Recently published standards have brought in new demands for valve inspectors. The S-562 (Supplementary Requirements to API Specification 6D Ball Valves) and the S-611 (Supplementary Requirements to API 600 Steel Gate Valves and to API 603 CRA Gate Valves) specify that new tests and procedures are to be performed.
For these new procedures, the people involved need to be properly trained. This can add layers of complexity to inspections, which remain a vital process to safeguard future valve performance. In this article, we will be highlighting 10 factors that should receive special attention in order to avoid problems in the field.
A successful inspection, carried without interruptions, must be preceded by adequate planning. Two of the most important products of this phase are:
Pre-inspection Agreements: Discussions with the supplier must result in agreements on several topics, such as delivery and inspection schedules, clarification of technical doubts, list of contacts, manufacturing locations, sub-supplier list, standards and other contractual obligations that will govern the inspection (such as the supplier covering the costs and wages of the inspector when there is an inspection notice but the valve is not available).
Elaboration of the ITP (Inspection and Test Plan): The ITP is a document developed by the supplier that contains all the inspection activities conducted throughout the manufacturing process, including those occurring in sub-suppliers. The ITP must indicate the type and extent of checks, tests and verifications to be performed, correspondent ruling standard or procedure, acceptance criteria, qualifications and certifications needed for personnel involved, and type of participation.
Type of participation defines if a given task is a Hold Point (HP, the activity shall not proceed without formal approval by the purchaser, and there is a hold in production); a Witness Point (WP, the supplier shall notify the purchaser in advance about any activity taking place, so the purchaser may witness the execution of said activity); and, Review Point (RP, which involves document review). Some ITPs also include a Monitoring or Surveillance Point (MP or SP, the end user or its representative reserves the right to review or observe a given activity, operation or process). There is no hold in the production for WPs, RP and MPs.
2) Drawings, Procedures and Certificates
The review of drawings, procedures and certificates is generally the first phase of the inspection related to a specific purchase order. The review begins with a comparison between the valve drawings and the valve data sheet and/or specification. After that, the verification of procedures and certificates follows, which includes such things as heat treatment procedures, non-destructive examination procedures, and welding procedures (including repair). Additionally, other certificates like fire type-tests and fugitive emission design validations may be required.
Inspections of raw castings usually take place in a foundry, where test specimens are stamped and used to perform mechanical and chemical analysis. Frequently considered a Hold Point, end-users or third-party representatives are often summoned to witness the testing. Recurrent problems can arise when the end-user requires extra test specimens for a given batch, or there are supplementary tests to be performed. As the end-user often communicates with the valve manufacturer rather than directly with the foundry, it is vital to seek confirmation from the foundry that they have understood the additional requirements.
Forged valve parts usually have less testing requirements than similar casted parts, but even a common forged material like ASTM A105 may require test specimens. For example, if valve parts are to be machined from a bar, test specimens for tensile testing will be required, according to the S-563 (Material Data Sheets for Piping and Valve Components).
Weld repair for forged parts is not commonly accepted for correcting material defects. For castings, weld repairs must use qualified procedures and be in accordance with the material standard and any supplementary requirement stated in the contract or purchase order. A clear distinction between major and minor defects and their correspondent documentation must be defined prior to the inspection.
4) Heat Treatment
When necessary, heat treatment is performed in accordance with a heat treatment plan, which contains, as a minimum:
a) The material’s requirements, as stated in the material’s standard and any supplementary requirement agreed on contract;
b) the traceability of the materials treated along with the respective test specimens;
c) the location in the oven of the parts being treated;
d) the location of the thermocouples, according to the oven layout;
e) the resolution and frequency of calibration of all thermo-couples and graph recorders;
f) the heat treatment graph with thermal cycle.
5) NDE (Non-Destructive Examination) and Dimensional Check
Some verifications need to be made prior to assembling the valve. Dimensional checks are made in accordance to the manufacturer’s drawings and must cover all the pressure-containing and pressure-controlling parts. Typical dimensions verified are thickness of body and cover/bonnet, face-to-face length, and flange dimensions and finish.
