Procedure For Steel Structure Fabrication

This procedure is developed in order to achieve the fabrication program with proper handling and problem solving during prefabrication, assembly and installation of standard specifications, codes and codes of structural steel systems.

Shop drawing shall be developed in accordance with client approved for construction drawings, specifications and codes. On the shop drawings shall be shown all information of shop and yard assembly, welding symbols and details, detail of connections and material list with piece marks and materials shall be included and incorporated. The accuracy of dimensions shown on shop drawings shall be properly concerned.

Material

1. Prior to take any further action the designated material for designated project activities shall be inspected first to ensure the material grade, sizes, thickness, condition and types are met to specified requirement (see BDM QA/QC Manual)
2. Certificate of each material shall be available where required.

Mold Lofting

Mold Lofting shall be drawn on detailed structure of the main portion based upon shop drawing. In case any difficulty comes up during fabrication, inadequate portion of shop drawing shall be reviewed and revised.

• Template : Plastic Sheets of approx. 0.3 mm thk.
• Tapes : Steel hoops of 0.55 mm thk by 19 mm width.

Marking

1. Cutting lines, center lines, working points, bolt holes, etc. shall be marked on steel members by mean templates and tapes.
2. In case of tubular members are welded with other structural members, marking shall be performed so that welded joint of the structural members will not be on the longitudinal seam of the tubular while of circumferential slices of tubular members, the longitudinal seams of adjoining rolled plates shall not be in line, but minimum 90o. Circumferential and longitudinal seams shall be shown on shop drawing.
3. Except for hole drilling portion, marking shall be made by mean punch and chisel, ink and marking are not required. The radius of tip punch shall be minimum of 0.8 mm.
4. Heat number for HSS (High Strength Steel) materials shall be transferred during marking or before cutting off.

Fabrication

Cutting 

a. Cutting of bevelling shall be performed by using Automatic Gas Cutting Machine (over 1/4” thk) or shear cutting machine ( up to 1/4”)

b. Cutting of steel piles shall be performed by using Semi Automatic Pipe Cutting Machine and bevelling by using Semi Automatic Cutting Machine or Manual Gas Cutter.

c. Cutting of steel shapes shall be performed by using Saw or Automatic Cutting Machine

d. Slugs, notches and burns cut and bevelled surface shall be removed. In case notches depth on bevelled surfaces are over 1 mm, it shall be repaired by welding and finished by grinding.

e. Accuracy of cutting curves shall be inspected/evaluated by comparing the edge of cut and coped pipes to the templates or model or leg pipes, if necessary.

Bevelling

a. Bevelling shall be performed by using Semi Automatic Cutting Machine for girth weld joints or manual gas cutter for TKY joints, grinding shall be done on surface finishing of roughness beyond the acceptance limit specified in AWS 3.5.4.

b. For rusty bevelled surface, it is necessary to brushed clean prior to welding. 

c. NDE (UT/MPI/PT) will be applied where required.

d. Lamination check shall be performed on thick materials where required or if any lamination found the material shall be rejected/replaced.

Drilling and Finishing

a. Drilling of small diameter hole shall be made with drill process. Hole section shall be de-burred.

b. Hole diameter shall be 1/16” bigger than bolt diameter itself.

c. Roughness of hole surface shall be max. 100 s

d. The edges/tip of steel material shall be removed and grinding smooth prior to coating

Assembling

Assembling shall be carried out according to the following requirements :

Level

(1) Assembly of structural steel shall be performed on levelled and fixed supports. Sufficient check of blocking and level shall be performed, i.e. after each setting of major structural or mechanical assemblies or if there is evidence of instability of supporting working surface, when any portion the structure settles out if level, then the settled section shall be re-levelled by shimming on bottom surface, or other action required.

(2) Provision shall be made for correction of alignment at any stage the fabrication.

Tack Welding

Tack welding for assembly purpose shall be carried out in accordance with the following:

(1) Length of weld for joining pieces shall be min. 40 mm.

(2) Length to tack weld in level shall be min. 40 mm prior to root pass. Both ends of tack weld shall be grinned.

(3) Tack welding shall be performed by qualified welders or tack welder. Quality of welding electrodes for tack welding shall be in accordance with WPS.

