Collect like terms: 11c+6d-5c-8d = 6c-2d
If -6d = 42 then 6d = -42. then divide by 6, d = -7
-6d = -42-6(7) = -42d = 7
72-6d=6 subtract 72 from both sides -6d=66 divide by -6 d=-11
It's quite easy. API 6A speaks about wellhead and x-mas tree equipment, API 6D speaks about pipeline valves. If you are phisically looking to one valve, you can also understand if it belows to 6A or 6D giving a look to the valve label. On the label you can read the class of the valve. If the class is 2000 or 3000 or 5000 or 10000 or 15000 or 20000 the valve is 6A. If the class is 125 or 150 or 300 or 400 or 600 or 900 or 1500 or 2500 the valve probably is a 6D ("probably" because the same classes of API 6D are used also by other API standards, like 594, 600, 608, ecc ecc).
yes you can
9d-19=6d+2 ... add 19 to both sides and subtract 6d from both sides... 9d-6d=2+19 3d=21 d=21/3 d=7
The pressure test for API 598 is slightly less pressure and less duration than API 6D. API 6D is specifically for pipeline valves.
6d = c Divide both sides by 6: d = c/d
API 6D exceeds API 598 in both pressure and duration.
3c - 4d = 6d + 4c Subtract 4c from both sides: -c - 4d = 6d Add 4d to both sides: -c = 10d or c = - 10d
sajid