refinery at evening

LDAR field experiences: packing selection

Barrie Kirkman - 4 May 2017

Last year in Valve World Magazine I raised an important question: “how to bring the existing valve leakers down to the required levels and over what time period?” The conclusion was some countries like the USA tend to opt for refurbishment/ reconditioning shops In Europe these shops are used far less and the on-site repairs are preferred. On site repairs are 98% using an acceptable packing with no other valve modifications. This is a major difference indeed!

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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Whatever route is decided the end user is responsible for assessing and selecting the required packing. I will try to explain what should be considered and some of the fundamental questions that an end user should ask which will be totally different from those normally asked by either the valve or packing manufacturer.

End user impact on the supply chain

One thing I have learnt over the years is that an informed end user can cause many suppliers to re-think their marketing strategies or even change the packing technology. Examples of this over the last few decades have been with Exxon, BP and Chevron Texaco. Where the end user works with the sealing company history indicates long term and effective solutions are achieved. Pulling valves from the supply chain or from end user warehouses indicate the low emission tags given have been, in some instances, found after some simple testing to be wanting!* 

How do the international standards achieve low emission valves / packings
All the international standards, API 622, API 624, pending API 641 & ISO 15848 assume certain valve tolerances and stem finishes are met such that the packing passes the required thermal and mechanical testing to required leakage level say 100ppm. Also modern packings now have various levels of PTFE up to 9% plus which enables compliance more readily. 

The issues that arise from this are twofold. Firstly the consistency in the production valves to ensure all the tolerances and design are met. For mass produced commodity valves this has proven to be difficult especially with multiple production/ subcontractors. 

Secondly mass production of the packings that pass the above tests sometimes requires increasing even further the PTFE content for ease of production. This practice invalidates the tests. 

So this indicates to an end user the packing itself is no longer 100% graphite so the allowable working temperature will be reduced and the valve manufacturing costs will rise to achieve the valve tighter tolerances. A potential premium price has to be paid. The Supply chain is always very keen to indicate this. The end user should always give a structured push back on this.


Can low emission packings plus “others” perform well in existing leaking valves?

The answer is straight forward. Yes as qualified below.
Let us now look at the end users existing valve population with identified leakers. The route just to replace the packing in situ likewise requires “a good FE packing”. At present these have been identified as low emission packings by the tests above. But as an end user the question that should be asked is, will all of these packings therefore work on existing site valves?

The packing company will quickly point to the warranty as certain tolerances have to be met for the packing to perform. My experience is to throw the warranty in the bin, it has no real value to an end user. It’s the packing and valve combination that rules. The end user should undertake their evaluation.

So why do many end users outside of the USA use some of these tested packings plus others that have not been through the test protocol? The answer is simple: “experience” and “understanding what is required of a good packing to achieve low emissions in the field.” Note: it’s the packing design that requires evaluation, for example what actually happens when the gland bolt loading is applied? The skill is to enable vertical loading to be effectively transferred radially to seal against the stuffing box wall and the stem. The vertical load should also be low. That’s simple enough? Isn’t it? 

End users have seen so many packing salesmen and listened to all the arguments why their product is superior. The key question to be answered is, “Have the emission packings been fitted in old valves in the field?” If so how many (10’s? 100’s?…1000’s?) and please provide details of where? At the same time also ask about new valves both cast and forged. Getting actual numbers will be difficult as such real data does not exist.

The industry knows which packings are performing well but it’s kept quiet unless the end user starts their investigations. You can probably count on one hand the proven in situ packings with large volume success. 

Field Experience: 

From review of the global LDAR activities in USA, Europe, Africa, Middle East  and Australia after the retighten of the gland bolts there are major differences in repair which still deliver the correct result…low emissions valves. In brief use of refurbishment/ reconditioning shops versus repair of the leaking valve at the site location (i.e. the valve is isolated, gas free and safe.) The Return on Investment (ROI) is significantly different between the two options

USA tend to opt for refurbishment/ reconditioning shops. In Europe these shops are used far less and the on-site repairs are preferred. On site repairs are 98% using an acceptable packing with no other valve modifications. 

So what low emission packings really work in insitu valves?

With 50 plus low emission packings available as proven by the tests for new valves only a small percentage about 10% will indeed perform well in insitu field valves. The remaining 90% may indeed may start off well but in time will leak requiring re-tightening and eventually replacing. Many end users have sorted and tried these 10% packings and are confidently using them to meet low emissions. In addition the end users are using packings that have not been subject to the international tests. API 622 sadly is not considered relevant. Experience often rules after 10 and 25 years success in the field.


Evaluation of the current low emission packings

With 50 plus low emission packings now available as proven by the tests a small percentage – about 10% - will indeed perform well in old valves in situ in the field whilst the remaining 90% may indeed start off well but in time will likely leak requiring re-tightening. How has this situation arisen, especially after the volume of testing? 100% of the effort in the international codes arena has been qualifying packings for new valves and not in situ repairs. The packing companies state it is very difficult to innovate and have chosen the simpler route. The smart end user dialogue within the end user community will soon to begin to identify those that work and those that do not irrespective of packing supplier’s glossy literature and claims.

The end user should be grouping these packings by types, shapes and the same material. Some are clearly just for new valves. Others are exactly the same but have different brand names. And some are just direct copies of the successful packings which often fail. Many sealing companies have absolutely no idea of old site valves requirements. End users should be adding their tests protocol.*

What is the end user requirement for packings?
The end user requirement is to fit a good emission packing to old existing valves in situ that does not need re-tightening and offers low emissions through out a 25 year life. 

Differentiating between good and poor low emission packings

When looking at the graph we can see that a good emission packing follows the lower orange line pulling the leakers down such that there is no “bounce back with re-occurring leakers” (BBLDAR). The blue, red and green lines indicate that the packing selected does not have the long term durability and fails.

Generically infield packings are braided based but there are those that are engineered. To fit the packings rings in situ they have to be spliced to fit round the stem. Again there are good splices and bad ones where the ends are frayed. Also they can be supplied pre-cut. Too often the temptation is use the cheapest braided spool, cut on site which fails very quickly.
 
Within various global end users where the valve replacement strategy is implemented in the USA the in situ packing replacement option is frequently employed elsewhere in their company in Europe, Middle East and Far East. Why is this? The answer is it’s simple, practical and definitely far more cost effective. 

Once correctly implemented the numbers of leakers decline and those re-occurring are so low that valve emissions are no longer on the agenda. If you talk to these end users they are lukewarm about the API / ISO tests as they see little value to the existing valve in situ repairs. When speaking to the maintenance engineers on the plant experience rules as other key factors come into play such as packing availability, technical support, economic scale of repair costs and repeatability of success.

Closing remarks

Why I am so confident about old valves can be upgraded in situ with the correct packing? Simply that, over the past 25 years example after example with so many end users together with packing designs and their variations have been successfully performed in the field. The two case studies shown illustrate old valve upgrade in situ. Other examples exist.The debate will continue in the industry as arguments from both sides are presented. If you have any questions or comments as always they are most welcome. Thank you for your time.
 

 * Details of suggested end user tests will follow in a follow up post.

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