Instrumentation manifold standards ignored

Important standards that safeguard the reliability of instrumentation manifolds are starting to be ignored, warns Parker Instrumentation.

Important standards that safeguard the reliability of instrumentation manifolds are starting to be ignored, warns Parker Instrumentation, who has become aware of inferior-quality product being installed.

The decline in standards - which most users will find it difficult to spot - could threaten the integrity of instrumentation systems and potentially result in premature failure.

The problem has been identified on double block and bleed (DBB) manifolds, for connecting instruments to process piping - for working pressures up to ANSI Class 2500 or 6,000 PSI, or more (some customers ask for compliance with the API specification for example, which is 10,000 PSI).

ANSI-B 16.5 and 16.34 standards are widely specified for these products, and state that such components must be machined from 'close to net shape forgings'.

This stipulation ensures that the grain flow of the metal is in line with the finished machined shape - for optimum strength and resistance to corrosion attack.

Parker has identified instances where double block and bleed manifolds have been produced from bar stock material, which has a unidirectional grain flow.

Machining the contours required for a double block and bleed manifold cuts through the flow lines, exposing grain ends.

This reduces strength, and increases susceptibility to corrosion.

Double block and bleed manifolds typically have narrow middle sections, which if machined from bar stock, become weak points.

These weak points can be subjected to large bending moments, due to the loading force of instruments and other components, and are often subjected to vibration as well.

With internal flow diameters up to one inch, the ramifications of failure can be severe.

The linear grain flow of bar stock offers another potential failure mechanism.

Resistance to corrosion is crucial for many DBB manifold users such as oil and gas platform operators, who specify materials carefully to ensure very long service lifetimes and performance in the presence of corrosive media and environments.

Exposed grain ends that result from machined bar stock manifolds can render the material more liable to fatigue and more sensitive to stress corrosion.

"Most users we deal with specify and rely on ANSI standards, and believe that's what they are buying," says Spencer Nicholson, Parker Instrumentation's Innovation and Technology Manager.

"But in this field you cannot tell low quality parts by external appearance, and in some cases users are not getting what they specify.

You need to cross-section and etch a component to see if it complies with standards.

It is easy to understand how end users can be confused when terminology such as 'machined from forged bar stock' - is used.

Clearly this is not a close to net shape forging, and does not comply with relevant standards.

If DBB manifold users are concerned about quality and want to verify the use of forgings,.

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