1                           PREPARATION basis

GB 50236-98	Code for the Field Welding of Equipment and Industrial Piping
JB 4708-92	Steel Pressure Vessel Welding Procedure Assessment
JB/T 4709-92	Steel Pressure Vessel Welding Specification
JB4730-94	Pressure Vessel Non-destructive Testing and No.1 Revision Notice
GB 50252-94	Standard for Quality Inspection and Assessment of Industrial Installation Works
SH 3703-97	Specification for Project Construction Hand-over Technical Documents
ASMEB31.3

2                           Construction quality control and technical specifications

2.1                     Welding Material Quality Control

The materials applied in the welding work should be complied with the design documents.  They must be provided with the quality certificates of the manufacturers. The quality and specification of the welding materials must be complied with the relevant national standards.  The welding engineer should review the welding materials and their quality certificates (including re-check reports), making sure the chemical composition and mechanical property items are complete and qualified. The application of materials with incomplete quality control documents and disqualified physical or chemical properties is strictly forbidden. When one or more of the chemical/physical properties are missing on the testing report, the welding contractor cannot use the material unless it is re-checked and found qualified. The welding engineer should also check the actual quality of the material, those with ambiguous labels or those that are not in line with the quality certificate, or those disqualified must not be used.

 

 

2.2                     Welding Material Management Control

The welding contractor must have strict regulation on the storage, baking, issuing and returning to deposit of welding materials. The welding engineer must check and make sure the welding material storage, baking, issuing and returning to deposit are complied with the regulation. The construction site must have proper storage venue, baking and cleaning facilities for welding materials in conformity with the technical requirements so as to ensure that the usage of welding materials is complied with the regulation.

 

2.3                     Review of Welding Procedure Assessment

The welding contractor must make procedure assessment for welding workpieces according to Section 4 of GB50236-98 Welding Procedure Assessment. The welding engineer shall review the procedure assessment for its completeness and conformity to the standard according to GB50236-98. In case of any incompliance, the welding engineer must instruct the welding contractor to rectify till the requirements are met. When the welding method is changed, welding procedure assessment must be re-conducted. Before welding, the Welding Operation Instructions must be prepared based on welding procedure assessment report.

 

2.4                     Review of Qualification of Welders

Before welding, the welding contractor must submit the Name List of Licensed Welders and Welder Qualification Certificate of his welders involved in the project. The welding engineer must check the welders’ qualification certificates, certificate valid duration (usually three years) and relevant welding items specified by the certificate based on welder examination rules. Unqualified welders cannot conduct welding. The welding engineer should instruct the welding contractor to replace unqualified persons in time. Only qualified worker can officially start welding work. The welder(s) with unstable welding quality on site should also be dismissed.

 

2.5                     Welding Equipment Management

Before welding, the welding engineer should check the welding equipment. The welding contractor should arrange specific personnel to maintain the welding equipment. Ammeters and voltage meters should be in good condition. The welding team cannot start welding unless the welding equipment is in good condition for sure. The welding team who has problematic welding equipment must be requested to rectify before the welding.

 

2.6                     Control Before Welding

The welding engineer should check to see if the quality control system of the welding contractor is running well and whether the self-check, mutual check, and specific person check (triple check system) is implemented. If there is any abnormality, a Notification for Rectification shall be issued, instructing the welding contractor to rectify.

2.6.1                 The main structure size, groove size and groove surface of components shall be checked before pairing-up.

(1)  Structure size should be complied with the specification of design documents.

(2) Groove type and size should be complied with the specification in design documents and Welding Operation Instructions.

(3)      When non-destructive testing is required for groove surface in related design documents and specifications, the testing and treatments for defects must be completed before welding.

(4) On the groove surfaces there should not be any defects such as inclusion, cracks, work damage, burrs or flame cutting etc. The grooves and their inside and exterior surfaces of at least10MMshould be cleaned.

 

2.6.2                 After pairing-up, the shape of component, position of welding seam, unfitness of joints, angular deformation, pairing-up clearance and overlap of lap joints should be checked.

(1) Component shape and position of welding seam should be complied with the design documents and Section6.1.2of GB50236-98.

(2)      Unfitness of joints should be complied with the Section6.2.5of GB50236-98(3).

(3)      Angular deformation, pairing clearance and overlap of lap joints should be complied with the design documents, Welding Operation Instructions and relevant codes.

