sheep in the field

A ha'p'orth of tar…

David Sear - 25 June 2015

The importance of correct tube selection and fabrication

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Mr David Sear
David Sear is Online Editor. He is contributing to articles, interviews and reports to KCI’s magazines and websites. David also works on videos for KCI Television.
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There’s a very quant proverb which is popular in the UK – and probably elsewhere, as far as I know. In full, it reads “Don't spoil the ship for a ha'p'orth of tar”.

A “ha’p’orth” stands for “half a penny’s worth”, whilst “ship” is actually a dialect word for a sheep. So the proverb is directed at farmers and is very practical in nature: don’t risk the health of your sheep (and your future profits) by trying to save money and not applying enough tar to keep flies off their sores.

Now I apologise if this is starting to sound like an English lesson, but the point I want to make is this: it isn’t wise to risk the failure of a large project by trying to economize on trivial things. Or put another way: there’s no point spending a lot of money on top quality headline equipment if you overlook other equally vital components.

sandvik tubingIn fact, that’s why this proverb sprang immediately to mind today when I opened my mailbox and saw a press release from Sandvik Materials Technology, who develop and produce advanced stainless steels, special alloys, titanium and other high-performance materials. One paragraph in particular read:

“Whether you’re operating an oil rig or a petrochemical plant, the need to boost output without sacrificing safety is ever-present. In the big scheme of things, your choice of hydraulic and instrumentation tubing might not seem critical, but it does make a difference in eliminating risks,” explained Sandvik’s James Doughty, Sales Manager - MENA region for Tube, Core and Standard Products.

sanvik tubingIn their press release, Sandvik then go on to warn that not all instrumentation tubing might be suitable for specific applications – even if it meets applicable international standards.

“International standards, like ASTM and EN certifications, help guide distributors and their buyers. The challenge is that many of these standards only provide recommendations for minimum or maximum levels…..It really is important to ask yourself whether your supplier is providing the optimum quality for your particular application, even if the quality supplied is technically within the standard.”

This prompted me to look for more background information. Indeed, back-tracking to the SMT website, I found a reference indicating that is directly relevant to the valve industry:

…the loss of hydraulic fluids or chemicals [from hydraulic or instrumentation lines] could lead to a valve shutdown or a loss of instrumentation control.

The message about the importance of correcting tube selection and fabrication was reinforced on visiting the Parker Hannifin website and finding a document on instrumentation tubing.

Not only do Parker offer equipment to fabricate tubing systems, it seems they can also provide training courses as well. These courses, they say, can teach anybody the right way to measure, cut, and bend tubing.

With so much tubing being used to operate flow control systems, then perhaps the humble tube is a product which deserves its fair share of attention to ensure system reliability?

Sandvik indicate they always look beyond the minimum standard for H&I tubing achieving higher pitting corrosion resistance, or PRE numbers. As an example, Sandvik 3R60 H&I tubing has a minimum 2.5% Mo content for higher corrosion resistance compared to the minimum ASTM standard of 2% Mo.

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