Review of valve design

Review of valve designs - Part 6

Barrie Kirkman - 28 May 2015

Through audits end user's try to gain confidence in the valve manufacturer design capabilities.

About the author

Mr Barrie Kirkman
Barrie Kirkman, BSc CEng MIMechE, writes a regular column for Valve World, bringing his own personal views from inside the valve business.
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In this article of the series we will be investing the end user’s review of valve design during their audits. Depending on the type of valve and their intended application the questions and investigations vary considerably. Whether it’s a commodity valve or a specialized high pressure / temperature valve on an aggressive cyclic duty, the end user investigates the design capabilities of the valve manufacturer.

The auditor enters the design / engineering office. They know there is an audit and all the employees have their heads down and are hard at work. 3D Autocad drawings are displayed on the computer screens. The process flow is explained by the head of engineering.

First audit question: Do you have a maintained controlled list of all the international standards used? Please may I see this document?

The manufactures response varies.

Typical Design Questions

A top class response is when the engineering manager provides within seconds a full list of international standards, with correct issue dates, the responsible person for the standard is identified and a method of controlling current / obsolete standards is presented for both electronic and paper versions. This is very impressive. Discussions are held on how they ensure latest code revisions are maintained and they are challenged to establish what process they have in position to know what code updates are pending. Random checks with the engineers confirm compliance with the process.

For well established international manufacturers the above response tends to be common. For developing manufacturers who are trying to receive end user approvals such a response often lacks such clarity. Lists of international standards are incomplete, out of date and are not controlled. Multiple issues of the standards are used with no master control. One major issue is the local language where this varies from English. Poor uncontrolled translations often contribute to issues.

Second audit question: How do you maintain, control end user specifications and ensure their requirements are incorporated within the valve design?

Design interrogation

When an end user visits a valve manufacturer their interpretation and expectations of international standards varies considerably especially where they have added their own requirements in their specifications.

It is important that the valve manufacturer assesses and understands the end user requirements and responds appropriately. Their processes should clearly identify how they add and manage such requirements through all aspects of manufacture. Also “change orders” fall into a similar category.

Normally the end user has their check list to quiz the valve manufacturer. Unfortunately, on many occasions this has not been done, which results in an immediate negative response from the end user. The common excuse is that the specifications are too many to review?

Much effort and time is put into the writing of the ISO / API standards with committee meetings and discussions. The committees (or work groups members) consist of industry experts from end users, distributors and manufacturers. The standards content “is an agreed position on a particular subject” which is voted on by its members.

Some end users accept and use these standards without any “additions” or “modifications” thus enabling the best valve cost to be obtained.

Other end users “add their own requirements to the standard” which often impacts the valve cost and delivery.

Valve manufacturers must become skilled in this area and seek to have meaningful discussions. Their engineering department should operate a clear document control of the various specifications identifying the end user requirements. During the bidding phase a visible process between “sales” and “engineering” should be seen to clearly identify end user requirements.

Subsequent technical questions may be raised, for example on requirements for H2S, impact properties, fugitive emission design, or the pros and cons of hollow versus solid ball valve balls. The aim is to establish the technical competence of the manufacturer.

Third audit question: Please explain the basis of the valve design including the pressure containment part of the valve?

Audit Corrective Actions

For the commodity valve, often it’s quoted “by experience”. Alarm bells start to ring for the auditor….it’s a copy? Design control folders should be produced to demonstrate compliance with minimum code requirements with appropriate allowances for corrosion. Specific design features should be identified such as radii in sharp corners, design of internals etc.

For other / special valves an analysis should be presented with finite element or similar. Assessment for high temperature applications within the creep range of the materials considered.

The design history would be explored including new developments, computer hardware and software capabilities interface with manufacturing facilities.

Prototype testing to achieve new valve designs should be discussed. The manufacturer should explain what steps are in position to assure that the original valve design parameters are being reproduced on a continuous basis in the manufacturing facility.

Is there a risk assessment for product development? E.g. FMEA?

Fourth audit question: What are the design principles for sealing elements, gaskets, packings etc?

End user experiences on operational sites often give rise to problems with seals. (Explosive decompression of O rings, lip seal failure, gasket leakage, stems packing leakage and large / rectangular flange design.)

The end user will question aspects of design on surface finishes, tolerances, seal designs (suppliers), bolt tightening procedures and request details of proven experience. Novel or unusual designs should be interrogated and risks assessed. The last thing an end user requires are such designs failing whilst in service on the sea bed!!!! Other questions could flow, and demonstration of 2D /3D Autocad systems etc.

Fifth audit question: What are the training requirements for engineers? How do you maintain technology innovations?

Perhaps you can answer this question?

Conclusion

The end user through such discussions will aim to gain confidence in the valve manufacturer design capabilities. Are they acceptable for the type of valve selected and likely process conditions? Please note the above questions are very elementary.

Thank you for your continued support. Please contact me if you have any questions or different views.

Barrie Kirkman, BSc CEng MIMechE, writes a regular column for Valve World, bringing his own personal views from inside the valve business.

Barrie can be reached on: barriekirkman@ntlworld.com.


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