Everything you Need to Know about Dished Ends

Everything you Need to Know about Dished Ends

March 26, 2019 apvheads 0

Australian Pressure Vessel Heads is Australia’s leading manufacturer of dished ends, pipe caps, pressure vessel heads and tank heads for use in the fabrication of pressure vessels, storage tanks and process vessels. Our valued customers include large and small companies in the petrochemical, chemical, power, water treatment, food and offshore industries.

Australian Pressure Vessel Heads manufacturers dished ends of up to 10 meters in diameter, with material thickness ranging from 5mm to 125mm, and has the capability to manufacture larger segmented configurations.

With more than 60 years’ experience and products of the highest quality, we are able to provide our customers with complete peace of mind.

This is an informative guide to help buyers of dished ends ensure they ask they right questions before making a decision on what dished ends manufacturer to select.

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How Do I Order a Dished End?

It is important to know the following specifications when ordering your Dished ends

  1. Quantity  
  2. Material type or grade
  3. The manufacturer code
  4. Shape
  5. Inside and outside diameter
  6. For Torispherical we need to know the Inside crown radius (ICR) and inside knuckle radius (IKR) 
  7. The straight flange 
  8. The minimum thickness after forming 
  9. If it’s a Torisperical shape the ITH (Inside tangential Height)

Industry Jargon

The common terms and industry abbreviations are as follows:

  • Internal Diameter (ID)
  • Outside Diameter (OD)
  • Inside Crown Radius (ICR) – The radius that dictates the shape and depth of the Dished End
  • Inside Knuckle Radius (IKR) – the corner radius where the crown radius blends into the Straight Flange
  • Straight Flange (SF)
  • Thickness (T) – minimum thickness after forming and there is a plate thickness prior to forming. So for example if we start off with a 10mm plate, we allow 10% for thinning so we can guarantee that after forming that plate will be a minimum of 9.0mm thickness

 

What is the difference between hot pressed and cold forming?

Hot pressed Dished Ends are formed within the Dished Ends normalising range. This results in no inherent stresses built into the finished product. A cold pressed or formed Dished End has stresses formed into it and depending on the material it may need to be stress relieved once finished. This is a form of heat treatment. These stresses occur when cold forming Dished Ends or Pipe Caps exceeds 5% fibre strain. This is one of the benefits of Hot Pressing as there is no fibre strain issues.

 

What are the common causes of Dished End failures?

  1. Microscopic cracks –  a common issue in cold formed dished ends where it could suffer excessive thinning in the process (cold forming). This rarely happens when using the hot pressed method.  Based on record, there is a 10% maximum thinning. It’s usually only 5% based on our history.
  2. Incorrect welding procedure.
  3. Manufacturing and Design errors.

 

How important Is the appearance of a Dished End or Pipe Cap?

The appearance does not determine the quality of the Dished Ends. In fact a hot pressed dished end usually products a rougher finish but better quality dished end, while cold forming is the opposite.

The more common cold pressed dish ends generally appear shinier because of its finish.  While hot pressed types, which is usually superior to cold pressed, can be shined up with a shot blasting and prime coat painting.

 

What has happened to the Dished End and Pipe Cap manufacturing industry in Australia?

Australian Pressure Vessel Heads are the only company to hot press dished ends in Australia. All others have shut down due to the expense involved. However we perfected the approach of pressing Pipe Caps and Dished Ends in a one press operation. This means the plate is heated a less amount of times and more cost effective than a pre-dished approach which is what our previous hot pressed competitors did. The result is a higher quality outcome at a more competitive price. This, along with the fact that we use Australian steel is one of the reasons why James Cameron used our products for his record breaking Deepsea Challenger vessel.

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Why buy Australian made steel?

Australian made steel is fully certified and made to some of the highest standards in the world. The certificates that come with our steel are authentic whereas overseas material certification can be unreliable.

 

How would you know the quality of the Dished End by looking at it?

