Monthly Archives: November 2018

bellows seal, mechanical seal

The Development of the Stationary Metal Bellows Seal

Figure 1. Early concept (ca 1976) of stationary metal bellows seal for low temperature.

Stationary metal bellows seals as we know them today were developed as part of a seal reliability program at Exxon’s Baton Rouge refinery in the 1970s.  The Exxon “Pump Team” was not satisfied with reliability and performance of seals in hot oil services because the oils decomposed and locked rotating flexible sealing elements in place.  Beginning in January 1976, prototype stationary metal bellows seals were designed, manufactured and assembled by the Exxon Pump Team using parts from various seal manufacturers fitted into custom assemblies manufactured in the Exxon machine ship.

The Exxon Pump Team tested 19 prototypes in many variations before deciding to turn over the designs and results to the seal manufacturers.  There was some consideration for seeking a patent but it was thought that commercial development of the concept would be better done by the seal OEMs.

I know this for a certainty because I was there and took an active part in this project.

The story of the stationary metal bellows seal is told in more detail on this page of SealFAQs.

API 682, mechanical seal

API 682 Mating Ring Clearances

Mating Ring Clearance Illustration

Before the 4th Edition, API 682 did not specify a minimum clearance between the inside diameter of a stationary seal part and the outside diameter of a rotating seal part. The 4th Edition specifies this minimum clearance – typically the clearance between the sleeve OD and the mating ring ID. The clearances specified in 4th Edition are representative of standard clearances that have been used for decades.  I’ve written a historical perspective on how those sleeve to mating ring clearances came to be.

It should be emphasized that the minimum clearance specified in API 682 4th Edition applies only to equipment within the scope of the standard. Equipment outside that scope, such as non-cartridge seals, older pumps, non-API 610 pumps and certain severe services, might benefit from larger clearances.

SealFAQs

SealFAQs statistics for October 2018

October was the best month, so far, of 2018.

SealFAQs has been officially launched for ten months now.  In October, unique visitors increased quite a bit from previous months.  Here are the statistics according to Awstats (Advanced Web Statistics).

SealFAQs had 2634 unique visitors during October and a total of 3769 visits (1.43 visits/visitor).  Visitors averaged looking at 2.3 pages per visit.  Bandwidth was up to 2.4GB.  So the visits per visitor and pages per visit has remained about the same for several months. This means that many visitors do not make a return visit and also look at only a few pages.

Visits per day during October averaged 121; the most visits in a day was 166.   As usual, most people visit during the week and the middle part of the day.  There has always been a drop off in visits on the weekends.

By far, the most visitors are from the United States and distantly followed by India and China.

The average time of a visit decreased to 304 seconds in duration but 80% of all visits are still for less than 30 seconds.  It does appear that some people are logging in and staying on the site an hour or more – forgetting to log out or reading/studying?

Access to SealFAQs via search engines was based on 16 different keyphrases including, as usual, several searches for information on piping plans.

I check SealFAQs for comments every day.  Almost no one has submitted a real comment but several bits of spam or faked comments show up daily.  The lack of comments and discussion continues to be troublesome to me.