Base Metal Repair Procedure by Welding

What is a welding Repair

Weld repairs can be divided into two specific areas:
1. Production
2. In-service

The reasons for making a weld repair are many and varied (can be due to manufacturing defects or in-service failure) and involves the removal of weld defects induced during manufacture to a quick and temporary running repair to an item of the production plant.

In these terms, the subject of welding repairs is also wide and varied and often confused with maintenance and refurbishment where the work can be scheduled.

Welding Repair Procedure and Method Statement.pdf

What is Base metal repair?

Base Metal Repair: It is the application of a weld material to a base metal so as to restore the design thickness and/or structural integrity. This build‐up may be with a chemistry different from the base metal chemistry which has been qualified via a standard butt-welded test coupon. Also, may be called base metal repair or buildup.

What is In-process Welding Repair?

In‐process repairs are defined as repairs in which a welding imperfection or flaw or defect is mechanically removed and a repair weld is made before welding of a joint is presented for final visual inspection. Examples of such repairs are areas of removal of porosity, incomplete fusion, etc., where sufficient metal has been mechanically removed that localized addition of weld metal is necessary in order to make the surface geometry suitable for continuation of normal welding.

Does Separate WPS qualification is required for weld repairs?

As per ASME Section IX, Clause QW 202.3, an pre-existing WPS can be used to perform the weld repairs within the limits specified as below:

WPS qualified on groove welds shall be applicable for weld repairs to groove and fillet welds and for weld buildup under the following provisions:
(a) There is no limitation on the thickness of base metal or deposited weld metal for fillet welds.
(b) For other than fillet welds, the thickness range for base metal and deposited weld metal for each welding process shall be in accordance with QW-451, except there need be no upper limit on the base metal thickness provided qualification was made on a base metal having a thickness of 11/2 in. (38 mm) or more.

Steps for Base Metal Welding Repair procedure

  1. Prior to the repair of base material defects the extent of defects shall be determined. Defective areas shall be prepared for welding by grinding, gouging, or other suitable means. Surface conditions shall meet the WPS or as specified by the client requirements, as applicable prior to repair welding.
  2. Base metal defects shall be completely removed to sound metal. Prior to making welded repairs, the defect removal areas shall be inspected as specified by the Engineer. Joint geometries, including applicable tolerances, shall be essentially in conformance with the WPS approved for use in the repair.
  3. Areas to be repaired by welding shall be thoroughly cleaned by grinding, power brushing.
  4. The WPS used in making repairs shall meet the requirements of of the applicable reference code or standards such as AWS D1.1 or ASME Section IX or ISO 15614-1.
  5. After completing the welded repair, the repaired areas shall be examined for fusion and base material damage (such as undercut). If visual inspection of the repaired areas is acceptable, they shall be blended smooth, flush and uniformly into the surrounding surfaces. Blending may be done by grinding or machining. Chemical cleaning, if required, shall be specified by the Engineer.
  6. Repaired areas shall be inspected by an appropriate NDT method or as specified by the Engineer. Acceptance criteria of welded repairs shall be per applicable material specifications, or the approved ITP or any other requirements as applicable.

Steps for Welding Repair procedure

  1. Removal and Repair of Welds: The removal of rejectable weld metal or portions of the base metal may be done by machining, grinding, chipping, plasma, or air carbon arc gouging. The process(es) used for removal shall be controlled in such a manner that the adjacent weld metal or base metal is not nicked, gouged or without substantial removal of the base metal. Oxyfuel gas gouging is not permitted.
  2. The affected surfaces of materials shall be cleaned thoroughly to bright metal by mechanical means before rewelding. Chemical cleaning to remove residual surface oxides is also permitted. If chemical cleaning is used, the chemical’s characteristics should be evaluated by the Engineer for safety, corrosion and weldability effects.
  3. Repaired or replaced welds shall be performed using qualified WPSs. Repaired or replaced welds shall be re-examined by the same methods and quality acceptance criteria originally used unless otherwise specified by the Engineer. For example, the original defect was found using Ultrasonic Testing & Penetrant Testing. So, UT and PT shall be used for the verification after the welding repair.
  4. During the welding operation, the contractor has the option of repairing an unacceptable weld, by removing the defective area or by replacing the entire weld. Welds found rejectable by NDE methods after welding is complete shall be repaired.

According to API 582 ”Repairing a PWHT’d component without PWHT requires that the repair meet all applicable construction code requirements, or follow NB-23 or API 510. Purchaser approval shall be obtained prior to performing the repair. Procedure qualifications shall be done in accordance with ASME IX.” If any PWHT was originally conducted due to service requirements, specifically environmental cracking prevention, PWHT of the repair should be strongly considered.

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