Steel girders fabrication- Part 1 (Steel Bridge)

8/6/2019 Steel girders fabrication- Part 1 (Steel Bridge)

1/13

SITE VISIT (KKB FABRICATION YARD)

In the morning on 23th Feb 2011, a factory visited with JKR representative and contractor side toKKB fabrication yard to check on the progress of the steel girders fabrication.

The flow of the work sequence for the steelworks:1. Surface preparation

2. Prime coating

3. Cutting

4. Jointing (transverse weld-flange to flange)

5. Fitting/ fit up (Assembly)

6. Jointing (flange & web)

7. Painting & coating application

During the visiting on 23th & 29 Feb 2011, the overall progress is covering the item 1 to item 4,which jointing / welding got the flange to flange connection.

SURFACE PREPARATION:

Degreasing Any grease and dirt shall be removed by emulsion cleaner prior to start blastingwork.

Blasting Cleaning- All rough welds, burns, weld spatter, indentation and all sharp surface project shall be ground smooth and steel surface must be free from oil andgrease.

All basted surface shall be coated with in 4 hours. Oxidized surface shall be sweep blasted.


2/13

Shot blast machines by OMSG include an integral abrasive recovery and cleaning system.After passing through the blast wheel, the abrasive is collected, separated from the resultingdust and other contaminants, and then stored in a hopper, ready for reuse. Collectedcontaminants are stored in a separate hopper for periodic disposal.

Before After

The surface was clean and free of rust after steel shot blasting

In

O u t


3/13

PRIME COATING

The priming coat shall be applied to the surface immediately after cleaning is completed. The primer shall be capable of welding the steel surface and forming an adherent film on it to provide a base for the following coats.

International Intergard 251

A two component epoxy anti-corrostive premer pigmented withzinc phophate


4/13

Primer coat on the steel plate after steel shot blasting

CUTTING

Prior of cutting activities been carried out, proper cutting plan was submitted to minimize thewastage of the steel plates. As plates are cut up, each piece is marked for identification andmaterial traceability according to the heat no. shown on the parent plate.

During the factory visiting, we observed that all plate was cut by the Mechanized or automaticcutting which is widely used in production work where a large number of works. The portable flame cutting is more suitable for using in camber cutting.FLAME CUTTING MAECHINE

A machine cutting tourch, sometimes refered to as a blowpipe. Operates ina similar manner to hand a cutting torch but it is high consistantcy on thespeed and the supply of the gas. It may require 2 oxygen regulators, one for

perheat oxygeb and another for sutting oxygen stream. The addition of separator cutting supply allows the flame to be more accurately adjustedand allows the pressures to be adjusted during a cut without disturbingthe other parts of the flame.


5/13

FLAME CUTTING

The steel girders will be cut from plate by flame cutting equipment mounted on gantries. These

closely controlled techniques are generally accurate and efficiency is dependent largely on the process.Other components such as bracings should be detailed for simplicity with the aim of minimizingthe number of pieces to cut. Ends of bracings should be cut square rather than mitred and singlemembers should be used in preference to back-to-back members.

Variations in camber can arise in practice:

Fabrication pre-camber to allow for flame cutting and welding effects is difficult toachieve with precision due to the number of imponderables which are involved, includingthe residual stresses which exist in the material

The per-camber was marked / offset with the interval of 2.0m in order to obtain thedesired camber profile.

Mechanized or automatic cutting will cut along the per-setup gantries which match thecamber profile


6/13

The flame cutting was used in the preparation of the jointing with the ability of adjust the angleof cutting. The photo above shown the cutting of double bevel for the joint flange to flange

Portable flamecutting

Machine

cutting torchPre-setgantrie


7/13

PLATE EDGE PREPARATION FOR BUTT WELDS

The illustrations show standard terminology for the various features of plate edge preparationsfor the flange to flange joints


8/13

WELDING

The jointing of the bottom flange of 25mm steel plate was carried on. The transverse welds withthe runoff plate provided were prepared to weld.

Submerged arc welding (SAW)

Runof f

Transverse


9/13

This is probably the most widely used process for welding bridge web to flange fillet welds andin-line butts in thick plate to make up flange and web lengths. The process feeds a continuouswire into a contact tip where it makes electrical contact with the power from the rectifier. Thewire feeds into the weld area, where it arcs and forms a molten pool. The weld pool is submerged

by flux fed from a hopper. The flux, immediately covering the molten weld pool, melts forming

a slag protecting the weld during solidification; surplus flux is re-cycled. As the weld cools theslag freezes and peels away leaving high quality, good profile welds.

Solid wires of diameters from 1.6 to 4.0 mm are commonly used with granular fluxes.Mechanical properties of the joint and the chemistry of the weld are influenced by carefulselection of the wire/flux combination.

The process is inherently safer than other processes as the arc is completely covered during

welding, hence the term submerged; this also means that personal protection requirements arelimited. High deposition rates are a feature of the process because it is normally mechanized ongantries, tractors or other purpose built equipment. This maintains control of parameters and

provides guidance for accurate placement of welds.

Flux fed

Hopper

Moltenpool

Fed Wire

Mechanized ongantries

Runoff plate


10/13

GOUING

Back-gouging is the process to remove the weld metal and base metal from the side opposite of a partially welded joint to facilitate complete joint penetration. It can ensure 100% joint fusion atthe roof and remove the discontinuities of the root pass.

Gouging processesGouging operations can be carried out using the following thermal processes:

oxyfuel gas flame manual metal arc air carbon arc plasma arc

It is also an essential part of welding fabrication. Used for rapid removal of unwanted metal, thematerial is locally heated and molten metal ejected - usually by blowing it away. Normal oxyfuelgas or arc processes can be used to produce rapid melting and metal removal.


11/13

WELD MARKING

The complete weld flange o flange joint are ready for testing purpose. Each joint were markedwith the following

Jt No (Joint No) : BG1/3 (member mark)

Visual check : Acc (Accepted)

NDT(non destructive test) :UT(ultrasonic test) & MPI (magnetic particle inspection)


12/13

VISUAL CHECK (SURFACE CHECK)

Defects, which can be detected by visual inspection, can be grouped under five headings.1. Cracks.2. Surface irregularities.

3. Contour defects.4. Root defects.

SURFACE CRACKSA crack is a linear discontinuity produced by fracture. Cracks may be longitudinal,transverse, edge, crater, centreline, fusion zone, underbead, weld metal or parent metal.

2. SURFACE IRREGULARITIESUndercut, overlap, carter pipe, spatter and stray flash.

3. CONTOUR DEFECTSThe profile of a finished weld may considerably affect performance of the joint under load

bearing conditions. Specifications normally include details of acceptable weld profiles to beused as a guide.

Excess weld metal

Lack of fusion

Incompletely filled groove

Bulbous contour

Unequal legs


13/13

4. ROOF DEFECTS

Incomplete roof penetration.

Lack of root fusion

Excess penetration bead

Root concavity (underwashing)

Shrinkage groove

Burnthrough (melt through)

Documents

Steel girders fabrication- Part 1 (Steel Bridge)