checked at each stage in accordance with the fabrication procedure, tolerances (if given) and the final survey shall meet the defined tolerances. The Contractor shall submit his dimensional control procedures indicating proposed methods of monitoring dimensions, their tolerances compatibility and construction method philosophy to the Client before commencing fabrication.

6.2 FORMING

6.2.1 Tubular fabrication

Tubular may be formed with calendar rolls axis both parallel or orthogonal to the longitudinal axis of the plate (plate rolling direction).

Tubular may be re rolled after welding in order to reduce deformations. In this case WPQ mechanical testing shall be performed in the same final condition, in order to demonstrate that the joint is not impaired by the re rolling process. Re rolling carried out with an equipment type different from that used for forming shall be subject to Client's approval.

6.2.2 General

Contractor is to qualify each complete forming process, including final re forming calibration process, when forseen.

Qualification shall be carried out within the terms and as specified in paragraph 6.2.7.

The forming shall be not carried out in the temperature range from 200 to 450°C or above 800°C. TM steel shall not be hot formed, i.e. above 600°C.

For TM steels Contractor shall seek the advice of the steel-maker before start any warm forming activity.

6.2.3 Surface preparation

Plates having surface condition that may impair the forming operation or which may have scale incorporated into its surface shall be restored by blasting, SA 2 level, before forming.

All defects that may appear after forming shall not exceed 3mm in depth.

6.2.4 Cold forming

Cold forming is considered the forming carried out at ambient temperature.

When the cold forming is executed on plates which have already pass successfully through the ageing test foreseen in the specification 08832 STR-MME-SPC " OFFSHORE PLATFORMS - Steel for structure" Rev.7 and the true deformation is higher, the plate shall be submitted to a new ageing test with a strain value not less than the real one, or to a thermal relieving treatment. For assembled elements, the relieving treatment can be executed just before the start of operations.

When the cold forming is executed on a plate which has not been submitted to any ageing test, and the actual diameter/thickness ratio is less than 30, one plate for eache heat / steel quality and thickness shall be submitted to an ageing test with a deformation value not less than the real value; as an alternative, the item shall be submitted to a thermal relieving treatment before the start of operations.

In all the other cases, cold forming can be carried out on plates without any additional test.

6.2.5 Warm forming

Forming processes carried out from 450°C up to 600°C shall be considered as "warm forming".

6.2.6 Hot forming

Hot forming is carried out beyond 600°C up to 800°C.

TM steels should not be hot formed.

Forming process shall be followed by normalization heating treatment to restore the mechanical steel characteristics

All forming processes, heat treatment included, shall be carried out according to a procedure previously approved by the Client.

6.2.7 Qualification of the forming procedure

Each forming process, including cold re rolling for tube calibration after welding, shall be qualified with the tube in its final condition.

For this purpose, an element of welded tube shall be carried out for every grade and quality of steel according to the proposed procedure, subsequent welded according to that foreseen by the fabrication specification and cold sizing, including re rolling where used.

The local deformation at weld level shall be measured by a straight gouge 300mm long, measuring the gap between the weld and gouge itself. Deformations greater than qualified value shall require new qualification.

The length of the sample shall be equal to the diameter of the tube used and can not be less than 1m.

From the sample coupon shall be obtained in order to carried out the tests indicated in table 6.1.

TABLE 6.1: TYPE AND TEST NUMBER

Thickness Type and number of tests

< 16 mm 1 set for KCV impact test (1) 1 tensile test on base material

3 macro and hardness on base material and HAZ (2)

> 16 mm 2 set for KCV impact test (1) 1 tensile test on base material

3 macro and hardness on base material and HAZ (2)

Note: (1) Impact test specimen set (KCV) shall be taken at 2 mm under the surface with axis perpendicular to the longitudinal tube axis. Specimen shall be taken on base material close to the welding. First specimens set shall be taken from the outer surface, the second specimens set shall be taken from the inner surface.

(2) Test shall be carried out on base material and HAZ with at least three readings for each test

The tests and requisite conditions shall be the same as those described in paragraph 3.6 for the grade and quality steel on test.

Previous qualifications accepted by Client avoid new qualification.

6.2.8 Validity limits of forming qualifications procedure

The forming procedure is valid within the following limits:

 same fabricator;

 steel grade lower than those qualify;

 impact properties lower than specify;

 same manufacturing process;

 D/t ratio greater than the qualification value;

 cold expansion rate or deformation after welding restored by the re-rolling not beyond the tested value;

 same calender process.

6.2.9 Hot Straightening

Hot straightening may be applied to recover excessive deformations caused by welding or stress relieving. All class "a" elements, jacket legs, deck legs, jacket nodes and padeyes shall not be submitted to hot straightening in any care. Hot straightening shall be carried out to a Client's approved procedure.

The following requirements shall be fulfilled:

 gas torch may be used, but heated areas shall not be larger than 60mm;

 maximum temperature shall not be greater than 550°C and shall be kept under full control at least by means of portable contact thermocouple;

 steels with 500MPa tensile strength, or higher, shall not be fast cooled, by water or other means.

 Follow the advice (recommended practice) provided by the steel manufacturer;

 The heating should be rapid, in order to introduce as little heat as possible, and to limit the amount of heat that is conducted away from the zone to be heated;

 If possible utilize mechanised equipment to moving of the heat source;

 The depth of the visible HAZ in a transverse macrosection should not exceed 2.5 mm;

 Conduct a qualification test of the flame straightening procedure in question. The qualification test should incorporate:

- metallographic examination, - hardness measurements, - impact test ,

- tensile test.

All hot straightening operations shall be witnessed by Client.