When preheating is required before welding for welding seams, the welding contractor should strictly control the preheating temperature. The welding engineer should check if the preheating temperature complies with the procedure requirements. If not, the welding contractor must rectify in time.

 

2.7                     Control During Welding

For welding seams for which intermediate test is required, the welding engineer should be present in checking whether the welding condition of testing piece is the same as the actual part to be welded. The welding contractor should submit the result of intermediate test to the welding engineer. If the result is qualified, the engineer could sign and let it pass, and welding work can go on at the welding seam it represents.

2.7.1                 After completion of tack welding, the welding seam should be checked after cleaned of welding slag. Welding cannot be done unless found defects are removed.

When there is requirement for weld heat input, the arc voltage, current and welding velocity should be measured and recorded. The weld heat input should be complied with the Welding Operation Instructions.

2.7.2                 When there is definite specification for welding layers, the welding layer number should be checked. The number of layers and thickness of each layer should be complied with the Welding Operation Instructions.

2.7.3                 Upon completion of each layer in case of multi-layer welding, interlayers should be cleaned up and checked immediately. Welding cannot go on to next layer unless the defects are removed.

2.7.4                 When non-destructive testing is required for inter-layers, the non-destructive testing should be conducted after appearance check is qualified. Welding cannot go on unless the non-destructive testing is evaluated as qualified.  

2.7.5                 When interlayer temperature control is required, interlayer temperature should be checked and recorded.

2.7.6                 When welding is interrupted, the welding seams should be checked and cleaned up, found defects should be removed and specified preheated temperature should be reached before restart of welding.

2.7.7                 During welding of double side welding pieces, the back of welding seam root should be checked and cleaned up. Welding cannot be done at the back welding seam unless defects are removed. For welding seams for which back chipping is required, appearance check and specified non-destructive testing should be done after back chipping, and welding cannot be performed unless defects are removed.

 

2.8                     Control After Welding

After welding, the welder should clean the slag and spatter immediately. Then appearance check should be done. The appearance quality should be classified in accordance with Table 11.3.2 of GB50236-98. The appearance quality should be in conformity to Table 11.3.3 of GB50236-98. For unqualified items, the welding engineer must instruct the welding team to rework till qualified.

As for the workpiece that needs non-destructive testing, the welding contractor must perform the detection according to the ratio and qualification level specified by the design documents and related codes. If the result is not qualified, re-detection should be done according to specified ratio. If again unqualified, 100% detection should be performed. For detected parts that are not qualified, the welding contractor must prepare rework procedure, and rework according to the procedure. Generally rework on the same part should not exceed two times. After rework the re-detection should be qualified and the detection engineer should confirm the rework results. 

After completion of detection and rework as confirmed by the welding engineer, the welding contractor should make ready and submit the detection report, part photos and single line detection pictures to the welding engineer for review.

The detection engineer should check carefully the detection methods, detection ratio, extra detection ratio, qualification level and compulsory detection items (T type connections and 100% detection items). When necessary he may spot check the negative film and notify the welding contractor to rectify in time if any problem is found. The detection engineer may arrange extra detection to the doubtful parts and parts that need random check. If any problem is found, the welding contractor should rework to assure the interior quality of the welding seams.

 

2.9                     Post-welding Heat Treatment

For the welding seams of the workpiece that need to be heat-treated, the heat treatment should be performed after non-destructive testing is qualified. The welding contractor should draft post-welding heat treatment procedures and submit it to the welding engineer for review. The parameters of post-welding heat treatment should be complied with the design documents and relevant standards or Welding Operation Instructions.

During heat treatment after welding, the welding contractor should give good control on the temperature of heat-treatment and make random check. Temperature curve shall be recorded. The recorded curve should be submitted to the welding engineer for check after the completion of heat-treatment. The recorded curve must be complied with the post-welding heat treatment technical requirements.

 

2.10                 Handover and Acceptance of Welding Works

After completion of welding, the welding contractor should carefully make ready the relevant welding documents. As welding is a part of on-site piping and equipment works, it will not be handed over individually. The welding documents should be filed together with the handover documents of related unit works.

 

 

 

 

 

              ATTACHED ILLUMINATION：

              This Standard Is Kept By Technique Department.

              This Standard Was Prepared By Construction Management Department.