Root Opening

Root opening for assembly purposes shall be in accordance with the following :

(1) Fillet Welding 

* Gap is maximum 1/16” (1.6 mm)

* If the gap is equal or greater than 1/16”, the filled weld size shall be increase by amount of the gap but not exceed 3/16”.

(2) Groove Welding

* Root opening : 1/16" up to 1/8" of specified root gap for joint penetration

* Root face : 1/16", 1/32" of specified root face for joint penetration

Fit-up Procedure

(1) Fit up Leg, Pile, and Conductor Component Prior to set up the leg, pile and conductor components on the support or turning roller, all support or turning roller shall be levelled and aligned. Each components shall be fitted to minimize the offset and tack welded by using SMAW after straightness check of leg, pile and conductor have completed.

(2) Fit-up Brace Component Each brace components shall be fitted by means of outer clamps to minimize the offset and tack welded using SMAW when straightness checking have completed.

(3) TKY Tubular Joints

All bracing where the ends points are shaped and have dimension shall be erected so that the end points are within +1/2” of design dimension. Braces shall be fitted to the leg in order to specify gap in between. When completed the gap, location and dimension checking, braces shall be tack welded to the leg by minimum 1 pass at each location. Tack weld shall be done by qualified welders.

(4) Fit-up Deck Framing Components

Each Deck Framing Components shall be fitted in order to meet proposed WPS. Temporary supports will be used for Deck Framing fit up. Keep level and alignment of panel is a must.

Dimensional Check and Levelling

Maintaining dimensional and levelling during fabrication is a must.

Welding

Control of Welding Material

(1) Electrodes for manual shielded metal welding shall be dried in accordance with manufacturer’s requirement before used.

(2) Material Certificates

All welding materials for this work shall be confirmed with manufacturer’s certificates in order.

Welding Detail

See “Welding Procedure Specification”

Drying of Welding Metal

Low hydrogen electrode can only be used after drying with control method stipulated in AWS 3.8.1. These electrodes shall be kept dry in portable container.

Cleaning of Welded Zone

Before commencing weld over the previous deposit metal, all slag shall be removed. The welded and adjacent base metal shall be clean brushed.

Pre-heating

Prior to tack weld and during welding process of the assembly, pre-heating at certain temperature shall be maintained in accordance with the following table. The pre-heating are shall extent to minimum 3” from welded zone. Pre-heating temperature shall be controlled by using temperature chalk stick.

Welder

Welder which will be employed for this job must be qualified by AWS Qualification Test. Welder qualification test may be waived documented with evidence that the welder has been qualified in accordance with AWS D1.1. ‘95 and must satisfy the period of effectiveness requirements of AWS D1.5.30. Welders identification for each welding shall be done by marking on the weld and recorded on a sheet.

Repair Of Defected Zone

The following procedure shall be applied for repairing the defected zone

Efect range on steel surface is visually clear To be welded and finished by grinder, minimum welding bead.

Defect range on steel surface is not clear After removal of defect zone using air gouging, it shall be repaired by welding and grind finishing

Arc Strike When arc strike occurs on base metal. it shall be repaired by welding and grind finishing

Crack on welding zone Welding metal including the crack shall be removed out and re-weld.

Undercut more than depth specified by AWS D1.1 shall be repaired by using welding. Minimum bead length shall be 40 mm.

Temporary Attachment

(1) Temporary attachment shall be welded to the structure with applying the same procedure as permanent weld.

(2) All temporary attachment shall be grind flush when removed to the original surface.

(3) NDE (UT/MT/PT) shall be applied where required.

Quality Control And Inspection

1 The contractor QC is responsible for the quality and ensuring all the work are performed and compliance with client requirement and approved procedures.

2 The contractor QC shall perform inspection of all material and fabricated item (see PAS quality manual for the detail).

3 The contractor QC inspector shall accompany client Inspector Rep and response the comment if required.

Safety

1 All crew shall aware and implement of PAS Safety Procedure and client safety requirement.

2 Personnel Protective Equipment (PPE) shall be provided and worn during performing the work at work location.

3 All equipment shall be in good condition, safe and operable.

4 Supervisor at site should monitor closely and regularly of all safety aspect during at site and the work activity.

5 First Aid Equipment and medicine shall be available at site all time.

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