Working Pressure

Advanced manufacturing methods

With advanced manufacturing methods, Elfab performs working pressure procedures to an extremely high standard. This service provides customers with the following key advantages:

  • The manufacture of every product to a zero-manufacturing design range (MDR). We provide this service at no additional charge.
  • Assurance of a better-than-industry-standard performance tolerance of 3% rather than 5%.
  • Enables you to work the process to a higher pressure using the same set pressure for the rupture disc.
  • Shorter process times, tighter safety margins and the possibility of rationalising your stock-holding inventory.

The working pressure procedure

As an example, the following table sets out typical parameters of what we would supply for a rupture disc ordered at 100 psig:

ElfabZero MDR35% MDR10% MDR
Lowest possible marked burst pressure (psig1) 1001009590
Burst pressure tolerance +/-2%3%5%5%5%
Minimum burst pressure (psig)97959085
Operating ratio 4%92909090
Maximum working pressure (psig)929085.581

The marked burst of the 100 psig rupture disc is stated in one of two ways. With the zero manufacturing design range (MDR), the marked burst is the same as the ordered burst. Alternatively, with the ten per cent manufacturing design range, the marked burst is the mean of the actual test bursts which must lie between this limit. The following points provide an example:

  • Burst pressure ordered = 100 psig +/- 5% @ 68°F with 0% MDR
  • Marked burst on disc tag = 100 psig +/- 5% @ 68°F
  • Burst pressure ordered = 100 psig +/- 5% @ 68°F with 10% MDR
  • Actual test burst mean = 90 psig marked burst = 90 psig +/- 5% @ 68°F

Burst pressure tolerance is the limit of the burst pressure of the disc, normally stated as a plus or minus percentage.

MDR is the range (normally expressed as zero, minus five per cent or minus ten per cent) applied to the requested burst pressure. The mean of the test burst results must lie within this range.

Operating ratio is the maximum recommended pressure that the rupture disc should be subjected to in service. Above this figure, the rupture disc will fatigue and give a reduced service life. It is stated as a percentage of the marked burst.