General Welding Procedure

   

GENERAL WELDING PROCEDURE

REVISION LOG A

REV. NO.
REV. DATE
REVISED PAGE
REVISION DESCRIPTION


TABLE OF CONTENTS

1.  SCOPE…………………………………………..         4

2.  DEFINITION……………………………………..       4

3.  REFERENCE……………………………………        4

4.  RESPONSIBILITY……………………………….       5

5.  GENERAL………………………………………         5

6.  PROCEDURE……………………………………        5

7.  WELDING INSPECTION…………………………     12

8.  ATTACHMENT…………………………………..       13

       
1.  SCOPE

This Procedure covers the general requirements of welding process, welding condition and welding inspection during the installation of pipes, equipments, pile, structural steels to be executed by Hyundai-HEC Joint Venture in EfW Project @ Sakra at Jurong Island Singapore.


2.  DEFINITION

2.1.Welding Procedure Specification (WPS): A WPS is a written qualified welding procedure prepared to provide direction for making production welds to code requirements.

2.2.Procedure Qualification Record (PQR): A PQR is a record of the welding data used to weld a test coupon.

2.3.Pass: A single progression of a welding or surfacing operation along a joint, weld deposit or substrate.

2.4.Peening: The mechanical working of metals using impacts blows.

2.5.Back-gouging: The removal of weld metal and base metal from the other side of a partially welded joint to ensure complete penetration upon subsequent welding from that side.

2.6.Backing gas: A gas, such argon, helium, nitrogen, or reactive gas, which is employed to exclude oxygen from root side of weld joints.

2.7.Seal weld: Any weld designed primarily to provide a specific degree of tightness against leakage.


3.  REFERENCE 

3.1.ASME SEC.IX, Welding and Brazing Qualification

3.2.ASME B31.3, Process Piping

3.3.AWS D1.1, Structural Welding Code-Steel

4.  RESPONSIBILITY

4.1.The QA/QC Manager or his designee is responsible for insuring of site surveillance activities for welding works.

4.2.The Construction Manager is responsible for control of Parties welding works.


5.  GENERAL

5.1.Production welding shall be in accordance with qualified Welding Procedures Specification (WPS) and carried out by qualified welders.

5.2.All butt-groove welds in pipe shall be full penetration welds and root pass shall be made by GTAW process.

5.3.All butt and fillet welds shall be made at least two passes.

5.4.Welded joints shall be made by completion each layer before the following layers are deposited.

5.5. Welds passes shall not start or stop at the same point.

5.6.Peening of welds in not permitted.

5.7.Permanent backing rings and consumable inserts shall not be used.

5.8.Weather condition

    5.8.1.  Welding shall not be done when the quality of the weld would be impaired by the prevailing weather conditions, including airborne moisture, blowing sands, or high winds.

    5.8.2.  If weather conditions become too severe, welding operations shall be stopped. However, the welding could be performed with proper protecting from such a weather condition.

    5.8.3  During welding, the welds shall be properly protected from wind, rain, humidity, moisture.

    5.8.4  No welding shall be done on wet base materials.

5.9. Control of welding consumables

    5.9.1.  Manufacturer’s mill certificates of welding consumables should be available in site for each heat, lot or batch. Mill certificates should show chemical and mechanical properties.

    5.9.2.  Electrodes, filler wires and fluxes shall be kept clean and dry, and properly stored according to manufacturer’s recommendations.


    5.9.3.  No electrodes, filler wires or fluxes that are damaged, damp, greasy or oxidized may used.

    5.9.4.  Low hydrogen electrodes and fluxes shall be baked in a dry oven at 250°C ~ 350°C for one hour, or manufacturers recommendation and held at a minimum temperature of 80°C in holding oven.

    5.9.5.  Welding electrode shall be issued for production from holding ovens only and shall be placed in portable canister capable of maintaining minimum temperature of 80°C.

    5.9.6.  After six hours, the remaining unused electrodes not in the portable canister shall be placed in a drying oven and held at 250 ~ 350°C for one hour or as recommended by the manufacturer if at a higher temperature, and then transferred to a holding oven prior to reissue.


6.  PROCEDURE

6.1. Control of welding preparation

    6.1.1.  Weld bevels shall conform to the joint design used in the Welding Procedure Specification(WPS), or drawings.

    6.1.2.  The root opening shall be in accordance with fit-up requirements of WPS.

    6.1.3.  Double-sided weld joints shall be back gouged to sound metal prior to back welding.

    6.1.4.  Weld bevels shall be made by machining; grinding or thermal cutting and the beveled ends shall be reasonably smooth and uniform.

6.2. Joint alignment

    6.2.1.  Piping components shall be adequately supported and aligned by the means of jigs, clamps or their suitable devices during tacking. Cold pulling shall not be allowed to alignment.

    6.2.2.  For pipe ends of the same nominal wall thickness, the offset shall not exceed 1.5 mm (1/16 inch).

    6.2.3.  If the large offset is caused by dimensional variations, it shall be equally distributed around the circumference of the pipe.

    6.2.4.  Where parts with internal diameters differing by more than 1.5 mm are joined concentrically, the inside of the smaller bore shall be tapered to match the larger bore within 1.6 mm.

    6.2.5.  Welding joining components of different material thickness shall be made in such a manner that the slope through the transition zone does not exceed 1:3.