The valve design standard is the starting point for NDE Requirements, which usually involves the following techniques: Visual Testing (VT), Ultrasonic Testing (UT), Penetrant Testing (PT), Magnetic-particle Testing (MT) and Radiographic Testing (RT). The design standard also defines the extent and the acceptance criteria for each technique. Some corrosion resistant alloys (CRAs) may require additional testing, such as a ferrite content check (for duplex steels, for example).
End users may adopt more stringent NDE procedures than stipulated in the design standard. They may ask for RT when there is no provision in the design standard, inspect the full lot instead of sampling or modifying the extent of what should be inspected, or even change the acceptance criteria. This, of course, must be previously agreed upon. Such deviations must be outlined during the Pre-Inspection phase and carefully verified in the ITP.
6) Materials Traceability
The criticality of the valve will influence the level of traceability required for the materials used in the valve. A common guide used to define traceability requirements is the standard EN 10204 (Metallic products – Types of inspection documents). Despite the name, this standard is also referenced for non-metallic parts as well. Pressure-containing and pressure-controlling parts tend to have more stringent requirements than the other parts of a valve.
The inspector will compare mill certificates, NACE compliance, hardness and impact reports and other documentation with the markings used in the appropriate parts. PMI checks (Positive Materials Identification) for some alloys and verification of storage conditions for welding consumables and non-metallic parts can also be done in this phase.
7) Functional Testing
Functional testing is the phase most people regard as the “core” of the inspection process. The tests to be performed and to what extent (full batch or sampling) are defined by the valve standard and supplementary requirements. For ball valves, tests that can be addressed in this phase are:
• Antistatic testing;
• High-pressure hydrostatic shell test;
• Torque test;
• High-pressure hydrostatic seat test;
• Functional test;
• Seat cavity relief test;
• Low-pressure pneumatic seat test;
• High-pressure pneumatic seat test;
• DBB (double block and bleed) testing;
• High-pressure pneumatic shell test;
• Fugitive emission test.
Two common points of contention often arise in this phase. One is related to the use of automated benches for testing. There are end users that consider that these benches may “help” the valve in some tests. With both extremities of the valve firmly held in place and under compression, there is little room for the valve to deform and maybe leak. As this situation may not be similar to the one in the field, large valve sizes are often required to be tested with blind flanges. The other point of contention is related to the duration of the tests: many consider the minimum duration stipulated in the standards too low, and inspectors demand the test to be held for longer.
When the painting process is defined under contract, the supplier must present the painting procedure and painting inspection plan for approval before it can begin. Both documents must be signed by a certified painting professional. Records of training for the professionals involved in the painting process must also be presented. The instruments to be used for checking the coating quality (e.g. thickness) must be cited in the painting inspection plan. Some inspectors may require the use of electronic gages for evaluation of dry film thickness instead of the analog magnetic pull-off gage. One crucial point to be enforced in this phase is the prohibition of abrasive jet-blasting after the assembly stage.
9) Data Book
All documentation to be retained by the manufacturer and then sent along with the valve to the customer is fully defined in most design standards. The depth of information can vary significantly. API 6D, for example, defines several items for 10 years retention, but regarding the documentation sent with the valves, it allows for a single certificate of conformance (as a minimum). Due to this discrepancy, some companies ask for supplementary documentation to be shipped with the valve, such as the documents provided by the S-562 standard. All this documentation, along with the installation, operating and maintenance instructions manual, is frequently sealed in a waterproof envelope attached to the valve or shipping container.
10) Final Inspection
Before the valve is shipped, some final verifications need to take place, such as a visual inspection for markings (serial numbers, arrows for flow direction, etc.) and nameplates. The inspector also must verify if the manufacturer’s instructions regarding stem packing (loose or tighten?), obturator position (open or closed?) and preservation are being followed correctly. Additional items, such as spare parts and accessories are also checked to be included in the shipment.
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