When performing a visual inspection, it is highly important to look for the following signs to make sure that you are getting a product of superior quality:

  1. Crown radius – make sure the dished end was deep enough.  
  2. Check the corner radius, or the knuckle radius, and make sure that radius was not too small.  It would have to be at least 10 or 15%, if it’s a Torispherical or Semi Ellipsoidal.
  3. If it’s cold formed, check to see if it has a weld seam. If it has, it should be radiographed or ultrasonically examined to check for cracks in the weld, or the weld affected zone.  
  4. Irregularities in shape
  5. Irregularities in size
  6. Making sure it adheres to code requirements

 

What are the consequences of buying a poor-quality Dished End?

  1. Poor quality dished ends may not fit the barrel that has been rolled for that particular job
  2. It may have cracks built into it that nobody can see, and they won’t become obvious until the vessel is in service.
  3. Explosion from dished end failure which could result result in injury or worse, death.  

 

What are the various shapes of Dished Ends?

  1. Torispherical (Tori) –  The shallowest of the three main dished ends – this type has less dishing and so it is cheaper to produce
  2. Semi Ellipsoidal (Also called Semi Elliptical or Semi) – has a bit deeper dishing There’s more drawing time.  The blank size is bigger. So, there’s a higher material cost, and a higher forming cost. It can withstand a higher pressure than the Torispherical for the same diameter and thickness.
  3. Hemispherical (Hemi) –  Can withstand a higher pressure.  It is deeper, and the blank is bigger. This the the most efficient among the three types, but is the dearest to make.  

 

What criteria would you use to find the best supplier of Dished Ends?

One should look for a supplier with a past record.  A good track record. Australian Pressure Vessel Heads has been in the business supplying top quality Dished Ends for around 70 years.  It has supplied Dished Ends to all of the refineries in Australia, none of our Dished Ends or pressure vessels have ever failed to this day.  

 

What makes a great Dished End?

A great Dished End is formed strictly following specific codes and all Australian Pressure Vessel Heads Dished Ends strictly conform to these requirements.  Customers are assured they get the right size and shape for their requirement. All of our Dished Ends are formed to AS1210, BS550 and ASME VIII which are the highest certifications in the industry.

This ensures that the Dished End produced and pressed or formed to the right size, with the right material.

How to choose what material to use in making your Dished End.  

There are different types of products that are used to create Dished Ends

  1. Standard boiler plate – it is the most common steel used with various material types depending on function:
    • PT460NR for designing vessels
    • PT490NR (slightly thinner than PT460NR)
    • ASTM A316 or ASTMA304  for corrosive environments
  2. Chromium molybdenum steel.  
  3. Nickel-based steel.

 

What types of things can Dished Ends be used for?

Dished Ends can be used for a variety of products. Some of the products that we have produced dished ends for includes:

  1. Seal off the ends of a pressure vessel, and, or a storage tank – the most common use   
  2. For council arts and outdoor art installations.  
  3. Oil sumps.  
  4. Bollards.  
  5. Pup plants
  6. Barriers
  7. Dive Tanks
  8. Hyperbaric Chambers.  
  9. Medical Equipment
  10. For Marine Equipment
  11. Oxygen tanks for divers

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Famous Dished Ends

Academy award film director James Cameron who’s known for the film Titanic trusted Australian Pressure Vessel Heads to manufacture the casing of the pod of the vessel that set a world record for diving to the lowest point of the Earth in the Mariana Trench at a depth of 11 kilometres below the ocean’s surface. His life really was at risk with all of the intense pressures at that level so choosing the best quality material for the vessel was imperative.

Like any other loyal customer, James Cameron trusted that he could rely on the quality of the product that was being produced by Australian Pressure Vessel Heads.  Because they have been hot forming these Dished Ends for 70 years and have never had one fail yet.


The benefit of Australian Made

Buying Australian steels do not just guarantee its customers a quick turnaround,   they are also fully certified following strict Australian standards.

 

What’s the potential impact of material that’s a lower quality than expected in terms of costs and safety to the incline?

  • The pressure vessel could fail under service, which could result in an explosion, resulting in death or injury
  • The company that would sell a defective product,  would eventually suffer a significant reputational risk, a reputational damage.

As such when selecting a Dished End manufacturer, it is important to look at their track record and how long they have been in business for.

 

Get in Touch

For a quote on your Dished End requirement click on the button below

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To speak to one of our engineering experts, call us on +61 3 9311 7722

 

  AUSTRALIAN PRESSURE VESSEL HEADS

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