6.3.Requirements for location of welds

    6.3.1.  Distance between two successive girth  welds shall not be less than three times the pipe thickness.

    6.3.2.  Distance between two successive longitudinal weld seam shall not be less than five times the pipe thickness.

    6.3.3   Where attachment of non-pressure part weld by which cross existing main weld, minimum 60mm distance from toe of main weld should not be welded.


6.4.Cleaning

    6.4.1.  Surface to be welded shall be clean and free from paint, oil, dirt, scale, oxides and other materials detrimental to welding.

    6.4.2.  Cleaning shall be done in a manner that will not lead to contamination of the weld or base metal.

    6.4.3.  Only stainless steel brushes and tools shall be used on stainless steels, nickel and non-ferrous materials. Grinding discs containing sulfur shall not be used on stainless steels, nickel or non-ferrous materials. The tools for stainless steel such as grinder, power brash etc. shall be color marked.

    6.4.4.  Upon completion of each welding pass, the weld shall be cleaned of spatter, slag and flux deposits.

    6.4.5.  All pipes to be internally cleaned from any foreign material.

6.5.Tack welds

    6.5.1.  Tack welds shall be of sufficient cross-section and length in order to avoid cracks.

    6.5.2.  Tack welds incorporated into the final weld shall be ground to a feather at each end to ensure adequate fusion on the root pass.

6.6. Temporary welds on permanent pipe or equipment

    6.6.1.  Temporary welds shall be minimized. Welding shall be performed with the same materials, electrodes, minimum preheating and procedures as for the production welding.

    6.6.2.  The temporary welds shall subsequently be removed and ground flush with the base materials.

    6.6.3.  The method of removing attachment shall not injure the metal surface.

6.7.Preheating

    6.7.1.  Preheating shall be in accordance with the qualified WPS, or applicable Code and Standard .

    6.7.2.  Preheat shall be applied uniformly around the circumferential weld using gas or electrical means.

    6.7.3.  Temperature shall be measured using contact thermometer or indicating crayons of the melting type.

    6.7.4.  In weld assembly of different base materials, preheat temperature shall be the highest of those which are requested for each material.

6.8. Production welding

    6.8.1.  For production welding, welding preparation that are edge preparation, types and sizes of electrodes, current/voltages used and preheating requirements etc, shall be the same condition as those defined in the applicable WPS.

    6.8.2.  All surface to be welded shall be visually inspected and they shall contain no lamination or other injurious defects.

    6.8.3.  Cleanliness shall be maintained after completion of welding. All stubs, rod and foreign materials shall be removed from the equipment or piping.

6.9.Flux and slag removal

    6.9.1.  Weld beads shall be contoured to permit complete fusion at the side of the bevel and to minimize slag inclusions.

    6.9.2.  Flux, slag, and weld spatter shall be completely removed from weld beads and adjoining base material.

6.10.Weld reinforcement

    6.10.1. Weld reinforcements or internal weld protrusion shall be as required by the below Table

     

    6.10.2. Weld reinforcements shall not impair the interpretation of NDT results.

6.11. Weld surface shall be free of cracks, excessive porosity, slag inclusions and other defects indicative or poor workmanship.

6.12. Arc strikes shall be avoided. Should this occur, however, the deposit shall be carefully removed by mechanical means.

    6.12.1. All arc strikes shall be cleaned.

6.13. Socket and fillet welding.

    6.13.1. When socket weld fitting or valves are used, the pipe face shall be spaced approximately 1.6 mm clear from the root face of socket to avoid “bottoming”.

    6.13.2. Socket welds shall be made with at least two passes.

6.14. Seal welds are not applied on threaded assemblies, except where specifically required on the drawing or specification.

    6.14.1. The joints which are seal welded shall be made up clean and without the use of any seal tape or compound.

    6.14.2. A qualified welder with certificate shall do seal welding.

6.15. Repair and removal of defects

    6.15.1. Complete repair of a weld shall include removal of the defected weld, beveling of new edges, and re-welding.

    6.15.2. For partial repairs, the cutout portion shall be sufficiently deep and long to remove the defect. At the ends and sides of the cut, there shall be a taper from the base of the cut to the surface of the weld metal. The width and the profile of the cut shall provide adequate access for re-welding.

    6.15.3. Special care shall be taken to remove weld defects located at the root in order to obtain an acceptable root gap.
 
    6.15.4. Preheating, where required, and inter-pass temperatures shall be maintained during all weld repairs according to applicable WPS.

6.16. All welds shall be marked with identification symbol of joint, welder or welding operator.

6.17. All welds in DWG shall be notified, inspected and reported using ‘Visual Inspection Report for Daily Welding’ form (Form 1)


7.  WELDING INSPECTION

7.1. All welds shall be marked with identification symbols of joint, welder or welding operator.

7.2. Visual inspection of all welds shall be done after cleaning and prior to any subsequent NDT  except for pile work.
7.3. Visual inspection shall include;

    7.3.1.  Joint preparation and cleanliness
    7.3.2.  Fit-up and internal alignment prior to welding
    7.3.3.  Preheating (If necessary)
    7.3.4.  Welding position and other parameters in the WPS
    7.3.5.  Appearance of the finished weld.

8.  ATTACHMENT

8.1 Visual Inspection Report for Daily Welding (Form 1)