Steel valve casting NDE acceptance
By BVAA’s Technical Consultant, Peter Churm
Steel valve pressure containing castings are specified with a range of quality acceptance tests and supporting documentation to ensure the integrity of the intended pressure vessel. As required, attributes such as mechanical strength, toughness, hardness and the identification of material defects may be requested by the purchaser and specified referring to international standards.
Meetings of ISO/TC67/SC2/WG2 have been held since April 2011 with the intent of drafting a revision to ISO 14313: 2007 ‘Petroleum and natural gas industries – Pipeline transportation systems - Pipeline valves’ which will address the issues surrounding material quality acceptance when used in pipeline valves.
The purpose of the revision process is also to keep both API Spec 6D ‘Specification for Pipeline Valves’ and ISO 14313 aligned. The draft ISO 14313 standard, as modified by this WG, has been submitted to API 6D TG technical experts for consideration and discussions to further the revision process before the document can, following editing, be issued by ISO as a Draft International Standard (DIS) for comment, which is anticipated by the end of 2012.
Many sections of ISO 14313 have been reviewed and changes proposed but it is the issues surrounding material non destructive examination (NDE) for pipeline valve castings that are a cause of concern. Material NDE requirements are and have normally been identified by the purchaser’s Technical Specification whilst the design, materials, testing and marking are specified by the standard.
The standard states that the manufacturer identifies the material specification for pressure containing and pressure controlling parts showing – chemical analysis – carbon equivalent – heat treatment – mechanical properties – testing and certification. In a normative Annex A the standard “specifies the requirements for non destructive examination (NDE) that shall be performed by the manufacturer if specified by the purchaser”.
An Informative ANNEX G Quality Specification Level (QSL) for pipeline valves has now been added to the standard. This annex specifies quality levels QSL1 to QSL4 for pipeline valves and includes specific requirements for non-destructive examination (NDE), pressure testing, and documentation of the manufacturing process. QSL1 is the quality level as specified in the normative text of ISO 14313 only and is generally accepted to be a high quality specification.
QSL2 to QSL4 are optional increased quality levels that may be specified by the purchaser.
The major change to this NDE specification procedure is that the purchaser’s specification will no longer be separate and additional to the standard but the requirements will be contained within the standard itself. This change is intended to ensure that any additional NDE will be identified and controlled by the requirements of the standard and not be subject to user choice which may be subject to interpretations which could be problematic should there be litigation issues resulting from use in the field.
It is evident that changes are being proposed that move ISO 14313 closer to the requirements for valves specified for API 6A “Wellhead and Christmas Tree Equipment” in material, quality, NDE and testing.
However, by referring to valves manufactured and controlled to ISO 14313, QSL2 to QSL4, where QSL1 has previously been acceptable there is a danger of over specifying unnecessarily stringent NDE procedures and acceptance standards which impose increased costs and add time to the manufacturing process whilst adding no value to the product. This is a cause of concern for valve manufacturers in a competitive market where valves complying with ISO 14313 are still subject to competitive purchase price demands.
Further to this, normative Annex A (Requirements for NDE) has been changed to introduce penetrant testing and magnetic particle testing of machined sealing surfaces stipulating that there shall be no indications in the seal areas.
Additionally the revised draft standard will specify hardness testing of all metallic pressure containing and pressure controlling parts after final heat treatment with the hardness testing consisting of a minimum of one indication at various locations on each part.
This NDE issue is a cause of concern for BVAA member companies who have been reliably manufacturing pipeline valves for many years in a competitive market place. UK steel foundries confirm the increased casting costs that will inevitably be associated with these changes and they will reflect in valve selling prices.
If you have a view on these proposals, it would be a good idea to get involved and comment via your own National Standards Body.
Published in Valve User Magazine Issue 21
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