Modified Valves

Published: 5th December 2013 | Issue 27

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The modification of standard valves to suit alternative and often very specific use is nothing new. More and more contractors and end users are turning to modified valves to provide an alternative solution to manufacturer lead-times when they need to find something quick to fill a gap. It may be tail end project items that have been missed, or urgent replacements for a forthcoming maintenance shut-down. It may even be something so specific that the major manufacturer cannot justify interrupting their day to day commodity production.

However, we wonder how many end users actually know the provenance of the modified valve they’re buying, particularly when the valve has passed through many hands on its way along the supply chain.

In our experience, often things such as warranty, legislative compliance, and fitness for purpose are simply assumed by the end user when in fact they have become watered down through the supply chain to a point where responsibility becomes questionable.

An example of this came to us recently. The end user had been supplied with a small class 1500 stainless steel ball valve which somewhere along the supply route had been modified with the addition of a cryogenic bonnet. The user was reporting that cryogenic product was leaking from between the top of the valve body and the bottom of the bonnet extension. Having experienced difficulty going back down the original supply chain, the distributor turned to us for a solution. Once we had all the details of the valve in question a reason for the leakage experienced was fairly clear; the ISO5211 F04 mounting pad on the top of the valve body, whilst perfectly adequate to attach an actuator or switch box, did not provide a suitable means of attachment for the extended bonnet under pressure at 204 barg. Fortunately the consequence for the user had ‘only’ the cost of down time while a suitable replacement was installed. It could have been a whole lot worse.

When modifications are done correctly, the modified product can be considered equal to the manufacturer’s original product in terms of quality and performance. This is assuming that due consideration of intended design and operating conditions, is taken by an organisation capable of accurate technical assessment of the implications the modification may have on the product’s compliance with applicable standards and Modified Valves can you afford to take the risk? legislation. Additionally certified approval/authority to modify from the original manufacturer, and the means to ensure compliance is maintained following modification, should be considered.

It’s worth noting that even the simplest modification, such as the practice of machining a screwed end valve to socket weld, may invalidate compliance with the Pressure Equipment Directive if it’s not something that the original manufacturer has considered during their technical conformance process. CE marking for European Directives such as the PED not only provides an indication that the marked product can be considered safe to use within declared parameters, if marked correctly it also provides traceability back to the manufacturer. The manufacturer will be quick to relinquish responsibility for their product if it’s no longer in its originally declared form. However, if the modification has been performed by an organisation with, for example, a valid Module H PED Certificate,there ought to be evidence that the implications of the modification have been considered and adequately catered for by design.

Material selection is an area of significant importance. Those familiar with the PED will be aware of the constraints placed on manufacturers to use approved materials for pressure bearing components. The same constraints are in place when modifying a valve. Whether by use of Particular Material Appraisal or harmonised material standards, the need to control and monitor original material manufacture is crucial to ensuring materials of a necessary quality are used. Material approval for category III & IV pressure equipment must be conducted by a PED Notified Body. When designing a valve, vessel or assembly based on a material standard’s specified mechanical and chemical properties, adequate controls must be in place to ensure the material used does actually provide these properties. For example, austenitic stainless steels normally associated with low temperature such as ASTM A351 CF8M may only be permitted for use at -196 degrees C if consideration has been given to the material’s impact properties at this extreme temperature. As such, modification of a standard valve for cryogenic duty should involve much more than welding a bit of tube around an extended stem. Material selection is critical, and welding activities too must be controlled to ensure the mechanical and chemical properties of the weld are compatible with those of the parent metal.

Another example of a common modification is the joining of number of valves together to form a manifold assembly. The directive defines an assembly as several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and functional whole. As such, a manifold may be required to comply with the PED, undergo technical conformity assessment in accordance with the relevant sections of the directive and be CE marked if appropriate.

In the current financial climate the need to save short term cost is prominent in the mind of most decision makers. Cost shouldn’t be allowed to compromise quality, but, as a number of large food retailers have discovered recently, the risk is there.

A PED compliant valve, where appropriate, will bear a CE mark and Notified Body identification, also a means of identifying the manufacturer or legal entity applying the CE mark and some means of traceability such as a serial or batch number. If modified by someone other than the manufacturer this could be negated. In the case of CE marked valves, modification in compliance with the PED will require the organisation doing the modification to take ownership of the product, apply their CE mark, identification mark and traceability. As such, where it’s obvious that modification has taken place, the provenance of the modified product ought to be just as obvious to those further down the supply chain. Where the original manufacturer remains as the sole means of identification on obviously modified product, the purchaser should be querying the provenance with their supplier.

In conclusion, done the right way, there should be no greater risk associated with the use of modified valves as there is with original manufacturer’s products.

Adanac Valve Specialities Ltd
Tel: + 44 (0) 1359 240404
www.adanac.co.uk

Telephone:	01359 240 404
Email:	sales@adanac.co.uk
Website:	www.adanac.co.uk
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